title: Class II histone deacetylases are associated with VHL-independent regulation of hypoxia-inducible factor 1 alpha.
abstract: Hypoxia-inducible factor 1 alpha (HIF-1 alpha) 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-1 alpha 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-1 alpha 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-1 alpha protein via a VHL-independent mechanism and reduction of HIF-1 alpha transcriptional activity. HIF-1 alpha inhibition by LAQ824 was associated with HIF-1 alpha acetylation and polyubiquitination. HIF-1 alpha 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-1 alpha. Hydroxamic acid derivatives with known activity against both class I and class II HDACs were effective in inhibiting HIF-1 alpha at low nanomolar concentrations. In contrast, valproic acid and trapoxin were able to inhibit HIF-1 alpha only at concentrations that are effective against class II HDACs. Coimmunoprecipitation studies showed that class II HDAC4 and HDAC6 were associated with HIF-1 alpha protein. Inhibition by small interfering RNA of HDAC4 and HDAC6 reduced HIF-1 alpha protein expression and transcriptional activity. Taken together, these results suggest that class II HDACs are associated with HIF-1 alpha stability and provide a rationale for targeting HIF-1 alpha with HDAC inhibitors against class II isozymes.
authors.affiliation: The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins School of Medicine, Baltimore, MD 21231, USA.
authors.forename: David Z
authors.initials: DZ
authors.lastname: Qian
authors.forename: Sushant K
authors.initials: SK
authors.lastname: Kachhap
authors.forename: Spencer J
authors.initials: SJ
authors.lastname: Collis
authors.forename: Henk M W
authors.initials: HM
authors.lastname: Verheul
authors.forename: Michael A
authors.initials: MA
authors.lastname: Carducci
authors.forename: Peter
authors.initials: P
authors.lastname: Atadja
authors.forename: Roberto
authors.initials: R
authors.lastname: Pili
mesh_terms: D002292:Carcinoma, Renal Cell; D045744:Cell Line, Tumor; D056464:Histone Deacetylase 2; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D006900:Hydroxylation; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000502:physiology*; D007680:Kidney Neoplasms; D007700:Kinetics; D012334:RNA, Neoplasm / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism*; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics / Q000502:physiology*
chemical_list: C497442:HIF1A protein, human; D006877:Hydroxamic Acids; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C477361:LAQ824; D012334:RNA, Neoplasm; D012097:Repressor Proteins; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D056464:Histone Deacetylase 2; D006655:Histone Deacetylases; C497446:VHL protein, human