Protease-activated receptor-2 accelerates intestinal tumor formation through activation of nuclear factor-κB signaling and tumor angiogenesis in Apc mice.

Hepatocyte growth factor activator inhibitor-1 (HAI-1), encoded by the SPINT1 gene, is a membrane-bound protease inhibitor expressed on the surface of epithelial cells. Hepatocyte growth factor activator inhibitor-1 regulates type II transmembrane serine proteases that activate protease-activated receptor-2 (PAR-2). We previously reported that deletion of Spint1 in Apc mice resulted in accelerated formation of intestinal tumors, possibly through enhanced nuclear factor-κB signaling. In this study, we examined the role of PAR-2 in accelerating tumor formation in the Apc model in the presence or absence of Spint1. We observed that knockout of the F2rl1 gene, encoding PAR-2, not only eliminated the enhanced formation of intestinal tumors caused by Spint1 deletion, but also reduced tumor formation in the presence of Spint1. Exacerbation of anemia and weight loss associated with HAI-1 deficiency was also normalized by compound deficiency of PAR-2. Mechanistically, signaling triggered by deregulated protease activities increased nuclear translocation of RelA/p65, vascular endothelial growth factor expression, and vascular density in Apc -induced intestinal tumors. These results suggest that serine proteases promote intestinal carcinogenesis through activation of PAR-2, and that HAI-1 plays a critical tumor suppressor role as an inhibitor of matriptase, kallikreins, and other PAR-2 activating proteases.