Abstract. ADAM17, also known as tumor necrosis factor-α converting enzyme (TACE), is involved in proteolytic ectodomain shedding of cell surface molecules and cytokines. Although aberrant expression of ADAM17 has been shown in various malignancies, the function of ADAM17 in prostate cancer has not been clarified. In the present study, we sought to elucidate whether ADAM17 contributes to prostate cancer cell invasion, as well as the mechanism involved in the process. The expression pattern of ADAM17 was investigated in human prostate cancer cells. The results showed that ADAM17 expression levels are correlated with the invasive ability of androgen-independent prostate cancer cell lines. Further, ADAM17 was overexpressed in cells showing high invasion characteristics, activation of the EGFR-MEK-ERK pathway, up-regulation of MMP-2, MMP-9, and an increased TGF-α release into the supernatant. However, AG1478, PD98059 and antibody against TGF-α deactivating the EGFR-MEK-ERK signaling pathway, abolished up-regulation of MMP-2, MMP-9 and prevented cell invasion. In addition, cells with knockdown of ADAM17 by siRNA exhibited low invasive ability, deactivated EGFR-MEK-ERK signaling pathway, reduced TGF-α released and down-regulation of MMP-2, MMP-9. However, these effects could be reversed by simultaneous addition of TGF-α. These data demonstrated that ADAM17 contributes to androgen-independent prostate cancer cell invasion by shedding of EGFR ligand TGF-α, which subsequently activates the EGFR-MEK-ERK signaling pathway, leading finally to overexpression of MMP-2 and MMP-9. This study suggests that the ADAM17 expression level may be a new predictive biomarker of invasion and metastasis of prostate cancer, and ADAM17 could provide a target for treating metastatic PCa.
IntroductionProstate cancer (PCa) is one of the most common malignancies among Western males with an occurrence of approximately 192,280 new cases and 27,360 deaths in the US, in 2009 (1). The growth and maintenance of cancerous cells in the early stages of prostate cancer is androgen-dependent and therapy often involves androgen deprivation (2). In the later stages therapeutic alternatives are not available, as the tumor progresses from androgen-dependence to -independence. The lack of effective therapies for advanced PCa is related to a large extent to poor understanding of the molecular mechanisms underlying the progression of disease toward invasion and metastasis (3). Therefore, the identification of new predictive biomarkers, especially those that are indicative of invasiveness of the disease, which could serve as targets for establishing effectiveness of therapeutic and chemopreventive interventions, will improve clinical management of PCa (4).The ADAMs (a disintegrin and metalloproteinase) are members of the metzincin superfamily of Zn-dependent matrix metalloproteinases. They are transmembrane and secreted proteins with important roles in diverse biological functions, such as fertilization, adhesion, migration, proteolysis and signaling (5,6). Recent...