NSP1 of human rotaviruses commonly inhibits NF-κB signaling by inducing β-TrCP degradation.

Rotavirus is a leading cause of severe gastroenteritis in infants worldwide. Rotavirus nonstructural protein 1 (NSP1) is a virulence factor that inhibits innate host immune responses. NSP1 from some rotaviruses targets host interferon response factors (IRFs), leading to inhibition of type I interferon expression. A few rotaviruses encode an NSP1 that inhibits the NF-kappa B pathway by targeting beta-TrCP, a protein required for I kappa B degradation and NF-kappa B activation. Available evidence suggests that these NSP1 properties involve proteosomal degradation of target proteins. We show here that NSP1 from several human rotaviruses and porcine rotavirus CRW-8 inhibits the NF-kappa B pathway, but cannot degrade IRF3. Furthermore, beta-TrCP levels were much reduced in cells infected with these rotaviruses. This provides strong evidence that beta-TrCP degradation is required for NF-kappa B pathway inhibition by NSP1 and demonstrates the relevance of beta-TrCP degradation to rotavirus infection. C-terminal regions of NSP1, including a serine-containing motif resembling the beta-TrCP recognition motif of I kappa B, were required for NF-kappa B inhibition. CRW-8 infection of HT-29 intestinal epithelial cells induced significant levels of IFN-beta and CCL5 but not IL-8. This contrasts with monkey rotavirus SA11-4F, whose NSP1 inhibits IRF3 but not NF-kappa B. Substantial amounts of IL-8 but not IFN-beta or CCL5 were secreted from HT-29 cells infected with SA11-4F. Our results show that human rotaviruses commonly inhibit the NF-kappa B pathway by degrading beta-TrCP and thus stabilizing I kappa B. They suggest that NSP1 plays an important role during human rotavirus infection by inhibiting the expression of NF-kappa B-dependent cytokines, such as IL-8.