CREB1 and squamous cell carcinoma: Given our previous findings that IMQ phosphorylates cAMP-response element binding protein (CREB), a direct substrate of PKA, in human epidermoid carcinoma cell line (HEp-2) and A549 cells [22], we initially measured the impact of IMQ on CREB phosphorylation in Calu-3 and CRFK cells.