Transforming growth factor-b1/activin receptor-like kinase 5-mediated cell migration is dependent on the protein proteinase-activated receptor 2 but not on proteinase-activated receptor 2-stimulated G_q-calcium signaling

Transforming growth factor-b (TGF-b), serine proteinases such as trypsin, and proteinase-activated receptor 2 (PAR2) promote tumor development by stimulating invasion and metastasis. Previously, we found that in cancer cells derived from pancreatic ductal adenocarcinoma (PDAC) PAR2 protein is necessary for TGF-b1-dependent cell motility. Here, we show in the same cells that, conversely, the type I TGF-b receptor activin receptor-like kinase 5 is dispensable for trypsin and PAR2 activating peptide (PAR2-AP)-induced migration. To reveal whether G_q-calcium signaling is a prerequisite for PAR2 to enhance TGF-b signaling, we investigated the effects of PAR2-APs, PAR2 mutation and PAR2 inhibitors on TGF-b1-induced migration, reporter gene activity, and Smad activation. Stimulation of cells with PAR2-AP alone failed to enhance basal or TGF-b1-induced C-terminal phosphorylation of Smad3, Smad-dependent activity of a luciferase reporter gene, and cell migration. Consistently, in complementary loss of function studies, abrogation of the PAR2-G_q-calcium signaling arm failed to suppress TGF-b1-induced cell migration, reporter gene activity, and Smad3 activation. Together, our findings suggest that the calcium-regulating motif is not required for PAR2 to synergize with TGF-b1 to promote cell motility. Additional experiments in PDAC cells revealed that PAR2 and TGF-b1 synergy may involve TGF-b1 induction of enzymes that cause autocrine cleavage/activation of PAR2, possibly through a biased signaling function. Our results suggest that although reducing PAR2 protein expression may potentially block TGF-b’s prooncogenic function, inhibiting PAR2-G_q-calcium signaling alone would not be sufficient to achieve this effect.