The Membrane Protein of Severe Acute Respiratory Syndrome Coronavirus Functions as a Novel Cytosolic Pathogen-Associated Molecular Pattern To Promote Beta Interferon Induction via a Toll-Like-Receptor-Related TRAF3-Independent Mechanism

Wang, Yi; Liu, Li

The SARS-CoV M gene product activates the IFN-␤ signaling pathway at or upstream of TBK1. To further confirm the above results, increased doses of the pCMV-Myc-M gene were transiently transfected into HEK293ET cells. The cell lysates prepared from the transfection were examined for the activation of the downstream modulator and/or effector molecules, such as TBK1, IRF3, and NF-B. Figure 2A clearly demonstrates that SARS-CoV M gene products not only enhanced the phosphorylation level of TBK1 but also promoted the activation of both NF-B p65 and IRF3, indicating that M gene products may stimulate IFN-␤ activation by promoting its enhanceosome activity. To further define the activation level of M-mediated IFN-␤ induction, specific siR-NAs that selectively targeted either TBK1 ( Fig. 2B and C) or IRF3 ( Fig. 2E and F) mRNAs were generated. Individually diminishing either TBK1 or IRF3 mRNA expression by siTBK1 or siIRF3 sig-nificantly reversed M-mediated IFN-␤ induction ( Fig. 2D and G, respectively), indicating that M-mediated IFN-␤ induction functions at a level at or above the signaling molecule TBK1. The SARS-CoV M gene product preferentially activates IFN-␤ production through Toll-like-receptor-related signaling pathways in HEK293ET cells. RLR and TLR are two main PRRs