Regulation of membrane type-matrix metalloproteinases (MT-MMPs) in non-malignant and malignant cells

MT3-MMP and MT1-MMP are two closely related membrane-anchored matrix metalloproteinases that promote pericellular proteolysis and tumor cell invasion. Unique MMP regulation upon phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene loss was characterized in prostate epithelial PTEN knockout mouse model. Semi-quantitative RT-PCR shows MT1-MMP mRNA level is similar in both PTEN wild-type and knockout cells. However, MT2-MMP mRNA is significantly decreased and MT3-MMP mRNA is extensively increased in PTEN KO cells compared with PTEN wild type. Moreover, level of MMP-2 and MMP-9 are increased in PTEN KO cells in semi-quantitative RT-PCR and gelatin zymography assay. Despite no change of MT1-MMP mRNA, MT1-MMP protein is elevated on the cell surface of PTEN KO cells and activated pro-MMP-2 on the cell surface. Pharmacological inhibitor of PI3K, LY294002 decreased MT1-MMP protein level in PTEN KO cells showing that MT1-MMP protein is up-regulated under the control of PI3K/Akt pathway as a consequence of PTEN loss. Functional studies show that loss of PTEN gene mediated increased cell motility, accelerated invasion into type I collagen, and tumorigenicity of prostate epithelial cells. Together, these results suggest that elevated level of MT1-MMP on the cell surface play unique roles in cell growth, motility, and invasiveness of prostate tumor cells upon loss of PTEN function. We found that MT3-MMP and MT1-MMP mRNAs are readily detected in several human cell lines and primary cells by semi-quantitative RT-PCR or real time PCR. However, MT3-MMP protein, in contrast to MT1-MMP, was consistently undetectable, as determined by immunoblotting, immunoprecipitation, plasma membrane fractions, surface biotinylation, metabolic labeling, and pulse-chase analysis implying that lack of MT3-MMP protein detection is not due to protein instability. By analyzing untranslated regions of MT3-MMP and MT1-MMP mRNA we identified a GC-rich region in the 5'UTR of MT3-MMP, which possibly affects repression of MT3-MMP translation. These studies suggest that MT3-MMP exhibits a unique mode of regulation at the translational level, which may play a key role in tightly controlling protein expression of MT3-MMP with the involvement of untranslated regions (UTRs) of its mRNA. Our study showed that MT1- and MT3-MMP expression is controlled by unique regulatory modalities.