Host Deficiency in Caveolin-2 Inhibits Lung Carcinoma Tumor Growth by Impairing Tumor Angiogenesis

Abstract

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 immunohistochemistry with anti-CD31 antibodies, suggesting impaired pathological 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 to 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 anti-angiogenic 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.

Attenuated rapid onset vasodilation with greater force production in skeletal muscle of caveolin-2−/− mice

“…The absence of Cav2 protein following genetic deletion (29) provides a positive control, consistent with earlier studies of Cav2 Ϫ/Ϫ mice generated independently (37). The present data are also consistent with Cav2 Ϫ/Ϫ offspring being viable and exhibiting postnatal growth and body mass not different from WT mice (37,40).…”

“…Whereas integral roles have been identified for Cav1 in the vasculature and Cav3 in skeletal muscle, less is known about the physiological role of Cav2. Only 38% of the amino acid sequence between Cav1 and Cav2 is identical, suggesting different functional roles for respective protein isoforms (29,46). In mice, genetic deletion of Cav2 resulted in hypercellularity of the lung parenchyma, where thickened alveolar septa was associated with exercise intolerance attributed to impaired pulmonary gas exchange (37).…”

“…Cav2 Ϫ/Ϫ mice were generated using C57BL/6N background with the assistance of the University of California, Davis, Mouse Biology Program (Davis, CA). Thereby, the entire exon 2 and a 5=-portion of exon 3 of the Cav2 gene were deleted using sequence replacement strategy as described previously (29). Mice were bred and housed in the animal care facilities of the University of Missouri while maintained at ϳ24°C on a 12:12-h light-dark cycle with food and water provided ad libitum.…”

Stroma-derived but not tumor ADAMTS1 is a main driver of tumor growth and metastasis

“…Remarkably our results also support a pro-tumorigenic and pro-metastatic activity of ADAMTS1, and we provided for the first time the finding that ADAMTS1 originated in the stroma contributes more significantly than ADAMTS1 derived from tumor cells. The use of a syngeneic model with genetically-modified animals has been described for a variety of extracellular molecules [37–42]. In this study we added the manipulation of our gene of interest in the implanted tumor cells, revealing its minor contribution, at least in this tumor model.…”

Role of caveolin-2 in subcutaneous tumor growth and angiogenesis associated with syngeneic mouse Lewis lung carcinoma and B16 melanoma models

“…In our recent paper using newly developed Cav-2 KO mice we have examined the role of host-expressed Cav-2 in regulating tumor growth and tumor growth-induced angiogenesis using subcutaneously implanted Lewis lung carcinoma (LLC) and B16-F10 melanoma cells as the two independent syngeneic mouse models [16] . Our results showed that LLC tumors implanted into Cav-2 KO mice displayed a defective growth and ultimately regressed, which was in a striking contrast to wild type (WT) mice in which LLC tumors displayed a continuous growth.…”