Membrane activator of the 72 kDa type IV collagenase in malignant breast carcinoma patients: Expression of membrane-type 1-matrix metalloproteinase (MT1-MMP)

In this study, we determined proMMP-2 activating capacity of membrane extract prepared from the tissue of invasive ductal carcinoma of breast by zymogram gel analysis. We compared the effect of membrane extract on the activation of the latent type IV collagenases with that of the organic mercurial compound leg, APMA)-induced self cleavage of the latent type IV collagenases. We also compared the expression levels of MT1-MMP between invasive carcinoma and normal tissue by Western blot, Northern blot and semi-quantitative RT-PCR analysis. Our result demonstrated that the specificity of processing by breast carcinoma membrane activator corresponds to the specificity of MT1-MMP, which clearly showed the conversion of 72-kDa proMMP-2 to the activated form while APMA processed both 72- and 92-kDa proMMPs to their activated forms. MT1-MMP protein and mRNA were expressed both in invasive carcinoma and normal tissues, and the expression levels in both tissues were comparable. Quantitative analysis of the mRNA level by RT-PCR revealed that the difference of MT1-MMP mRNA between carcinomas and normal tissues was not statistically significant on Wilcoxon signed-ranks test (P>0.05). The results from the study on the expression of MT1-MMP gene suggest that the cellular activation of MMP-2 in breast tissue, requires additional effects in addition to up-regulation of MT1-MMP.