Membrane-type-1 matrix metalloproteinase and gelatinase A activation

Gelatinase A has been postulated to play an important role in invasion and metastasis of cancer cells. This enzyme is secreted as a latent proenzyme and its activation at the cell surface by a new member of MMP family, MT1-MMP, appears to be a critical step in determining the overall gelatinase A activity. Our studies with two fibroblastic cell models having different phenotypes in gelatinase A activation indicate that there is no direct correlation between MT1-MMP mRNA expression and gelatinase A activation. We have found that the lysates of these human fibroblastic cells contain membrane-type-1 metalloproteinase (MT1-MMP) in three separate forms of about 63-kDa and 60-kDa and 43-kDa. The appearance of 43-kDa form correlates to the release of activated gelatinase A to the culture medium. In discrepancy with some recent reports which have suggested a Golgi associated furin dependent pathway for MT1-MMP activation, we have found that in our cell models MT1-MMP is activated at the cell surface to the 60-kDa form and under conditions where activated gelatinase A is released to the culture medium it is very rapidly processed further to the 43-kDa form. In addition, we have detected the 60-kDa activated form of MT-MMP-1 also from furin-deficient LoVo cell lysates, but not from the lysates of transfected COS-7 cells expressing endogenous furin. Furthermore, our results suggest that the changes at the intracellular calcium levels by calcium ionophores and thapsigargin repress the gelatinase A activation by inhibiting the MT1-MMP processing.