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Sizing up cancer

Graduate student Zhaoqi Li investigates how cancer cells grow by harnessing exceptional chemical reactions

Justin Chen
January 11, 2018

Cancer cells use extreme measures to fuel their growth. In fact, researchers like Zhaoqi Li, a third-year graduate student, witness chemical reactions in these cells that would be impossible in the context of normal cells. In a petri dish, normal cells stop dividing once they cover the bottom of the dish and fit neatly together like mosaic tiles. In contrast, cancer cells continue to proliferate and pile haphazardly into small mounds. Within the human body, this abnormal growth — when combined with the spread of cancer cells throughout the body — interferes with organ function and causes death.

Li, a member of Professor Matthew Vander Heiden’s lab located in the Koch Institute, studies cancer metabolism. His work describes the chemical reactions cancer cells use to create energy and materials to make new cells such as membranes, proteins, and DNA. By tracking the flow of nutrients through cancer cells, Li and his labmates are learning how such cells change their metabolism to stimulate growth. These insights will help scientists develop new ways to treat the disease.

Cell metabolism comprises all the chemical reactions occurring in the cell, but researchers are particularly interested in a few reactions that aren’t required by normal cells but are critical for cancer growth. Stopping these reactions with drugs would disrupt the metabolism of cancer cells and hinder tumor development.

“Even though many people may not think of metabolism as a treatment target for cancer, this strategy has been used unwittingly for a long time,” Li says. “Many chemotherapies, such as antifolates, were originally used by doctors without knowing exactly how they worked. Since then, we’ve discovered that those treatments target metabolic pathways. By understanding the details of cancer metabolism we are hoping to design drugs in a more rational way.”

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Li might never have joined the Vander Heiden lab or studied cancer metabolism were it not for the unique structure of graduate training at MIT.

During their first year at MIT, graduate students are required to take four classes. Unlike their counterparts at many other PhD programs, they do not work in laboratories until their second semester. This allows students to focus initially on coursework — covering biochemistry, genetics, and research methodology — designed to build a foundation of knowledge. As a result, students discover new interests and develop the confidence to move out of their comfort zones. When it comes time to select a lab, they can choose from 56 spread across six locations, spanning a wide breadth of biological research.

Li could study how the brain forms memories, interpret X-rays to deduce protein structure, or even build miniature organs for drug testing. Before making his decision, he rotated in three laboratories. During each month-long rotation, he performed a small project allowing him to experience the culture of the lab and learn more about its research.

“The first two labs I visited were studying topics I was familiar with and thought were interesting,” he says. “But when I visited the Vander Heiden lab it was so different and caught me off guard. That’s why I eventually joined, even though I had never imagined myself working in a metabolism lab before.”

Diagram showing a metabolism pathway
Cellular metabolism is comprised of a network of interconnected biochemical reactions resembling a subway system. Zhaoqi Li compares normal and diseased cells to determine the differences in the way nutrients travel through this network. Credit: Justin Chen

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Although he is new to the community of researchers specializing in metabolism, Li has long known that he wanted to interact with the world through science. As an immigrant who moved from China to southern Tennessee at the age of six, Li struggled to learn English and began to view science as a universal language that transcended culture.

“My parents were also non-native speakers and the English as a Second Language classes in my elementary school were geared towards Spanish speakers, so I had a really hard time,” Li says. “I joke that the only reason I passed the first grade was because I was good at math.”

Li’s contrasting relationship with science and English continued as an undergraduate at Columbia University. There he majored in biochemistry and also studied literature of the Western Canon to fulfill his general degree requirements.

“I took four semesters worth of classes that started with Plato and ended with Virginia Woolf,” he says, “It was an eye-opening experience, but I never really loved it. I found biology more intuitive because it doesn’t rely on being familiar with a specific cultural lens. Most every society in the world values the scientific method to some extent.”

Li began working in a lab during his sophomore year at Columbia. To his surprise, he was mentored by a professor who valued his input and encouraged creative thinking. Li’s supervisor also introduced him to basic science — a type of research driven not by the desire to find a specific answer or cure, but by curiosity and the need to better understand the natural world.

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During his second semester rotation at MIT, Li searched for similarly open-minded environments, and was attracted to cancer metabolism because the field was relatively young.

“In other more established areas of biology, if you have a question someone has probably answered it in some capacity,” Li says. “The Vander Heiden lab was using new techniques so there was a lot of space to explore. Many questions I asked — even during my initial rotation —  didn’t have an answer, which was exciting.”

The great challenge confronting the metabolism field is translating decades’ worth of research on enzymes — proteins that manage chemical reactions — from the test tube to the cell and human body. By studying enzymes individually in the controlled setting of test tubes, researchers have documented almost all the chemical reactions that occur in the cell. When combined, these reactions look like a giant subway map where each stop, indicated by a dot, is a different molecule, and the line between stops represents a chemical reaction where atoms are added or subtracted. Some pathways are a straight line but others have nodes or intersections where a molecule can take part in several different reactions. Other pathways are circular where the molecule that starts the pathway is remade at the end so that the line circles back on itself.

Despite the ability to study chemical reactions in a test tube, scientists have struggled to understand what is actually happening in the complex environment of cells, which coordinate millions of reactions that not only affect each other, but are also influenced by outside stresses like nutrient deprivation.

To Li, using the metabolism map to figure out what chemical reactions are occurring and how atoms are moving through the cell is like using a subway map to track how people are traveling through a city.

“The map describes all the possible routes people could take,” Li says, “but you have to track the passengers to figure out where they are actually going. You could imagine people commuting into the city during the week and going to entirely different places on the weekend. There are a lot of different patterns of movement that you can’t infer just from looking at a map.”

