ERN1 and infection: AdV-C5 infection for 24–48 h readily induced XBP1s in mouse embryonic fibroblasts (MEFs) expressing Flag-IRE1α, but not in cells lacking IRE1α (I-KO)43, akin to the short-term chemical stimulation of ER stress by thapsigargin (5 h), which inhibits the ER calcium pump and depletes calcium ions from ER stores44 (Fig. 2a).