Initiation of human colon cancer cell proliferation by trypsin acting at protease-activated receptor-2

The protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor t hat is cleaved and activated by trypsin. We investigated the expression of PAR-2 and the role of trypsin in cell proliferation in human colon cancer c ell lines. A total of 10 cell lines were tested for expression of PAR-2 mRN A by Northern blot and RT-PCR. PAR-2 protein was detected by immunofluoresc ence. Trypsin and the peptide agonist SLIGKV (AP2) were tested for their ab ility to induce calcium mobilization and to promote cell proliferation on s erum-deprived cells. PAR-2 mRNA was detected by Northern blot analysis in 6 out of 10 cell lines [HT-29, CI.19A, Caco-2, SW480, HCT-8 and T84]. Other cell lines expressed low levels of transcripts, which were detected only by RT-PCR. Further results were obtained with HT-29 cells: (1) PAR-2 protein is expressed at the cell surface; (2) an increase in intracellular calcium concentration was observed upon trypsin (1-100 nM) or AP2 (10-100 muM) chal lenges; (3) cells grown in serum-deprived media supplemented with trypsin ( 0.1-1 nM) or AP2 (1-300 muM) exhibited important mitogenic responses (3-fol d increase of cell number). Proliferative effects of trypsin or AP2 were al so observed in other cell lines expressing PAR-2. These data show that subn anomolar concentrations of trypsin, acting at PAR-2. promoted the prolifera tion of human colon cancer cells. The results of this study indicate that t rypsin could be considered as a growth factor and unravel a new mechanism w hereby serine proteases control colon tumours. (C) 2001 Cancer Research Cam paign.