Research Area: Cancer Biology

New technique reveals how gene transcription is coordinated in cells

By capturing short-lived RNA molecules, scientists can map relationships between genes and the regulatory elements that control them.

Anne Trafton | MIT News
June 5, 2024

The human genome contains about 23,000 genes, but only a fraction of those genes are turned on inside a cell at any given time. The complex network of regulatory elements that controls gene expression includes regions of the genome called enhancers, which are often located far from the genes that they regulate.

This distance can make it difficult to map the complex interactions between genes and enhancers. To overcome that, MIT researchers have invented a new technique that allows them to observe the timing of gene and enhancer activation in a cell. When a gene is turned on around the same time as a particular enhancer, it strongly suggests the enhancer is controlling that gene.

Learning more about which enhancers control which genes, in different types of cells, could help researchers identify potential drug targets for genetic disorders. Genomic studies have identified mutations in many non-protein-coding regions that are linked to a variety of diseases. Could these be unknown enhancers?

“When people start using genetic technology to identify regions of chromosomes that have disease information, most of those sites don’t correspond to genes. We suspect they correspond to these enhancers, which can be quite distant from a promoter, so it’s very important to be able to identify these enhancers,” says Phillip Sharp, an MIT Institute Professor Emeritus and member of MIT’s Koch Institute for Integrative Cancer Research.

Sharp is the senior author of the new study, which appears today in Nature. MIT Research Assistant D.B. Jay Mahat is the lead author of the paper.

Hunting for eRNA

Less than 2 percent of the human genome consists of protein-coding genes. The rest of the genome includes many elements that control when and how those genes are expressed. Enhancers, which are thought to turn genes on by coming into physical contact with gene promoter regions through transiently forming a complex, were discovered about 45 years ago.

More recently, in 2010, researchers discovered that these enhancers are transcribed into RNA molecules, known as enhancer RNA or eRNA. Scientists suspect that this transcription occurs when the enhancers are actively interacting with their target genes. This raised the possibility that measuring eRNA transcription levels could help researchers determine when an enhancer is active, as well as which genes it’s targeting.

“That information is extraordinarily important in understanding how development occurs, and in understanding how cancers change their regulatory programs and activate processes that lead to de-differentiation and metastatic growth,” Mahat says.

However, this kind of mapping has proven difficult to perform because eRNA is produced in very small quantities and does not last long in the cell. Additionally, eRNA lacks a modification known as a poly-A tail, which is the “hook” that most techniques use to pull RNA out of a cell.

One way to capture eRNA is to add a nucleotide to cells that halts transcription when incorporated into RNA. These nucleotides also contain a tag called biotin that can be used to fish the RNA out of a cell. However, this current technique only works on large pools of cells and doesn’t give information about individual cells.

While brainstorming ideas for new ways to capture eRNA, Mahat and Sharp considered using click chemistry, a technique that can be used to join two molecules together if they are each tagged with “click handles” that can react together.

The researchers designed nucleotides labeled with one click handle, and once these nucleotides are incorporated into growing eRNA strands, the strands can be fished out with a tag containing the complementary handle. This allowed the researchers to capture eRNA and then purify, amplify, and sequence it. Some RNA is lost at each step, but Mahat estimates that they can successfully pull out about 10 percent of the eRNA from a given cell.

Using this technique, the researchers obtained a snapshot of the enhancers and genes that are being actively transcribed at a given time in a cell.

“You want to be able to determine, in every cell, the activation of transcription from regulatory elements and from their corresponding gene. And this has to be done in a single cell because that’s where you can detect synchrony or asynchrony between regulatory elements and genes,” Mahat says.

Timing of gene expression

Demonstrating their technique in mouse embryonic stem cells, the researchers found that they could calculate approximately when a particular region starts to be transcribed, based on the length of the RNA strand and the speed of the polymerase (the enzyme responsible for transcription) — that is, how far the polymerase transcribes per second. This allowed them to determine which genes and enhancers were being transcribed around the same time.

The researchers used this approach to determine the timing of the expression of cell cycle genes in more detail than has previously been possible. They were also able to confirm several sets of known gene-enhancer pairs and generated a list of about 50,000 possible enhancer-gene pairs that they can now try to verify.

Learning which enhancers control which genes would prove valuable in developing new treatments for diseases with a genetic basis. Last year, the U.S. Food and Drug Administration approved the first gene therapy treatment for sickle cell anemia, which works by interfering with an enhancer that results in activation of a fetal globin gene, reducing the production of sickled blood cells.

The MIT team is now applying this approach to other types of cells, with a focus on autoimmune diseases. Working with researchers at Boston Children’s Hospital, they are exploring immune cell mutations that have been linked to lupus, many of which are found in non-coding regions of the genome.

“It’s not clear which genes are affected by these mutations, so we are beginning to tease apart the genes these putative enhancers might be regulating, and in what cell types these enhancers are active,” Mahat says. “This is a tool for creating gene-to-enhancer maps, which are fundamental in understanding the biology, and also a foundation for understanding disease.”

The findings of this study also offer evidence for a theory that Sharp has recently developed, along with MIT professors Richard Young and Arup Chakraborty, that gene transcription is controlled by membraneless droplets known as condensates. These condensates are made of large clusters of enzymes and RNA, which Sharp suggests may include eRNA produced at enhancer sites.

“We picture that the communication between an enhancer and a promoter is a condensate-type, transient structure, and RNA is part of that. This is an important piece of work in building the understanding of how RNAs from enhancers could be active,” he says.

The research was funded by the National Cancer Institute, the National Institutes of Health, and the Emerald Foundation Postdoctoral Transition Award.

