Research Area: Human Disease

Susumu Tonegawa

Education

  • PhD, 1968, University of California, San Diego
  • BS, 1963, Chemistry, Kyoto University

Research Summary

We are interested in the molecular, cellular and neural circuit mechanisms underlying learning and memory in rodents. We generate genetically engineered mice, and analyze them through multiple methods including molecular and cellular biology, electrophysiology, microscopic imaging, optogenetic engineering, and behavioral studies. Ultimately, we aim to detect the effects of our manipulations at multiple levels in the brain — deducing which behaviors or cognitions are causally linked to specific processes and events taking place at the molecular, cellular, and neuronal circuit levels.

Awards

  • The Nobel Foundation, Nobel Prize in Physiology or Medicine, 1987
  • Albert and Mary Lasker Award in Basic Research, 1987
  • National Academy of Sciences, Member, 1986
New player in cellular signaling

Researchers have identified a key nutrient sensor in the mTOR pathway that links nutrient availability to cell growth.

Nicole Giese Rura | Whitehead Institute
November 9, 2017

To survive and grow, a cell must properly assess the resources available and couple that with its growth and metabolism — a misstep in that calculus can potentially cause cell death or dysfunction. At the crux of these decisions is the mTOR pathway, a cellular pathway connecting nutrition, metabolism, and disease.

The mTOR pathway incorporates input from multiple factors, such as oxygen levels, nutrient availability, growth factors, and insulin levels to promote or restrict cellular growth and metabolism. But when the pathway runs amok, it can be associated with numerous diseases, including cancer, diabetes, and Alzheimer’s disease. Understanding the various sensors that feed into the mTOR pathway could lead to novel therapies for these diseases and even aging, as dialing down the mTOR pathway is linked to longer lifespans in mice and other organisms.

Although the essential amino acid methionine is one of the key nutrients whose levels cells must carefully sense, researchers did not know how it fed into the mTOR pathway — or if it did at all. Now, Whitehead Institute Member David Sabatini and members of his laboratory have identified a protein, SAMTOR, as a sensor in the mTOR pathway for the methionine derivative SAM (S-adenosyl methionine). Their findings are described in the current issue of the journal Science.

Methionine is essential for protein synthesis, and a metabolite produced from it, SAM, is involved in several critical cellular functions to sustain growth, including DNA methylation, ribosome biogenesis, and phospholipid metabolism. Interestingly, methionine restriction at the organismal level has been linked to increased insulin tolerance and lifespan, similar to the antiaging effects associated with inhibition of mTOR pathway activity. But the connection between mTOR, methionine, and aging remains elusive.

“There are a lot of similarities between the phenotypes of methionine restriction and mTOR inhibition,” says Sabatini, who is also a Howard Hughes Medical Institute investigator and a professor of biology at MIT. “The existence of this protein SAMTOR provides some tantalizing data suggesting that those phenotypes may be mechanistically connected.”

Sabatini identified mTOR as a graduate student and has since elucidated numerous aspects of its namesake pathway. He and his lab recently pinpointed the molecular sensors in the mTOR pathway for two key amino acids: leucine and arginine. In the current line of research, co-first authors of the Science paper Xin Gu and Jose Orozco, both graduate students Sabatini’s lab, identified a previously uncharacterized protein that seemed to interact with components of the mTOR pathway. After further investigation, they determined that the protein binds to SAM and indirectly gauges the pool of available methionine, making this protein — SAMTOR — a specific and unique nutrient sensor that informs the mTOR pathway.

“People have been trying to figure out how methionine was sensed in cells for a really long time,” Orozco says. “I think that this is the first time in mammalian cells a mechanism has been found to describe the way methionine can regulate a major signaling pathway like mTOR.”

The current research indicates that SAMTOR plays a crucial role in methionine sensing. Methionine metabolism is vital for many cellular functions, and the Sabatini lab will further investigate the potential links between SAMTOR and the extended lifespan and increased insulin sensitivity effects that are associated with low methionine levels.

“It is very interesting to consider mechanistically how methionine restriction might be associated in multiple organisms with beneficial effects, and identification of this protein provides us a potential molecular handle to further investigate this question,” Gu says. “The nutrient-sensing pathway upstream of mTOR is a very elegant system in terms of responding to the availability of certain nutrients with specific mechanisms to regulate cell growth. The currently known sensors raise some interesting questions about why cells evolved sensing mechanisms to these specific nutrients and how cells treat these nutrients differently.”

This work was supported by the National Institutes of Health, the Department of Defense, the National Science Foundation, and the Paul Gray UROP Fund.

Retinoic acid regulates transitions in mouse sperm production
November 7, 2017

CAMBRIDGE, MA – Sperm production requires progression through a well-orchestrated series of transitions in the testes that move diploid spermatogonia cells, with two complete sets of chromosomes, through a series of transitions to produce haploid sperm, with one copy of each chromosome, poised to swim and fertilize an available egg. There are four major transitions in sperm production, or spermatogenesis. The first is spermatogonial differentiation, during which spermatogonia differentiate, losing their stem-cell like qualities. The resulting spermatocytes then initiate meiosis and undergo two rounds of cell division to generate haploid spermatids. The spermatids undergo elongation and then the resulting sperm are released.

