Calicivirus 3C-like proteinase inhibits cellular translation by cleavage of poly(A)-binding protein

Caliciviruses are single-stranded RNA viruses that cause a wide range of diseases in both humans and animals, but little is known about the regulation of cellular translation during infection. We used two distinct calicivirus strains, MD145-12 (genus Norovirus) and feline calicivirus (FCV) (genus Vesivirus), to investigate potential strategies used by the caliciviruses to inhibit cellular translation. Recombinant 3C-like proteinases (r3CL ^pro) from norovirus and FCV were found to cleave poly(A)-binding protein (PABP) in the absence of other viral proteins. The norovirus r3CL ^pro PABP cleavage products were indistinguishable from those generated by poliovirus (PV) 3C^pro cleavage, while the FCV r3CL ^pro products differed due to cleavage at an alternate cleavage site 24 amino acids downstream of one of the PV 3C^pro cleavage sites. All cleavages by calicivirus or PV proteases separated the C-terminal domain of PABP that binds translation factors eIF4B and eRF3 from the N-terminal RNA-binding domain of PABP. The effect of PABP cleavage by the norovirus r3CL^pro was analyzed in HeLa cell translation extracts, and the presence of r3CL ^pro inhibited translation of both endogenous and exogenous mRNAs. Translation inhibition was poly(A) dependent, and replenishment of the extracts with PABP restored translation. Analysis of FCV-infected feline kidney cells showed that the levels of de novo cellular protein synthesis decreased over time as virus-specific proteins accumulated, and cleavage of PABP occurred in virus-infected cells. Our data indicate that the calicivirus 3CL^pro, like PV 3C^pro, mediates the cleavage of PABP as part of its strategy to inhibit cellular translation. PABP cleavage may be a common mechanism among certain virus families to manipulate cellular translation.