Regulation of hypoxia-inducible factor-1α, regulated in development and DNA damage response-1 and mammalian target of rapamycin in human placental BeWo cells under hypoxia.

INTRODUCTION: Hypoxia-inducible factor-1 (HIF-1), regulated in development and DNA damage response-1 (REDD1) and mammalian target of rapamycin (mTOR) are crucial mediators of many metabolic processes in various cell types under hypoxia. The involvement and regulation of these three factors underlying trophoblasts' response to hypoxia remains to be determined.

METHODS: Specific siRNAs were applied to inhibit the expression of the corresponding genes and to investigate the roles of HIF-1α in modulating REDD1/mTOR and REDD1 in regulating mTOR/HIF-1α in the human choriocarcinoma cell line BeWo under normoxia and hypoxia.

RESULTS: Exposure of BeWo cells to 1% oxygen (compared with 21% oxygen) led to a remarkable increase of both HIF-1α and REDD1 and an obvious decrease of mTOR at both the mRNA and protein levels. Interference of HIF-1α expression by siRNA resulted in an apparent reduction of REDD1 parallel with that of HIF-1α during normoxia and hypoxia. Additionally, the hypoxia-induced REDD1 increase was blocked through loss of HIF-1α, and the downregulation of mTOR in hypoxia could be partly obstructed by HIF-1α-siRNA transfection. Separately, the modulation effect of REDD1 was confirmed in an experiment demonstrating that the hypoxia-induced decrease of mTOR was inhibited by REDD1 knockdown, which was measured by changes in both the mRNA and protein levels. The disruption of REDD1 expression also led to increased accumulation of HIF-1α under both normoxia and hypoxia.

DISCUSSION: The HIF-1α-REDD1-mTOR pathway was involved in the response to hypoxia in BeWo cells. Hypoxia-induced REDD1 upregulation is mediated by a HIF-1α-dependent pathway. Disruption of REDD1 blocked the effects of hypoxia on suppressing mTOR and resulted in additional accumulation of HIF-1α in BeWo cells.