LAUSR

The hypoxia-inducible transcription factors (HIF)-1α and -2α play a critical role in cellular response to hypoxia in solid tumors. Elevated HIF-α expression correlates with poor patient survival in a large number of cancers including breast cancers. HIF-α activates expression of genes promoting angiogenesis, metastasis, increased tumor growth and resistance to treatments. Understanding transcriptional regulation HIF-α under physiologically relevant hypoxic conditions would be helpful to reduce breast cancer growth. Our recent studies identified that intracellular bioactive sphingosine-1-phosphate (S1P) generated from nuclear sphingosine kinase 2 (SphK2) acts as an endogenous modulator of histone deacetylases (HDACs) epigenetically regulates gene transcription in breast cancer cells. We wonder whether nuclear S1P epigenetically regulates acetylated histones, positive transcription marks in hypoxia and regulate transcription of HIF-α and target genes in breast cancer cells. We have used estrogen receptor positive human breast cancer MCF-7 cells, triple-negative human breast cancer MDA-231 cells, and lung metastatic LM-2-4 cells derived from MDA-231 cells cells for our studies. We found that hypoxic condition enhances nuclear bulk histone acetylation in breast cancer cells and enhances HIF-α synthesis. Down regulation of SphK2 with siRNA or using selective inhibitor of SphK2 (K145 compound) reduces nuclear S1P as well as bulk histone acetylation and consequently reduces nuclear HIF-α synthesis in breast cancer cells. Downregulation of cytosolic sphingosine kinase 1 (SphK1) with siRNA reduces cytosolic S1P does not alter nuclear bulk histone acetylation neither significantly alter nuclear HIF-α synthesis in breast cancer cells. We also found that targeting SphK2 with K145 compound dramatically reduces in vitro tumorosphere formation in breast cancer cells. Our data suggested that targeting the SphK2/S1P signaling could represent an attractive strategy for therapeutic intervention in hypoxic breast cancers. Supported by Health Research, Inc. (HRI) Grant 71-4084 (NCH), National Cancer Institute Grant R01CA160688 (KT). Citation Format: Nitai C. Hait, Aparna Maiti. SphK2/S1P axis regulates hypoxia-mediated HIF-α synthesis in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1388. doi:10.1158/1538-7445.AM2017-1388