The nuclear protein Sam68 is cleaved by the FMDV 3C protease redistributing Sam68 to the cytoplasm during FMDV infection of host cells

Abstract

Picornavirus infection can lead to disruption of nuclear pore traffic, shut-off of cell translation machinery, and cleavage of proteins involved in cellular signal transduction and the innate response to infection. Here, we demonstrated that the FMDV 3C(pro) induced the cleavage of nuclear RNA-binding protein Sam68 C-terminus containing the nuclear localization sequence (NLS). Consequently, it stimulated the redistribution of Sam68 to the cytoplasm. The siRNA knockdown of Sam68 resulted in a 1000-fold reduction in viral titers, which prompted us to study the effect of Sam68 on FMDV post-entry events. Interestingly, Sam68 interacts with the internal ribosomal entry site within the 5' non-translated region of the FMDV genome, and Sam68 knockdown decreased FMDV IRES-driven activity in vitro suggesting that it could modulate translation of the viral genome. The results uncover a novel role for Sam68 in the context of picornaviruses and the proteolysis of a new cellular target of the FMDV 3C(pro).

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).…”

Nuclear Protein Sam68 Interacts with the Enterovirus 71 Internal Ribosome Entry Site and Positively Regulates Viral Protein Translation

“…Sam68 is a multifunctional RNA-binding protein that has been implicated in both transcriptional and posttranscriptional regulation of gene expression (42,43). Sam68 also plays important roles in the life cycle of FMDV and participates in the translation of virus proteins (31). These facts led us to investigate the importance of Sam68 in the life cycle of EV71, especially in synthesis of virus protein.…”

“…Interestingly, Sam68 relocalized from the nucleus to the cytoplasm and interacted with the poliovirus RNA polymerase during poliovirus infection (30). The binding of Sam68 to the footand-mouth disease virus (FMDV) IRES during infection could potentially enhance translation of the viral RNA (31). Furthermore, Sam68 can significantly enhance the translation of retrovirus genes by marking the viral RNA transcripts (32).…”

Enterovirus 71 Infection Cleaves a Negative Regulator for Viral Internal Ribosomal Entry Site-Driven Translation

“…For example, viral protease 2A pro can cleave eukaryotic initiation factor 4G (eIF4G) (18)(19)(20), poly(A)-binding protein (PABP) (21,22), beta interferon (IFN-␤) promoter stimulator-1 (IPS-1) (17), and 62-kDa nucleoporin (Nup62) (23). Viral protease 3C pro can cleave PABP (24), polypyrimidine tract-binding protein (PTB) (25), cleavage stimulation factor 64 (CstF-64) (26), IPS-1 (17), retinoic acid-inducible gene I (RIG-I) (16), Toll-interleukin 1 receptor (TIR) domain-containing adaptor inducing IFN-␤ (TRIF) (27), and the 68-kDa Src-associated substrate during mitosis (Sam68) (28). Racaniello and colleagues have demonstrated that poliovirus infection-induced cleavage of MDA-5 (melanoma differentiation-associated gene 5) is associated with virus-induced proteasome and caspase activities (15).…”