Multiple poliovirus-induced organelles suggested by comparison of spatiotemporal dynamics of membranous structures and phosphoinositides

Abstract

ABSTRACTPoliovirus (PV) infection induces membranes with elevated levels of phosphatidylinositol-4-phosphate (PI4P) and invaginated, tubular structures that appear as vesicular clusters in cross section. Here, we characterize PV mutants, termed EG and GG, which exhibit aberrant proteolytic processing of the P3 precursor that can delay the onset of genome replication and/or impair virus assembly. For WT PV, changes to the PI4P pool were observed as early as 30 min post-infection. PI4P remodeling occurred even in the presence of guanidine hydrochloride, a replication inhibitor. Vesicular clusters were not apparent until 3 h post-infection, a time too slow for these structures to be responsible for genome replication. Delays in the onset of genome replication observed for EG and GG PVs were explained completely by the reduced kinetics of virus-induced remodeling of PI4P pools, consistent with PI4P serving as a marker of the genome-replication organelle. Infectious virus produced by GG PV is known to be reduced nearly 5 logs. We show that GG PV was unable to make virus-induced vesicular clusters. Instead, GG PV-infected cells accumulated elongated tubules. Our results are consistent with the existence of distinct organelles for genome-replication and virus assembly. We suggest that the pace of formation and spatiotemporal dynamics of PV induced organelles may be set by the rate of P3 precursor processing to form 3AB and/or 3CD proteins.AUTHOR SUMMARYAll positive-strand RNA viruses replicate their genomes in association with host cell membranes. PV does not just remodel existing membranes, but induces membranes with unique structure and lipid composition. There has been some suggestion that the functions of the PV induced structures observed during infection may not be those that perform genome-replication. This study uses kinetic analysis of virus-induced membrane formation and PI4P induction by two PV mutants to provide evidence for the existence of a virus-induced genome-replication organelle distinct from a second organelle, the absence of which impairs virus assembly. In addition, our studies suggest that formation of both organelles may require participation of viral proteins, 3AB and/or 3CD. Therefore, this study provides a new perspective on the cell biology of PV infection and should inspire a fresh look at picornavirus-induced organelles, their functions and the role of P3 proteins in their formation.