To analyze what chemical reactions are occurring in the cell, Li utilizes cutting edge technology to track carbon atoms — an essential element that is required to build all components of the cell. By tagging carbon with an extra neutron, Li makes the experimentally altered atom heavier and distinguishable from naturally occurring carbon in the cell. Feeding cells nutrients like glucose made with heavy carbons allows Li to compare how molecules are broken down and used by normal and cancerous cells.

Person at lab instrument with sample“Returning to the subway map analogy, this labeling technique is similar to not only being inside the subway, but also giving everyone in Downtown Boston a red shirt,” Li says. “After 12 hours, we can look at the rest of the city. If we see a lot of red shirts in Allston, we would know that this particular route is really popular.”

In the case of glucose, Li and his labmates observed that normal cells break down the sugar to release energy and heavy carbons in the form of carbon dioxide. In contrast, cancer cells alter their metabolism so that the heavy carbons originally found in glucose are used to build new parts of the cells that are required for cancer cells to grow, such as membranes, DNA, and proteins.

Li’s observations demonstrate how cancer cells sustain abnormal growth by accumulating carbon. For his thesis project, Li has chosen to investigate one of the main tricks cancer cells use to hoard carbon atoms: a process known as carbon fixation. This type of chemical reaction, originally studied in plants performing photosynthesis, attaches carbon dioxide to other molecules. Li’s initial findings suggest that a protein, Malic Enzyme 1, helps cancer cells use carbon dioxide to build components required for growing and dividing.

“This is surprising,” he says, “because the textbook version of this enzyme actually catalyzes the reverse reaction in normal cells where carbon dioxide is removed from molecules.  Malic Enzyme 1 is an example of how cancer performs remarkable chemical reactions — who would have thought that cancer cells use carbon like plants do?”

Li is at the beginning stages of his research, and can’t predict where his project will take him. His current goal is to determine how cancer cells react when they are missing Malic Enzyme 1. Such loss could slow growth, but Li will have to perform experiments to be sure, since cancer is a resourceful and elusive target.

Like a detour rerouting travelers around a closed metro stop, cancer cells may further contort their metabolism, taking advantage of little-used or still unidentified chemical reactions to maintain growth. In the face of such adaptability, Li and his labmates believe the best course of action is to be as curious as possible to understand as much as they can about how cancer works. Working together, they discuss confounding results, adjust hypotheses, and design new experiments.

“It’s really encouraging to be part of Matt’s lab and the Koch Institute in general where researchers take a basic science approach,” Li says. “We try to keep an open mind because there’s probably no single thing that cancer cells depend on. Everyone’s work builds together to form a cumulative understanding.”

Photo credit: Raleigh McElvery
Combatting chemotherapy resistance

Graduate student Faye-Marie Vassel investigates a protein that helps cells tolerate DNA damage, sharing her expertise with budding scientists to further STEM education

Raleigh McElvery
December 8, 2017

Combatting chemotherapy resistance

Person with long, dark hair and lab coat stares into microscope.

Graduate student Faye-Marie Vassel investigates a protein that helps cells tolerate DNA damage, sharing her expertise with budding scientists to further STEM education

Raleigh McElvery

 

Faye-Marie Vassel has a protein. Well, as a living entity, technically she has many, but just one she affectionately refers to as her own. “My protein, REV7.” And it makes sense — if you were hard at work characterizing a single protein for all six years of your graduate career, you’d be pretty attached, too. Plus, the stakes are high. REV7, which aids in DNA damage repair, could ultimately provide insight into ways to combat chemotherapy resistance.

Although Vassel’s mother trained as an OB/GYN in Russia before moving to the U.S., serving as what Vassel describes as a “quiet” scientific role model, Vassel spent her early childhood emulating her father, a social worker, and engrossed in the social sciences. She intended to one day work in science policy — until high school when she joined an after-school program at the American Museum of Natural History in New York City, and discovered an additional interest.

Here, Vassel took a series of molecular biology classes and met her first female research mentor, a postdoctoral fellow at Rockefeller University, who encouraged her to participate in another, more advanced science program funded by the National Science Foundation.

“I initially had my doubts, but just having that support changed everything,” Vassel says. “That was my first time doing research of any kind, and I got a sense of the sheer diversity of potential research projects. That’s also when I heard there was something called biophysics.”

From that point on, Vassel was hooked. As an undergraduate at Stony Brook University, she initially declared a major in physics before switching to biochemistry. Later, when it came time to select a graduate school, she was split between MIT and the University of California, Berkeley. As she recalls, MIT’s graduate preview weekend made all the difference.

“I had the chance to stay with biology students and speak with professors,” she says. “The whole experience made the department seem personal, and demystified the graduate school process by making it more tangible.”

She proposed a joint position between two labs: Graham Walker’s lab, based in Building 68, and Michael Hemann’s lab situated in the Koch Institute for Integrative Cancer Research. Walker’s lab focuses on microbiology, DNA repair, and antibiotic resistance, while Hemann’s lab investigates chemotherapy resistance in hopes of improving cancer therapies. After stumbling upon one of their joint papers, Vassel decided she’d like to combine the two.

“It’s invaluable to have both perspectives,” she says. “Mike’s lab just celebrated its 10th anniversary, while Graham‘s just had its 35th. It’s been interesting seeing the different ways they approach their respective research questions, because they were trained in such different scientific eras.”

Although Vassel is currently the only student formally working in both labs, the collaboration between Walker and Hemann, aimed at combatting chemotherapy resistance, has been ongoing.

