Cellular Protein Modification by Poliovirus: the Two Faces of Poly(rC)-Binding Protein

Abstract

During picornavirus infection, several cellular proteins are cleaved by virus-encoded proteinases. Such cleavage events are likely to be involved in the changing dynamics during the intracellular viral life cycle, from viral translation to host shutoff to RNA replication to virion assembly. For example, it has been proposed that there is an active switch from poliovirus translation to RNA replication mediated by changes in RNA-binding protein affinities. This switch could be a mechanism for controlling template selection for translation and negative-strand viral RNA synthesis, two processes that use the same positive-strand RNA as a template but proceed in opposing directions. The cellular protein poly(rC)-binding protein (PCBP) was identified as a primary candidate for regulating such a mechanism. Among the four different isoforms of PCBP in mammalian cells, PCBP2 is required for translation initiation on picornavirus genomes with type I internal ribosome entry site elements and also for RNA replication. Through its three K-homologous (KH) domains, PCPB2 forms functional protein-protein and RNA-protein complexes with components of the viral translation and replication machinery. We have found that the isoforms PCBP1 and -2 are cleaved during the mid-to-late phase of poliovirus infection. On the basis of in vitro cleavage assays, we determined that this cleavage event was mediated by the viral proteinases 3C/3CD. The primary cleavage occurs in the linker between the KH2 and KH3 domains, resulting in truncated PCBP2 lacking the KH3 domain. This cleaved protein, termed PCBP2-⌬KH3, is unable to function in translation but maintains its activity in viral RNA replication. We propose that through the loss of the KH3 domain, and therefore loss of its ability to function in translation, PCBP2 can mediate the switch from viral translation to RNA replication.

Differential effect of acute and persistent Junín virus infections on the nucleo-cytoplasmic trafficking and expression of heterogeneous nuclear ribonucleoproteins type A and B

“…hnRNP A1 is upregulated during differentiation of epithelial cells infected with human papillomavirus type 16, facilitating the appropriate alternative splicing necessary for virus late transcription (Cheunim et al, 2008). In contrast, during the mid-to-late phase of PV infection, hnRNP E is cleaved by viral proteases 3C/3CD as a way to regulate virus translation and RNA replication (Perera et al, 2007). The dynamic interplay between virus and host components is an important aspect of viral pathogenesis.…”

New insights into internal ribosome entry site elements relevant for viral gene expression

“…Partial processing of other RNA-binding proteins, PABP and PCBP, was observed in PV and CBV infection (Perera et al, 2007;Kuyumcu-Martinez et al, 2002, 2004Lerner & Nicchitta, 2006). Subsequently, cleavage of eIF3a and b, PABP and PTB was reported in FMDV-infected cells (Rodriguez Pulido et al, 2007).…”

“…PCPB2 forms functional complexes with components of the viral translation and replication machinery. PCBP1 and 2 are cleaved during the mid-late phase of PV infection by the viral proteases 3C/3CD (Perera et al, 2007). The cleavage results in a truncated PCBP2 that is unable to function in translation but maintains its activity in viral RNA replication.…”

Cleavage of Poly(A)-Binding Protein by Poliovirus 3C Proteinase Inhibits Viral Internal Ribosome Entry Site-Mediated Translation

“…In contrast, PTB is partly cleaved by 3C pro in PV infection and expression of cleavage-related truncated PTB fragments in cells inhibited PV reporter translation (2), providing another potential mechanism for viral translation shutoff. Similarly, PCBP2 is also partly cleaved late in infection, producing a fragment that will not rescue viral translation in PCBP2-depleted translation extracts (49).…”