Turning off cancer's growth signals

 

One hallmark of cancer cells is uncontrollable growth, provoked by inappropriate signals that instruct the cells to keep dividing. Researchers at MIT and Brigham and Women’s Hospital have now identified a new way to shut off one of the proteins that spreads those signals — a receptor known as HER3.

Drugs that interfere with HER3’s better-known cousins, EGFR and HER2, have already proven effective in treating many types of cancer, and early-stage clinical trials are underway with antibodies directed against HER3. HER3 is of great interest to cancer biologists because it is commonly involved in two of the deadliest forms of the disease, ovarian and pancreatic cancer, says MIT Professor Linda Griffith, who led the research team with Harvard Stem Cell Institute and Brigham and Women’s cardiologist Richard Lee.

The study, published online May 26 in the Journal of Biological Chemistry, resulted from a serendipitous finding in a regenerative-medicine project. Co-first author Luis Alvarez, who earned his PhD from MIT during a three-year leave from the Army, was interested in regenerative medicine because he knew many soldiers who had been wounded in Iraq and Afghanistan.

While looking for ways to promote bone regrowth, Alvarez developed a series of paired proteins that the researchers thought might promote interactions between growth receptors such as HER3 and EGFR to control growth and differentiation.

Alvarez’s proteins had some impact on regeneration, but the researchers also noticed that in some cases, they appeared to shut off cell growth and migration. Alvarez and others in Griffith’s lab decided to see what would happen if they treated cancer cells with the protein. To their surprise, they found that the cells stopping growing, and in some cases died.

“It was not something we were expecting to see — you don’t expect to shut off a receptor with something that normally activates it — but in retrospect it seemed obvious to try this approach for HER3,” says Griffith, the School of Engineering Professor of Innovative Teaching in MIT’s Department of Biological Engineering and director of the Center for Gynepathology Research. “We pursued it only because we had people in the lab working with cancer cells, and we thought, ‘Since it had these effects in stem cells, let’s just try this in tumor cells, and see if something interesting happens.’”

Targeting vulnerability

Around the same time, Griffith developed a personal interest in this family of cell receptors: She was diagnosed with a form of breast cancer that often overexpresses the receptor EGFR.

EGFR has received much attention from biologists — the cancer drugs Erbitux, Iressa and Tarceva all target it — but not all cancers that overexpress the EGFR respond to targeted therapies. The first highly successful targeted chemotherapy, Herceptin, goes after another member of the family, the HER2 receptor.

The new MIT protein targets a specific vulnerability of HER3: To convey its growth-stimulating signals to the rest of the cell, HER3 must pair up with another receptor, usually HER2.

The new protein, which consists of a fused pair of neuregulin molecules, disrupts that pairing. Single molecules of neuregulin normally stimulate the HER3 receptor, promoting cell growth and differentiation. However, when the paired neuregulin is given to cells, it binds together two adjacent HER3 receptors, preventing them from interacting with the HER2 receptors they need to send their signals.

The researchers tested the molecule in six different types of cancer cells that overexpress HER3, and found that it effectively shut off growth in all of them, including a cell type that is resistant to drugs that target EGFR.

Mark Moasser, a professor of oncology at the University of California at San Francisco, described the new technique as clever and elegant, adding that more experiments are needed to determine if it will be effective in living organisms. “Based on the mechanism, it has potential, and it lays the groundwork for a lot of future work,” says Moasser, who was not involved in this study.

The MIT and Brigham and Women’s team is now working on a new version of the molecule that would be more suited to tests in living animals. They plan to undertake such testing soon under the leadership of Steven Jay, a joint MIT/Brigham and Women’s postdoc and co-first author of the new paper. MIT postdoc Elma Kurtagic and graduate student Seymour de Picciotto are also first authors of the paper.
This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

More information: Paper online: http://www.jbc.org … 093.abstract

Provided by Massachusetts Institute of Technology (news : web)

Scientists discover new component of key growth-regulating signaling pathway

Researchers in the lab of Whitehead Institute Member David Sabatini have identified a new substrate of the mammalian target of rapamycin (mTOR) kinase, called Grb10, by using a two-pronged approach of mass spectrometry and kinase specificity profiling.

“These results show that mTOR participates in most key cellular processes, consisting with its established role in common diseases like diabetes, cancer, and neurodegeneration” says Sabatini, who is also a Howard Hughes Medical Institute (HHMI) investigator and a professor of biology at MIT.