Frontline chemotherapies, including one anticancer agent called cisplatin, kill cancer cells by damaging their DNA and preventing them from synthesizing new genetic material. Just how sensitive cancer cells are to cisplatin — and therefore how effective the treatment is — depends on whether the cell can repair the damage and bypass DNA-damage induced cell death. In some cases, cells increase production of “translesion polymerases,” which are specialized DNA polymerases that can help cells tolerate certain kinds of DNA damage by synthesizing across from damaged DNA or DNA bound to a carcinogen.

Vassel’s protein, REV7, is a structural subunit of one key translesion polymerase, and its expression is deregulated in many different cancer cells. As Vassel suggests, if one aspect of these translesion polymerases — say, the REV7 subunit — could be altered to hinder repair, then perhaps cancer-ridden cells could regain drug sensitivity.

Thanks to recently-developed CRISPR-Cas9 gene editing techniques, Vassel has removed REV7 entirely from drug resistant lung cancer cells, and watched as cisplatin sensitivity was restored. She also conducted rescue experiments, adding REV7 back into cell lines lacking the protein to see whether those cells become resistant to the drug once again. Most recently, she has been working in murine models to see whether REV7 has similar effects in a living system.

If her hypothesis is correct, REV7 would be a powerful target for drug development. Treatments that inhibit REV7, she explains, could be used in tandem with frontline chemotherapies like cisplatin to prevent resistance.

Since her foray into biology at the American Museum of Natural History almost a decade ago, Vassel has maintained her passion for science outreach. During her time at MIT, she has served as a math tutor for middle schoolers in the Cambridge public school system. She also volunteered as a science and math mentor for high school students, as part of a dual athletic and academic program founded by MIT.

As Vassel wraps up her final year of graduate studies, she is torn between completing an academic postdoc and indulging her early interest in science education policy.

“Growing up in New York City, it was not lost on me that — despite the city’s wonderful diversity — people from historically underserved groups were still missing from many science-related positions,” Vassel says. “It got me thinking about the dire need for policymakers to improve curricula to make science more inclusive of all life experiences. There’s this idea that science is apolitical when it’s really not, and that mindset can have detrimental effects on equity and diversity in science.”

Photo credit: Raleigh McElvery
An eye for a mouth: How regenerating flatworms keep track of body parts

Graduate student Lauren Cote identifies genes directing regeneration

Justin Chen
November 16, 2017

An eye for a mouth: How regenerating flatworms keep track of body parts

Person with brown hair in pony tail sits in front of computer and microscope.

Graduate student Lauren Cote identifies genes directing regeneration

Justin Chen

 

Peering down through a microscope at a petri dish, Lauren Cote, a sixth-year graduate student, watches the tip of a worm’s tail. Alone in the petri dish, the brown globule of tissue is regenerating an entirely new digestive system, a brain, and a pair of eye spots. After just a few weeks, the animal — a quarter-inch-long ribbon of flesh capped by a triangular head — is complete again. Swimming through the dish, the worm’s grainy, mahogany body fades to a translucent gray-blue along the edges, stretching and contracting as if hinting at its malleability.

Many animals regenerate. Salamanders replace their tails while zebrafish regrow damaged heart muscle. Even humans can renew large parts of their livers. However, few creatures can regenerate like planarians, a class of flatworms found in fresh and salt water habitats around the world — and in the Reddien lab at the Whitehead Institute.

Because planarians are masters of regeneration, able to replace any body part and even create a new animal from small chunks of tissue, they have become a focus of intense study. By examining the flatworm species Schmidtea mediterranea, Cote and other members of the Reddien lab have uncovered the ways cells communicate after injury to coordinate regeneration. Their work provides insight into how the ability to regenerate evolved, and how the healing process works in a variety of animals, including humans.

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Although regeneration seems mysterious, researchers have simplified the feat into two steps. First, planarians create the raw material to make new body parts by stimulating a group of rapidly dividing cells, called stem cells, that are the source of all new tissue in the worm. Second, these new cells need instructions to know what kind of tissue to become. Cote’s goal is to demystify this second step by locating a grid of information, like latitude and longitude lines on a map, that helps planarians keep track of their body parts and sense what is missing.

Hands suctioning small, black dots from petri dish.
Few creatures can regenerate like planarians, a class of flatworms found in fresh and salt water habitats around the world.

“The animal could have lost just the tip of its head or entire left side of its body,” Cote says, “and somehow it regrows the precise anatomy needed to make a complete worm.”

Over the past few years, research in the Reddien lab has demonstrated that a network of muscle cells spread throughout the worm’s body guides regeneration. To accomplish this task, muscle cells rely on a group of genes called position control genes (PCGs) which, based on Cote’s model, are predicted to encode proteins involved in cell communication. Depending on what PCGs are activated or expressed, muscle cells would send out a unique combination of signaling molecules that determine which body parts, such as eyes, stomach, or tail, would form.

“We like to imagine that muscle cells function like satellites and beam down information,” Cote says. “This allows stem cells to know where they are and what new body part to become.”

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To systematically identify PCGs from the roughly 20,000 genes expressed in Schmidtea mediterranea, Cote worked in tandem with postdoctoral researcher Lucila Scimone in the Reddien lab to perform a two-part study. First they created maps of gene expression by examining individual muscle cells. After inventorying the genes each individual muscle cell expressed, they aggregated the data into a whole body map, showing gene activity across the entire worm. Some genes were expressed in all muscle cells, implying a general function such as controlling contraction and relaxation. In contrast, other genes were expressed in precise regions of the worm, like the head or midsection, suggesting that they could act as PCGs by defining the identity of each area.

In the second half of the study, Cote and Scimone used molecular techniques to disrupt the activity of potential PCGs. “We hypothesized that if a gene were needed to direct regeneration, the worm would still be able to renew itself without that gene’s activity,” Cote says, “but the animal would end up with an abnormal body.”

