Long noncoding RNAs (lncRNAs) are involved in many aspects of cellular processes, including the antiviral immune response. To identify influenza A virus (IAV)-related lncRNAs, we performed RNA deep sequencing to compare the profiles of lncRNAs in A549 and HEK293T cells with or without IAV infection. We identified an IAV-upregulated lncRNA named lnc-ISG20 because it shares most of its sequence with ISG20. We found that lnc-ISG20 is an interferon-stimulated gene similar to ISG20. Overexpression of lnc-ISG20 inhibited IAV replication, while lnc-ISG20 knockdown favored viral replication, suggesting that lnc-ISG20 is inhibitory to IAV replication. Further study indicated that overexpression of lnc-ISG20 enhances ISG20 protein levels, while knockdown of lnc-ISG20 reduces ISG20 protein levels in A549 cells induced with poly(I·C) and Sendai virus. We demonstrated that lnc-ISG20 inhibits IAV replication in an ISG20-dependent manner. As lnc-ISG20 did not affect the mRNA level of ISG20, we postulated that lnc-ISG20 may function as endogenous RNA competing with ISG20 to enhance its translation. Indeed, we identified that microRNA 326 (miR-326) is a mutual microRNA for both ISG20 and lnc-ISG20 that targets the 3' untranslated region of ISG20 mRNA to inhibit its translation. We confirmed that lnc-ISG20 can bind miR-326, which in turn decreased the amount of miR-326 bound to ISG20 mRNA. In conclusion, we identified that the IAV-upregulated lnc-ISG20 is a novel interferon-stimulated gene that elicits its inhibitory effect on IAV replication by enhancing ISG20 expression. We demonstrated that lnc-ISG20 functions as a competitive endogenous RNA to bind miR-326 to reduce its inhibition of ISG20 translation. Our results revealed the mechanism by which lnc-ISG20 inhibits IAV replication. The replication of influenza A virus is regulated by host factors. However, the mechanisms by which lncRNAs regulate IAV infection are not well understood. We identified that lnc-ISG20 is upregulated during IAV infection and is also an interferon-stimulated gene. We demonstrated that lnc-ISG20 can enhance ISG20 expression, which in turn inhibits IAV replication. Our studies indicate that lnc-ISG20 functions as a competing endogenous RNA that binds miR-326 and reduces its inhibitory effect on ISG20. Taken together, our findings reveal the mechanistic details of lnc-ISG20 negatively regulating IAV replication. These findings indicate that lnc-ISG20 plays an important role during the host antiviral immune response.
Chronic hepatitis B virus infection is a major risk factor for hepatocellular carcinoma. HBV infection affects lncRNA expression in infected cells, but the detailed mechanism and biological significance are not yet clear. In this study, we focused on exploring the function of the HBV-upregulated lncRNA SAMD12-AS1 in cell proliferation. We found that there is a higher level of SAMD12-AS1 expression in tumors than in adjacent nontumorous liver tissues. We showed that ectopic expression of SAMD12-AS1 promotes cell growth and blocks apoptosis, while knockdown of SAMD12-AS1 inhibits cell proliferation and enhances etoposide-induced apoptosis. Using RNA immunoprecipitation and mass spectrometry, we determined that SAMD12-AS1 interacts with NPM1 and confirmed that SAMD12-AS1(1-350) is required for the interaction with NPM1. As it is known that NPM1 interacts with the E3 ligase HDM2 and reduces HDM2-mediated p53 degradation, we examined whether SAMD12-AS1 can affect p53 stability. Overexpression of SAMD12-AS1 caused a reduction in p53 protein levels by shortening its half-life. Conversely, knockdown of SAMD12-AS1 prolonged the half-life of p53. We further demonstrated that SAMD12-AS1 increased the interaction of HDM2 and p53 and enhanced p53 ubiquitination. Our findings reveal that HBV-upregulated SAMD12-AS1 regulates cell proliferation and apoptosis via the NPM1-HDM2-p53 axis.
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