Hypoxic inactivation of glycogen synthase kinase-3β promotes gastric tumor growth and angiogenesis by facilitating hypoxia-inducible factor-1 signaling.

Since the molecular mechanism of hypoxic adaptation in cancer cells is cell-type specific, we investigated whether glycogen synthase kinase-3 (GSK-3) activation is involved in hypoxia-induced gastric tumor promotion. Stable gastric cancer cell lines (SNU-638, SNU-484, MKN1, and MKN45) were cultured under hypoxic conditions. Cells overexpressing wild-type GSK-3 (WT-GSK-3) or kinase-dead mutant of GSK-3 (KD-GSK-3) were generated and used for cell culture and animal studies. In cell culture experiments, hypoxia decreased GSK-3 activation in gastric cancer cells. Cell viability and the expressions of HIF-1 protein and VEGF mRNA in gastric cancer cells were higher in KD-GSK-3 transfectants than in WT-GSK-3 transfectants under hypoxic conditions, but not under normoxic conditions. Gastric cancer xenografts showed that tumor growth, microvessel area, HIF-1 activation, and VEGF expression were higher in KD-GSK-3 tumors than in WT-GSK-3 tumors in vivo. In addition, the expression of hypoxia-induced HIF-1 protein was regulated by GSK-3 at the translational level. Our data suggest that GSK-3 is involved in hypoxic adaptation of gastric cancer cells as an inhibitory upstream regulator of the HIF-1/VEGF signaling pathway.