ABSTRACT Data from seminal studies on the functional roles of polyoma gene products along with recent results from cancer genomics have converged to highlight the multimeric enzyme protein phosphatase PP2A as an important tumor suppressor which is frequently mutated in a variety of human cancers. The overriding objective of the Functional Proteomics Core (FPC) is to provide state-of-the-art proteomic approaches for tandem affinity purification followed by mass spectrometry (TAP-MS) as well as quantitative proteomic/phosphoproteomic technologies. Data from these studies will advance our understanding of how ST/MT alter PP2A protein associations, as well as host cell signaling networks and protein expression profiles, ultimately contributing to cellular transformation and human cancers. The FPC will serve as a technical and intellectual resource where researchers within all Projects can collaborate, compare, and interpret their proteomic data within the context of human cancer. We will work collaboratively with Program members through two specific aims: Aim 1. Utilize tandem affinity purification followed by mass spectrometry (TAP-MS) to characterize ST/MT-mediated alterations in PP2A protein complexes. We will utilize our proven platform for TAP-MS platform to: (Project 2) quantify the dynamics of YAP-PP2A complexes as a function of ST or MT expression; (Project 3) compare protein binding partners of PP2A A and PP2A A; (Project 4) quantify changes in the assembly of PP2A-STRIPAK multi-component protein complexes as a function of ST expression. Aim 2. Utilize quantitative mass spectrometry to interrogate alterations in protein expression and PP2A-associated signaling cascades resulting from expression of ST/MT gene products. We will use our DEEP SEQ quantitative mass spectrometry platform to: (Project 1) identify signaling pathways influenced by expression of Merkel ST and determine whether these oppose or work synergistically with mTOR in the context of cellular proliferation and oncogenic transformation; (Project 2) quantify changes in PP2A signaling that result from ST/MT-mediated changes in YAP protein complexes; (Project 3) quantify perturbations in phosphorylation that result from ST/MT targeting of PP2A-A; (Project 4) identify changes in phosphorylation sites associated with expression of SV40 ST or depletion of specific PP2A subunits. In addition we will work with Project 1 to interrogate alterations in protein expression resulting from MCPyV ST. These data will be integrated with the DeCaprio Lab’s RNA-seq results to prioritize metabolic regulators for further study. In addition our DEEP SEQ proteomic data may reveal transcription-independent mechanisms by which MCPyV ST commandeers cellular pathways.