Abstract 4274: HIF2α/Sp1/mTOR interaction mediates a deacetylation-dependent FVII gene activation under serum deprived condition in ovarian cancer cells

Abstract

Abstract Hypoxia-inducible factors HIF1α and HIF2α are major transcription factors required for adaptive responses to hypoxia. HIFs form a complex with arylhydrocarbon receptor nuclear translocator (ARNT) in order to bind to the regulatory region of target genes. The acetylation of histones by histone acetyltransferases (HATs) is one of the epigenetic marks associated with active chromatin. Indeed, HIFs recruit p300 HAT to hypoxia response elements (HRE) within gene regulatory regions. Blood coagulation factor VII (fVII) is a key enzyme in the extrinsic coagulation cascade predominantly produced by hepatocytes. fVII interacts with its cellular receptor, tissue factor (TF) and, when bound to TF, is converted to its active form (fVIIa), thereby triggering a downstream coagulation cascade. In addition to being a major cause of thrombosis in cancer patients, formation of the TF-fVIIa complex is known to initiate key pathogenic mechanisms in cancer, including cell motility, invasion, cell survival and angiogenesis. In addition, TF-fVIIa complex can be a cause of a common complication of cancer, venous thromboembolism particularly in ovarian clear cell carcinoma (CCC). Here, we report an unusual transcriptional activation mediated by HIFs in ovarian clear cell carcinoma (CCC). While characterizing coagulation factor VII (FVII) gene induction under hypoxia, which can initiate key pathogenic mechanisms in cancer, we observed that the interaction of HIF2α with Sp1, but not with ARNT, could induce transcription of FVII in a HRE-independent manner. Immunoprecipitation, followed by western blotting analysis revealed that PAS domains can associate with Sp1. Unexpectedly, this gene activation is associated with histone deacetylation. We found that a class II HDAC, HDAC4, is recruited with HIF2α to the FVII promoter as a coactivator, while p300 HAT negatively regulates this process.We next examined whether serum starvation affects FVII activation since we consider that hypoxic cancer tissues should be devoid of serum factors other than O2 and nutrients. We found that FVII activation under hypoxia can be coupled with mTOR signaling when cells are simultaneously exposed to hypoxic and serum-free conditions, which synergistically enhances transcription via a deacetylation-dependent pathway. On the other hand, we found that unfolded protein response is not responsible for the synergistic activation although cells exposed to both hypoxia and serum-free conditions undergo endoplasmic reticulum stress. Further we did not observe such synergism when cells were treated with glucose-free condition, in which expression of HIFs is largely decreased compared to serum starved condition. These results suggest the presence of a stress-responsive transcription mediated by HIF2α/Sp1/HDAC4/mTOR network. 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 4274. doi:1538-7445.AM2012-4274