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

SARS-CoV M protein may function as a novel intracellular PAMP to induce IFN-␤ production. One critical question remaining to be answered is whether the driving force for M protein-mediated IFN-␤ induction is generated intracellularly or extracellularly. To answer this question directly, the TRAP␥ gene, an endoplasmic reticulum (ER)-associated gene, was cotransfected with M into HeLa cells. Brefeldin A (BFA) was employed in the assay system to block M protein transport from the rough endoplasmic reticulum to the cell surface. Indeed, the addition of BFA effectively increased the retention of M proteins in the ER compartment (Fig. 6A) . Figure 6B shows that addition of BFA also effectively inhibited the secretion of IFN-␤ into the cell culture medium (right panel) but did not inhibit M-mediated IFN-␤ induction at either the mRNA level or the protein level (left panel), indicating that the driving force for M-mediated IFN-␤ induction was indeed derived from intracellular stimulation by M proteins.