REGULATION OF MEMBRANE-TYPE MATRIX METALLOPROTEINASE-1 EXPRESSION BY GROWTH-FACTORS AND PHORBOL 12-MYRISTATE 13-ACETATE

Overexpression of membrane-type matrix metalloproteinase (MT-MMP-1) re sults in the activation of both endogenous and exogenous 72-kDa gelati nase. To understand the effects of MT-MMP-1 on 72-kDa gelatinase activ ation, we analyzed its expression in human Fibroblasts and HT-1080 fib rosarcoma cells. Both cell types expressed the MT-MMP-1 mRNA constitut ively at a considerable level and treatment of cells with PMA enhanced the expression about 2-3-fold. Concanavalin A treatment increased MT- MMP-1 mRNA levels in fibroblasts about 4-fold. Induction of MT-MMP-1 b y phorbol 12-myristate 13-acetate (PMA) required protein synthesis as shown by cycloheximide inhibition, The induction was also inhibited by dexamethasone. Analysis of MT-MMP-1 mRNA stability using actinomycin D indicated that the half-life was rather long and not affected by PMA , suggesting transcriptional regulation. Only HT-1080 cells had signif icant 72-kDa gelatinase processing activity after treatment with PMA o r concanavalin A, while fibroblasts were virtually negative. Immunoblo tting analysis of fibroblast lysates indicated that MT-MMP-1 was prese nt mainly in a 60-kDa form. PMA and concanavalin A caused 2-4-fold inc reases in its protein levels, while in HT-1080 cells PMA, concanavalin A, or overexpression of MT-MMP-1 did not significantly enhance the le vel of the 60-kDa protein. Instead, an immunoreactive, proteolytically processed 43-kDa form was observed, and its appearance correlated to 72-kDa gelatinase processing activity. Thus 72-kDa gelatinase activati on, while enhanced by MT-MMP-1 expression, needs additional co-operati ng factors.