Angiopoietin-like protein 2 is an important facilitator of tumor proliferation, metastasis, angiogenesis and glycolysis in osteosarcoma

Background: Solid tumors are often exposed to hypoxia. Hypoxia inducible factor (HIF-1 alpha) upregulates numerous target genes associated with the malignant behavior of hypoxic cancer cells. Angiopoietin-like protein 2 (Angptl2), a member of the angiopoietin family, is a hypoxia-inducible gene. However, the role and potential mechanism of Angptl2, and the relationship between Angptl2 and hypoxia in osteosarcoma (OS) remain unclear. Methods: In this study, quantitative RT-PCR was performed to detect the levels of Angptl2 and HIF-1 alpha, and western blot assay was performed to measure the expression of Angptl2, HIF-1 alpha, CDK2, cyclin E1, P21, MMP2, MMP9, VEGFA, Ang II and HK2 in osteosarcoma cells and tissue. Subsequently, cell viability and cycle were analyzed using CCK-8 and flow cytometer assays. Cell migration, invasion and glycolysis were analyzed with Transwell, Scratch Test and glucose/ lactic acid detection kits, respectively. Experiments in vivo were performed to value the effects of Angptl2 on the growth of osteosarcoma xenografts in mice. Immunofluorescent and immunohistochemistry staining were conducted to detect the expression of Ki-67 and Angptl2, respectively. Results: The results demonstrated that Angptl2 was highly expressed in OS cells, which was induced by hypoxia (HIF-1 alpha). Additionally, Angptl2 overexpression regulated cell proliferation, invasion, migration and G1 phase arrest in OS cells. Moreover, Angptl2 promoted OS tumor growth in vivo tumor xenografts. Angptl2 might enhance angiogenesis and glycolysis by promoting VEGFA, Ang II and HK2 both in vitro and in vivo. Conclusion: In conclusion, the present findings indicated that hypoxia-induced Angptl2 expression was independent of HIF-1 alpha in hypoxic OS cells. Angptl2 might promote OS cell proliferation, metastasis, angiogenesis and glycolysis, which could be regarded as a favorable marker for predicting a long survival time in patients with OS.