Tumor cell invasion is promoted by activation of protease activated receptor-1 in cooperation with the alpha(v)beta(5) integrin

The first prototype of the protease activated receptor (PAR) family, the th rombin receptor PAR1, plays a central role both in the malignant invasion p rocess of breast carcinoma metastasis and in the physiological process of p lacental implantation. The molecular mechanism underlying PAR1 involvement in tumor invasion and metastasis, however, is poorly defined. Here we show that PAR1 increases the invasive properties of tumor cells primarily by inc reased adhesion to extracellular matrix components. This preferential adhes ion is accompanied by the cytoskeletal reorganization of F-actin toward mig ration-favoring morphology as detected by phalloidin staining. Activation o f PAR1 increased the phosphorylation of focal adhesion kinase and paxillin, and the induced formation of focal contact complexes. PAR1 activation affe cted integrin cell-surface distribution without altering their level of exp ression. The specific recruitment of alpha (v)beta (5) to focal contact sit es, but not of alpha (v)beta (3) or alpha (5)beta (1), was observed by immu nofluorescent microscopy. PAR1 overexpressing cells showed selective recipr ocal co-precipitation with alpha (v)beta (5) and paxillin but not with alph a (v)beta (3), that remained evenly distributed under these conditions. Thi s co-immunoprecipitation failed to occur in cells containing the truncated form of PAR1 that lacked the entire cytoplasmic portion of the receptor. Th us, the PAR1 cytoplasmic tail is essential for conveying the cross-talk and recruiting the alpha (v)beta (5) integrin. While PAR1 overexpressing cells were invasive in vitro, as reflected by their migration through a Matrigel barrier, invasion was further enhanced by ligand activation of PAR1. Moreo ver, the application of anti-alpha (v)beta (5) antibodies specifically atte nuated this PAR1 induced invasion. We propose that the activation of PAR1 m ay-lead to a novel cooperation with the alpha (v)beta (5) integrin that sup ports tumor cell invasion.