Indeed, Cote found that disrupting four genes in particular, encoding signaling molecules and receptor-like proteins, led to defective regeneration; worms either grew extra eyes on their head or grew extra feeding tubes sprouting out of their midsection like elongated suction cups.  Together these four genes, along with a few previously identified genes controlling head and tail regeneration, comprise a short but expanding list of PCGs controlling the location and identity of new tissues. As scientists begin to understand the molecular details of planarian regeneration, they will test whether similar genes are used by other animals and humans.

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Although a biologist now, Cote began her academic life focusing on mathematics. As an undergraduate math major at the University of Chicago, she studied branches of mathematics such as analysis, algebra, and algebraic topology, a discipline that describes the properties of multidimensional shapes. After a summer project, Cote realized that — while she enjoyed learning mathematics — she found the research far too abstract.

“I was having a mid-college crisis,” she recalls. “I wanted to study something more visual where you could actually see what is going on.” Following this urge, Cote began to work in a lab examining fly development during her junior year. “I remember watching sheets of cells on the outside of a fly embryo folding in on themselves and sliding under the surface away from view. It made me wonder how cells make decisions and choreograph their movements to build a body. That’s how I got interested in developmental biology.”

After graduating from the University of Chicago, Cote worked as a lab technician for two years. During this time, she realized that her background in math and ability to think logically was an asset. “Putting together a mathematical proof is similar to publishing a research paper,” she says. “In both cases you are piecing together smaller bits of evidence into a cohesive argument.”

A series of blobs with white, green, purple and yellow specs inside them.
Gene expression maps from the first half of Cote’s and Scimone’s study. The head of the worm faces the top of the screen while the tail of the worm faces the bottom of the screen. Each worm is marked by purple, yellow, and green dots indicating the expression of three different genes expressed in muscle cells. These colors show how genes are localized to different areas of the worm and could act as PCGs.  In the second half of the study, Cote and Scimone identified PCGs by using molecular techniques to disrupt gene activity and looking for worms that regenerated abnormal bodies.

Encouraged by her successful venture into biological research, Cote decided to pursue a PhD in biology. She learned about the Reddien lab while taking a genetics course during her first year at MIT. Like Cote, many members of this group have backgrounds in other areas of science — including computational biology, development, evolution, biochemistry, and immunology — which helps them examine planarian regeneration from many perspectives.

“They were beginning to put together a story linking muscle cells to regeneration that was really intriguing,” Cote says. “I also liked the challenge of working with planarians because they are a fairly new lab animal. We’re still developing a lot of research tools so there is room to be creative and ask fundamental questions.”

By following an initial strand of curiosity as an undergraduate and identifying PCGs as a graduate student, Cote has begun to decipher the molecular language of regeneration.  As scientists learn more about how planarians replace missing body parts, new areas of exploration open. One pressing question­ is how planarian regeneration compares to that of other animals. To pursue that mystery, Cote plans on studying another animal as a postdoctoral researcher and eventually starting her own laboratory.

“I still haven’t made up my mind, “she says, “but I’m considering a lot of possibilities such as crustaceans, sea squirts, zebrafish, and axolotls.” Regardless of her final choice, Cote will be investigating how cells — essentially fatty membranes encasing a slurry of water and proteins — manage to form complex and intricate structures. She will be pursuing the same questions that first captivated her as an undergraduate in Chicago. “How do cells make decisions? How do they know to become an eye or a stomach or a brain?” she asks. “There is a lot more that I want to understand.”

Photo credit: Raleigh McElvery
School of Science Infinite Kilometer Awards for 2017

Eight research staffers and postdocs are recognized for their extraordinary contributions and dedication to programs, colleagues, and the Institute.

School of Science
January 16, 2018

The MIT School of Science has announced the 2017 winners of the Infinite Kilometer Award. The Infinite Kilometer Award was established in 2012 to highlight and reward the extraordinary — but often underrecognized — work of the school’s research staff and postdocs.

Recipients of the award are exceptional contributors to their research programs. In many cases, they are also deeply committed to their local or global MIT community, and are frequently involved in mentoring and advising their junior colleagues, participating in the school’s educational programs, making contributions to the MIT Postdoctoral Association, or contributing to some other facet of the MIT community.

In addition to a monetary award, honorees and their colleagues, friends, and family are invited to a celebratory lunch in May.

The 2017 Infinite Kilometer winners are:

Rodrigo Garcia, McGovern Institute for Brain Research;

Lydia Herzel, Department of Biology;

Yutaro Iiyama, Laboratory for Nuclear Science;

Kendrick Jones, Picower Institute for Learning and Memory;

Matthew Musgrave, Laboratory for Nuclear Science;

Cody Siciliano, Picower Institute for Learning and Memory;

Peter Sudmant, Department of Biology;

Ashley Watson, Picower Institute for Learning and Memory;

The School of Science is also currently accepting nominations for its Infinite Mile Awards. Nominations are due by Feb. 16 and all School of Science employees are eligible. Infinite Mile Awards will be presented with the Infinite Kilometer Awards this spring.

Biologists’ new peptide could fight many cancers

Drug that targets a key cancer protein could combat leukemia and other types of cancer.

Anne Trafton | MIT News Office
January 15, 2018

MIT biologists have designed a new peptide that can disrupt a key protein that many types of cancers, including some forms of lymphoma, leukemia, and breast cancer, need to survive.

The new peptide targets a protein called Mcl-1, which helps cancer cells avoid the cellular suicide that is usually induced by DNA damage. By blocking Mcl-1, the peptide can force cancer cells to undergo programmed cell death.

“Some cancer cells are very dependent on Mcl-1, which is the last line of defense keeping the cell from dying. It’s a very attractive target,” says Amy Keating, an MIT professor of biology and one of the senior authors of the study.

