JNK1 Mediates Degradation HIF-1α by a VHL-Independent Mechanism that Involves the Chaperones Hsp90/Hsp70

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) is a master transcription factor that is critical for the regulation of a variety of cellular functions. HIF-1 alpha is rapidly degraded under normoxic conditions by ubiquitin-mediated proteasome pathway controlled by the tumor suppressor von Hippel Lindau (VHL). Several recent studies reveal that heat-shock proteins (Hsp) can regulate HIF-1 alpha protein degradation by a VHL-independent pathway. Here, we demonstrate that the stress kinase c-Jun NH2-terminal kinase 1 (JNK1) is required for Hsp-dependent regulation of HIF-1 alpha. Stabilization of HIF-1 alpha was impaired in JNK1-/- cells but could be rescued by JNK1 reconstitution under hypoxic conditions. These effects could be phenocopied in other cell settings by JNK1 silencing. Accordingly, HIF-1 transcriptional activity and target gene expression were dramatically reduced in JNK1-/- cells. Further, decreased levels of endogenous Hsp90/Hsp70 proteins in JNK1-/- cells affected the protective roles of these chaperones in stabilizing newly synthesized HIF-1 alpha, whereas enforced expression of Hsp90/Hsp70 in JNK1-/- cells increased HIF-1 alpha stability relative to parental control cells. Furthering this connection, we also found that defective expression of the Hsp90 acetyltransferase HDAC6 in JNK1-/- cells was associated with reduced Hsp90 chaperone activity. Taken together, our studies define a novel function for JNK1 in regulating HIF-1 alpha turnover by a VHL-independent mechanism. Cancer Res; 70(2); 813-23. (C) 2010 AACR.