Abstract 217: Modulation of Hsp90 chaperone activity by hypoxic condition: Hypoxia stimulates ARD1-mediated Hsp90 post-translational modification

Abstract

Abstract Arrest defective-1 protein (ARD1, also known Naa10p) is an N-acetyltransferase known to be involved in cell cycle control. Several reports have implicated ARD1 in regulation of cell proliferation and apoptosis in mammalian cells. Although a potential role for ARD1 in controlling cell proliferation and apoptosis has been identified, little is known about the relevance of ARD1 to cancer development. Heat Shock Protein 90 (Hsp90), an essential molecular chaperone in eukaryotic cells, maintains the functional conformation of a subset of proteins that are typically key components of multiple regulatory and signaling networks mediating cancer cell proliferation, survival and metastasis. Reversible acetylation has been implicated as a regulatory post-translational modification of Hsp90. Although an acetyltransferase responsible for acetylating Hsp90 has yet to be identified, several groups recently identified Histone deacetylase 6 (HDAC6) as an one of the Hsp90 deacetylase. This study, we show that hypoxia leads to increased Hsp90 acetylation via ARD1 binding to Hsp90 and disrupted interaction between Hsp90 and client proteins and co-chaperone proteins. We found that treatment with the HDAC inhibitor trichostatin A (TSA) or sodium butyrate (NaB) enhanced Hsp90 acetylation and led to the dissociation of Hsp90 and client protein Hif-1a. To gain further insight into protein acetylation in the cytoplasm, we searched cellular targets for Hypoxia. By using an immunoprecipitation approach, we identified ARD1 as a prominent Hsp90 interacting partner. Transfection of ARD1 leads to Hsp90 hyperacetylation, its dissociation from an essential co-chaperone proteins and a loss of chaperone activity. Transfected ARD1 and Hsp90 can be abundantly and specifically co-immunoprecipitated under hypoxia condition. Those interactions prevented the formation of the Hsp90 chaperon complex, resulting in reduced chaperone function of Hsp90. We suggest that ARD1 functions as a tumor suppressor by disrupting the function of Hsp90, and thus inactivating of PI3K/Akt pathway and Hif-1a in cancer cells under hypoxic condition. We conclude that a coordinated interaction between Hsp90 and ARD1 under hypoxic condition may be an important mechanism for hypoxic cell signal to homeostasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 217. doi:1538-7445.AM2012-217