POSSIBLE INVOLVEMENT OF M-CALPAIN IN VASCULAR SMOOTH-MUSCLE CELL-PROLIFERATION

Vascular smooth muscle cell (VSMC) proliferation still remains a poorl y understood process, although it is believed to play a critical role in pathological states, including atherosclerosis and hypertension, Se veral reports have suggested that proteases may be directly involved i n this process; however, it was still unclear which protease is respon sible for VSMC proliferation. In this study, by use oi a cell-permeabl e calpain inhibitor (calpeptin; benzyloxycarbonyl-Leu-nLeu-H), its ana logue (benzyloxycal-bonyl-Leu-Met-H), the cell-impermeable serine prot ease inhibitor leupeptin, and antisense oligonucleotide against nl-cal pain to inhibit proliferation of primarily cultured human VSMCs, we in vestigated whether calcium-activated neutral protease (calpain) is inv olved in VSMC proliferation, Calpeptin and its analogue, more specific for m-calpain, equally inhibited the proliferation of VSMCs in a-dose -related manner, whereas a more limited antiproliferative effect was o bserved in leupeptin-treated VSMCs. Antisense oligonucleotide against m-calpain, but not scrambled antisense, dose-dependently inhibited In- calpain expression and proliferation of VSMCs, Maximal inhibition was an approximate to 50% reduction of cell number and In-calpain antigen observed at 50 mu mol/L of antisense oligonucleotide. Calpeptin or ant isense oligonucleotide against m-calpain increased the expression of t he endogenous calpain substrate pp125FAK (focal adhesion kinase), wher eas the expression of the endogenous calpain inhibitor calpastatin was not affected. These results suggest that the proliferation of VSMCs r equires protease activity, some of which is due to m-calpain.