Green tea polyphenol EGCG suppresses lung cancer cell growth through upregulating miR-210 expression caused by stabilizing HIF-1α

(-)-Epigallocatechin-3-gallate (EGCG) has been reported to affect many cellular regulatory pathways. This study aims to determine whether EGCG could target microRNA (miRNA), one of the mechanisms for cells to achieve subtle change in multiple targets. We found that, in both human and mouse lung cancer cells in culture, EGCG specifically upregulated the expression of miR-210, a major miRNA regulated by HIF-1 alpha. Furthermore, we found that overexpression of miR-210 led to reduced cell proliferation rate and anchorage-independent growth as well as reduced sensitivity to EGCG. On the mechanisms of miR-210 regulation by EGCG, we demonstrated that the regulation was mediated through the hypoxia-response element in miR-210 promoter. Consistently, the upregulation of miR-210 was found to be correlated with the stabilized HIF-1 alpha in lung cancer cell lines after EGCG treatment. This EGCG-induced stabilization of HIF-1 alpha was further shown by the stabilization of HA-tagged HIF-1 alpha but not the P402A/P564A-mutated HIF-1 alpha by EGCG, suggesting that EGCG targets the oxygen-dependent degradation (ODD) domain. Direct evidence was obtained by affinity binding assay showing that EGCG specifically binds HIF-1 alpha with a K-d = 3.47 mu M. This result suggests that EGCG binding interferes with the hydroxylation of key Pro residues in the ODD domain, preventing HIF-1 alpha from the Pro hydroxylation-dependent ubiquitination and subsequent proteosome-mediated degradation. In summary, our results demonstrated, for the first time, the elevation of miR-210 by EGCG in lung cancer cell lines and this is mediated by the stabilization of HIF-1 alpha. This event contributes to the anticancer activity of EGCG.