Activation of NF-κB signaling pathway during HCG-induced VEGF expression in luteal cells

Vascular endothelial growth factor (VEGF) plays an essential role in luteal angiogenesis, the present study therefore utilized luteal cells cultured in vitro to further investigate the activation and contribution of nuclear factor (NF)-kappa B to VEGF expression induced by human chorionic gonadotrophin (HCG). The present results showed HCG induced VEGF expression as well as hypoxia-inducible factor (HIF)-1 alpha mRNA and protein expressions, which was blocked by NF-kappa B inhibitor pyrrolidine dithiocarbamate (PDTC). Further analysis found that these increases of VEGF and HIF-1 alpha mRNA induced by HCG were also blocked by NF-kappa B siRNA transfection, which was consistent with PDTC treatment. However, HIF-1 alpha siRNA treatment significantly decreased HCG induced-VEGF expression with no effect on NF-kappa B mRNA expression. Furthermore, combination of HIF-1 alpha siRNA and PDTC treatment did not further decrease VEGF mRNA expression, and the result of chromatin immunoprecipitation indicated NF-kappa B may regulate HIF-1 alpha transcription through binding with its promoter. Taken together, the present results clearly demonstrated that NF-kappa B was activated to regulate VEGF expression by increasing HIF-1 alpha transcription in luteal cells treated with HCG. Therefore, the present study provided a new and important mechanism of luteal angiogenesis during the formation of corpus luteum in mammals.