MUC5B and lung carcinoma: In our study, CRISPR/Cas9‐mediated deletions (535 or 746 bp) of −7 kb or −3.5 kb upstream regions of MUC5AC or MUC5B, which was bound by the transcription factor SPDEF, reduced the expression of MUC5AC or MUC5B by ~90% in human A549 lung carcinoma cells (Figs 7 and 8), which indicates that the upstream enhancer regions are indispensable for the expression of MUC5AC or MUC5B in human IMA.