Glycogen Synthase Kinase 3 Phosphorylates Hypoxia-Inducible Factor 1α and Mediates Its Destabilization in a VHL-Independent Manner

Abstract

Hypoxia-inducible transcription factor 1α (HIF-1α) is a key player in the response to hypoxia. Additionally, HIF-1α responds to growth factors and hormones which can act via protein kinase B (Akt). However, HIF-1α is not a direct substrate for this kinase. Therefore, we investigated whether the protein kinase B target glycogen synthase kinase 3 (GSK-3) may have an impact on HIF-1α. We found that the inhibition or depletion of GSK-3 induced HIF-1α whereas the overexpression of GSK-3β reduced HIF-1α. These effects were mediated via three amino acid residues in the oxygen-dependent degradation domain of HIF-1α. In addition, mutation analyses and experiments with von Hippel-Lindau (VHL)-defective cells indicated that GSK-3 mediates HIF-1α degradation in a VHL-independent manner. In line with these observations, the inhibition of the proteasome reversed the GSK-3 effects, indicating that GSK-3 may target HIF-1α to the proteasome by phosphorylation. Thus, the direct regulation of HIF-1α stability by GSK-3 may influence physiological processes or pathophysiological situations such as metabolic diseases or tumors.

This study was supported by a grant from the Fonds der Chemischen Industrie to T.K. and by grants from the sixth European framework program (EUROXY) and Fondation Leducq to A.G. C.M. is senior research associate of FNRS (National Funds for Scientific Research, Brussels).

There are no conflicts of interest with this study.