Heterogeneous Nuclear Ribonucleoprotein M Facilitates Enterovirus Infection

Abstract

Picornavirus infection involves a dynamic interplay of host and viral protein interactions that modulates cellular processes to facilitate virus infection and evade host antiviral defenses. Here, using a proteomics-based approach known as TAILS to identify protease-generated neo-N-terminal peptides, we identify a novel target of the poliovirus 3C proteinase, the heterogeneous nuclear ribonucleoprotein M (hnRNP M), a nucleocytoplasmic shuttling RNA-binding protein that is primarily known for its role in pre-mRNA splicing. hnRNP M is cleaved in vitro by poliovirus and coxsackievirus B3 (CVB3) 3C proteinases and is targeted in poliovirus-and CVB3-infected HeLa cells and in the hearts of CVB3-infected mice. hnRNP M relocalizes from the nucleus to the cytoplasm during poliovirus infection. Finally, depletion of hnRNP M using small interfering RNA knockdown approaches decreases poliovirus and CVB3 infections in HeLa cells and does not affect poliovirus internal ribosome entry site translation and viral RNA stability. We propose that cleavage of and subverting the function of hnRNP M is a general strategy utilized by picornaviruses to facilitate viral infection. IMPORTANCEEnteroviruses, a member of the picornavirus family, are RNA viruses that cause a range of diseases, including respiratory ailments, dilated cardiomyopathy, and paralysis. Although enteroviruses have been studied for several decades, the molecular basis of infection and the pathogenic mechanisms leading to disease are still poorly understood. Here, we identify hnRNP M as a novel target of a viral proteinase. We demonstrate that the virus subverts the function of hnRNP M and redirects it to a step in the viral life cycle. We propose that cleavage of hnRNP M is a general strategy that picornaviruses use to facilitate infection. P roteases play fundamental roles in cells by ultimately changing the fate and function of its substrates through proteolytic cleavage or degradation (1-9, 72). Many viruses have exploited these strategies to promote infection. For instance, picornaviruses translate their RNA genome as a single polyprotein, which is then processed by virus-encoded proteinases to produce the mature viral proteins. In addition, viral proteinases target a subset of host proteins to modulate cellular processes, inhibit antiviral responses, and subvert host proteins to aid in specific steps of the viral life cycle, such as viral translation and replication. One of the best characterized is the rapid host translational shutoff that occurs in poliovirus-infected cells, which is facilitated through cleavage of eukaryotic translation initiation factors eIF4G and the poly(A) binding protein (PABP) by the viral proteinases 2A and 3C (10-14). Overall inhibition of protein synthesis leads to release of translation factors and ribosomes that are then diverted to poliovirus protein synthesis. The identification of host protein substrates of viral proteinases has provided important insights into the virus-host interaction strategies that contribute to the...

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