Gastrin and EGF synergistically induce cyclooxygenase-2 expression in Swiss 3T3 fibroblasts that express the CCK2 receptor

Over‐expression of cyclooxygenase‐2 (COX‐2) has been demonstrated to be tumorigenic in transgenic mice. Chronic treatment with NSAIDs is chemoprotective for colorectal cancer. Gastrin is a growth factor for gastric mucosa and has been shown to promote proliferation of colorectal cells. Recent studies suggest that COX‐2 expression levels could mediate the growth effects of gastrin. Here, we report that gastrin increased PGE2 secretion in Swiss 3T3 cells expressing the CCK2 receptor. Gastrin dose dependently induced COX‐2 protein levels in a time dependent manner. COX‐2 mRNA levels were rapidly induced by a dose dependent increase in gastrin. Prior treatment of the cells with the CCK2 receptor specific antagonist, L365,260, inhibited gastrin‐induced COX‐2 protein and mRNA expression. Pretreatment with L364,714, the CCK1 receptor specific antagonist did not block COX‐2 induction by gastrin. Inhibition of de novo protein synthesis by cycloheximide did not block COX‐2 mRNA induction by gastrin. Also, gastrin‐dependent COX‐2 expression did not require PKC activity, activation of ERK, or transactivation of EGFR. However, co‐stimulation with EGF and gastrin synergistically induced COX‐2 protein and mRNA expression and PGE2 secretion. Measurements of COX‐2 mRNA stability and COX‐2 gene transcription reveal that EGF significantly increased the half‐life of COX‐2 mRNA with only a slight increase in the COX‐2 transcription rate. Conversely, gastrin significantly increased COX‐2 gene transcription rates but did not enhance COX‐2 mRNA stability. J. Cell. Physiol. 196: 454–463, 2003. © 2003 Wiley‐Liss, Inc.