DDIT3 and cystic fibrosis: We found that CF HBECs harboring class II (ΔF508/ΔF508) and class III (G551D/ΔF508) mutations showed an increase in ER stress, mainly by upregulation of BiP, XBP1s, CHOP and IL-6 transcripts, as described before (Figure 1A) (15).