MCMV modulates <i>Xbp1</i> splicing.

<p>(A) NIH-3T3 cells were infected with MCMV at an MOI of 5 or treated with tunicamycin (Tun) for 4 h. <i>Xbp1</i> mRNA transcripts were amplified by RT-PCR, digested with PstI, and separated on an ethidium bromide-stained agarose gel. The spliced transcript, <i>Xbp1s</i>, lacks the PstI site and migrates slower than the digested unspliced transcript, <i>Xbp1u</i>. (B) NIH-3T3 cells were treated as described for panel A. <i>Xbp1s</i> and <i>Xbp1u</i> transcripts were quantified by real-time RT-PCR. Changes in the <i>Xbp1s</i>/<i>Xbp1u</i> ratio relative to untreated cells are plotted as bar diagram showing means ±SEM of four replicates. (C) NIH-3T3 cells were infected as above and treated in addition with Tun for the last 4 h before harvest. <i>Xbp1</i> transcripts were analyzed as in A. (D) NIH-3T3 cells were treated as in C, and <i>Xbp1</i> transcripts were quantified as in B. (E) NIH-3T3 cells were MCMV-infected and treated with thapsigargin (Tg) for the last 4 h before harvest. <i>Xbp1</i> transcripts were quantified as in B. (F) NIH-3T3 cells were MCMV-infected and treated with Tun for the last 4 h before harvest. Nuclear protein extracts were analyzed by immunoblot for the presence of XBP1s protein. Heterochromatin protein 1α (HP1α) was used as a loading control. (G) NIH-3T3 cells were infected with MCMV at an MOI of 5 and treated with Tun for 4 h. <i>ERdj4</i> transcripts were quantified by real-time RT-PCR. Results are shown as fold induction relative to untreated cells (means ±SEM of four replicates).