“Rosetta Stone” of cell signaling could expedite precision cancer medicine

An atlas of human protein kinases enables scientists to map cell signaling pathways with unprecedented speed and detail. Michael Yaffe, the David H. Koch Professor of Science at MIT, the director of the MIT Center for Precision Cancer Medicine, a member of MIT’s Koch Institute for Integrative Cancer Research, and a senior author of the new study published in Nature, is hoping to apply the comprehensive atlas of enzymes that regulate a wide variety of cellular activities to individual patients’ tumors to learn more about how the signaling states differ in cancer cancer, which could reveal new

Megan Scudellari | Koch Institute
June 3, 2024

A newly complete database of human protein kinases and their preferred binding sites provides a powerful new platform to investigate cell signaling pathways.

Culminating 25 years of research, MIT, Harvard University, and Yale University scientists and collaborators have unveiled a comprehensive atlas of human tyrosine kinases — enzymes that regulate a wide variety of cellular activities — and their binding sites.

The addition of tyrosine kinases to a previously published dataset from the same group now completes a free, publicly available atlas of all human kinases and their specific binding sites on proteins, which together orchestrate fundamental cell processes such as growth, cell division, and metabolism.

Now, researchers can use data from mass spectrometry, a common laboratory technique, to identify the kinases involved in normal and dysregulated cell signaling in human tissue, such as during inflammation or cancer progression.

“I am most excited about being able to apply this to individual patients’ tumors and learn about the signaling states of cancer and heterogeneity of that signaling,” says Michael Yaffe, who is the David H. Koch Professor of Science at MIT, the director of the MIT Center for Precision Cancer Medicine, a member of MIT’s Koch Institute for Integrative Cancer Research, and a senior author of the new study. “This could reveal new druggable targets or novel combination therapies.”

The study, published in Nature, is the product of a long-standing collaboration with senior authors Lewis Cantley at Harvard Medical School and Dana-Farber Cancer Institute, Benjamin Turk at Yale School of Medicine, and Jared Johnson at Weill Cornell Medical College.

The paper’s lead authors are Tomer Yaron-Barir at Columbia University Irving Medical Center, and MIT’s Brian Joughin, with contributions from Kontstantin Krismer, Mina Takegami, and Pau Creixell.

Kinase kingdom

Human cells are governed by a network of diverse protein kinases that alter the properties of other proteins by adding or removing chemical compounds called phosphate groups. Phosphate groups are small but powerful: When attached to proteins, they can turn proteins on or off, or even dramatically change their function. Identifying which of the almost 400 human kinases phosphorylate a specific protein at a particular site on the protein was traditionally a lengthy, laborious process.

Beginning in the mid 1990s, the Cantley laboratory developed a method using a library of small peptides to identify the optimal amino acid sequence — called a motif, similar to a scannable barcode — that a kinase targets on its substrate proteins for the addition of a phosphate group. Over the ensuing years, Yaffe, Turk, and Johnson, all of whom spent time as postdocs in the Cantley lab, made seminal advancements in the technique, increasing its throughput, accuracy, and utility.

Johnson led a massive experimental effort exposing batches of kinases to these peptide libraries and observed which kinases phosphorylated which subsets of peptides. In a corresponding Nature paper published in January 2023, the team mapped more than 300 serine/threonine kinases, the other main type of protein kinase, to their motifs. In the current paper, they complete the human “kinome” by successfully mapping 93 tyrosine kinases to their corresponding motifs.

Next, by creating and using advanced computational tools, Yaron-Barir, Krismer, Joughin, Takegami, and Yaffe tested whether the results were predictive of real proteins, and whether the results might reveal unknown signaling events in normal and cancer cells. By analyzing phosphoproteomic data from mass spectrometry to reveal phosphorylation patterns in cells, their atlas accurately predicted tyrosine kinase activity in previously studied cell signaling pathways.

For example, using recently published phosphoproteomic data of human lung cancer cells treated with two targeted drugs, the atlas identified that treatment with erlotinib, a known inhibitor of the protein EGFR, downregulated sites matching a motif for EGFR. Treatment with afatinib, a known HER2 inhibitor, downregulated sites matching the HER2 motif. Unexpectedly, afatinib treatment also upregulated the motif for the tyrosine kinase MET, a finding that helps explain patient data linking MET activity to afatinib drug resistance.

Actionable results

There are two key ways researchers can use the new atlas. First, for a protein of interest that is being phosphorylated, the atlas can be used to narrow down hundreds of kinases to a short list of candidates likely to be involved. “The predictions that come from using this will still need to be validated experimentally, but it’s a huge step forward in making clear predictions that can be tested,” says Yaffe.

Second, the atlas makes phosphoproteomic data more useful and actionable. In the past, researchers might gather phosphoproteomic data from a tissue sample, but it was difficult to know what that data was saying or how to best use it to guide next steps in research. Now, that data can be used to predict which kinases are upregulated or downregulated and therefore which cellular signaling pathways are active or not.

“We now have a new tool now to interpret those large datasets, a Rosetta Stone for phosphoproteomics,” says Yaffe. “It is going to be particularly helpful for turning this type of disease data into actionable items.”

In the context of cancer, phosophoproteomic data from a patient’s tumor biopsy could be used to help doctors quickly identify which kinases and cell signaling pathways are involved in cancer expansion or drug resistance, then use that knowledge to target those pathways with appropriate drug therapy or combination therapy.

Yaffe’s lab and their colleagues at the National Institutes of Health are now using the atlas to seek out new insights into difficult cancers, including appendiceal cancer and neuroendocrine tumors. While many cancers have been shown to have a strong genetic component, such as the genes BRCA1 and BRCA2 in breast cancer, other cancers are not associated with any known genetic cause. “We’re using this atlas to interrogate these tumors that don’t seem to have a clear genetic driver to see if we can identify kinases that are driving cancer progression,” he says.

Biological insights

In addition to completing the human kinase atlas, the team made two biological discoveries in their recent study. First, they identified three main classes of phosphorylation motifs, or barcodes, for tyrosine kinases. The first class is motifs that map to multiple kinases, suggesting that numerous signaling pathways converge to phosphorylate a protein boasting that motif. The second class is motifs with a one-to-one match between motif and kinase, in which only a specific kinase will activate a protein with that motif. This came as a partial surprise, as tyrosine kinases have been thought to have minimal specificity by some in the field.

