Abstract PD15-09: Sox4 and smarca4 upregulate glycolysis-driven tumor proliferation through hexokinase 2 in tnbc
Authors: Khanna Pooja , Mehta Gaurav , Gatza Michael L 
Published: February 2021

Abstract
Background Triple-negative breast cancer (TNBC) accounts for nearly 1-in-4 breast cancer related deaths in the United States each year despite representing 10-12% of newly diagnosed cases. This aggressive disease, which is largely synonymous with the basal-like molecular subtype, predominantly affects younger women and women of African American decent. Despite a number of recent advances, overall survival has not drastically improved, highlighting the need to better understand mechanisms regulating tumor growth and progression as a means to identify novel therapeutic opportunities in these patients.
Methods In order to identify the functional impact of overexpression of the oncogenic transcription factor SOX4 and its co-factor SMARCA4 in TNBC, RNAseq and ChIPseq analyses were used to identify SMARCA4-dependent and -independent SOX4 gene expression programs. Analyses of more than 3,000 tumor samples from the METABRIC and TCGA cohorts was used to investigate the functional implications and clinical association of these gene expression programs in human tumors. Mass spectrometry (MS)-based metabolomic profiling in conjunction with genetic and pharmacological-based in vitro studies were used to demonstrate the impact of these programs on tumor cell metabolism, cell viability and proliferation.
Results We, and others, have previously demonstrated that the oncogenic transcription factor SOX4 is overexpressed in basal-like tumors. In order to identify mechanisms by which this protein mediates breast cancer tumorigenesis, we first identified SOX4 co-factors. Immunoprecipitation follow by MS was used to identify the SWI/SNF ATPase SMARCA4 as a prominent SOX4 cofactor that is concurrently overexpressed in basal-like tumors. Mechanistic studies showed that this complex is required to maintain an active open chromatin conformation at regulatory regions upstream of SOX4-regulated genes. ChIPseq and RNAseq-based analyses were next used to investigate the role of this complex in TNBC signaling and tumorigenesis. Our analyses identified SMARCA4-dependent and -independent SOX4 gene expression programs and demonstrated that SMARCA4-dependent SOX4 signaling is associated with poor clinical outcome. Further in silico analyses of human tumors indicate that each program mediates distinct down-stream signaling; SMARCA4-dependent signaling is associated with altered tumor metabolism and increased proliferative signaling. Consistent with this premise, in vitro studies showed that SOX4 and SMARCA4 are essential for breast tumor cell proliferation, survival and colony formation. Metabolomic profiling of breast cancer cell lines demonstrated that SOX4 overexpression resulted in increased glycolysis. The effect of SOX4 and SMARCA4 on cell metabolism was validated by demonstrating that this complex can mediate intracellular glucose consumption. Finally, we determined that SOX4 and SMARCA4 cooperatively regulate mRNA expression of hexokinase 2 (HK2), which catalyzes for the first step in glucose metabolism, and demonstrated that HK2 activity is essential for SOX4/SMARCA4-regulation of glycolysis. Importantly, in vitro genetic and pharmacological studies identified a link between HK2 activity, glycolysis and SOX4/SMARCA4-mediated cell proliferation and viability in TNBC.
Conclusions Our studies have identified SOX4 and its transcriptional cofactor SMARCA4 as being uniformly overexpressed in basal-like or TNBC tumors. These analyses demonstrate that SOX4 and SMARCA4 cooperatively promote tumorigenesis in TNBC cells, in part, by modulating glycolysis and cell proliferation through transcriptional regulation of HK2. Given the drug-ability of the glycolysis pathway, these results have potential clinical implications for treatment of TNBC patients.
Citation Format: Pooja Khanna, Gaurav Mehta, Michael L Gatza. Sox4 and smarca4 upregulate glycolysis-driven tumor proliferation through hexokinase 2 in tnbc [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD15-09.