Class II Histone Deacetylases Are Associated with VHL-Independent Regulation of Hypoxia-Inducible Factor 1α

Abstract

Hypoxia-inducible factor 1A (HIF-1A) plays a critical role in transcriptional gene activation involved in tumor angiogenesis. A novel class of agents, the histone deacetylase (HDAC) inhibitors, has been shown to inhibit tumor angiogenesis and HIF-1A protein expression. However, the molecular mechanism responsible for this inhibition remains to be elucidated. In the current study, we investigated the molecular link between HIF-1A inhibition and HDAC inhibition. Treatment of the VHL-deficient human renal cell carcinoma cell line UMRC2 with the hydroxamic HDAC inhibitor LAQ824 resulted in a dose-dependent inhibition of HIF-1A protein via a VHLindependent mechanism and reduction of HIF-1A transcriptional activity. HIF-1A inhibition by LAQ824 was associated with HIF-1A acetylation and polyubiquitination. HIF-1A immunoprecipitates contained HDAC activity. Then, we tested different classes of HDAC inhibitors with diverse inhibitory activity of class I versus class II HDACs and assessed their capability of targeting HIF-1A. Hydroxamic acid derivatives with known activity against both class I and class II HDACs were effective in inhibiting HIF-1A at low nanomolar concentrations. In contrast, valproic acid and trapoxin were able to inhibit HIF-1A only at concentrations that are effective against class II HDACs. Coimmunoprecipitation studies showed that class II HDAC4 and HDAC6 were associated with HIF-1A protein. Inhibition by small interfering RNA of HDAC4 and HDAC6 reduced HIF-1A protein expression and transcriptional activity. Taken together, these results suggest that class II HDACs are associated with HIF-1A stability and provide a rationale for targeting HIF-1A with HDAC inhibitors against class II isozymes. (Cancer Res 2006; 66(17): 8814-21)

Hepatitis B virus X protein induces the expression of MTA1 and HDAC1, which enhances hypoxia signaling in hepatocellular carcinoma cells

“…GST, glutathione-S-transferase; HBx, HBV regulatory protein; HIF-1a, hypoxia-inducible factor-1a; ODD, oxygen-dependent degradation; WT, wild type. Jeong et al, 2002;Qian et al, 2006), the acetylation hypothesis remains controversial since human ARD1 does not, at least directly, acetylate HIF1a (Arnesen et al, 2005;Bilton et al, 2005Bilton et al, , 2006Fisher et al, 2005;Murray-Rust et al, 2006). Instead, diverse other mechanisms have been proposed for the HDAC inhibitor-induced HIF-1 regulation; Kong et al (2006) showed that HDAC inhibitors induced the proteasomal degradation of HIF-1a by interacting with HSP70 and thereby disrupted the HSP70/HSP90 axis function.…”

Histone deacetylase inhibitors: molecular mechanisms of action

“…Further, HDACi can induce HIF-1a degradation in a VHL-independent mechanism . Class II HDACs, HDAC4 or HDAC6, physically associate with HIF-1a, and their selective inhibition by siRNA induced HIF-1a degradation (Qian et al, 2006). Moreover, HIF-1a binds to HSP90, and HDACi can disrupt HSP90 chaperone function, exposing HIF-1a to proteasomal degradation.…”

HDAC6, at the crossroads between cytoskeleton and cell signaling by acetylation and ubiquitination

“…Accordingly, HDAC6 appears to play a role, directly or indirectly via HSP90, in the control of the stability of HIF-1a, a transcriptional regulator involved in tumor angiogenesis (Qian et al, 2006), the breast cancer metastasis suppressor 1, BRMS1 (Hurst et al, 2006), Bcr-Abl, FLT-3, c-Raf and AKT (Bali et al, 2005).…”