The research is published in the June 10 issue of Science.

The Grb10 protein was known to interact with insulin receptors and to inhibit the ability of cells to respond to insulin. By identifying the relationship between Grb10 and mTOR, Peggy Hsu, a former graduate student in the Sabatini lab and first author of the Science paper, was able to show that Grb10 is important for mTOR to inhibit signaling downstream of extracellular growth factors like insulin. This provides researchers with a more detailed understanding of the function of mTOR, especially in the context of cancer, and opens up new areas for mTOR research.

“These results show that mTOR participates in most key cellular processes, consisting with its established role in common diseases like diabetes, cancer, and neurodegeneration” says Whitehead Member David Sabatini.

The role of mTOR in nutrient sensing and regulation of cell growth has been conserved from yeast to worms, flies, and mice.  In humans, it is also important in overall organismal nutrient metabolism and organism size; dysregulation of mTOR has been linked to diabetes and some cancers. Despite its biological and medical importance—drugs that inhibit mTOR are used to treat certain cancers and to suppress the immune system to prevent transplant rejections—little is actually known about the substrates that mTOR targets or the precise manner in which it affects multiple cellular processes.

Hsu, who is now finishing her medical degree at Harvard Medical School, says that until recently, the search for mTOR substrates has been non-systematic and hamstrung by rapamycin’s limited inhibition of mTOR. With the advent of new mTOR inhibitors that target mTOR directly, including the inhibitor Torin1 that Hsu used in her work, researchers are now able to get a more complete picture of what mTOR regulates.

According to Hsu, use of these new mTOR inhibitors in conjuction with mass spectrometry and the kinase specificity profiling method will transform both future and current mTOR research.

“I think this will open up different areas of potential exploration,” says Hsu, who worked closely with the labs of Michael Yaffe at MIT and Jarrod Marto at Harvard Medical School. “I hope this work allows other reseachers to make a connection very quickly by looking through our data, and to basically say, ‘Aha! I thought mTOR would be involved in process X. And now maybe I have a way to study it.’ ”

More information: “The mTOR-Regulated Phosphoproteome Reveals a Mechanism of mTORC1-Mediated Inhibition of Growth Factor Signaling” Science, June 10, 2011

Provided by Whitehead Institute for Biomedical Research (news : web)

Researchers find new clues about protein linked to Parkinson's disease

Researchers at the Keck School of Medicine of the University of Southern California (USC) have uncovered structural clues about the protein linked to Parkinson's disease (PD), which ultimately could lead to finding a cure for the degenerative neurological disorder.

The alpha-synuclein (?-synuclein) protein is commonly found in the healthy human brain even though its function is not clear. The protein has been the subject of substantial Parkinson's research, however, because it is a major component in the protein clumps found in PD cases.

Unlike most proteins, which are typically rigid and occur in one definitive form, the alpha-synuclein protein can fold and change its structure. Researchers Tobias S. Ulmer, Ph.D. and Sowmya Bekshe Lokappa, Ph.D. at the Keck School-affiliated Zilkha Neurogenetic Institute have determined that the energy difference between two particular alpha-synuclein structures is less than previously speculated.

Their study, to be published in the June 17 issue of The Journal of Biological Chemistry, is the first to quantify that energy difference, 1.2±0.4 kcal/mol.

"We're trying to understand the mechanisms of protein folding and misfolding," said Ulmer, the study's principal investigator and an assistant professor in the Department of Biochemistry and Molecular Biology at the Zilkha Neurogenetic Institute. "Then we can say why something is going wrong, which is essential to treating neurodegenerative disorders like Parkinson's."

If proteins misfold, they are repaired or they break down. However, when alpha-synuclein misfolds it aggregates and becomes toxic to surrounding nerve cells, Ulmer said. Understanding its folding and finding what causes aberrant folding is therefore key to determining the root cause of the disorder, he added.

To put the discovery into perspective, Ulmer compared the energy that researchers thought was needed to change the protein's structure to hurricane-force winds and the actual energy required to a light summer breeze. The experiments were conducted in 2010, measuring the energy of elongated and broken helix forms of alpha-synuclein through circular dichroism spectroscopy, fluorescence spectroscopy and isothermal titration calorimetry.

"There may be a continuous interconversion between folded alpha-synuclein structural states that might contribute to its pathological misfolding," said Lokappa, a post-doctoral research associate at the Center for Craniofacial Molecular Biology at USC and the study's co-author. "But we need to have even better insight into the mechanisms of protein folding and misfolding to explain what's going wrong in the brain."