The signals that control progression through these transitions were poorly understood until 2015, when David Page, Member and Director of Whitehead Institute, professor of biology at Massachusetts Institute of Technology, and investigator with Howard Hughes Medical Institute and colleagues determined that retinoic acid (RA), a derivative of vitamin A that has been shown to play a key role in a number of developmental processes, was responsible for coordinating the first two stages of spermatogenesis-differentiation and meiosis. Now, in a paper published this week in the journal Proceedings of the National Academy of Sciences, Page, first author Tsutomu Endo, and colleagues extend those findings to show that RA signaling in mice coordinates the second two transitions as well.

Diagram of model by which retinoic acid coordinates spermatogenesisThe researchers used chemical manipulation of RA levels to determine that RA controlled the second two transitions, spermatid elongation and sperm release, in addition to the first two. With this knowledge in hand, the researchers were then able to drill down and get a better picture of how RA regulates male gamete production. One outstanding question has been how males are able to continually produce sperm throughout their lifetime, in contrast with females whose egg production and maturation is limited. Page and colleagues measured RA levels in the testes and discovered that it is cyclically produced, driving production of sperm during the male lifetime. In addition to the timing of RA production, the researchers also examined its source. From which cells was the RA signal coming? During the first two transitions, they determined that the RA was coming from the somatic Sertoli cells, the support cells of the testes, and in the second two transitions they determined that it was being released by the germ cells themselves-the meiotic (pachytene-stage) spermatocytes were found to be secreting RA to other germ cells in the testes.

These findings not only contribute to our fundamental understanding of male gamete formation, they also provide important clues for the field of reproductive technology. For years, scientists have been working on making gametes in the laboratory, but have had difficulty making functional sperm. This discovery of the role of RA in spermatogenesis adds important tools to the toolbox of assisted reproduction. The work shows that RA is required in both the early and late transitions of spermatogenesis and sheds light on an important component of laboratory efforts for sperm production.

Other researchers involved include Elizaveta Freinkman and Dirk G. de Rooij.

This research was supported by Howard Hughes Medical Institute (HHMI) and the United States Department of Defense (DoD W81XWH-15-1-0337)

Written by Lisa Girard
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David Page’s primary affiliation is with Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted. He is also a Howard Hughes Medical Institute Investigator and a Professor of Biology at the Massachusetts Institute of Technology.
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Paper cited: Endo, T et al.  Periodic production of retinoic acid by meiotic and somatic cells coordinates four transitions in mouse spermatogenesis. Proc Natl Acad Sci. DOI: 10.1073/pnas.1710837114. Epub 2017 Nov 6.
Other work cited: Endo T et al. Periodic retinoic acid-STRA8 signaling intersects with periodic germ-cell competencies to regulate spermatogenesis. Proc Natl Acad Sci. DOI: 10.1073/pnas.1505683112. Epub 2015 Apr 20.
A new workflow for natural product characterization comes ashore with red algae
October 30, 2017

CAMBRIDGE, Mass. – A few years ago while paddling off the coast near La Jolla, California, avid surfer Roland Kersten noticed a piece of red algae (Laurenica pacifica) bobbing alongside his surfboard. Kersten, whose background is in natural product chemistry, was intrigued.

Natural products—chemicals from living organisms such as plants and algae—represent a rich source of potential therapeutics. A majority of anti-cancer drugs are natural product-based or inspired. One such well-known natural product—the potent anti-cancer drug Taxol—was identified in the bark of a yew tree.

Marine algae, like the red algae Kersten found, are often rich in compounds called sesquiterpenes, some of which have been shown to have potential medicinal attributes. Since the 1970s, scientists identified many sesquiterpenes produced by Laurencia species with anti-cancer properties. The identification techniques usually required about tens of milligrams of purified compounds, which were obtained from more than a kilogram of algae. Because Laurencia and the reef ecosystems in which it thrives are protected, and such large-scale harvesting for scientific or medicinal purposes is no longer tenable, Kersten had to devise a different approach to analyze its sesquiterpenes.

Kersten received a collection permit to clamber over the rocky shore at deep low tide to collect a hand-sized sample of the red algae. Now a postdoctoral fellow in the lab of Whitehead Member and Massachusetts Institute of Technology assistant professor of biology Jing-Ke Weng, Kersten’s first task was to search the RNA sequences of all genes expressed in his red algae sample to find those whose product seemed likely to be enzymes that make sesquiterpenes.  In order to determine the product generated by these enzymes, he engineered them in yeast and isolated its sesquiterpene products.

In order to define the first step in the biogenesis of sesquiterpenes in red algae, Kersten wanted to see the precise 3-D structure of the isolated sesquiterpene. But the small handful of algae he had obtained produced only a fraction of the amount required for x-ray crystallography, the established method for determining a compound’s absolute structure. So Kersten tried a method recently developed by collaborator Makoto Fujita at the University of Tokyo that requires only a few nanograms of material: soaking extracted compounds into a special crystalline sponge, which supports the sample’s molecular shape while it is bombarded with x-rays to accurately determine the 3-D conformation of a molecule. A new combination of the crystalline sponge method and nuclear magnetic resonance spectroscopy by the Fujita group revealed the structure of prespatane.

