Protease-activated receptor (PAR)-1 and PAR-2 participate in the cell growth of alveolar capillary endothelium in primary lung adenocarcinomas

Abstract

Background: Cell growth can be induced via elicitation of protease-activated receptors (PAR) with serine proteases such as thrombin and trypsin.

Methods: To understand whether PAR are involved in tumor vessel formation in the neoplastic cell-bearing alveolar walls, immunohistochemical and reverse transcriptase-polymerase chain reaction analyses were performed using the lung tissues from 16 patients with primary lung adenocarcinomas.

Results: In microdissected tumor alveolar walls, the expressions of PAR-1 and PAR-2 mRNA were increased by 10-fold (P < 0.05) and 16-fold (P < 0.01), respectively, as compared with normal alveolar walls. Confocal microscopy revealed that tumor capillary endothelial cells in alveolar walls lost thrombomodulin expression. Instead, the expression of PAR-2 often became obvious at the normal border. Both PAR-1 and PAR-2 were expressed in the microvessel endothelial cells in tumors. Trypsin mRNA was expressed in 7 of the 16 cancer cell-bearing tissue specimens in contrast to 1 of the 14 normal alveolar walls. Immunohistochemically, trypsin was positive in the neoplastic cells from 10 patients and in lung adenocarcinoma cell lines (A549, HLC-1, LC-2, and PC-14). An in vitro assay showed a significant increase in idoxuridine (IdU) or bromodeoxyuridine uptake in human pulmonary artery endothelial cells and human umbilical cord vein endothelial cells after treatments with alpha-thrombin or activating peptides; SFLLRN for PAR-1 and SLIGKV for PAR-2, respectively.

Conclusions: Thus, proliferation of alveolar capillary endothelial cells is initialized in part by PAR activation with serum thrombin and neoplastic cell-released trypsin. These results suggest a synergistic effect of PAR with vascular endothelial growth factor in alveolar angiogenesis.