Half of patients with muscle-invasive bladder cancer develop metastatic disease, and this is responsible for most of the deaths from this cancer. Low expression of RhoGTP dissociation inhibitor 2 (RhoGDI2; also known as ARHGDIB and Ly-GDI) is associated with metastatic disease in patients with muscle-invasive bladder cancer. Moreover, a reduction in metastasis is observed upon reexpression of RhoGDI2 in xenograft models of metastatic cancer. Here, we show that RhoGDI2 suppresses lung metastasis in mouse models by reducing the expression of isoforms V1 and V3 of the proteoglycan versican (VCAN; also known as chondroitin sulfate proteoglycan 2 [CSPG2]). In addition, we found that high versican levels portended poor prognosis in patients with bladder cancer. The functional importance of tumor expression of versican in promoting metastasis was established in in vitro and in vivo studies in mice that implicated a role for the chemokine CCL2 (also known as MCP1) and macrophages. Further analysis indicated that RhoGDI2 suppressed metastasis by altering inflammation in the tumor microenvironment. In summary, we demonstrate what we believe to be a new mechanism of metastasis suppression that works by reducing host responses that promote metastatic colonization of the lung. Therapeutic targeting of these interactions may provide a novel adjuvant strategy for delaying the appearance of clinical metastasis in patients.
IntroductionOne-half of patients with muscle-invasive (MI) urothelial cancer (UC) of the bladder develop distant metastases, even after radical surgery of the primary tumors. We identified RhoGTP dissociation inhibitor 2 (RhoGDI2; also known as ARHGDIB and Ly-GDI, and abbreviated herein as GDI2) as an invasion and metastasis suppressor in human bladder cancer cell lines (1) and have shown that its expression is inversely associated with clinical outcome after treatment of MI tumors (2). Independently, in comparative gene expression profiling of invasive bladder cancer cell lines and human MI UC samples, we identified versican (VCAN; also known as chondroitin sulfate proteoglycan 2, [CSPG2]) as highly expressed in invasive and metastatic cancers (3).Versican is a highly conserved structural component of the ECM that is involved in neuronal development (4-8), the inflammatory phase of pulmonary-vascular diseases, atherosclerosis (9-12), and the invasive and metastatic signatures of many cancers (13-25). Four isoforms or spliced variants have been reported for versican, and the roles of V0, V1, and V3 and to a lesser extent V2 isoforms are recognized in cancer, vascular disease, and neuronal development (detailed in refs. 8, 26, 27, and the references cited therein). These isoforms contribute to proliferative, adhesive, and migratory states of tumor cells and modulate their interactions with stroma in the tumor microenvironment (26,28,29).Versican expression is regulated by cytokines, chemokines, and hypoxia (6, 7, 9-12, 21, 26, 29-36) via transcription factors such as TCF-4, SP-1, AP-1, and p53, which have bin...