Role of hCG in Vasculogenic Mimicry in OVCAR-3 Ovarian Cancer Cell Line

Objectives: Vasculogenic mimicry (VM) is induced by hypoxia in 3-dimensional culture of ovarian cancer cells. By using this 3D model system, we explored the expression of human chorionic gonadotropin (hCG) and its effects on VM formation in ovarian cancer cell line OVCAR-3 both under normoxic and hypoxic conditions. Methods: Vasculogenic mimicry was identified by morphological observation and detection of vascular cell marker expressed by OVCAR-3. Potential formation of tumor channels was observed by light microscopy and scanning electron microscopy. Expression of vascular cell marker CD31, vascular endothelial growth factor, and Factor VIII were detected by flow cytometry, immunochemistry, and Western blot. Expression of hCG was investigated by enzymelinked immunosorbent assay, chemiluminescence immunoassay, real-time polymerase chain reaction (PCR), and Western blot. Expression of hypoxia-inducible factor-1 alpha (HIF-1 alpha) was detected by real-time PCR, Western blot, and blocked by small interference RNA. Incubation of OVCAR-3 with recombinant hCG was used to evaluate its effect on VM formation. The specificity of the effect of hCG was assessed by inhibition with the neutralizing anti-hCG antibody. Results: OVCAR-3 cells formed vessel-like network structures and expressed vascular marker significantly under hypoxia in 3D. The expression level of hCG under hypoxia was significantly higher than that under normoxia. Attenuating hypoxia-inducible factor (HIF)-1 alpha expression via small interference RNA resulted in a significantly decreased hCG expression in OVCAR-3, which indicated that the effect of hypoxia on hCG expression was mediated through HIF-1 alpha. Treatment of OVCAR-3 with 5000 mU/mL hCG resulted in the presence of tumor cell-lined vasculature and significant elevation in vascular marker expression, even under normoxia. Expression level of vascular marker and HIF-1 alpha in OVCAR-3 increased in response to hCG treatment in a dose-dependent manner. The effect of hCG was inhibited by the neutralizing anti-hCG antibody. Conclusions: Human chorionic gonadotropin has the potential to induce VM in OVCAR-3. Human chorionic gonadotropin might have synergistic hypoxia-induced effect on vascular marker and HIF-1 alpha expression.