FIG. 5.
SARS-CoV S protein does not stimulate UPRE or XBP1 splicing. (A) 293FT cells were cotransfected with pUPRE-Luc and escalating amounts of pLenti-S. In the control group, an expression plasmid for a constitutively active version of ATF6 containing 1 to 373 amino acids was cotransfected. Cells were harvested for dual luciferase assay as described for Fig. 2. ATF6 (1-373) is known to stimulate UPRE, as reported previously (8). (B) 293FT and FRhK4 cells were mock infected (lane 1), infected with SARS-CoV (lane 2), transfected with pLenti-Topo empty vector (vec; lanes 5 and 7), transfected with pLenti-S plasmid (lanes 6 and 8), or treated with MG132 (lane 3), Tg (lanes 4 and 10), or DMSO (lane 9) for 8 h. Unspliced (u) and spliced (s) forms of XBP1 transcript were examined by reverse transcription-PCR as described previously (26). GAPDH mRNA (G) was also detected as a positive control.