||Network of the high-confidence interactions observed for the human protein phosphatases
Reversible protein phosphorylation occurs with precise regulation, ensuring that a cell responds to its environment with efficiency and speed. Two families of enzymes, kinases and phosphatases, add and remove phosphate respectively, and many members of both enzyme families are disrupted in cancer and other diseases. However, while several kinases have been well studied and exploited as targets for successful drugs, much less is known about the phosphatases. In a new study published in Cell Reports, LTRI scientists Anne-Claude Gingras and Laurence Pelletier aim to bridge that gap, providing a wealth of new data towards understanding these enigmatic enzymes.
First, their research teams generated a comprehensive reagent set for 140 phosphatases, including DNA plasmids and stable cell lines. Using these tools, they mapped protein-protein interactions for each phosphatase in human cells. The result is a treasure trove of interactions (1335, to be exact) between the phosphatases and a variety of proteins, which are collectively involved in a myriad of cellular processes and disease states. The dataset, available for interactive browsing at http://prohits-web.lunenfeld.ca
, will provide the signal transduction field with valuable starting points for the characterization of individual phosphatases.
To dig deeper into the dataset, the authors next performed a complementary high-resolution depletion screen assaying the phosphatases for roles in cell division, a process often disrupted in cancer. Mitosis, the target of several widely used cancer chemotherapies, is highly regulated by phosphorylation, and phosphatases involved could represent new leads for targeted therapies.
"We wanted to go beyond the standard long list of interactions, and see if we could use the interactions to predict the reasons why loss of certain phosphatases caused issues with cell division,” says LTRI postdoctoral fellow and lead author Dr. Nicole St-Denis. Combining the datasets allowed the identification of potential roles for CDC14A in microtubule organization, DUSP19 in mitotic progression, PTPRF in mitotic cell adhesion, and DUSP23 in centriole duplication, demonstrating the power of the combined approaches. “This study was really made possible by an excellent collaboration, bringing together expertise in proteomics and microscopy and image analyses," said Dr. Gagan Gupta, a major contributor to the project. Intriguingly, while the majority of mitotic phosphorylation involves serine and threonine residues, these enzymes (and several more identified) are tyrosine phosphatases, suggesting that tyrosine phosphorylation may play unexpected yet important roles in cell division. Collectively, the results shine new light on a family of oft-neglected enzymes, highlight the importance of phosphatases in a variety of processes and will provide insight into potential therapeutic interventions.
This research was primarily supported by operating grants from the Canadian Institutes of Health Research and the Krembil Foundation.