Peptides, or small protein fragments, are often too unstable to use as drugs, but in this study, the researchers also developed a way to stabilize the molecules and help them get into target cells.

Loren Walensky, a professor of pediatrics at Harvard Medical School and a physician at Dana-Farber Cancer Institute, is also a senior author of the study, which appears in the Proceedings of the National Academy of Sciences the week of Jan. 15. Researchers in the lab of Anthony Letai, an associate professor of medicine at Harvard Medical School and Dana-Farber, were also involved in the study, and the paper’s lead author is MIT postdoc Raheleh Rezaei Araghi.

A promising target

Mcl-1 belongs to a family of five proteins that play roles in controlling programmed cell death, or apoptosis. Each of these proteins has been found to be overactive in different types of cancer. These proteins form what is called an “apoptotic blockade,” meaning that cells cannot undergo apoptosis, even when they experience DNA damage that would normally trigger cell death. This allows cancer cells to survive and proliferate unchecked, and appears to be an important way that cells become resistant to chemotherapy drugs that damage DNA.

“Cancer cells have many strategies to stay alive, and Mcl-1 is an important factor for a lot of acute myeloid leukemias and lymphomas and some solid tissue cancers like breast cancers. Expression of Mcl-1 is upregulated in many cancers, and it was seen to be upregulated as a resistance factor to chemotherapies,” Keating says.

Many pharmaceutical companies have tried to develop drugs that target Mcl-1, but this has been difficult because the interaction between Mcl-1 and its target protein occurs in a long stretch of 20 to 25 amino acids, which is difficult to block with the small molecules typically used as drugs.

Peptide drugs, on the other hand, can be designed to bind tightly with Mcl-1, preventing it from interacting with its natural binding partner in the cell. Keating’s lab spent many years designing peptides that would bind to the section of Mcl-1 involved in this interaction — but not to other members of the protein family.

Once they came up with some promising candidates, they encountered another obstacle, which is the difficulty of getting peptides to enter cells.

“We were exploring ways of developing peptides that bind selectively, and we were very successful at that, but then we confronted the problem that our short, 23-residue peptides are not promising therapeutic candidates primarily because they cannot get into cells,” Keating says.

To try to overcome this, she teamed up with Walensky’s lab, which had previously shown that “stapling” these small peptides can make them more stable and help them get into cells. These staples, which consist of hydrocarbons that form crosslinks within the peptides, can induce normally floppy proteins to assume a more stable helical structure.

Keating and colleagues created about 40 variants of their Mcl-1-blocking peptides, with staples in different positions. By testing all of these, they identified one location in the peptide where putting a staple not only improves the molecule’s stability and helps it get into cells, but also makes it bind even more tightly to Mcl-1.

“The original goal of the staple was to get the peptide into the cell, but it turns out the staple can also enhance the binding and enhance the specificity,” Keating says. “We weren’t expecting that.”

Killing cancer cells

The researchers tested their top two Mcl-1 inhibitors in cancer cells that are dependent on Mcl-1 for survival. They found that the inhibitors were able to kill these cancer cells on their own, without any additional drugs. They also found that the Mcl-1 inhibitors were very selective and did not kill cells that rely on other members of the protein family.

Keating says that more testing is needed to determine how effective the drugs might be in combating specific cancers, whether the drugs would be most effective in combination with others or on their own, and whether they should be used as first-line drugs or when cancers become resistant to other drugs.

“Our goal has been to do enough proof-of-principle that people will accept that stapled peptides can get into cells and act on important targets. The question now is whether there might be any animal studies done with our peptide that would provide further validation,” she says.

Joshua Kritzer, an associate professor of chemistry at Tufts University, says the study offers evidence that the stapled peptide approach is worth pursuing and could lead to new drugs that interfere with specific protein interactions.

“There have been a lot of biologists and biochemists studying essential interactions of proteins, with the justification that with more understanding of them, we would be able to develop drugs that inhibit them. This work now shows a direct line from biochemical and biophysical understanding of protein interactions to an inhibitor,” says Kritzer, who was not involved in the research.

Keating’s lab is also designing peptides that could interfere with other relatives of Mcl-1, including one called Bfl-1, which has been less studied than the other members of the family but is also involved in blocking apoptosis.

The research was funded by the Koch Institute Dana-Farber Bridge Project and the National Institutes of Health.

How the brain selectively remembers new places

Neuroscientists identify a circuit that helps the brain record memories of new locations.

Anne Trafton | MIT News Office
December 25, 2017

When you enter a room, your brain is bombarded with sensory information. If the room is a place you know well, most of this information is already stored in long-term memory. However, if the room is unfamiliar to you, your brain creates a new memory of it almost immediately.

MIT neuroscientists have now discovered how this occurs. A small region of the brainstem, known as the locus coeruleus, is activated in response to novel sensory stimuli, and this activity triggers the release of a flood of dopamine into a certain region of the hippocampus to store a memory of the new location.

“We have the remarkable ability to memorize some specific features of an experience in an entirely new environment, and such ability is crucial for our adaptation to the constantly changing world,” says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and director of the RIKEN-MIT Center for Neural Circuit Genetics at the Picower Institute for Learning and Memory.

“This study opens an exciting avenue of research into the circuit mechanism by which behaviorally relevant stimuli are specifically encoded into long-term memory, ensuring that important stimuli are stored preferentially over incidental ones,” adds Tonegawa, the senior author of the study.

Akiko Wagatsuma, a former MIT research scientist, is the lead author of the study, which appears in the Proceedings of the National Academy of Sciences the week of Dec. 25.

New places

In a study published about 15 years ago, Tonegawa’s lab found that a part of the hippocampus called the CA3 is responsible for forming memories of novel environments. They hypothesized that the CA3 receives a signal from another part of the brain when a novel place is encountered, stimulating memory formation.