The final class includes motifs for which there is no clear match to one of the 78 classical tyrosine kinases. This class includes motifs that match to 15 atypical tyrosine kinases known to also phosphorylate serine or threonine residues. “This means that there’s a subset of kinases that we didn’t recognize that are actually playing an important role,” says Yaffe. It also indicates there may be other mechanisms besides motifs alone that affect how a kinase interacts with a protein.

The team also discovered that tyrosine kinase motifs are tightly conserved between humans and the worm species C. elegans, despite the species being separated by more than 600 million years of evolution. In other words, a worm kinase and its human homologue are phosphorylating essentially the same motif. That sequence preservation suggests that tyrosine kinases are highly critical to signaling pathways in all multicellular organisms, and any small change would be harmful to an organism.

The research was funded by the Charles and Marjorie Holloway Foundation, the MIT Center for Precision Cancer Medicine, the Koch Institute Frontier Research Program via L. Scott Ritterbush, the Leukemia and Lymphoma Society, the National Institutes of Health, Cancer Research UK, the Brain Tumour Charity, and the Koch Institute Support (core) grant from the National Cancer Institute.

Taking RNAi from interesting science to impactful new treatments

Alnylam Pharmaceuticals is translating the promise of RNA interference (RNAi) research into a new class of powerful, gene-based therapies. These days Alnylam is not the only company developing RNAi-based medicines, but it is still a pioneer in the field. The company’s founders — MIT Institute Professor Phil Sharp, Professor David Bartel, Professor Emeritus Paul Schimmel, and former MIT postdocs Thomas Tuschl and Phillip Zamore — see Alnylam as a champion for the field more broadly.

Zach Winn | MIT News
May 13, 2024

There are many hurdles to clear before a research discovery becomes a life-changing treatment for patients. That’s especially true when the treatments being developed represent an entirely new class of medicines. But overcoming those obstacles can revolutionize our ability to treat diseases.

Few companies exemplify that process better than Alnylam Pharmaceuticals. Alnylam was founded by a group of MIT-affiliated researchers who believed in the promise of a technology — RNA interference, or RNAi.

The researchers had done foundational work to understand how RNAi, which is a naturally occurring process, works to silence genes through the degradation of messenger RNA. But it was their decision to found Alnylam in 2002 that attracted the funding and expertise necessary to turn their discoveries into a new class of medicines. Since that decision, Alnylam has made remarkable progress taking RNAi from an interesting scientific discovery to an impactful new treatment pathway.

Today Alnylam has five medicines approved by the U.S. Food and Drug Administration (one Alnylam-discovered RNAi therapeutic is licensed to Novartis) and a rapidly expanding clinical pipeline. The company’s approved medicines are for debilitating, sometimes fatal conditions that many patients have grappled with for decades with few other options.

The company estimates its treatments helped more than 5,000 patients in 2023 alone. Behind that number are patient stories that illustrate how Alnylam has changed lives. A mother of three says Alnylam’s treatments helped her take back control of her life after being bed-ridden with attacks associated with the rare genetic disease acute intermittent porphyria (AIP). Another patient reported that one of the company’s treatments helped her attend her daughter’s wedding. A third patient, who had left college due to frequent AIP attacks, was able to return to school.

These days Alnylam is not the only company developing RNAi-based medicines. But it is still a pioneer in the field, and the company’s founders — MIT Institute Professor Phil Sharp, Professor David Bartel, Professor Emeritus Paul Schimmel, and former MIT postdocs Thomas Tuschl and Phillip Zamore — see Alnylam as a champion for the field more broadly.

“Alnylam has published more than 250 scientific papers over 20 years,” says Sharp, who currently serves as chair of Alnylam’s scientific advisory board. “Not only did we do the science, not only did we translate it to benefit patients, but we also described every step. We established this as a modality to treat patients, and I’m very proud of that record.”

Pioneering RNAi development

MIT’s involvement in RNAi dates back to its discovery. Before Andrew Fire PhD ’83 shared a Nobel Prize for the discovery of RNAi in 1998, he worked on understanding how DNA was transcribed into RNA, as a graduate student in Sharp’s lab.

After leaving MIT, Fire and collaborators showed that double-stranded RNA could be used to silence specific genes in worms. But the biochemical mechanisms that allowed double-stranded RNA to work were unknown until MIT professors Sharp, Bartel, and Ruth Lehmann, along with Zamore and Tuschl, published foundational papers explaining the process. The researchers developed a system for studying RNAi and showed how RNAi can be controlled using different genetic sequences. Soon after Tuschl left MIT, he showed that a similar process could also be used to silence specific genes in human cells, opening up a new frontier in studying genes and ultimately treating diseases.

“Tom showed you could synthesize these small RNAs, transfect them into cells, and get a very specific knockdown of the gene that corresponded to that the small RNAs,” Bartel explains. “That discovery transformed biological research. The ability to specifically knockdown a mammalian gene was huge. You could suddenly study the function of any gene you were interested in by knocking it down and seeing what happens. … The research community immediately started using that approach to study the function of their favorite genes in mammalian cells.”

Beyond illuminating gene function, another application came to mind.

“Because almost all diseases are related to genes, could we take these small RNAs and silence genes to treat patients?” Sharp remembers wondering.

To answer the question, the researchers founded Alnylam in 2002. (They recruited Schimmel, a biotech veteran, around the same time.) But there was a lot of work to be done before the technology could be tried in patients. The main challenge was getting RNAi into the cytoplasm of the patients’ cells.

“Through work in Dave Bartel and Phil Sharp’s lab, among others, it became evident that to make RNAi into therapies, there were three problems to solve: delivery, delivery, and delivery,” says Alnylam Chief Scientific Officer Kevin Fitzgerald, who has been with the company since 2005.

Early on, Alnylam collaborated with MIT drug delivery expert and Institute Professor Bob Langer. Eventually, Alnylam developed the first lipid nanoparticles (LNPs) that could be used to encase RNA and deliver it into patient cells. LNPs were later used in the mRNA vaccines for Covid-19.

