Specific MT1-MMP silencing reduces prostate cancer cell proliferation and bone matrix degradation

2926 Membrane type 1- matrix metalloproteinase (MT1-MMP, also known as MMP-14) was originally identified as an activator of pro-MMP-2, but recent studies demonstrated its type I collagenolytic activity. We reported that MT1-MMP expression is associated with the transition from benign prostate epithelium to prostatic intraepithelial neoplasia in radical prostatectomy specimens ( Clin Cancer Res 5: 4105, 1999). MT1-MMP has also been shown to be highly expressed in various human prostate cancer (PC) cell lines. Type I collagen is the major component of the bone extracellular matrix (ECM), and remodeling of the bone ECM is a hallmark of PC metastasis. We hypothesized that metastatic PC cells use proteases such as MT1-MMP to degrade bone ECM thereby promoting secondary tumor growth. In the current study, an expression vector with a DNA insert encoding human MT1-MMP siRNA was designed based on preliminary transfection experiments with MT1-MMP siRNA oligonucleotides. DU145 PC cells, which express relatively high levels of MT1-MMP, were stably transfected with either the MT1-MMP siRNA vector or a control vector containing a scrambled DNA insert. RT-PCR and immunoblot showed a substantial downregulation of MT1-MMP expression at both the gene and protein levels in cloned populations of MT1-MMP siRNA expressing cells. A specific MT1-MMP activity assay revealed a 78% reduction of MT1-MMP enzymatic activity (P