34: Expression and function of ADAR1 and PACT and their impact on PKR activation during HIV-1 infection

Abstract

A poor innate immune response contributes to the establishment of viral latency and persistence in human immunodeficiency virus (HIV)-1 infection. The protein kinase RNA-activated (PKR) is an Interferon-stimulated gene (ISG) that senses RNA viruses. PKR is a potent HIV-1 suppressor through the phosphorylation of the translation initiation factor eIF2 α and consequent inhibition of protein synthesis. We showed that PKR is activated at the beginning of HIV-1 infection followed by a deactivation due, in part, to cellular proteins TRBP and ADAR1. Although PACT is a PKR activator, we showed that it becomes a PKR inhibitor in HIV-expressing cells [1] . Our hypothesis is that PKR inhibition contributes to HIV-1 replication and persistence through multiple mechanisms. Our objective is to elucidate how ADAR1 and PACT contribute to PKR inhibition during HIV-1 infection. We analysed the expression of PKR, ADAR1 and PACT in HIV-infected patients and in peripheral blood mononuclear cells (PBMCs) infected with HIV-1 by western blots and immunoprecipitations. We used short hairpin (sh)RNAs against ADAR1 and PACT to assess their impact on HIV-1 production. We assessed the interaction between ADAR1 and PACT and its impact on PACT function. ADAR1 and PACT expression are increased in HIV-1 infected PBMCs and immunoprecipitate with PKR. This is correlated with PKR deactivation and increased viral expression. A decrease of either ADAR1 or PACT inhibits HIV-1 production. A direct interaction between ADAR1 and PACT suggests a functional significance on PACT and PKR functions during HIV replication. The increased expression of both ADAR1 and PACT contribute to PKR inhibition in HIV-1 infected cells. PACT changes its function for a PKR inhibitor in HIV-infected cells, which could be due to its interaction with ADAR1, thereby contributing to viral persistence in patients.