“Alnylam has invested over 20 years and more than $4 billion in RNAi to develop these new therapeutics,” Sharp says. “That is the means by which innovations can be translated to the benefit of society.”

From scientific breakthrough to patient bedside

Alnylam received its first FDA approval in 2018 for treatment of the polyneuropathy of hereditary transthyretin-mediated amyloidosis, a rare and fatal disease. It doubled as the first RNAi therapeutic to reach the market and the first drug approved to treat that condition in the United States.

“What I keep in mind is, at the end of the day for certain patients, two months is everything,” Fitzgerald says. “The diseases that we’re trying to treat progress month by month, day by day, and patients can get to a point where nothing is helping them. If you can move their disease by a stage, that’s huge.”

Since that first treatment, Alnylam has updated its RNAi delivery system — including by conjugating small interfering RNAs to molecules that help them gain entry to cells — and earned approvals to treat other rare genetic diseases along with high cholesterol (the treatment licensed to Novartis). All of those treatments primarily work by silencing genes that encode for the production of proteins in the liver, which has proven to be the easiest place to deliver RNAi molecules. But Alnylam’s team is confident they can deliver RNAi to other areas of the body, which would unlock a new world of treatment possibilities. The company has reported promising early results in the central nervous system and says a phase one study last year was the first RNAi therapeutic to demonstrate gene silencing in the human brain.

“There’s a lot of work being done at Alnylam and other companies to deliver these RNAis to other tissues: muscles, immune cells, lung cells, etc.,” Sharp says. “But to me the most interesting application is delivery to the brain. We think we have a therapeutic modality that can very specifically control the activity of certain genes in the nervous system. I think that’s extraordinarily important, for diseases from Alzheimer’s to schizophrenia and depression.”

The central nervous system work is particularly significant for Fitzgerald, who watched his father struggle with Parkinson’s.

“Our goal is to be in every organ in the human body, and then combinations of organs, and then combinations of targets within individual organs, and then combinations of targets within multi-organs,” Fitzgerald says. “We’re really at the very beginning of what this technology is going do for human health.”

It’s an exciting time for the RNAi scientific community, including many who continue to study it at MIT. Still, Alnylam will need to continue executing in its drug development efforts to deliver on that promise and help an expanding pool of patients.

“I think this is a real frontier,” Sharp says. “There’s major therapeutic need, and I think this technology could have a huge impact. But we have to prove it. That’s why Alnylam exists: to pursue new science that unlocks new possibilities and discover if they can be made to work. That, of course, also why MIT is here: to improve lives.”

Scientists develop a rapid gene-editing screen to find effects of cancer mutations

With the new technique, MIT researchers hope to identify mutations that could be targeted with new cancer therapies.

Anne Trafton | MIT News
March 12, 2024

Tumors can carry mutations in hundreds of different genes, and each of those genes may be mutated in different ways — some mutations simply replace one DNA nucleotide with another, while others insert or delete larger sections of DNA.

Until now, there has been no way to quickly and easily screen each of those mutations in their natural setting to see what role they may play in the development, progression, and treatment response of a tumor. Using a variant of CRISPR genome-editing known as prime editing, MIT researchers have now come up with a way to screen those mutations much more easily.

The researchers demonstrated their technique by screening cells with more than 1,000 different mutations of the tumor suppressor gene p53, all of which have been seen in cancer patients. This method, which is easier and faster than any existing approach, and edits the genome rather than introducing an artificial version of the mutant gene, revealed that some p53 mutations are more harmful than previously thought.

This technique could also be applied to many other cancer genes, the researchers say, and could eventually be used for precision medicine, to determine how an individual patient’s tumor will respond to a particular treatment.

“In one experiment, you can generate thousands of genotypes that are seen in cancer patients, and immediately test whether one or more of those genotypes are sensitive or resistant to any type of therapy that you’re interested in using,” says Francisco Sanchez-Rivera, an MIT assistant professor of biology, a member of the Koch Institute for Integrative Cancer Research, and the senior author of the study.

MIT graduate student Samuel Gould is the lead author of the paper, which appears today in Nature Biotechnology.

Editing cells

The new technique builds on research that Sanchez-Rivera began 10 years ago as an MIT graduate student. At that time, working with Tyler Jacks, the David H. Koch Professor of Biology, and then-postdoc Thales Papagiannakopoulos, Sanchez-Rivera developed a way to use CRISPR genome-editing to introduce into mice genetic mutations linked to lung cancer.

In that study, the researchers showed that they could delete genes that are often lost in lung tumor cells, and the resulting tumors were similar to naturally arising tumors with those mutations. However, this technique did not allow for the creation of point mutations (substitutions of one nucleotide for another) or insertions.

“While some cancer patients have deletions in certain genes, the vast majority of mutations that cancer patients have in their tumors also include point mutations or small insertions,” Sanchez-Rivera says.

Since then, David Liu, a professor in the Harvard University Department of Chemistry and Chemical Biology and a core institute member of the Broad Institute, has developed new CRISPR-based genome editing technologies that can generate additional types of mutations more easily. With base editing, developed in 2016, researchers can engineer point mutations, but not all possible point mutations. In 2019, Liu, who is also an author of the Nature Biotechnology study, developed a technique called prime editing, which enables any kind of point mutation to be introduced, as well as insertions and deletions.

“Prime editing in theory solves one of the major challenges with earlier forms of CRISPR-based editing, which is that it allows you to engineer virtually any type of mutation,” Sanchez-Rivera says.

When they began working on this project, Sanchez-Rivera and Gould calculated that if performed successfully, prime editing could be used to generate more than 99 percent of all small mutations seen in cancer patients.

However, to achieve that, they needed to find a way to optimize the editing efficiency of the CRISPR-based system. The prime editing guide RNAs (pegRNAs) used to direct CRISPR enzymes to cut the genome in certain spots have varying levels of efficiency, which leads to “noise” in the data from pegRNAs that simply aren’t generating the correct target mutation. The MIT team devised a way to reduce that noise by using synthetic target sites to help them calculate how efficiently each guide RNA that they tested was working.

