TYROSINE PHOSPHORYLATION MEDIATES CONA-INDUCED MEMBRANE TYPE 1-MATRIXMETALLOPROTEINASE EXPRESSION AND MATRIX METALLOPROTEINASE-2 ACTIVATION IN MDA-MB-231 HUMAN BREAST-CARCINOMA CELLS

ConA-induced cell surface activation of pro-matrix metalloproteinase-2 (pro-MMP-2) by MDA-MB-231 human breast cancer cells is apparently med iated by up-regulation of membrane type 1 MMP (MT1-MMP) through transc riptional and posttranscriptional mechanisms. Here, we have explored t he respective roles of cell surface clustering and protein tyrosine ph osphorylation in the ConA-induction effects. Treatment with succinyl-C onA, a variant lacking significant clusterability, partially stimulate d MT1-MMP mRNA and protein levels but did not induce MMP-2 activation, suggesting that clustering contributes to the transcriptional regulat ion by ConA but appears to be critical for the nontranscriptional comp onent. We further found that genistein, an inhibitor of tyrosine phosp horylation, blocked ConA-induced pro-MMP-2 activation and ConA-induced MT1-MMP mRNA level in a dose-dependent manner, implicating tyrosine p hosphorylation in the transcriptional aspect. This was confirmed by th e dose-dependent promotion of pro-MMP-2 activation by sodium orthovana date in the presence of suboptimal concentrations of ConA (7.5 mu g/ml ), with optimal effects seen at 25 mu g/ml orthovanadate. Genistein di d not inhibit the ConA potentiation of MMP-2 activation in MCF-7 cells , in which transfected MT1-MMP is driven by a heterologous promoter, s upporting the major implication of phosphotyrosine in the transcriptio nal component of ConA regulation. These data describe a major signalin g event upstream of MT1-MMP induction by ConA and set the stage for fu rther analysis of the nontranscriptional component.