Host deficiency in caveolin-2 inhibits lung carcinoma tumor growth by impairing tumor angiogenesis.

Caveolin-2 (Cav-2), a member of caveolin protein family, is largely different from better known caveolin-1 (Cav-1) and thus might play distinct functions. Here, we provide the first genetic evidence suggesting that host-expressed Cav-2 promotes subcutaneous tumor growth and tumor-induced neovascularization using two independent syngeneic mouse models. Host deficiency in Cav-2 resulted in defective and reduced growth of subcutaneously implanted Lewis lung carcinoma (LLC) and B16-F10 melanoma tumors, respectively. Consistent with the defective growth, LLC and B16-F10 melanoma tumors implanted into Cav-2 KO mice displayed reduced microvascular density (MVD) determined by IHC with anti-CD31 antibodies, suggesting impaired pathologic angiogenesis. Additional studies involving LLC tumors extracted from Cav-2 KO mice just 10 days after implantation determined reduced cell proliferation, massive necrotic cell death, and fibrosis. In contrast with day 10, only MVD but not cell proliferation and survival was reduced in the earliest palpable LLC tumors extracted 6 days after implantation into Cav-2 KO mice, suggesting that impaired angiogenesis is the causative factor. Mechanistically, impaired LLC tumor growth and angiogenesis in Cav-2 KO mice was associated with increased expression levels of antiangiogenic thrombospondin-1 and inhibited S1177 phosphorylation of endothelial nitric oxide synthase. Taken together, our data suggest that host deficiency in Cav-2 impairs tumor-induced angiogenesis, leading to compromised tumor cell survival/proliferation manifested by the defective tumor growth. In conclusion, host-expressed Cav-2 may promote tumor growth via supporting tumor-induced angiogenesis. Thus, Cav-2 expressed in tumor microenvironment may potentially become a novel target for cancer therapy.