“We can design multiple prime-editing guide RNAs with different design properties, and then we get an empirical measurement of how efficient each of those pegRNAs is. It tells us what percentage of the time each pegRNA is actually introducing the correct edit,” Gould says.

Analyzing mutations

The researchers demonstrated their technique using p53, a gene that is mutated in more than half of all cancer patients. From a dataset that includes sequencing information from more than 40,000 patients, the researchers identified more than 1,000 different mutations that can occur in p53.

“We wanted to focus on p53 because it’s the most commonly mutated gene in human cancers, but only the most frequent variants in p53 have really been deeply studied. There are many variants in p53 that remain understudied,” Gould says.

Using their new method, the researchers introduced p53 mutations in human lung adenocarcinoma cells, then measured the survival rates of these cells, allowing them to determine each mutation’s effect on cell fitness.

Among their findings, they showed that some p53 mutations promoted cell growth more than had been previously thought. These mutations, which prevent the p53 protein from forming a tetramer — an assembly of four p53 proteins — had been studied before, using a technique that involves inserting artificial copies of a mutated p53 gene into a cell.

Those studies found that these mutations did not confer any survival advantage to cancer cells. However, when the MIT team introduced those same mutations using the new prime editing technique, they found that the mutation prevented the tetramer from forming, allowing the cells to survive. Based on the studies done using overexpression of artificial p53 DNA, those mutations would have been classified as benign, while the new work shows that under more natural circumstances, they are not.

“This is a case where you could only observe these variant-induced phenotypes if you’re engineering the variants in their natural context and not with these more artificial systems,” Gould says. “This is just one example, but it speaks to a broader principle that we’re going to be able to access novel biology using these new genome-editing technologies.”

Because it is difficult to reactivate tumor suppressor genes, there are few drugs that target p53, but the researchers now plan to investigate mutations found in other cancer-linked genes, in hopes of discovering potential cancer therapies that could target those mutations. They also hope that the technique could one day enable personalized approaches to treating tumors.

“With the advent of sequencing technologies in the clinic, we’ll be able to use this genetic information to tailor therapies for patients suffering from tumors that have a defined genetic makeup,” Sanchez-Rivera says. “This approach based on prime editing has the potential to change everything.”

The research was funded, in part, by the National Institute of General Medical Sciences, an MIT School of Science Fellowship in Cancer Research, a Howard Hughes Medical Institute Hanna Gray Fellowship, the V Foundation for Cancer Research, a National Cancer Institute Cancer Center Support Grant, the Ludwig Center at MIT, a Koch Institute Frontier Award, the MIT Research Support Committee, and the Koch Institute Support (core) Grant from the National Cancer Institute.

How phase separation is revolutionizing biology

Postdocs from Whitehead Institute Member Richard A. Young's lab found that imaging and molecular manipulation reveal how biomolecular condensates form and offer clues to the role of phase separation in health and disease.

February 27, 2024
News brief: Calo Lab

How do cells respond to disruptions in splicing?

Lillian Eden | Department of Biology
March 4, 2024

New research from the Calo Lab in the Department of Biology has identified the protein Mdm2 generating a form that activates a cascade of cellular stress responses when splicing is disrupted.

To create proteins, DNA is transcribed into RNA, and that RNA is then “translated” into protein. Between the creation of the RNA and the translation to protein is often a step called splicing. During splicing, segments called introns are removed, and the remaining pieces, called exons, are joined together to form the blueprint for translation. By splicing together different exons, the cell can create different proteins from the same section of genetic code. When splicing goes awry, it can lead to diseases and cancers. 

New research recently published in Disease Models & Mechanisms from the Calo Lab in the Department of Biology at MIT has identified the mechanism for how cells respond to disruptions in splicing, which involves activating a cellular stress response. The stress response, once activated, causes widespread effects, including changes to cell metabolism. 

Researchers have discovered cellular stress responses for other core cellular processes, such as ribosome biogenesis. However, this is the first time researchers have identified how cells respond to perturbing the splicing process.

A particular protein acts as a kind of canary in a coal mine: Mdm2, which responds to a broad range of splicing disruptions. Mdm2 does not cause a stress response by itself. Rather, Mdm2 is itself spliced differently in response to splicing disruptions. Downstream, the alternative splicing of Mdm2 leads to the activation of a protein called p53, which is known to orchestrate a cascade of responses to stress.

Researchers have long wondered why some cell types seem more sensitive to splicing disruptions than others. For example, some disorders caused by mutations in proteins that perform RNA splicing, despite affecting the whole organism, induce more noticeable changes in tissues derived from the neural crest—a collection of stem cells that contributes to the formation of the face, jaw, retinas, limbs, and heart during development. Certain splicing inhibitors have also increased the effectiveness of some cancer treatments, but the mechanism is unknown. 

One of the p53-induced stress responses includes changing the metabolism of cells and how they use sugars, which may explain why some cells are more sensitive to splicing disruptions than others. Inhibiting glycolysis, the reactions that extract energy from glucose, can affect how cells divide and migrate. 

The way cells divide and migrate is critical during development; in experiments, zebrafish treated with glycolysis inhibitors exhibited similar changes to craniofacial features as those where splicing was disrupted. Cancerous cells, too, are known to require high levels of sugar metabolism and, therefore, may be especially sensitive to treatments that induce changes in the splicing pathway. 

The researchers knocked down genes to mimic milder splicing disruptions instead of knocking them out entirely. Splicing is so essential that knocking out the splicing machinery can lead to extreme responses like cell death. In organismal models like zebrafish, those severe phenotypes don’t accurately reflect how splicing disruptions present in human diseases.

First author Jade Varineau, a graduate student in the Calo lab, was drawn to the project because it allowed her to explore what was happening at the RNA and cellular level while also observing how splicing perturbations were affecting the whole organism. 