The paper is the sixth in a series of studies that Ulmer has published on alpha-synuclein.

Parkinson's is a neurological disorder that has no cure or determined cause. It is a slow-progressing degenerative disease that most commonly affects motor function. According to the National Parkinson Foundation, the disorder is the second-most common neurodegenerative disease after Alzheimer's, affecting 1 million people in the United States and some 4 million worldwide.

More information: http://www.jbc.org … 4/21450.full

Provided by University of Southern California (news : web)

'Artificial leaf' moves closer to reality

 

An important step toward realizing the dream of an inexpensive and simple "artificial leaf," a device to harness solar energy by splitting water molecules, has been accomplished by two separate teams of researchers at MIT. Both teams produced devices that combine a standard silicon solar cell with a catalyst developed three years ago by professor Daniel Nocera. When submerged in water and exposed to sunlight, the devices cause bubbles of oxygen to separate out of the water.

The next step to producing a full, usable artificial leaf, explains Nocera, the Henry Dreyfus Professor of Energy and professor of chemistry, will be to integrate the final ingredient: an additional catalyst to bubble out the water’s hydrogen atoms. In the current devices, hydrogen atoms are simply dissociated into the solution as loose protons and electrons. If a catalyst could produce fully formed hydrogen molecules (H2), the molecules could be used to generate electricity or to make fuel for vehicles. Realization of that step, Nocera says, will be the subject of a forthcoming paper.

The reports by the two teams were published in the journals Energy & Environmental Science on May 12, and the Proceedings of the National Academy of Sciences on June 6. Nocera encouraged two different teams to work on the project so that each could bring their special expertise to addressing the problem, and says the fact that both succeeded “speaks to the versatility of the catalyst system.”

Ultimately, Nocera wants to produce a low-cost device that could be used where electricity is unavailable or unreliable. It would consist of a glass container full of water, with a solar cell with the catalysts on its two sides attached to a divider separating the container into two sections. When exposed to the sun, the electrified catalysts would produce two streams of bubbles — hydrogen on one side, oxygen on the other — which could be collected in two tanks, and later recombined through a fuel cell or other device to generate electricity when needed.

“These papers are really important, to show that the catalyst works” when bonded to silicon to make a single device, Nocera says, thus enabling a unit that combines the functions of collecting sunlight and converting it to storable fuel. Silicon is an Earth-abundant and relatively inexpensive material that is widely used and well understood, and the materials used for the catalyst — cobalt and phosphorus — are also abundant and inexpensive.

Putting it together

Marrying the technologies of silicon solar cells with the catalyst material — dubbed Co-Pi for cobalt phosphate — was no trivial matter, explains Tonio Buonassisi, the SMA Assistant Professor of Mechanical Engineering and Manufacturing, who was a co-author of the PNAS paper. That’s because the splitting of water by the catalyst creates a “very aggressive” chemical environment that would tend to rapidly degrade the silicon, destroying the device as it operates, he says.

In order to overcome this, both teams had to find ways to protect the silicon surface, while at the same time allowing it to receive the incoming sunlight and to interact with the catalyst.

Professor of Electrical Engineering Vladimir Bulović, who led the other team, says his team's approach was to form the Co-Pi material on the surface of the silicon cell, by first evaporating a layer of pure cobalt metal onto the cell electrode, and then exposing it to a phosphate buffer solution under an electrical charge to transform it into the Co-Pi catalyst. By using the layer of Co-Pi, now firmly bonded to the surface, “we were able to passivate the surface,” says Elizabeth Young, a postdoc who was the lead author of the E&ES paper — in other words, it acts as a protective barrier that keeps the silicon from degrading in water.

“Most people have been staying away from silicon for water oxidation, because it forms silicon dioxide” when exposed to water, which is an insulator that would hinder the electrical conductivity of the material, says Ronny Costi, a postdoc on Bulović’s team. “We had to find a way of solving that problem,” which they did by using the cobalt coating.

Buonassisi’s team used a different approach, coating the silicon with a protective layer. “We did it by putting a thin film of indium tin oxide on top,” explains Joep Pijpers, a postdoc who was the lead author of the PNAS paper. Using its expertise in the design of silicon devices, that team then concentrated on matching the current output of the solar cell as closely as possible to the current consumption by the (catalyzed) water-splitting reaction. The system still needs to be optimized, Pijpers says, to improve the efficiency by a factor of 10 to bring it to a range comparable to conventional solar cells.