With the compound’s structure in hand, Kersten is closer to understanding how Laurenciabiosynthesizes its sesquiterpenes and how to engineer yeast to produce the same molecules for medicinal research at scale—without touching the red algae flourishing on protected reefs. And the novel workflow—spanning genomics, metabolomics, synthetic biology, and x-ray crystallography with crystalline sponges—established by Weng, Kersten, and their collaborators may expedite the identification of other promising compounds produced by organisms from both land and sea.

Other contributors to this work include Shoukou Lee of Tokyo University, Daishi Fujita of Tokyo University and Whitehead Institute, Tomáš Pluskal of Whitehead Institute.  The team also collaborated with researchers from Scripps Institution of Oceanography and Salk Institute of Biological Sciences.

This work was supported by Howard Hughes Medical Institute, the Simons Foundation, the Helen Hay Whitney Foundation, the Pew Scholars Program in the Biomedical Sciences, the Searle Scholars Program, and the Japan Science and Technology Agency.

 Written by Nicole Giese Rura
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Jing-Ke Weng’s primary affiliation is with Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted. He is also an assistant professor of biology at Massachusetts Institute of Technology.
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Full Citation:
“A Red Algal Bourbonane Sesquiterpene Synthase Defined by Microgram-scale NMR-coupled Crystalline Sponge XRD Analysis”
Journal of the American Chemical Society, online October 30, 2017.
Roland D. Kersten (1,6), Shoukou Lee (2,6) , Daishi Fujita (1,2) , Tomáš Pluskal (1) , Susan Kram (3), Jennifer E. Smith (3) , Takahiro Iwai (2) , Joseph P. Noel (4) , Makoto Fujita (2), Jing-Ke Weng (1,5).
1. Whitehead Institute for Biomedical Research, 455 Main Street, Cambridge, MA, United States
2. Graduate School of Engineering, The University of Tokyo, JST-ACCEL, Tokyo, Japan
3. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, United States
4. Howard Hughes Medical Institute, Jack H. Skirball Center for Chemical Biology and Proteomics, The Salk Institute for Biological Studies, La Jolla, CA, United States
5. Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States
6. These authors contributed equally
Stuck on the membrane

A pro-metastatic transcription factor’s journey from anonymity to a promising target for breast cancer therapy

October 20, 2017

An overwhelming majority of deaths from cancer are associated not with the primary tumor, but instead with its metastases to other sites in the body. For this reason, understanding the properties of cancer cells that give them a high metastatic potential, and identifying molecular strategies to intervene, is critical for improving clinical outcomes.

One of the hallmarks of cancer cells with high metastatic potential is an epithelial to mesenchymal transition (EMT). This shift in their gene expression landscape is a harbinger for both invasive behavior and anti-cancer drug resistance. One signaling pathway active in cells that have undergone EMT transition, the PERK pathway, has been of particular interest to Whitehead Institute Member and Massachusetts Institute of Technology associate professor of biology Piyush Gupta and postdoctoral researchers in Gupta’s lab, Yu-Xiong Feng and Dexter Jin. The PERK signaling pathway has been a sought-after target for a number of types of cancer, including breast cancer. Drug companies had largely given up on the PERK signaling pathway as a target, however, because when it is inhibited, it also has the unintended consequence of affecting glucose regulation to the degree that mice given PERK inhibitors typically develop diabetes within a few weeks. Gupta and colleagues hypothesized that downstream elements of the pathway could include targets with more specific effects on metastatic behavior, potentially enabling the development of therapies that do not result in the unintended consequences associated with inhibiting PERK. 

In a recent article in Nature Communications, Gupta, Feng, Jin, and colleagues describe CREB3L1, a factor downstream of the PERK pathway that is active in the subset of triple negative breast cancer cells and tumor cells that have undergone an EMT transition. CREB3L1 expression is associated with distant metastasis and is important for the transformed cell’s invasive and drug resistant properties. While factors like CREB3L1, called transcription factors, are usually difficult to target with small molecules, Gupta and his team zeroed in on a unique property it shares with only a small handful of other factors-it is normally stuck to the membrane of a cellular compartment called the endoplasmic reticulum and, in order for it to be active, it need to be cut free by factors called proteases. Gupta and colleagues show that certain protease inhibitors can actually stop the activation of CREB3L1 in its tracks, along with the invasive and drug resistance properties its activation confers. 

While the PERK signaling pathway has been an attractive target for anticancer therapy, its more general cellular role made it an intractable target. The downstream factor of the pathway  CREB3L1 is a potential new target for breast cancer therapy whose specificity of action makes it an attractive option for targeting metastatic behavior.