“I think this data can help us reframe the way we think about diseases and cancers that are impacted by splicing—that a treatment that works for one may work for another because all the symptoms may stem from the same cellular response,” Varineau says. 

Although the results indicate how cells broadly respond to splicing perturbations, the mechanism for how disruptions in splicing induce the alternate splicing of Mdm2 remains unclear. Senior author Eliezer Calo says the lab is also exploring how splicing mechanisms may be altered for things like cancer. Their work, he says, opens the door for further exploration of cell-type specificity of genetic disorders and improvements in cancer treatments using splicing inhibitors. 

 “We know that the sensor is encoded in the gene Mdm2—what are the molecules that allow Mdm2 to act as a sensor, and how does the sensor malfunction for things like cancer?” Calo says. “The next step is to find out how the sensor works.”  

How early-stage cancer cells hide from the immune system

A new study finds precancerous colon cells turn on a gene called SOX17, which helps them evade detection and develop into more advanced tumors.

Anne Trafton | MIT News
February 28, 2024

One of the immune system’s primary roles is to detect and kill cells that have acquired cancerous mutations. However, some early-stage cancer cells manage to evade this surveillance and develop into more advanced tumors.

A new study from MIT and Dana-Farber Cancer Institute has identified one strategy that helps these precancerous cells avoid immune detection. The researchers found that early in colon cancer development, cells that turn on a gene called SOX17 can become essentially invisible to the immune system.

If scientists could find a way to block SOX17 function or the pathway that it activates, this may offer a new way to treat early-stage cancers before they grow into larger tumors, the researchers say.

“Activation of the SOX17 program in the earliest innings of colorectal cancer formation is a critical step that shields precancerous cells from the immune system. If we can inhibit the SOX17 program, we might be better able to prevent colon cancer, particularly in patients that are prone to developing colon polyps,” says Omer Yilmaz, an MIT associate professor of biology, a member of MIT’s Koch Institute for Integrative Cancer Research, and one of the senior authors of the study.

Judith Agudo, a principal investigator at Dana-Farber Cancer Institute and an assistant professor at Harvard Medical School, is also a senior author of the study, which appears today in Nature. The paper’s lead author is MIT Research Scientist Norihiro Goto. Other collaborators include Tyler Jacks, a professor of biology and a member of MIT’s Koch Institute; Peter Westcott, a former Jacks lab postdoc who is now an assistant professor at Cold Spring Harbor Laboratory; and Saori Goto, an MIT postdoc in the Yilmaz lab.

Immune evasion

Colon cancer usually arises in long-lived cells called intestinal stem cells, whose job is to continually regenerate the lining of the intestines. Over their long lifetime, these cells can accumulate cancerous mutations that lead to the formation of polyps, a type of premalignant growth that can eventually become metastatic colon cancer.

To learn more about how these precancerous growths evade the immune system, the researchers used a technique they had previously developed for growing mini colon tumors in a lab dish and then implanting them into mice. In this case, the researchers engineered the tumors to express mutated versions of cancer-linked genes Kras, p53, and APC, which are often found in human colon cancers.

Once these tumors were implanted in mice, the researchers observed a dramatic increase in the tumors’ expression of SOX17. This gene encodes a transcription factor that is normally active only during embryonic development, when it helps to control development of the intestines and the formation of blood vessels.

The researchers’ experiments revealed that when SOX17 is turned on in cancer cells, it helps the cells to create an immunosuppressive environment. Among its effects, SOX17 prevents cells from synthesizing the receptor that normally detects interferon gamma, a molecule that is one of the immune system’s primary weapons against cancer cells.

Without those interferon gamma receptors, cancerous and precancerous cells can simply ignore messages from the immune system, which would normally direct them to undergo programmed cell death.

“One of SOX17’s main roles is to turn off the interferon gamma signaling pathway in colorectal cancer cells and in precancerous adenoma cells. By turning off interferon gamma receptor signaling in the tumor cells, the tumor cells become hidden from T cells and can grow in the presence of an immune system,” Yilmaz says.

Without interferon gamma signaling, cancer cells also minimize their production of molecules called MHC proteins, which are responsible for displaying cancerous antigens to the immune system. The cells’ insensitivity to interferon gamma also prevents them from producing immune molecules called chemokines, which normally recruit T cells that would help destroy the cancerous cells.

Targeting SOX17

When the researchers generated colon tumor organoids with SOX17 knocked out, and implanted those into mice, the immune system was able to attack those tumors much more effectively. This suggests that preventing cancer cells from turning off SOX17 could offer a way to treat colon cancer in its earliest stages.

“Just by turning off SOX17 in fairly complex tumors, we were able to essentially obliterate the ability of these tumor cells to persist,” Goto says.

As part of their study, the researchers also analyzed gene expression data from patients with colon cancer and found that SOX17 tended to be highly expressed in early-stage colon cancers but dropped off as the tumors became more invasive and metastatic.

“We think this makes a lot of sense because as colorectal cancers become more invasive and metastatic, there are other mechanisms that create an immunosuppressive environment,” Yilmaz says. “As the colon cancer becomes more aggressive and activates these other mechanisms, then there’s less importance for SOX17.”

Transcription factors such as SOX17 are considered difficult to target using drugs, in part because of their disorganized structure, so the researchers now plan to identify other proteins that SOX17 interacts with, in hopes that it might be easier to block some of those interactions.

The researchers also plan to investigate what triggers SOX17 to turn on in precancerous cells.

The research was funded by the MIT Stem Cell Initiative via Fondation MIT, the National Institutes of Health/National Cancer Institute, and a Koch Institute-Dana Farber Harvard Cancer Center Bridge Project grant.