“It’s really not trivial, integrating a low-cost, high-performance silicon device with the Co-Pi,” Buonassisi says. “There’s a substantial amount of innovation in both device processing and architecture.”

Both teams had to add an extra power source to the system, because the voltage produced by a single-junction silicon cell is not high enough to use for powering the water-splitting catalyst. In later versions, two or three silicon solar cells will be used in series to provide the needed voltage without the need for any extra power source, the researchers say.

One interesting aspect of these collaborations, says postdoc Mark Winkler, who worked with Buonassisi’s team, was that “materials scientists and chemists had to learn to talk to each other.” That’s trickier than it may sound, he explains, because the two disciplines, even when talking about the same phenomena, tend to use different terminology and even different ways of measuring and displaying certain characteristics.

Portable power?

Nocera’s ultimate goal is to produce an “artificial leaf” so simple and so inexpensive that it could be made widely available to the billions of people in the world who lack access to adequate, reliable sources of electricity. What’s needed to accomplish that, in addition to stepping up the voltage, is the addition of a second catalyst material to the other side of the silicon cell, Nocera says.

Although the two approaches to bonding the catalyst with a silicon cell appear to produce functioning, stable devices, so far they have only been tested over periods of a few days. The expectation is that they will be stable for long periods, but accelerated aging tests will need to be performed to confirm this.

Rajeshwar Krishnan, Distinguished University Professor of Chemistry and Biochemistry at the University of Texas at Arlington, says it remains to be seen “whether this ‘self-healing’ catalyst would hold up to several hours of current flow … under rather harsh oxidative conditions.” But he adds that these papers “certainly move the science forward. The state of the science in water photo-oxidation uses rather expensive noble metal oxides,” whereas this work uses Earth-abundant, low-cost materials. He adds that while there is still no good storage or distribution system in place for hydrogen, “it is likely that the solar photon-to-hydrogen technology will ultimately see the light of day — for transportation applications — with the hydrogen internal combustion engine.”

Meanwhile, Nocera has founded a company called Sun Catalytix, which will initially be producing a first-generation system based on the Co-Pi catalyst material, connected by wires to conventional, separate solar cells.

The “leaf” system, by contrast, is “still a science project,” Nocera says. “We haven’t even gotten to what I would call an engineering design.” He hopes, however, that the artificial leaf could become a reality within three years.

Bulović’s team was funded partly by the Chesonis Family Foundation and the National Science Foundation. Buonassisi’s team had support from the Netherlands Organization for Scientific Research (NOW-FOM), the National Science Foundation and the Chesonis Family Foundation. Nocera’s work was funded by the Chesonis Family Foundation, the Air Force Office of Scientific Research and the National Science Foundation.
This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Provided by Massachusetts Institute of Technology (news : web)

Do steaks make you big?

Adjusting the intake of high protein foods like meat, eggs and milk products could determine whether you become a rugby player or marathon runner and may help you lose weight, according to new research published this month in the Journal of Biological Chemistry.

Dr. Stefan Broer, head of the molecular nutrition group in the ANU College of Medicine, Biology and Environment at The Australian National University, said the study by a group of ANU and Sydney researchers could potentially lead to the development of new weight-loss drugs.

“When it comes to controlling your body weight, everybody thinks about reducing sugar and fat. But we also eat a lot of protein so we wanted to find out how it influences your body weight,” he said.

To investigate the problem, the team generated mice that could not digest protein as well as a normal mouse and measured a wide variety of physiological and physical properties.

“During digestion, your stomach and intestine breaks down protein into smaller subunits called amino acids,” Dr. Broer said.

“So we focused on mice that could not transport amino acids from the intestine into the cells of the body and therefore could not properly process proteins.

“One of the first things we noticed was that the animals were quite a bit smaller in size than normal mice, which suggests that eating more protein can increase our body size and possibly our sporting potential in the long term.

“When we gave these mice diets of different protein content, we found that they could not control their body weight, losing up to 20% in a couple of days. This indicates that varying protein intake in the short term affects our body weight.”

Dr. Broer said the study also revealed an influence of protein in our nutrition on insulin release, which controls the metabolism of sugar and fat in our bodies.

“This could explain some of the weight loss observed in the animals on different diets because we found that on a high protein diet a significant loss of fat occurred.

“This information may have potential in the future development of weight loss treatments.”

Provided by Australian National University