By Lisa Girard
Citation:
Feng Y-X, Jin DX, et al. “Cancer-specific PERK signaling drives invasion and metastasis through CREB3L1.” Nature Communications DOI:10.1038/s41467-017-01052-y
Genetic body/brain connection identified in genomic region linked to autism
October 6, 2017

CAMBRIDGE, Mass. – For the first time, Whitehead Institute scientists have documented a direct link between deletions in two genes—fam57ba and doc2a—in zebrafish and certain brain and body traits, such as seizures, hyperactivity, enlarged head size, and obesity.

“Finding the molecular connections between a brain and a body phenotype is indeed really paradigm shifting,” says Whitehead Institute Member Hazel Sive, who is also a professor of biology at MIT. “It lets us think about the common control of these two aspects of phenotype, which is very interesting and could be useful for developing therapies for these phenotypes.”

Both genes reside in the 16p11.2 region of human chromosome 16. About 1 in 2000, or around 4 million people worldwide, have deletions in this region, and these deletions are associated with multiple brain and body symptoms, including autism spectrum disorders, developmental delay, intellectual disability, seizures, and obesity.

Scientists have had difficulty teasing apart the relationship between specific traits and deletions in this region, because it includes at least 25 genes, and because there is not a one-to-one mapping of gene to phenotype. Instead, multiple genes seem to create a web of interactions that produce a variety of characteristics.

To solve such a complex puzzle, Jasmine McCammon, a postdoctoral researcher in Sive’s lab, enlisted the zebrafish as a “living test tube”.  The Sive group uses zebrafish to study the genetic/phenotype connections associated with human disorders. Like the human genome, the zebrafish genome has two copies of each gene, and scientists can remove the function of multiple genes to produce phenotypes that are reminiscent of human symptoms.

The results from McCammon’s initial screen with zebrafish indicate that two genes in the 16p11.2 region could be key for brain development: fam57ba and doc2a. (fam57b encodes a ‘ceramide synthase’ that makes a kind of lipid, and doc2a encodes a regulator of secretion.) McCammon investigated further by deleting one copy of fam57ba and doc2a individually; the effect was minimal. However, simultaneously removing a copy of both genes revealed significant synergy between them. Compared with controls, fish with only one copy of each gene exhibit hyperactivity, increased propensity for seizures, increased body and head size, and fat content. When both copies of only fam57ba are removed, the fish are much larger and with a higher fat content. All of the study’s results are published in the journal Human Molecular Genetics.

Although her findings use zebrafish and are far from the clinic, McCammon was struck by how much people affected by deletions in this genome identified with her results.

“When I spoke with the parents of some kids with neurodevelopmental disorders, I was surprised how much the brain/body connection that we described resonated with them,” she says. “They said that yes, their child has autism, but he also has really weak muscle tone. Or she has a gastrointestinal problem and that’s been more problematic than her behavior issues. For me, it’s been really revealing to talk to people who’ve actually experienced this as opposed to reading about statistics in journals.”

The mechanisms underlying this brain/body connection are still not well understood. One of the identified genes, fam57ba, provides some intriguing hints as to how metabolism and brain function could be intertwined, because it produces an enzyme that plays a role in lipid production and is believed to be a metabolic regulator.  The lipid type, ceramide, also has a functional role in various signaling pathways and affects synaptic function, although its primary role is not in the synapse, but providing structure in cell membranes.

For Sive, the two identified genes could be just the beginning. “Our data suggest that there may be metabolic genes involved in human neurodevelopmental disorders,” she says.  “This is a nascent field, that we’re very interested in going forward.”

This work was supported by Jim and Pat Poitras, Len and Ellen Polaner, and the Markell-Balkin-Weinberg Postdoctoral Fellowship.

Written by Nicole Giese Rura
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Hazel Sive’s primary affiliation is with Whitehead Institute for Biomedical Research, where her laboratory is located and all her research is conducted. She is also a professor of biology at Massachusetts Institute of Technology.
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Full Citation:
“The 16p11.2 homologs fam57ba and doc2a generate certain brain and body phenotypes”
Human Molecular Genetics, Volume 26, Issue 19, 1 October 2017.
Jasmine M. McCammon(1), Alicia Blaker-Lee(1), Xiao Chen(2), and Hazel Sive (1,2).
1. Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
2. Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Department of Biology hosts its first Science Slam

Eight biology trainees had just three minutes to explain their research and earn favor with the judges and audience in new yearly event.

Raleigh McElvery | Department of Biology
October 5, 2017

Nearly 300 spectators crowded into a lecture hall at the Ray and Maria Stata Center on a recent Tuesday to witness the first annual Science Slam, hosted by MIT’s Department of Biology.

A science slam features a series of short presentations where researchers explain their work in a compelling manner and — as the name suggests — make an impact. The presentations aren’t just talks, they’re performances geared towards a science-literate but non-specialized public audience. In this case, competitors were each given one slide and three minutes to tell their scientific tales and earn votes from audience members and judges.

The jury included Ellen Clegg, editorial page editor of The Boston Globe and co-author of two award-winning books, “ChemoBrain” and “The Alzheimer’s Solution;” Emilie Marcus, CEO of Cell Press and editor-in-chief of the flagship journal, Cell; and Ari Daniel, an independent science reporter who produces digital videos for PBS NOVA and co-produces the Boston branch of Story Collider.

