Inhibition of U snRNP assembly by a virus-encoded proteinase

Abstract

It has been proposed that defects in the assembly of spliceosomal uridine-rich small nuclear ribonucleoprotein (U snRNP) complexes could account for the death of motor neurons in spinal muscular atrophy (SMA). We discovered that infection of cultured cells with poliovirus results in the specific cleavage of the host factor Gemin3 by a virus-encoded proteinase, 2A pro . Gemin3 is a component of the macromolecular SMN complex that mediates assembly of U snRNP complexes by aiding the heptameric oligomerization of Sm proteins onto U snRNAs. Using in vitro Sm core assembly assays, we found that lowering the intracellular amounts of Gemin3 by either poliovirus infection or small interfering RNA (siRNA)-mediated knockdown of Gemin3 resulted in reduced assembly of U snRNPs. Immunofluorescence analyses revealed a specific redistribution of Sm proteins from the nucleoplasm to the cytoplasmic periphery of the nucleus in poliovirus-infected cells. We propose that defects in U snRNP assembly may be shared features of SMA and poliomyelitis.[Keywords: snRNP assembly; picornaviral proteinases; Gemins] Supplemental material is available at http://www.genesdev.org.

RNA nuclear export is blocked by poliovirus 2A protease and is concomitant with nucleoporin cleavage

“…pro (Almstead and Sarnow, 2007); however, proteolysis of this substrate was not observed in our assays, irrespective of the IRES-2A mRNA dose employed (Fig. 3C).…”

“…PV RNA contains an internal ribosome entry site (IRES) that ensures translation despite eIF4G cleavage (Martinez-Salas and Fernandez-Miragall, 2004). 2A pro and 3C pro also target some nuclear factors, including several transcription factors (Weidman et al, 2003) and, in the case of 2A pro , the structural component of small nuclear ribonucleoproteins (snRNPs) gemin-3, which is implicated in eukaryotic intron removal mediated by the spliceosome machinery (Almstead and Sarnow, 2007).…”

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

“…The number of host factors identified as targets of viral proteases has increased with the advances of proteomic analysis; characterization of the protein patterns in CVB3-infected cells revealed modification of UNR, nucleophosmin, lamin and the p38 mitogen-activated protein kinase (Rassmann et al, 2006). Specific cleavage of Gemin 3, a nuclear protein, was recently found during PV infection, together with a redistribution of the target proteins from the cell nucleus to the nuclear periphery (Almstead & Sarnow, 2007). Gemin 3 is a component of the macromolecular complex that mediates U snRNP assembly (Battle et al, 2006), and therefore its processing has a profound impact on mRNA splicing.…”

Picornavirus IRES elements: RNA structure and host protein interactions

“…This is noticed at the level of transcription, mRNA processing, nucleocytoplasmic transport, translation, or RNA granules composition. Among other proteins, proteolysis affects splicing factors, RNAprocessing proteins, RNA helicases, nuclear pore factors, stress granules assembly factors or antiviral response proteins (Almstead and Sarnow, 2007;Barral et al, 2009;Castello et al, 2009;Chen et al, 2013;Lawrence et al, 2012;Mukherjee et al, 2011;Park et al, 2010;Pineiro et al, 2012;Rozovics et al, 2012;Shiroki et al, 1999;Watters and Palmenberg, 2011;Weng et al, 2009;White et al, 2007).…”