Abstract 3337: Nuclear S1P binds PASB domain of HIFα to facilitate HIFα-HIF1β heterodimer formation in hypoxic TNBC cells

Abstract

Abstract Triple-negative breast cancers (TNBCs) have increased expression of hypoxia-inducible factor 1α (HIF1α) and HIF-direct genes that associated with decreased overall survival in patients. Previously we have shown that nuclear sphingosine-1-phosphate (S1P), a lipophilic pro-cancer signal mediator, a product of the catalytic reaction by sphingosine kinase 2 (SphK2), directly binds to and inhibits histone deacetylases-1 and -2 (HDAC1 and 2), thus, altered epigenetic landscape in breast cancer cells. SphK2/S1P signaling is essential for metastatic TNBC cell growth and survival. We hypothesize that SphK2/S1P epigenetically regulates HIFα functions in TNBC cells; TNBC subset with elevated SphK2 and HIF1α would be a marker for SphK2-mediated HIFα targeted therapy. METABRIC cohort gene expression analysis revealed that the mRNA expression of HIF1α mRNA and downstream angiogenesis gene, vascular endothelial growth factor B (VEGFB) are associated with overall poor survival for TNBC patients compared to non-TNBC patients. Here, we demonstrate that a subset of TNBC patient tissue samples nuclei has elevated HIF1α and SphK2 protein expressions. SphK2/S1P markedly enhances hypoxia-induced HIFα proximal promoter histone acetylation. SphK2/S1P is found in the nuclear protein complexes with HIFα. Moreover, S1P is docked well at the PASB domain of HIFα and facilitate HIFα-HIF1β heterodimer formation in hypoxia. SphK2/S1P markedly augmented HIF1α direct target gene HIF2α and VEGFA promoter occupancy in hypoxia. Down-regulation of SphK2 with siRNA markedly attenuated transcription of HIFα-direct target genes associated with cancer stem cells, angiogenesis, and metastasis. In agreement with an oncogenic role of SphK2, selective inhibition of SphK2 markedly reduced nuclear histone acetylation, HIF1α expression, and in vivo human TNBC tumor growth in mice. Our data strongly suggested that TNBC subset with elevated SphK2 and HIF1α would be a good candidate for SphK2 targeted therapy. Supported by Health Research, Inc. (HRI) Grant 71-4084-01 (NCH). Citation Format: Nitai C. Hait, Aparna Maiti. Nuclear S1P binds PASB domain of HIFα to facilitate HIFα-HIF1β heterodimer formation in hypoxic TNBC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3337.