Protease-activated receptor 2 suppresses lymphangiogenesis and subsequent lymph node metastasis in a murine pancreatic cancer model.

Protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor that functions as a cell-surface sensor for coagulation factors and other proteases associated with the tumour microenvironment. Pancreatic cancer cells express high levels of PAR-2 and activation of PAR-2 may induce their proliferation and migration. Interestingly, however, PAR-2 expression is increased in stroma-rich pancreatic cancer regions, suggesting a potential role of PAR-2 in the tumour microenvironment. Here, we assessed the importance of PAR-2 in the stromal compartment by utilizing an orthotopic pancreatic cancer model, in which tumour cells are PAR-2-positive, whereas stromal cells are PAR-2-negative. We assessed tumour weight and volume and analysed proliferation and (lymph)angiogenesis both in vivo and in vitro. We show that genetic ablation of PAR-2 from the stromal compartment inhibits primary tumour growth, which is accompanied by reduced vascularization in primary tumours and reduced in tube formation of vascular endothelial cells in vitro. In contrast to smaller primary tumours, the number of lymph node metastases was increased in PAR-2-deficient animals, which was accompanied by an increased number of lymphatic vessels. In vitro tube-formation assays show that PAR-2 does not inhibit the intrinsic tube-forming capacity of lymphatic endothelial cells, but that PAR-2 actually inhibits cancer cell-induced tube formation. Overall, stromal PAR-2 thus plays a dual role in pancreatic cancer development by potentiating primary tumour growth but limiting lymphangiogenesis and subsequent lymph node metastasis. Our data identify a novel role of PAR-2 in the tumour microenvironment and pinpoint PAR-2 as a negative regulator of lymphangiogenesis.