Among the competitors were five graduate students and three postdocs who hailed from labs scattered throughout Building 68, the Whitehead Institute, the Broad Institute, the Koch Institute for Integrative Cancer Research, and the Picower Institute for Learning and Memory. The storytellers were:

  • Sahin Naqvi, from David Page’s lab, who spoke about the evolution of genetic sex differences in mammals, as well as how these differences impact the likelihood of developing certain diseases based on gender;
  • Sudha Kumari, from Darrell Irvine’s lab, who spoke about her work investigating immune cell interactions — specifically how T cells communicate using physical contact;
  • Deniz Atabay, from Peter Reddien’s lab, who spoke about the ways cells in flatworms self-organize during regeneration to re-form organs, tissues, and even neural circuits;
  • Emma Kowal, from Christopher Burge’s lab, who spoke about her goals to demystify the ways in which certain noncoding regions of genetic sequence, known as introns, contribute to protein production;
  • Xin Tang, from Rudolf Jaenisch’s lab, who spoke about a technique to illuminate the seemingly invisible changes in brain cells that trigger disease, using a glowing enzyme from a firefly;
  • Nicole Aponte, from Troy Littleton’s lab, who spoke about her ability to manipulate brain cell activity in the fruit fly, and study how defects in neuronal connections contribute to developmental disorders;
  • Karthik Shekhar, from Aviv Regev’s lab, who spoke about his efforts to identify and manipulate different types of brain cells, understanding how they assemble into complex networks to facilitate learning, memory, and — in some cases — disease; and
  • Monika Avello, from Alan Grossman’s lab, who spoke about “bacterial sexology,” that is, how and why these organisms choose to block unwanted sexual advances from fellow bacteria.

Vivian Siegel, who oversees the department’s communications efforts, moderated the event. Siegel and the Building 68 communications team joined forces with three members of the Building 68 MIT Postdoctoral Association — Ana Fiszbein, Isabel Nocedal, and Peter Sudmant — to publicize the event and to host two pre-slam workshops, as well as one-on-one training sessions with individual participants.

“Participating in a Science Slam seemed like a great way for our trainees to learn how to communicate to a nonspecialized audience, which is something they will need to be able to do throughout their careers,” Siegel said. “We really wanted to develop a camaraderie among the participants, and bring trainees together from across the department to help each other tell compelling stories about their science.”

Kowal — whose talk was titled “Gone but Not Forgotten: How Do Introns Enhance Gene Expression?”  — ultimately took home both the audience and jury cash prizes. Kowal completed her undergraduate degree in chemical and physical biology at Harvard before coming to MIT for graduate school. Her dream is to write science fiction, so she decided she’d better study science so she’d know what to write about.

“I really enjoyed seeing people get stoked about introns, and the fact that they enhance gene expression,” she said. “It’s a great way to get comfortable explaining your project in a compelling way to a broad audience. Since you’ll probably be telling people about your work for a while, I think it’s a very good use of time to practice doing that.”

New target for treating “undruggable” lung cancer

Drug already in clinical trials may be effective on some aggressive adenocarcinomas.

Becky Ham | MIT News correspondent
October 2, 2017

Mutations in the KEAP1 gene could point the way to treating an aggressive form of lung cancer that is driven by “undruggable” mutations in the KRAS gene, according to a new study by MIT researchers.

KEAP1 mutations occur alongside KRAS mutations in about 17 percent of lung adenocarcinoma cases. Tyler Jacks, director of MIT’s Koch Institute for Integrative Cancer Research and co-senior author of the study, and his colleagues found that cancer cells with nonfunctioning KEAP1 genes are hungry for glutamine, an amino acid essential for protein synthesis and energy use. Starving these cells of glutamine may thus offer a way to treat cancers with both KRAS and KEAP1 mutations.

Indeed, small-molecule-based inhibitors of glutaminase, an enzyme crucial to glutamine metabolism, slowed cancer cell growth and led to smaller tumors overall in human lung adenocarcinoma cell lines and in tumors in mice with KEAP1 mutations, the researchers found.

The study offers a way to identify lung cancer patients who might respond well to drugs that block the work of glutaminase, says MIT graduate student Rodrigo Romero, a first author on the paper that appears in the Oct. 2 online edition of Nature Medicine.

“All cell lines that we have currently tested that are KEAP1-mutant — independent of their KRAS status — appear to be exquisitely sensitive to glutaminase inhibitors,” says Romero, a graduate student in Jacks’ lab, who participated in the MIT Summer Research Program (MSRP) as an undergraduate.

Hyperactivating the antioxidant response

Lung adenocarcinoma accounts for about 40 percent of U.S. lung cancers, and 15 to 30 percent of those cases contain a KRAS mutation. KRAS has been “notoriously difficult to inhibit” because the usual ways of blocking the KRAS protein’s interactions or interfering with the protein’s targets have fallen short, says Romero.

