FIGURE 1.
SARS coronavirus M protein inhibits dsRNA-induced production of type I interferons. A, Golgi localization of M protein. HeLa cells were transfected with an expression vector for Myc-tagged M protein and then stained for GM130 and Myc-tagged M. The GM130- (green) and M-specific (red) fluorescent signals were then merged. Nuclear morphology (blue) was visualized with 4′,6-diamidino-2-phenylindole. Colocalization appeared yellow. Bar, 20 μm. B, expression of M protein in cultured cells. HEK293 cells were transfected with increasing amounts of an expression vector for Myc-tagged M protein, and cell lysates were analyzed by Western blotting with anti-Myc and anti-α-tubulin (tub). C, M protein does not inhibit the activity of human T-cell leukemia virus type 1 long terminal repeats. HEK293/TLR3 cells were transfected with pLTR-Luc, pIEX, and increasing amounts of an expression plasmid for M protein. Cells in one control group (mock) did not receive the expression plasmid for M protein, whereas cells in another control group (no Tax) received neither pIEX nor the expression plasmid for M protein. Relative luciferase activity was expressed in arbitrary units (au), and the results represent the mean ± S.D. from three independent experiments. D and E, suppression of type I interferon production by M protein. HEK293/TLR3 cells were transfected with pIFNβ-Luc or pISRE-Luc and increasing amounts of plasmids expressing the indicated viral proteins (influenza A virus NS1, SARS coronavirus M, E, ORF7a, and N). At 24 h after transfection, cells were stimulated with 1 μg/ml poly(I:C) (pIC) for 12 h. Cells in one control group (no pIC) were not treated with poly(I:C).