Whitney Henry

Education

  • Graduate: PhD, 2016, Harvard University
  • Undergraduate: BS, 2010, Biology, Grambling State University

Research Summary

Ferroptosis is an iron-dependent form of cell death with profound implications in human health and disease. In the context of cancer, the use of ferroptosis inducers to target subpopulations of highly metastatic and therapy-resistant cancer cells has garnered much excitement over the last few years. However, to gain a comprehensive understanding of the full therapeutic potential of ferroptosis, our research focuses on (i) uncovering the molecular factors affecting ferroptosis susceptibility, (ii) studying its impact on the tumor microenvironment, and (iii) developing innovative ways to modulate ferroptosis resistance in vivo. We employ a multidisciplinary approach, combining functional genomics, metabolomics, bioengineering, and a range of in vitro and in vivo models to advance our understanding in this domain and to translate our findings into effective therapies.

Awards

  • The Margaret and Herman Sokol Postdoctoral Award, 2022
  • Ludwig Center at MIT Postdoctoral Fellowship, 2022
  • Jane Coffin Childs Memorial Fund Postdoctoral Fellowship, 2017
  • HHMI International Predoctoral Research Fellowship, 2013
Study explains why certain immunotherapies don’t always work as predicted

The findings could help doctors identify cancer patients who would benefit the most from drugs called checkpoint blockade inhibitors.

Anne Trafton | MIT News
September 14, 2023

Cancer drugs known as checkpoint blockade inhibitors have proven effective for some cancer patients. These drugs work by taking the brakes off the body’s T cell response, stimulating those immune cells to destroy tumors.

Some studies have shown that these drugs work better in patients whose tumors have a very large number of mutated proteins, which scientists believe is because those proteins offer plentiful targets for T cells to attack. However, for at least 50 percent of patients whose tumors show a high mutational burden, checkpoint blockade inhibitors don’t work at all.

A new study from MIT reveals a possible explanation for why that is. In a study of mice, the researchers found that measuring the diversity of mutations within a tumor generated much more accurate predictions of whether the treatment would succeed than measuring the overall number of mutations.

If validated in clinical trials, this information could help doctors to better determine which patients will benefit from checkpoint blockade inhibitors.

“While very powerful in the right settings, immune checkpoint therapies are not effective for all cancer patients. This work makes clear the role of genetic heterogeneity in cancer in determining the effectiveness of these treatments,” says Tyler Jacks, the David H. Koch Professor of Biology and a member of MIT’s Koch Institute for Cancer Research.

Jacks; Peter Westcott, a former MIT postdoc in the Jacks lab who is now an assistant professor at Cold Spring Harbor Laboratory; and Isidro Cortes-Ciriano, a research group leader at EMBL’s European Bioinformatics Institute (EMBL-EBI), are the senior authors of the paper, which appears today in Nature Genetics.

A diversity of mutations

Across all types of cancer, a small percentage of tumors have what is called a high tumor mutational burden (TMB), meaning they have a very large number of mutations in each cell. A subset of these tumors has defects related to DNA repair, most commonly in a repair system known as DNA mismatch repair.

Because these tumors have so many mutated proteins, they are believed to be good candidates for immunotherapy treatment, as they offer a plethora of potential targets for T cells to attack. Over the past few years, the FDA has approved a checkpoint blockade inhibitor called pembrolizumab, which activates T cells by blocking a protein called PD-1, to treat several types of tumors that have a high TMB.

However, subsequent studies of patients who received this drug found that more than half of them did not respond well or only showed short-lived responses, even though their tumors had a high mutational burden. The MIT team set out to explore why some patients respond better than others, by designing mouse models that closely mimic the progression of tumors with high TMB.

These mouse models carry mutations in genes that drive cancer development in the colon and lung, as well as a mutation that shuts down the DNA mismatch repair system in these tumors as they begin to develop. This causes the tumors to generate many additional mutations. When the researchers treated these mice with checkpoint blockade inhibitors, they were surprised to find that none of them responded well to the treatment.

“We verified that we were very efficiently inactivating the DNA repair pathway, resulting in lots of mutations. The tumors looked just like they look in human cancers, but they were not more infiltrated by T cells, and they were not responding to immunotherapy,” Westcott says.

The researchers discovered that this lack of response appears to be the result of a phenomenon known as intratumoral heterogeneity. This means that, while the tumors have many mutations, each cell in the tumor tends to have different mutations than most of the other cells. As a result, each individual cancer mutation is “subclonal,” meaning that it is expressed in a minority of cells. (A “clonal” mutation is one that is expressed in all of the cells.)

In further experiments, the researchers explored what happened as they changed the heterogeneity of lung tumors in mice. They found that in tumors with clonal mutations, checkpoint blockade inhibitors were very effective. However, as they increased the heterogeneity by mixing tumor cells with different mutations, they found that the treatment became less effective.

“That shows us that intratumoral heterogeneity is actually confounding the immune response, and you really only get the strong immune checkpoint blockade responses when you have a clonal tumor,” Westcott says.

Failure to activate

It appears that this weak T cell response occurs because the T cells simply don’t see enough of any particular cancerous protein, or antigen, to become activated, the researchers say. When the researchers implanted mice with tumors that contained subclonal levels of proteins that normally induce a strong immune response, the T cells failed to become powerful enough to attack the tumor.

“You can have these potently immunogenic tumor cells that otherwise should lead to a profound T cell response, but at this low clonal fraction, they completely go stealth, and the immune system fails to recognize them,” Westcott says. “There’s not enough of the antigen that the T cells recognize, so they’re insufficiently primed and don’t acquire the ability to kill tumor cells.”

To see if these findings might extend to human patients, the researchers analyzed data from two small clinical trials of people who had been treated with checkpoint blockade inhibitors for either colorectal or stomach cancer. After analyzing the sequences of the patients’ tumors, they found that patients’ whose tumors were more homogeneous responded better to the treatment.

“Our understanding of cancer is improving all the time, and this translates into better patient outcomes,” Cortes-Ciriano says. “Survival rates following a cancer diagnosis have significantly improved in the past 20 years, thanks to advanced research and clinical studies. We know that each patient’s cancer is different and will require a tailored approach. Personalized medicine must take into account new research that is helping us understand why cancer treatments work for some patients but not all.”

