Cellular Determinants and Function Consequences of PP2A-B56 Degradation by HIV-1 Vif

PROJECT SUMMARY The HIV-1 Vif protein is expressed late during infection and has a well-described function to ubiquitinate and degrade proteins in the APOBEC3 family, thus neutralizing their antiviral activities. More recently, an additional function of HIV-1 Vif was described by us and others to ubiquitinate and degrade protein phosphatase 2A holoenzymes containing B56 family regulatory subunits (PP2A-B56). The conservation of Vif-mediated PP2A- B56 degradation throughout globally circulating HIV-1 subtypes suggests that it is functionally important. However, there remains a gap in understanding the mechanisms by which PP2A-B56 degradation confers a fitness advantage to HIV-1. Furthermore, in contrast to APOBEC3 degradation, the host cellular determinants required for Vif-mediated ubiquitination and degradation of PP2A-B56 are undefined. In this project, we aim to address these gaps in understanding by defining the cellular determinants and functional effects of PP2A-B56 degradation by HIV-1 Vif. In Aim 1, we will apply unbiased protein interaction technologies to determine proteins interacting with PP2A-B56 while it is degraded by Vif. In Aim 2, we will carry out a genome- wide CRISPR/Cas9 genetic screen to identify genes regulating APOBEC3 and PP2A-B56 degradation. In Aim 3, will test the impact of individual phosphorylation sites regulated by PP2A-B56 in HIV-1 replication in primary CD4+ T cells. Successful completion of this project will advance understanding of the Vif-PP2A-B56 signaling axis, potentially leading towards the development of novel classes of antiretroviral therapies that target late processes of HIV-1 infection.