Lung cancers containing KRAS mutations often harbor other mutations, including KEAP1, which is the third most frequently mutated gene in lung adenocarcinoma. To find out more about how these co-mutations affect lung cancer progression, the MIT research team created KEAP1 mutations in mouse models of lung adenocarcinoma, using the CRISPR/Cas9 gene-editing system to target the gene.

The KEAP1 protein normally represses another protein called NRF2, which controls the activation of an antioxidant response that removes toxic, reactive oxygen species from cells. When the researchers disabled KEAP1 with loss-of-function mutations, NRF2 was able to accumulate and contribute to a “hyperactivation” of the antioxidant response.

Lung adenocarcinomas bearing the KEAP1 mutation may “take advantage of this [hyper-activation] to promote cellular growth or detoxify intracellular damaging agents,” Romero says.

In fact, when the researchers examined genes targeted by NRF2 across a sample of human lung adenocarcinoma tumors, they concluded that the expression of these genes was greater in advanced stage IV tumors, and that patients with such “up-regulated” NRF2 tumors had significantly worse survival rates than other lung adenocarcinoma patients.

Tumors hungry for glutamine

Romero and colleagues used CRISPR/Cas9 to learn more about other genetic interactions with KEAP1 mutants. Their screening demonstrated that lung cancer cells with KRAS and KEAP1 loss-of function mutations were more dependent than other cells on increased amounts of glutamine.

To learn whether this glutamine hunger could be a therapeutic vulnerability, the researchers tested two glutaminase inhibitors against the cancer cells, including one compound called CB-839 that is in phase I clinical trials for KRAS-mutant lung cancer. CB-839 slowed growth and kept tumors smaller than normal in lung adenocarcinoma with KEAP1 mutations, the researchers found.

Phase I clinical trials that treat KEAP1-mutant lung adenocarcinoma patients with a combination of CB-839 and the cancer immunotherapy drug nivolumab (Opdivo) are also underway, says Romero, who notes the MIT study might help identify patients who would be good candidates for these trials.

“There are also many clinical trials testing the efficacy of glutaminase inhibition in a variety of cancer types, independent of KRAS status. However, the results from these studies are still unclear,” Romero says.

Jacks emphasizes that his laboratory has and will continue to study several mutations beyond KEAP1 that may cooperate with KRAS in their mouse models of human lung adenocarcinoma. “The complexity of human cancer can be quite daunting,” he notes. “The genetic tools that we have assembled allow us to create models of many individual subtypes of the disease and in this way begin to define the exploitable vulnerabilities of each. The observed sensitivity of KEAP1 mutant tumors to glutaminase inhibitors is an important example of this approach. There will be more.”

Co-authors on the Nature Medicine paper include former Koch Institute postdoc Thales Papagiannakopoulos, now at New York University, and MIT professor of biology Matthew Vander Heiden. The research was funded by the Laura and Isaac Perlmutter Cancer Support Grant, the National Institutes of Health, and the Koch Institute Support Grant from the National Cancer Institute.

Biologists identify possible new strategy for halting brain tumors

Cutting off a process that cancerous cells rely on can force them to stop growing.

Anne Trafton | MIT News Office
September 28, 2017

MIT biologists have discovered a fundamental mechanism that helps brain tumors called glioblastomas grow aggressively. After blocking this mechanism in mice, the researchers were able to halt tumor growth.

The researchers also identified a genetic marker that could be used to predict which patients would most likely benefit from this type of treatment. Glioblastoma is usually treated with radiation and the chemotherapy drug temozolamide, which may extend patients’ lifespans but in most cases do not offer a cure.

“There are very few specific or targeted inhibitors that are used in the treatment of brain cancer. There’s really a dire need for new therapies and new ideas,” says Michael Hemann, an associate professor of biology at MIT, a member of MIT’s Koch Institute for Integrative Cancer Research, and a senior author of the study.

Drugs that block a key protein involved in the newly discovered process already exist, and at least one is in clinical trials to treat cancer. However, most of these inhibitors do not cross the blood-brain barrier, which separates the brain from circulating blood and prevents large molecules from entering the brain. The MIT team hopes to develop drugs that can cross this barrier, possibly by packaging them into nanoparticles.

The study, which appears in Cancer Cell on Sept. 28, is a collaboration between the labs of Hemann; Jacqueline Lees, associate director of the Koch Institute and the Virginia and D.K. Ludwig Professor for Cancer Research; and Phillip Sharp, an MIT Institute Professor and member of the Koch Institute. The paper’s lead authors are former MIT postdoc Christian Braun, recent PhD recipient Monica Stanciu, and research scientist Paul Boutz.

Too much splicing

Several years ago, Stanciu and Braun came up with the idea to use a type of screen known as shRNA to seek genes involved in glioblastoma. This test involves using short strands of RNA to block the expression of specific genes. Using this approach, researchers can turn off thousands of different genes, one per tumor cell, and then measure the effects on cell survival.