The findings also suggest that treating patients with drugs that block the DNA mismatch repair pathway, in hopes of generating more mutations that T cells could target, may not help and could be harmful, the researchers say. One such drug is now in clinical trials.

“If you try to mutate an existing cancer, where you already have many cancer cells at the primary site and others that may have disseminated throughout the body, you’re going to create a super heterogeneous collection of cancer genomes. And what we showed is that with this high intratumoral heterogeneity, the T cell response is confused and there is absolutely no response to immune checkpoint therapy,” Westcott says.

The research was funded by the Koch Institute Support (core) Grant from the U.S. National Cancer Institute, the Howard Hughes Medical Institute, and a Damon Runyon Fellowship Award.

Exploring the links between diet and cancer

Omer Yilmaz’s work on how diet influences intestinal stem cells could lead to new ways to treat or prevent gastrointestinal cancers.

Anne Trafton | MIT News Office
May 25, 2023

Every three to five days, all of the cells lining the human intestine are replaced. That constant replenishment of cells helps the intestinal lining withstand the damage caused by food passing through the digestive tract.

This rapid turnover of cells relies on intestinal stem cells, which give rise to all of the other types of cells found in the intestine. Recent research has shown that those stem cells are heavily influenced by diet, which can help keep them healthy or stimulate them to become cancerous.

“Low-calorie diets such as fasting and caloric restriction can have antiaging effects and antitumor effects, and we want to understand why that is. On the other hand, diets that lead to obesity can promote diseases of aging, such as cancer,” says Omer Yilmaz, the Eisen and Chang Career Development Associate Professor of Biology at MIT.

For the past decade, Yilmaz has been studying how different diets and environmental conditions affect intestinal stem cells, and how those factors can increase the risk of cancer and other diseases. This work could help researchers develop new ways to improve gastrointestinal health, either through dietary interventions or drugs that mimic the beneficial effects of certain diets, he says.

“Our findings have raised the possibility that fasting interventions, or small molecules that mimic the effects of fasting, might have a role in improving intestinal regeneration,” says Yilmaz, who is also a member of MIT’s Koch Institute for Integrative Cancer Research.

A clinical approach

Yilmaz’s interest in disease and medicine arose at an early age. His father practiced internal medicine, and Yilmaz spent a great deal of time at his father’s office after school, or tagging along at the hospital where his father saw patients.

“I was very interested in medicines and how medicines were used to treat diseases,” Yilmaz recalls. “He’d ask me questions, and many times I wouldn’t know the answer, but he would encourage me to figure out the answers to his questions. That really stimulated my interest in biology and in wanting to become a doctor.”

Knowing that he wanted to go into medicine, Yilmaz applied and was accepted to an eight-year, combined bachelor’s and MD program at the University of Michigan. As an undergraduate, this gave him the freedom to explore areas of interest without worrying about applying to medical school. While majoring in biochemistry and physics, he did undergraduate research in the field of protein folding.

During his first year of medical school, Yilmaz realized that he missed doing research, so he decided to apply to the MD/PhD program at the University of Michigan. For his PhD research, he studied blood-forming stem cells and identified new markers that allowed such cells to be more easily isolated from the bone marrow.

“This was important because there’s a lot of interest in understanding what makes a stem cell a stem cell, and how much of it is an internal program versus signals from the microenvironment,” Yilmaz says.

After finishing his PhD and MD, he thought about going straight into research and skipping a medical residency, but ended up doing a residency in pathology at Massachusetts General Hospital. During that time, he decided to switch his research focus from blood-forming stem cells to stem cells found in the gastrointestinal tract.

“The GI tract seemed very interesting because in contrast to the bone marrow, we knew very little about the identity of GI stem cells,” Yilmaz says. “I knew that once GI stem cells were identified, there’d be a lot of interesting questions about how they respond to diet and how they respond to other environmental stimuli.”

Dietary questions

To delve into those questions, Yilmaz did postdoctoral research at the Whitehead Institute, where he began investigating the connections between stem cells, metabolism, diet, and cancer.

Because intestinal stem cells are so long-lived, they are more likely to accumulate genetic mutations that make them susceptible to becoming cancerous. At the Whitehead Institute, Yilmaz began studying how different diets might influence this vulnerability to cancer, a topic that he carried into his lab at MIT when he joined the faculty in 2014.

One question his lab has been exploring is why low-calorie diets often have protective effects, including a boost in longevity — a phenomenon that has been seen in many studies in animals and humans.

In a 2018 study, his lab found that a 24-hour fast dramatically improves stem cells’ ability to regenerate. This effect was seen in both young and aged mice, suggesting that even in old age, fasting or drugs that mimic the effects of fasting could have a beneficial effect.

On the flip side, Yilmaz is also interested in why a high-fat diet appears to promote the development of cancer, especially colorectal cancer. In a 2016 study, he found that when mice consume a high-fat diet, it triggers a significant increase in the number of intestinal stem cells. Also, some non-stem-cell populations begin to resemble stem cells in their behavior. “The upshot of these changes is that both stem cells and non-stem-cells can give rise to tumors in a high-fat diet state,” Yilmaz says.

To help with these studies, Yilmaz’s lab has developed a way to use mouse or human intestinal stem cells to generate miniature intestines or colons in cell culture. These “organoids” can then be exposed to different nutrients in a very controlled setting, allowing researchers to analyze how different diets affect the system.

Recently, his lab adapted the system to allow them to expand their studies to include the role of immune cells, fibroblasts, and other supportive cells found in the microenvironment of stem cells. “It would be remiss of us to focus on just one cell type,” Yilmaz says. “We’re looking at how these different dietary interventions impact the entire stem cell neighborhood.”

While Yilmaz spends most of his time running his lab at MIT, he also devotes six to eight weeks per year to his work at MGH, where he is an associate pathologist focusing on gastrointestinal pathology.

“I enjoy my clinical work, and it always reminds me about the importance of the research we do,” he says. “Seeing colon cancer and other GI cancers under the microscope, and seeing their complexity, reminds me of the importance of our mission to figure out how we can prevent these cancers from forming.”