Cigarette smoke inhibits XBP1 splicing. A549 cells were exposed to air (Panel A, mock treatment) or 2R4F cigarette smoke (Panel B) for 20 minutes with 35 cc puffs diluted in 250 cc air. Cells were then placed in fresh media with or without 1 uM thapsigargin or 10 μg/ml tunicamycin for the time periods specified, followed by cell lysis and RNA purification. Spliced and unspliced XBP1 mRNA was detected using PCR methodology. Spliced XBP1 is 398 base pairs and the unspliced variant is 434 base pairs. For each lane the extent of splicing was quantified as described in the Methods section and is presented in additional file 3 – Supplemental Table S3: Suppression of XBP1 splicing by cigarette smoke.