Purpose. To determine whether Ski-interacting protein (SKIP) regulates TGF-β1-stimulated expression of urokinase-type plasminogen activator (uPA), matrix metalloproteinase-9 (MMP-9), and uPA Inhibitor (PAI-1) in the androgen-independent human prostate cancer cell model. Materials and Methods. PC-3 prostate cancer cell line was used. The role of SKIP was evaluated using synthetic small interference RNA (siRNA) compounds. The expression of uPA, MMP-9, and PAI-1 was evaluated by zymography assays, RT-PCR, and promoter transactivation analysis. Results. In PC-3 cells TGF-β1 treatment stimulated uPA, PAI-1, and MMP-9 expressions. The knockdown of SKIP in PC-3 cells enhanced the basal level of uPA, and TGF-β1 treatment inhibited uPA production. Both PAI-1 and MMP-9 production levels were increased in response to TGF-β1. The ectopic expression of SKIP inhibited both TGF-β1-induced uPA and MMP-9 promoter transactivation, while PAI-1 promoter response to the factor was unaffected. Conclusions. SKIP regulates the expression of uPA, PAI-1, and MMP-9 stimulated by TGF-β1 in PC-3 cells. Thus, SKIP is implicated in the regulation of extracellular matrix degradation and can therefore be suggested as a novel therapeutic target in prostate cancer treatment. 1. Introduction Transforming growth factor β1 (TGF-β1) is implicated in the regulation of cell proliferation, differentiation, and migration, as well as extracellular matrix (ECM) production, apoptosis and tumorigenesis [1]. TGF-β1 is frequently overexpressed in carcinoma cells, including prostate cancer cells, and leads to paracrine stimulation and modification of cellular and extracellular matrix components of tumour microenvironment [2]. The urokinase-type plasminogen activator (uPA) system is thought to play a key role in cancer invasion and metastasis. uPA is a secreted serine proteinase that converts plasminogen to plasmin, a trypsin-like serine proteinase, which in turn can degrade a wide variety of ECM components and enable the tumour cells to penetrate the basement membrane, by facilitating cell migration and invasiveness [3]. uPA is tightly controlled by the specific serpin inhibitor PAI-1, which is also upregulated in cancer. PAI-1 can promote cell migration and angiogenesis independent of its effects on uPA-activated plasmin [4]. Matrix metalloproteinases (MMPs) have also been regarded as critical molecules in assisting tumour cells during metastasis. MMP-9, a member of the type IV collagenases, is known to influence cell proliferation, differentiation, angiogenesis, apoptosis and metastasis. After
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