They believed this signal to be carried by chemicals known as neuromodulators, which influence neuronal activity. The CA3 receives neuromodulators from both the locus coeruleus (LC) and a region called the ventral tegmental area (VTA), which is a key part of the brain’s reward circuitry. The researchers decided to focus on the LC because it has been shown to project to the CA3 extensively and to respond to novelty, among many other functions.

The LC responds to an array of sensory input, including visual information as well as sound and odor, then sends information on to other brain areas, including the CA3. To uncover the role of LC-CA3 communication, the researchers genetically engineered mice so that they could block the neuronal activity between those regions by shining light on neurons that form the connection.

To test the mice’s ability to form new memories, the researchers placed the mice in a large open space that they had never seen before. The next day, they placed them in the same space again. Mice whose LC-CA3 connections were not disrupted spent much less time exploring the space on the second day, because the environment was already familiar to them. However, when the researchers interfered with the LC-CA3 connection during the first exposure to the space, the mice explored the area on the second day just as much as they had on the first. This suggests that they were unable to form a memory of the new environment.

The LC appears to exert this effect by releasing the neuromodulator dopamine into the CA3 region, which was surprising because the LC is known to be a major source of norepinephrine to the hippocampus. The researchers believe that this influx of dopamine helps to boost CA3’s ability to strengthen synapses and form a memory of the new location.

They found that this mechanism was not required for other types of memory, such as memories of fearful events, but appears to be specific to memory of new environments. The connections between the LC and CA3 are necessary for long-term spatial memories to form in CA3.

“The selectivity of successful memory formation has long been a puzzle,” says Richard Morris, a professor of neuroscience at the University of Edinburgh, who was not involved in the research. “This study goes a long way toward identifying the brain mechanisms of this process. Activity in the pathway between the locus coeruleus and CA3 occurs most strongly during novelty, and it seems that activity fixes the representations of everyday experience, helping to register and retain what’s been happening and where we’ve been.”

Choosing to remember

This mechanism likely evolved as a way to help animals survive, allowing them to remember new environments without wasting brainpower on recording places that are already familiar, the researchers say.

“When we are exposed to sensory information, we unconsciously choose what to memorize. For an animal’s survival, certain things are necessary to be remembered, and other things, familiar things, probably can be forgotten,” Wagatsuma says.

Still unknown is how the LC recognizes that an environment is new. The researchers hypothesize that some part of the brain is able to compare new environments with stored memories or with expectations of the environment, but more studies are needed to explore how this might happen.

“That’s the next big question,” Tonegawa says. “Hopefully new technology will help to resolve that.”

The research was funded by the RIKEN Brain Science Institute, the Howard Hughes Medical Institute, and the JPB Foundation.

Joan Ruderman PhD ’74: A lifelong enthusiasm for developmental biology

Studying the Humble Clam Leads to Environmental Work

Alice Waugh | MIT Technology Review
December 22, 2017

Joan Ruderman’s lifelong enthusiasm for developmental biology shines through, whether she’s talking about studying the reproductive habits of the humble clam or discussing the surprising effects of plastics components like bisphenol A (BPA) on fetal development.

Ruderman arrived at MIT in 1969, when the Department of Biology was still quite small. That fall there were more first-year graduate students—about half women—than there were faculty in the department. The field of developmental biology and her career would develop in parallel. She joined the Harvard Medical School (HMS) faculty in 1976 and by 2012 she had become the first female president and director of the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, a post she held for two years.

“The field of molecular biology was just beginning, and MIT was at the forefront of many of the early advances,” she says. Her doctoral work involved studying how fertilization activates messenger RNA in sea urchin eggs. She describes the initiation of cell division on a molecular level this way: “An unfertilized egg is a quiescent cell, but then the sperm hits, the doorbell rings, and this whole dinner party rapidly unfolds.”

As is the case with so many MIT graduates, ­Ruderman’s interests have shaped her career. As she was finishing her doctorate, she began her long association with the MBL when she took an embryology course there. During the summer, scientists from all over the world come to the lab to study topics like neurobiology and cell division in local marine organisms. One of those creatures is Spisula solidissima, which is familiar to anyone who enjoys clam chowder.

“A single female can put out several hundred million eggs on a good day,” Ruderman says. The clam embryo makes a good study subject because of its rapid development after fertilization: “In 24 hours, it’s a functional little animal.”

Later, Ruderman became interested in environmental issues. While on the HMS faculty, she took a class on human health and global environmental change taught by Eric Chivian, the onetime MIT Medical psychiatrist who went on to share the Nobel Peace Prize as cofounder of International Physicians for the Prevention of Nuclear War.

Now a professor emeritus at Harvard, ­Ruderman teaches at Princeton about the adverse effects of chemicals such as BPA, phthalates, and pesticides. Knowing what can get budding scientists hooked, she titled her class “Hormonally Active Pollutants.” “If I called it ‘Environmental Endocrine Disrupters,’ no one would take the course,” she says.

