Content area
Abstract
Vesicular stomatitis virus (VSV) is an enveloped non-segmented negative-stranded RNA virus and is a model to study different aspects of molecular biology and immunopathogenesis of viruses. To indentify cellular proteins that interact with VSV P protein, a subunit of the viral RNA-dependent RNA polymerase, I used immunoprecipitation followed by mass-spectrometry. I identified the poly(C) binding protein 1 and 2 (PCBP1/2) as interacting partners of the P protein. Modulating the expression levels of these proteins in mammalian cells, I found that PCBP2 was stronger than PCBP1 in inhibiting VSV gene expression and productive infection. To determine how PCBP2 inhibits VSV replication, I found that the interaction of the P protein with PCBP2 neither causes degradation of P protein nor dissociation amongst the viral replicative protein complexes (N, P and L). The mechanism of this inhibition remains elusive. Since PCBP2 is a component of cellular stress granules (SGs), I investigated the induction of SGs in VSV infected cells. I found that VSV infection induced granular structures containing cellular RNA-binding proteins including PCBP2, T-cell-restricted intracellular antigen 1 (TIA1) and TIA1-related protein (TIAR) together with viral RNA and replicative proteins. Similar to PCBP2, TIA1 inhibits VSV gene expression. VSV-induced granules lack bonafide SG markers eIF3, eIF4A or DCP1a (a marker for processing bodies (PBs)) and thus might not represent the canonical SGs or PBs. In addition, PBs and SGs induced by oxidative stress or heat-shock were not inhibited in VSV-infected cells. Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is the prototype protein of hnRNP subfamily containing three K homolog (KH) domains with conserved functions as described for PCBP1/2. However, my studies showed that it was required for VSV propagation. Interestingly, I also found a requirement of PCBP2 for the expression of TIA1 isoforms whereas hnRNP K physiologically suppressed TIA1b but favored TIA1a expression. Overall, I conclude that PCBP1, PCBP2, and TIA1 are antagonists but hnRNP K is a required factor for VSV infection. TIA1 represents a downstream factor for PCBP2 in VSV inhibition.
