The mechanisms responsible for prostate cancer metastasis are incompletely understood at both the cellular and molecular levels. In this regard, chemokines are a family of small, cytokine-like proteins that induce motility of neoplastic cells, leukocytes and cancer cells. The current study evaluates the molecular mechanisms of CXCL12 and CXCR4 in prostate cancer cell migration and invasion. We report that functional CXCR4 is significantly expressed by prostate cancer cell lines, LNCaP and PC3, when compared with normal prostatic epithelial cells (PrEC). As measured using motility and invasion chamber assays, prostate cancer cells migrated and invaded through extracellular matrix components in response to CXCL12, at rates that corresponded to CXCR4 expression. Anti-CXCR4 antibodies (Abs) significantly impaired the migration and invasive potential of PC3 and LNCaP cells. CXCL12 induction also enhanced collagenase-1 (metalloproteinase-1 (MMP-1)) expression by LNCaP and PC3 cells. Collagenase-3 (MMP-13) was expressed by prostate cancer cells, but it was not expressed by PrEC cells or modulated by CXCL12. CXCL12 increased MMP-2 expression by LNCaP and PC3; however, MMP-9 expression was elevated only in PC3 cells after CXCL12-CXCR4 ligation. PC3 cells also expressed high levels of stromelysin-1 (MMP-3) after CXCL12 stimulation. CXCL12 also significantly Keywords: chemokine; metastasis; metalloproteinase; stromal cell-derived factor-1; SDF-1 Despite the obvious importance of metastasis, this process remains incompletely understood at both the cellular and molecular levels. 1 Many factors have been implicated in the process of metastasis, but the precise mechanisms for the directional migration of malignant cells into different organs is unknown. [2][3][4] In this regard, chemokines are a super family of small, cytokine-like proteins that inducethrough G-protein-coupled receptor and cytoskeletal rearrangement-the adhesion of neoplastic cells or leukocytes to endothelial cells as well as the directional migration of cancer cells. 5,6 The ability of neoplastic cells to penetrate the basement membrane and then invade the interstitial stroma to initiate the metastatic process is largely mediated by proteolysis. Many proteinases are capable of degrading extracellular matrix (ECM) components, but matrix metalloproteinases (MMPs) appear to be particularly important for matrix degradation. 6 These proteolytic enzymes are involved in connective tissue remodeling as well as in embryonic growth, ovulation, wound healing and menstruation. 7,8 Moreover, abnormal production of these proteinases is implicated in a number of pathological conditions. 9 It has been shown that CXCL12-CXCR4 interactions may play a role in the metastasis of prostate cancer to bone. 10 However, these interactions alone do not explain the metastasis pattern of prostate cancer or the potential for neoplastic prostate cells to migrate and invade other tissues. We have tested the hypothesis that prostate carcinomas use CXCR4-