This article originally appeared in the November/December 2017 issue of MIT Technology Review magazine.
Pairing mismatch helps impaired fish RNA cleavage proceed swimmingly
December 21, 2017

Beyond tending to its multitudes of genetic, metabolic, and developmental processes, eukaryotic cells must additionally be vigilant against invasion by parasitic sequences such as viruses and transposons. RNA interference (RNAi) is a defense used by eukaryotic cells to protect themselves from such threats to their genomic harmony. Cellular RNAi components slice and destroy invading double-stranded RNA sequences and also help snip and process microRNAs, RNA sequences encoded by the genome that play key roles in gene regulation. An important process that occurs naturally in our cells, RNAi has also been harnessed by scientists as a tool to study gene function in common models such as worms, fruit flies, and mice. While many researchers have been using RNAi to tease apart gene function for over a decade, those using zebrafish, a powerful vertebrate model, have been forced to use other approaches because RNAi just did not seem to work well in these animals. Now, researchers at Whitehead Institute have uncovered how small changes in the fish Argonaute (Ago) protein, an RNA slicing protein, that happened in its lineage an estimated 300 million years ago greatly diminished the efficiency of RNAi in these animals, while another ancestral feature, in a critical pre-microRNA, was retained that enabled the microRNA to still be produced despite the fish’s impaired Ago protein.

In an article published December 21 in the journal Molecular Cell, graduate student Grace Chen, along with both Whitehead Member David Bartel, also a professor of biology at Massachusetts Institute of Technology (MIT) and investigator with the Howard Hughes Medical Institute, and Whitehead Member and MIT professor of biology Hazel Sive, describe their discovery of a roughly 300 million-year-old, two amino acid substitutions in the fish Ago protein. The substitution is present in the ancestor all teleost fish, the class of fish which includes not only zebrafish but also the vast majority of fish species spanning those populating the ocean, aquarium, and supermarket. These two changes reside in and near the protein’s catalytic site and greatly decrease the ability of the fish Ago to perform its RNA slicing function, offering an explanation for why RNAi has not been a useful tool in zebrafish.

Despite the zebrafish’s deficiencies in RNAi, it is still able to produce the microRNA miR-451, an important regulator of red blood cell maturation and the only microRNA processed by Ago (the rest are produced with another protein called Dicer). MicroRNAs are short stretches of RNA that can regulate gene expression by inhibiting translation of mRNA into a protein and directing the destruction of mRNA before it can be used to make more protein. Since Chen had discovered that zebrafish lack an efficient Ago protein, it was mysterious as to how are fish were able to produce Ago cleavage-dependent miR-451. The Ago protein must process miR-451 by slicing the sequence out of a longer strand of RNA that has folded up on itself, forming a hairpin structure. What they determined was that in the pre-miR-451 hairpin in zebrafish, at a critical position in the miRNA, they found a “G–G” pairing mismatch that actually appears to facilitate cleavage by the impaired zebrafish Ago. No mismatch, no efficient cleavage.

Exploring the effects of a seed sequence mismatch on Ago-catalyzed cleavage kinetics further, they then tested its ability to slice other bound transcripts. The researchers discovered that while, as might be expected, a G–G mismatch slows Ago binding, it significantly enhances both slicing efficiency as well as the release of the bound product, more than off-setting the slower binding reaction kinetics and suggesting that non- “Watson–Crick” base pairing creates an exceptionally favorable geometry for the cleavage and release parts of the reaction.

These findings offer interesting insights into how animals can survive and thrive without an efficient RNAi system and suggest how the Ago protein could be “repaired” in order to allow zebrafish researchers to use RNAi in their experiments. Restoring a function that a lineage hasn’t had for 300 million years might also fuel additional findings into how the teleost class has diverged over time.

Written by Lisa Girard
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David Bartel’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 professor of biology at Massachusetts Institute of Technology and investigator with the Howard Hughes Medical Institute.
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Paper cited:
Chen GR, Sive H, and Bartel DP. A Seed Mismatch Enhances Argonaute2-Catalyzed Cleavage and Partially Rescues Severely Impaired Cleavage Found in Fish. Molecular Cell, Dec 21 2017 DOI: 10.1016/j.molcel.2017.11.032.
Harnessing nature’s riches
December 19, 2017

Cambridge, MA – Researchers at Whitehead Institute have reconstructed the full suite of biochemical steps required to make salidroside, a plant-derived compound widely used in traditional medicine to combat depression and fatigue and boost immunity and memory. Their new study, which appears online this week in the journal Molecular Plant, resolves some long-standing questions about how this compound is manufactured by a type of high-altitude plant, known commonly as golden root. This work not only paves a path toward large-scale synthetic efforts—thereby protecting plants already in danger of extinction—but also provides a model for dissecting the biochemical synthesis of a host of natural products, which represent a treasure trove for modern medical discoveries.

“By cracking open the natural synthesis of this compound, known as salidroside, we have helped eliminate a major bottleneck in the broader development of plant-derived natural products into pharmaceuticals,” says Jing-Ke Weng, the senior author of the paper, a Member of Whitehead Institute, and an assistant professor of biology at Massachusetts Institute of Technology. “We simply can’t rely on the native plants as the sole sources of these biologically important molecules.”

Golden root, also called Tibetan ginseng, typically grows in high-altitude, arctic environments, such as Tibet. It is well known in Eastern cultures for its medicinal properties and produces a variety of chemical substances, particularly salidroside, which have garnered interest in the biomedical research community for their potential therapeutic effects.

“People have tried to farm golden root, but the medicinal value is much lower because the plants make much less salidroside when cultivated outside of their normal habitat,” says Weng.

That means collecting enough salidroside to fuel scientific studies is largely impossible, without risking the viability of these plants and their surroundings. So Weng and his team, including first author Michael Torrens-Spence, set out to find a better way. “If we can figure out how plants make these high-value natural products, then we can devise sustainable engineering approaches to recreate such molecules—we won’t have to destroy nature in order to harness its riches,” says Torrens-Spence, a postdoctoral researcher in Weng’s laboratory.

Torrens-Spence and his colleagues used a systematic multi-omics approach to characterize various tissues from a three-month-old, greenhouse-grown golden root plant. By correlating the active genes with the abundance of key metabolites between various tissue types, the researchers created a massive biochemical catalog of the plant’s tissues.