One of the top hits from this screen was the gene for a protein called PRMT5. When this gene was turned off, tumor cells stopped growing. Previous studies had linked high levels of PRMT5 to cancer, but the protein is an enzyme that can act on hundreds of other proteins, so scientists weren’t sure exactly how it was stimulating cancer cell growth.

Further experiments in which the researchers analyzed other genes affected when PRMT5 was inhibited led them to hypothesize that PRMT5 was using a special type of gene splicing to stimulate tumor growth. Gene splicing is required to snip out portions of messenger RNA known as introns, that are not needed after the gene is copied into mRNA.

In 2015, Boutz and others in Sharp’s lab discovered that about 10 to 15 percent of human mRNA strands still have one to three “detained introns,” even though they are otherwise mature. Because of those introns, these mRNA molecules can’t leave the nucleus.

“What we think is that these strands are basically an mRNA reservoir. You have these unproductive isoforms sitting in the nucleus, and the only thing that keeps them from being translated is that one intron,” says Braun, who is now a physician-scientist at Ludwig Maximilian University of Munich.

In the new study, the researchers discovered that PRMT5 plays a key role in regulating this type of splicing. They speculate that neural stem cells utilize high levels of PRMT5 to guarantee efficient splicing and therefore expression of proliferation genes. “As the cells move toward their mature state, PRMT5 levels drop, detained intron levels rise, and those messenger RNAs associated with proliferation get stuck in the nucleus,” Lees says.

When brain cells become cancerous, PRMT5 levels are typically boosted and the splicing of proliferation-associated mRNA is improved, ultimately helping the cells to grow uncontrollably.

Predicting success

When the researchers blocked PRMT5 in tumor cells, they found that the cells stopped dividing and entered a dormant, nondividing state. PRMT5 inhibitors also halted growth of glioblastoma tumors implanted under the skin of mice, but they did not work as well in tumors located in the brain, because of the difficulties in crossing the blood-brain barrier.

Unlike many existing cancer treatments, the PRMT5 inhibitors did not appear to cause major side effects. The researchers believe this may be because mature cells are not as dependent as cancer cells on PRMT5 function.

The findings shed light on why researchers have previously found PRMT5 to be a promising potential target for cancer treatment, says Omar Abdel-Wahab, an assistant member in the Human Oncology and Pathogenesis Program at Memorial Sloan Kettering Cancer Center, who was not involved in the study.

“PRMT5 has a lot of roles, and until now, it has not been clear what is the pathway that is really important for its contributions to cancer,” says Abdel-Wahab. “What they have found is that one of the key contributions is in this RNA splicing mechanism, and furthermore, when RNA splicing is disrupted, that key pathway is disabled.”

The researchers also discovered a biomarker that could help identify patients who would be most likely to benefit from a PRMT5 inhibitor. This marker is a ratio of two proteins that act as co-factors for PRMT5’s splicing activity, and reveals whether PRMT5 in those tumor cells is involved in splicing or some other cell function.

“This becomes really important when you think about clinical trials, because if 50 percent or 25 percent of tumors are going to have some response and the others are not, you may not have a way to target it toward those patients that may have a particular benefit. The overall success of the trial may be damaged by lack of understanding of who’s going to respond,” Hemann says.

The MIT team is now looking into the potential role of PRMT5 in other types of cancer, including lung tumors. They also hope to identify other genes and proteins involved in the splicing process they discovered, which could also make good drug targets.

Spearheaded by students and postdocs from several different labs, this project offers a prime example of the spirit of collaboration and “scientific entrepreneurship” found at MIT and the Koch Institute, the researchers say.

“I think it really is a classic example of how MIT is a sort of bottom-up place,” Lees says. “Students and postdocs get excited about different ideas, and they sit in on each other’s seminars and hear interesting things and pull them together. It really is an amazing example of the creativity that young people at MIT have. They’re fearless.”

The research was funded by the Ludwig Center for Molecular Oncology at MIT, the Koch Institute Frontier Research Program through the Kathy and Curt Marble Cancer Research Fund, the National Institutes of Health, and the Koch Institute Support (core) Grant from the National Cancer Institute.

Department of Biology welcomes three new faculty members

Recent additions bring diverse expertise and cultural perspectives to research community.

Raleigh McElvery | Department of Biology
July 25, 2017

On July 1, MIT Department of Biology welcomed three new faculty members. Since they were all born outside the continental U.S., these newcomers add to the diversity of cultural experiences and contribute to the global face of science at MIT and its affiliated institutions around Kendall Square. The triad also enhances the department’s diverse array of research initiatives. Their interests are as far-reaching as their roots, and range from investigating genetic diseases and cancer immunotherapy to exploiting parasite vulnerabilities.

“When creative individuals with distinct perspectives and approaches come together in an innovative environment like MIT, the possibilities for scientific collaboration and accomplishment are exceptional,” says Alan Grossman, head of the department. “I couldn’t be more pleased to welcome three such outstanding and accomplished individuals into our research community.”

