Activation of cellular invasion by trefoil peptides and src is mediated bycyclooxygenase- and thromboxane A2 receptor-dependent signaling pathways

We have investigated the possible functional relationships between cellular invasion pathways induced by trefoil factors (TFFs), src, and the cyclooxy genases COX-1 and COX-2. Pharmacological inhibitors of the Rho small GTPase (C3 exoenzyme), phospholipase C (U-73122), cyclooxygenases (SC-560, NS-398 ), and the thromboxane A2 receptor (TXA2-R) antagonist SQ-295 completely ab olished invasion induced by intestinal trefoil factor, pS2, and src in kidn ey and colonic epithelial cells MDCKts.src and PCmsrc. In contrast, invasio n was induced by the TXA2-R mimetic U-46619, constitutively activated forms of the heterotrimeric G-proteins G alphaq (AG alphaq), G alpha 12, G alpha 13 (AG alpha 12/13), which are signaling elements downstream of TXA2-R. Ec topic overexpression of pS2 cDNA and protein in MDCKts.src-pS2 cells and hu man colorectal cancer cells HCT8/S11-pS2 initiate distinct invasion signals that are Rho independent and COX and TXA2-R dependent. We detected a marke d induction of COX-2 protein and accumulation of the stable PGH2/TXA2 metab olite TXB2 in the conditioned medium from cells transformed by src. This le d to activation of the TXA2R-dependent invasion pathway, which is monitored via a Rho- and G alpha 12/G alpha 13-independent mechanism using the G alp haq/PKC signaling cascade. These findings identify a new intracrine/paracri ne loop that can be monitored by TFFs and src in inflammatory diseases and progression of colorectal cancers.