The researchers then mined these data and matched the likely biochemical precursors of salidroside with the candidate genes (and their corresponding enzymes) responsible for those compounds’ synthesis. This approach allowed Weng and his team to create a kind of draft blueprint of how salidroside is made in nature.

To test the validity of this draft blueprint—and the molecular players from the golden root plant that comprise it—the scientists turned to two well-studied laboratory organisms: the baker’s yeast Saccharomyces cerevisiae and the tobacco plant Nicotiana benthamiana. Normally, these organisms do not make salidroside. But if the researchers’ model was correct, by inserting the candidate genes involved in salidroside synthesis Weng and his colleagues should be able to bestow that special property upon them.

That is precisely what the researchers did. Using three key enzymes they identified through their “-omics” approach, including 4HPAAS (4-hydroxyphenylacetaldehyde synthase), 4HPAR (4-hydroxyphenylacetaldehyde reductase), and T8GT (tyrosol:UDP-glucose 8-O-glucosyltransferase), they engineered yeast and tobacco plants with the capacity to make salidroside. Notably, this biochemical pathway for synthesizing salidroside involves three enzymes, rather than four, as had previously been proposed.

“This is an exciting proof-of-principle for how we can systematically unlock the biochemistry behind a range of intriguing plant-derived natural products,” says Weng. “With this capability, we can accelerate biomedical studies of these unique compounds as well as their potential therapeutic development.”

Written by Nicole Davis
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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:
“Complete pathway elucidation and heterologous reconstitution of Rhodiola salidroside biosynthesis”
Molecular Plant, online December 19, 2017. DOI: 10.1016/j.molp.2017.12.007
Michael P. Torrens-Spence (1), Tomáš Pluskal (1), Fu-Shuang Li (1), Valentina Carballo (1) and Jing-Ke Weng (1,2).
1. Whitehead Institute for Biomedical Research, Cambridge, Massachusetts, USA
2. Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Small RNA mediates genetic parental conflict in seed endosperm
December 19, 2017

CAMBRIDGE, MA–When it comes to gene expression in the endosperm of seeds, gene provenance matters. In this specialized tissue, plants actively strive to keep the expression of genes inherited from the mother versus the father in balance, according to Whitehead Institute scientists.

The endosperm, the starchy part of a seed that envelopes and nourishes the developing embryo, comprises two-thirds of the calories in a typical human diet. It is the meat of a coconut and the sweet part of the corn on the cob we eat.  In a paper published online December 19 in the journal Cell Reports, Whitehead Member Mary Gehring, first author and former Gehring graduate student Robert Erdmann, and colleagues reveal that the endosperm is also the site where the plant must actively orchestrate a delicate balance between expression of genes inherited from the mother and those of the father.  If this critical balance errs toward one parent or the other, seeds can be too small or even abort.

Unlike most plant cells, which have two copies of the genome, cells within the endosperm have three copies: one inherited from the father, and two inherited from the mother. This ratio is established when a sperm cell in the fertilizing pollen grain fuses with the central cell associated with the egg cell in a flower’s ovule. Unlike most cells, the central cell has two nuclei, so when the sperm’s nucleus merges with the central cell, the resulting endosperm is triploid.

 The 2-to-1 ratio of maternal to paternal gene expression is crucial, and deviation can have dire consequences:  If maternal gene expression is too high, the seeds are too small; if paternal gene expression is too high, the seeds abort. Although plant biologists have known the importance of this ratio for seed viability, the balance was assumed to be passively maintained for the majority of genes.  Previously, Gehring determined that a subset of genes expressed in the endosperm are imprinted—their expression is inherited from their parent. But what about the remaining majority of the genome?

Now Gehring and colleagues have discovered a role for small RNAs—snippets of RNA that interfere with and can reduce gene expression—in actively maintaining this 2-to-1 balance in those genes that are not imprinted.  This the first time scientists have documented small RNAs maintaining such a ratio. Using Arabadopsis thaliana and Arabadopsis lyrata plants, Gehring and her lab determined that these small RNAs tamp down the expression of maternally inherited genes. When the enzyme that creates the small RNAs is mutated, fewer small RNAs are produced, and the plant’s carefully balanced gene expression is thrown off. The resulting seeds have excessive maternal gene expression. To understand the significance of this elevated maternal gene expression, Satyaki Rajavasireddy, a postdoctoral researcher in Gehring’s lab and an author of the Cell Reports paper, turned to plants with seeds that abort  because they have additional copies of paternal genes. When these plants with extra paternal DNA had their small-RNA-producing enzyme mutated, the outcome was striking: The seeds were rescued and developed to maturity.

Although the research analyzed this phenomenon in A. thaliana and A. lyrata, Gehring expects it to be a widespread manifestation of the tug-of-war between maternal and paternal genetic contributions.

“Maintaining this maternal/paternal balance is crucial for seed development, including in crop plants,” says Gehring, who is also an associate professor of biology at Massachusetts Institute of Technology.  “We’ve looked at two species that are separated by 10 million years of evolution, and I anticipate we will find this mechanism in other species as well.”

This work was supported by the National Science Foundation (NSF CAREER grant 1453459).

Written by Nicole Giese Rura
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Mary Gehring’s primary affiliation is with Whitehead Institute for Biomedical Research, where her laboratory is located and all her research is conducted. She is also an associate professor of biology at Massachusetts Institute of Technology.
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Full Citation:
“A small RNA pathway mediates allelic dosage in endosperm”
Cell Reports, online December 19, 2017.
Robert M. Erdmann (1,2), P.R. V. Satyaki (1), Maja Klosinska (1), Mary Gehring (1,2).
1. Whitehead Institute for Biomedical Research, Cambridge, MA 02142 USA
2. Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139 USA