Eliezer Calo

Eliezer Calo is no stranger to MIT. Although he grew up on a farm more than a thousand miles away in the mountains of Carolina, Puerto Rico, Calo first set foot in MIT’s Building 68 11 years ago — and hasn’t wavered in his decision to become a biologist since. In 2006, as part of the MIT Summer Research Program (MSRP), Calo spent 10 weeks studying under Professor Stephen Bell, examining DNA replication. At the time, Calo was a chemistry major at the University of Puerto Rico, but returned post-graduation to MIT’s Department of Biology, earning his PhD while serving as both a teaching assistant for MIT’s course 7.01 (Introduction to Biology) and MSRP program assistant.

“MIT is very unique,” he says. “I’ve done research at multiple institutions, and yet nothing quite compares. Here, the impossible is made possible.”

After completing his postdoctoral training at Stanford University, Calo returned to Cambridge, Massachusetts, this past January as an assistant professor and extramural member at the Koch Institute to head his own lab — exploring the ways in which errors in cellular organelles called ribosomes can lead to disease.

Ribosomes are vital to the translation of genetic code into the molecules integral to life, but are far less often acknowledged for their role in embryonic development. Calo suggests that when ribosomes are not constructed correctly, they are unable to carry out their cellular duties, hindering cell growth and causing developmental disorders. Calo is interested in one condition specifically: Treacher Collins syndrome, which stems from a mutation in a single gene that impedes proper ribosomal assembly. He will soon transfer his experiments from cell cultures to a new model system — zebrafish — in order to further unravel the relationship between ribosome structure and disease.

“The research I do now is purely based on my interest in understanding how cells work,” Calo says. “Specifically, how the mechanisms controlling growth and proliferation operate. These are essential processes that led to the emergence of multicellular organisms, and thus to our own existence.”

Stefani Spranger

One building over in MIT’s Koch Institute, newly-appointed Assistant Professor Stefani Spranger will work to harness the body’s own defense force to pinpoint and eradicate cancer. Spranger carried her passion for immunotherapy across seas from Munich, Germany. As the daughter of two engineers, Spranger was raised on science. “My parents fostered my curiosity,” she says, “which led to my initial motivation to go into science: to figure out how things work.”

While earning her bachelor’s and master’s degrees from the Ludwig-Maximilians University of Munich, Spranger discussed publications focusing on two clinical trials that used engineered immune cells to combat malignant melanoma. These publications ignited Spranger’s enthusiasm for immune-based therapies, which in turn spurred her doctoral and postdoctoral training at the Helmholtz-Zentrum Munich in the Institute for Molecular Immunology and the University of Chicago, respectively.

While Spranger’s education helped hone her immunology research skills, she is excited to experience a more varied academic environment encompassing a range of disciplines. “I was drawn to MIT because of its diverse faculty and the breadth of research interests,” she says.

Spranger’s lab will employ tumor models in mice to determine how cancer and immune cells interact. In particular, she aims to discern the many factors related to the cells, tissues, and environment that could affect the immune system’s anti-tumor response. Ultimately, Spranger hopes to contribute to new treatments that trigger the body’s defense to thwart cancer.

Sebastian Lourido

Trained as both an artist and a scientist, Sebastian Lourido works to counter an entirely different kind of invader spreading biological mayhem: parasites. Originally from Colombia, he was recently named assistant professor of biology, joining the cohort of 15 faculty members at the Whitehead Institute for Biomedical Research — one of just 28 individuals to ever receive this appointment. The title may be new, but this is familiar turf for Lourido. He became a Whitehead Fellow in 2012, after receiving his PhD in microbiology from Washington University in St. Louis and a bachelor’s in studio art and cell and molecular biology from Tulane University. A pioneer in more ways than one, Lourido formed his own lab as a fellow rather than following a more conventional postdoc path.

Lourido spent much of his childhood exploring his mother’s genetics lab, where he analyzed practically anything he could fit under a microscope. “That experience solidified my excitement for the invisible mechanisms that make up the living world,” he says. “I can’t remember a time when I didn’t know that genetic information was carried in our cells in the form of DNA, and passed from one generation to the next.”

Constantly seeking ways to merge his artistic endeavors with scientific ones, Lourido leverages his creativity to glean insight into the systems and structures that constitute life.  He probes a group of microscopic invaders known as Apicomplexan parasites, revealing their weaknesses in order to devise potential treatments. Lourido’s team was the first to perform a genome-wide functional analysis of an apicomplexan — gaining deeper understanding of the genes and molecules key for the invasion process. In 2013, Lourido received the National Institutes of Health (NIH) Director’s Early Independence Award, and with it a five-year grant to investigate motility in one kind of parasite, Toxoplasma gondii. This same interloper is also the subject of Lourido’s two-year NIH-funded project, for which he is the principal investigator.

Lourido has found the MIT community both welcoming and inclusive. Even as he was interviewing for his new position, he was struck by the collaborative, collegial, and nurturing environment.

“This level of engagement permeates the other elements of our community — students, postdocs, and staff scientists — who drive the exciting research happening every day at MIT,” he says. “There are many forces that shape the diversity of our campus, and we need to be vigilant and work hard to continue to encourage and support scientists from different backgrounds, experiences, and cultures.”