Researchers unlock mysteries of protein that plays key regulatory role in cancer therapies

Researchers from the University of Virginia, Lehigh University, and the Massachusetts Institute of Technology are pooling their respective labs' expertise to unlock the mysteries of a protein that plays a critical regulatory role in human health and disease. Knowing how the protein works could lead to improved therapies for cancers and other diseases.

UVA associate professor of chemical engineering Matthew Lazzara and Lehigh University associate professor of chemistry Damien Thévenin is the project principal investigators. Forest White, a professor of biological engineering at MIT, is also a collaborating investigator.

The project, "Promoting Receptor Protein Tyrosine Phosphatase Activity by Targeting Transmembrane Domain Interactions," is funded by a $1.6 million Project Research Grant (R01) from the National Institute of General Medical Sciences of the National Institutes of Health.

The protein at the center of the project is known as protein tyrosine phosphatase receptor type J (PTPRJ), also sometimes referred to as density-enhanced phosphatase-1 (DEP-1). PTPRJ is a member of the family of receptor-like protein tyrosine phosphatases (RPTP), which target and dephosphorylate, or deactivate, proteins involved in cell proliferation and survival.

The team anticipates that their work on the PTPRJ protein could yield insights that are relevant across the receptor-like protein tyrosine phosphatase family.

"The importance of RPTPs in normal cell function is clear, but we don't yet know much about the structure-function relationships that underpin the regulation of their activity," Lazzara said. "If we knew more, we might be able to design ways to augment their activity in settings, such as cancer, where RPTP substrates need to be turned off."

One goal of the project is to understand how to promote the activity of PTPRJ -- and eventually other RPTPs -- by interfering with the ability of the phosphatase to bind to itself, a process called homodimerization in which two identical proteins form a structure.

"Our collaborators at Lehigh have designed small peptide binders that disrupt PTPRJ homodimerization as a way to promote phosphatase activity," Lazzara said. "Because the phosphatase acts on, and effectively turns off, certain receptors that can promote tumor growth, we think this could eventually lead to a new method to interfere with signaling in cancer cells in a way that would not be circumvented by the common forms of drug resistance we see over and over again in oncology."

"Our approach has all kinds of exciting consequences on cell behavior and therapeutic applications," Thévenin said.

"Indeed, one of the main substrates of RPTPs are receptor tyrosine kinases, which are over-activated, or phosphorylated, in many cancers," Thévenin said. "Existing methods to target tumor-promoting kinases are limited to pharmacological inhibitors and antibodies. While some drug treatments can be highly effective, at least initially, resistance to these inhibitors virtually always arises through mutations or bypass signaling via alternative receptor tyrosine kinases. Promoting the activity of RPTPs could be an effective alternative approach to overcoming common acquired resistance mechanisms, as it should be immune to the effects of gatekeeper mutations."

A second project goal is to identify the circumstances under which interfering with PTPRJ dimerization might be most effective for changing how cells function.

"In cell biology, everything is about context," said Lazzara, who holds a courtesy appointment in biomedical engineering and is a member of the UVA Cancer Center. "The function of a protein in one cellular setting may be different than in another. That can happen for lots of reasons, including differences in the expression of interacting proteins. My lab's main role in the project is to execute a set of experiments designed to capture that complexity and then to use systems biology computational modeling approaches to interpret the data."

White, a former postdoctoral researcher at UVA, will contribute by using mass spectrometry to quantify protein phosphorylation events that change in response to modulating PTPRJ function in the lab. The use of mass spectrometry to quantify signaling protein phosphorylation is an area of expertise for which White is well known, Lazzara said.

Forest's approach can measure hundreds to thousands of unique phosphorylation events at a time in cells, which is substantially greater bandwidth than you can do with many other techniques. There are some other techniques that can measure hundreds of sites, but they are much less quantitative than his approach. Forest has used this method to study many different signaling processes in cancer."

Matthew Lazzara, Associate Professor of Chemical Engineering, University of Virginia

Lazzara noted for prolific and often collaborative research in cell signaling and cellular decision-making has received numerous grants from the National Science Foundation, National Cancer Institute, National Institute of General Medical Sciences, and the American Cancer Society.

His work contributes significantly to UVA chemical engineering's research programs, also providing graduate researchers with opportunities to engage in fundamental and potentially groundbreaking science.

"This project is a great example of how biological researchers are increasingly working collaboratively and integrating multiple areas of expertise to make advances," Lazzara said. "I expect we will continue to see that in cancer research especially."

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