Amplitude control of protein kinase C by RINCK, a novel E3 ubiquitin ligase. and knockout of TRIM41 increase host susceptibility to IAV contamination. As a ubiquitin E3 ligase, TRIM41 ubiquitinates NP and in cells. The TRIM41 mutant lacking E3 ligase activity fails to inhibit IAV contamination, suggesting that this E3 ligase activity is usually indispensable for TRIM41 antiviral function. Mechanistic analysis further revealed that the polyubiquitination leads to NP protein degradation and viral inhibition. Taking these observations together, TRIM41 is a constitutively expressed intrinsic IAV restriction factor that targets NP for ubiquitination and protein degradation. IMPORTANCE Influenza control strategies rely on annual immunization and require frequent updates of the vaccine, which is not always a foolproof process. Furthermore, the current antivirals are also losing effectiveness as new viral strains are often refractory to conventional treatments. Thus, there is an urgent need to find new antiviral mechanisms and develop therapeutic drugs based on these mechanisms. Targeting the virus-host interface is an emerging new strategy because host factors controlling viral replication activity will be ideal candidates, and cellular proteins are less likely to mutate under drug-mediated selective pressure. Here, we show that this ubiquitin E3 ligase TRIM41 is an intrinsic host restriction factor to IAV. TRIM41 directly binds the viral nucleoprotein and targets it for ubiquitination and proteasomal degradation, thereby limiting viral infection. Exploitation of this natural defense pathway may open new avenues to develop antiviral drugs targeting the influenza computer virus. family and a human respiratory pathogen that causes seasonal epidemics and occasional global pandemics with considerable economic and interpersonal impact (1, 2). The computer virus engages with the host cellular protein conversation network during contamination. The engagement either facilitates MGC102953 virus hijacking of the host molecular machinery to fulfill the viral life cycle or triggers the host immune defense to eliminate the virus. In recent years, host intrinsic restriction factors have gained increasing CK-1827452 (Omecamtiv mecarbil) importance in IAV inhibition (3). Host intrinsic restriction factors usually limit viral contamination by direct conversation with viral proteins. For example, plakophilin 2 (PKP2) competes with PB2 for PB1 binding, thus disrupting IAV polymerase complex and inhibiting viral replication (4). The therapeutics targeting intrinsic immunity factors are more encouraging because cellular proteins are less likely to mutate under drug-mediated selective pressure. The tripartite motif (TRIM) family members have been progressively recognized as intrinsic immunity factors that inhibit viral contamination. For example, TRIM5 is well known for species-specific retroviral restriction by binding to the viral capsid and inducing premature uncoating (5). TRIM79 restricts tick-borne encephalitis computer virus (6). TRIM28, also known as KAP1, restricts murine leukemia computer virus as well as facilitating the establishment of viral latency (7, 8). Recently, TRIM52 has been found to interact with the NS2A protein of Japanese encephalitis computer virus and target NS2A for proteasome-mediated destruction (9). Several TRIM proteins have been found to inhibit IAV contamination. For example, TRIM32 ubiquitinates PB1 and subsequently degrades PB1, thereby limiting viral contamination (10). TRIM19 (also known as PML), TRIM22, and TRIM56 display broad intrinsic antiviral activity and inhibit multiple viruses, including IAV (11,C13). In contrast, IAV evolves to subvert host immunity by targeting TRIM proteins (14). TRIM25 ubiquitinates and activates RIG-I-mediated innate immunity (15). The NS1 of IAV impairs the interferon (IFN)-dependent innate immune response by impeding TRIM25 multimerization and activation of RIG-I (16, 17). Our recent study around the IAV-host protein interaction network found that TRIM41 interacted with the nucleoprotein (NP) (4). TRIM41, also known as the RING finger-interacting protein with C kinase (RINCK), regulates PKC kinase signaling (18). TRIM41 is also found to interact with the nucleotide binding oligomerization domain-containing 2 (NOD2) protein, but how TRIM41 regulates NOD2 signaling is not clear (19). Recently, a screening of TRIM proteins found that TRIM41 along with seven other TRIM proteins inhibited hepatitis B computer virus (HBV) transcription (20). However, the role of TRIM41 in IAV contamination is unknown. Here, we characterized the physical interaction between NP and TRIM41. Furthermore, overexpression of Cut41 inhibits IAV infections while depletion of Cut41 increases web host susceptibility to viral infections. Being a ubiquitin E3 ligase, CK-1827452 (Omecamtiv mecarbil) Cut41 ubiquitinates NP, as well as the ubiquitination results in NP proteins degradation. Hence, our research establishes the function of Cut41 as a fresh web host limitation element in IAV infections. RESULTS Cut41 interacts and colocalizes with NP. Our prior proteomic study demonstrated that Cut41 connected with NP (4), however the interaction isn’t well defined. Hence, we validated the proteins interaction between Cut41 and NP initial. FLAG-tagged NP from influenza A/Puerto Rico/8/1934 (PR8) or A/New York/1682/2009 (NY) was cotransfected with hemagglutinin (HA)-tagged Cut41 into HEK293 CK-1827452 (Omecamtiv mecarbil) cells. Coimmunoprecipitation verified the relationship between Cut41 and both NP proteins (Fig. 1A). Next, we analyzed the Cut41-NP proteins relationship during viral infections. A549.
