Expression and tissue localization of membrane-type 1, 2, and 3 matrix metallotoproteinases in human astrocytic tumors

Three different membrane-type matrix metalloproteinases (MT1-, MT2-, and MT 3-MMPs) are known to activate in vitro the zymogen of MMP-2 (pro-MMP-2, pro gelatinase A), which is one of the key MMPs in invasion and metastasis of v arious cancers. In the present study, we have examined production and activ ation of pro-MMP-2, expression of MT1-, MT2-, and MT3-MMPs and their correl ation with pro-MMP-2 activation, and localization of MMP-2, MT1-MMP, and MT 2-MMP in human astrocytic tumors. The sandwich enzyme immunoassay demonstra tes that the production levels of pro-MMP-2 in the anaplastic astrocytomas and glioblastomas are significantly higher than that in the low-grade astro cytomas (P < 0.05 and P < 0.01, respectively), metastatic brain tumors (P < 0.05), or normal brains (P < 0.01). Gelatin zymography indicates that the pro-MMP-2 activation ratio is significantly higher in the glioblastomas tha n in other astrocytic tumors (P < 0.01), metastatic brain tumors (P < 0.01) , and normal brains (P < 0.01). The quantitative reverse transcription poly merase chain reaction analyses demonstrate that MT1-MMP and MT2-MMP are exp ressed predominantly in glioblastoma tissues (17/17 and 12/17 cases, respec tively), and their expression levels increase significantly as tumor grade increases. MT3-MMP is detectable in both astrocytic tumor and normal brain tissues, but the mean expression level is approximately 50-fold lower compa red with that of MT1-MMP and MT2-MMP in the glioblastomas, The activation r atio of pro-MMP-2 correlates directly with the expression levels of MT1-MMP and MT2-MMP but not MT3-MMP. In situ hybridization indicates that neoplast ic astrocytes express MT1-MMP and MT2-MMP in the glioblastoma tissues (5/5 cases and 5/5 cases, respectively). Immunohistochemically, MT1-MMP and MT2- MMP are localized to the neoplastic astrocytes in glioblastoma samples (17/ 17 cases and 12/17 cases, respectively),which are also positive for MMP-2. In situ zymography shows gelatinolytic activity in the glioblastoma tissues but not in the normal brain tissues. These results suggest that both MT1-M MP and MT2-MMP play a key role in the activation of pro-MMP-2 in the human malignant astrocytic tumors and that the gelatinolytic activity is involved in the astrocytic tumor invasion.