Regulation of protein phosphatase specificity in response to nutrient deprivation
Although much is known about how protein kinases function to regulate cell signaling pathways, how protein phosphatases are regulated to de-phosphorylate proteins and counteract kinase function has not been established. How serine-threonine protein phosphatases are regulated by extra- or intracellular signals to achieve specificity towards various substrates is poorly understood. Phosphatase specificity towards a substrate is largely controlled by its binding proteins. Protein phosphatase specificity is achieved through the assembly of a trimeric complex in which the catalytic C subunit interacts with the scaffolding A subunit. This AC complex can then associate with over 15 regulatory B subunits through the A subunit. Binding of a specific B subunit determines substrate specificity. Although protein phosphatase complexes function in almost all known signaling pathways such as stress signaling and cell cycle regulation, the central question that remains unanswered is: How are protein phosphatases actively regulated by different signals to acquire specificity despite the promiscuous activity of their catalytic subunit? A specific B subunit has been identified that is transcriptionally up-regulated in response to glucose deprivation. This B subunit may play a critical role in regulating cell survival under glucose limiting conditions. The proposed research will elucidate the mechanisms that regulate phosphatase substrate specificity in response to glucose deprivation.
Training objectives include learning techniques of mass spectrometry and phosphatase assays. Broader impacts include increasing the participation of underrepresented minorities at the postdoctoral level, as well as mentoring high school and college students from disadvantaged groups who will partake in research at the host institution.
Intellectual Merit: Despite advances in our understanding of protein kinase regulation in stress response, whether protein phosphatases actively modulate these signaling pathways has not been established. Protein phosphatase 2A (PP2A) play a critical role in regulation of cell survival upon metabolic or genotoxic stress, two environmental challenges that cells often encounter and adapt to. Here we show that, TIPRL, an evolutionarily conserved binding protein of PP2A family phosphatases, inhibits PP2A family phosphatase activity and promotes cell death upon genotoxic or metabolic stress. This study provides important evidence that PP2A phosphatase complexes are tightly regulated in stress response in which TIPRL plays a central role to inhibit phosphatase activity. In addition we uncovered that PP2A is regulated by different signals to acquire specificity. Broader Impacts: The conducted research and training plan promoted the training, teaching and learning of underrepresented groups being that the proposee was a member of an underrepresented group. The proposee also mentored and trained an undergraduate underrepresented student who partook in the proposed project. The proposed activities allowed for students and scientist to contribute to the understanding of the novel mechanism that may regulate protein phosphatase activity. In addition the proposee visited all second grade classrooms in a highly underserved area yearly over the 2 year award period and talked about her work as a scientist and informed and encouraged underrepresented students to pursue a career in science.
