Monocyte chemoattractant protein-induced protein 1 directly degrades viral miRNAs with a specific motif and inhibits KSHV infection

Kaposi's sarcoma-associated herpesvirus (KSHV) expresses miRNAs during latency. However, regulation of viral miRNAs remains largely unknown. Our prior studies demonstrated that MCPIP1 regulates KSHV miRNA biogenesis by degrading most KSHV pre-miRNAs through its RNase activity. Some viral pre-miRNAs are partially resistant to degradation by MCPIP1. Here, we further characterized MCPIP1 substrate specificity and its antiviral potential against KSHV infection. In vitro cleavage assays and binding assays showed that MCPIP1 cleavage efficiency is related to binding affinity. Motif-based sequence analysis identified that KSHV pre-miRNAs that are well degraded by MCPIP1 have a 5-base motif (M5 base motif) within their terminal loops and this motif region consists of multiple pyrimidine-purine-pyrimidine (YRY) motifs. We further demonstrated that mutation of this M5 base motif within terminal loop of pre-miRNAs inhibited MCPIP1-mediated RNA degradation. We also revealed that MCPIP1 has an antiviral effect against KSHV infection. MCPIP1 can reduce the expression of Dicer, which in turn restricts KSHV infection. Conclusively, our findings demonstrated that MCPIP1 inhibited KSHV infection and suppressed viral miRNA biogenesis by directly degrading KSHV pre-miRNAs and altering the expression of miRNA biogenesis factors.