Respiratory Syncytial Virus NS1 Protein Degrades STAT2 by Inducing SOCS1 Expression

<b><i>Objectives:</i></b> Respiratory syncytial virus (RSV) nonstructural protein NS1 (NS1) has been shown to block interferon (IFN)-inducible antiviral signaling. The suppressor of cytokine signaling (SOCS) gene family could utilize a feedback loop to block the activation of the JAK/STAT signaling pathway, further inhibiting the activation of host type I IFN. We evaluated the role of the SOCS1 and SOCS3 genes in this antiviral mechanism. <b><i>Material and Methods:</i></b> A humanized stable NS1 (rich in GC)-expressing plasmid was constructed, and A549 cells were transfected with it. Expression of the SOCS1, SOCS3, RIG-I, and TLR3 mRNAs was measured with real-time PCR. STAT2 and pSTAT2 expression was determined with Western blotting. <b><i>Results:</i></b> RSV NS1 upregulated SOCS1 mRNA expression 30-fold increase compared with the baseline level in very early phase (p < 0.01), and silence of RIG-I or TLR3 mRNA did not affect NS1-induced SOCS1 expression. NS1 inhibited IFN-α-induced STAT2 phosphorylation and degraded STAT2 in a time-dependent manner compared with the empty-vector control (p < 0.05). <b><i>Conclusion:</i></b> RSV NS1 upregulates SOCS1 expression in a RIG-I- and TLR3-independent pathway, to inhibit STAT2 phosphorylation.