OTUB1 contributes to the stability and function of Influenza A virus NS2.

The influenza A virus (IAV) consists of 8 single-stranded, negative-sense viral RNA (vRNA) segments. After infection, vRNA is transcribed, replicated, and wrapped by viral nucleoprotein (NP) to form viral ribonucleoprotein (vRNP). The transcription, replication, and nuclear export of the viral genome are regulated by the IAV protein, NS2, which is translated from spliced mRNA transcribed from viral NS vRNA. This splicing is inefficient, explaining why NS2 is present in low abundance after IAV infection. The levels of NS2 and its subsequent accumulation are thought to influence viral RNA replication and vRNP nuclear export. Here we show that NS2 is ubiquitinated at the K64 and K88 residues by K48-linked and K63-linked polyubiquitin (polyUb) chains, leading to the degradation of NS2 by the proteasome. Additionally, we show that a host deubiquitinase, OTUB1, can remove polyUb chains conjugated to NS2, thereby stabilizing NS2. Accordingly, knock down of OTUB1 by siRNA reduces the nuclear export of vRNP, and reduces the overall production of IAV. These results collectively demonstrate that the levels of NS2 in IAV-infected cells are regulated by a ubiquitination-deubiquitination system involving OTUB1 that is necessary for optimal IAV replication. Author summary: The influenza A virus (IAV) protein, NS2, plays a critical role in virus replication, as the abundance of NS2 influences viral transcription, viral RNA (vRNA) synthesis, and viral ribonucleoprotein (vRNP) export from the nucleus. Interestingly, high levels of NS2 are known to inhibit IAV transcription yet promote vRNA synthesis. In this study, we found that ubiquitination destabilizes NS2, and a host deubiquitinase, OTUB1, was shown to deubiquitinate and stabilize NS2, thus contributing to NS2 accumulation. OTUB1 has previously been reported to be a negative regulator of host cellular antiviral defense, and its upregulation enhances virion production. Our study sheds additional light on the role of OTUB1 during IAV infection which can now be considered for the development of anti-influenza strategies. [ABSTRACT FROM AUTHOR]