62The SLC1A1/EAAT3 dicarboxylic amino acid transporter is an epigenetically dysregulated nutrient carrier that sustains oncogenic metabolic programs

Abstract Background Epigenetic dysregulation, including accumulation of Histone H3 lysine 27 acetylation (H3K27ac), is a hallmark of pVHL-deficient clear cell Renal Cell Carcinomas (ccRCCs). H3K27ac is associated with transcriptional activation and its accumulation at cis-regulatory elements (eg, promoters and enhancers/super-enhancers) marks key oncogenes and regulators of cellular identity in many cancers. In ccRCC, specific alterations in H3K27ac have been linked to tumorigenesis and metastatic progression. Importantly, these earlier studies largely relied on the HIF2α-dependent 786-O cells (or their metastatic derivatives), perhaps, missing the importance of HIF-independent epigenetic programs. Altogether, we hypothesized that H3K27ac marks critical genes in pVHL-deficient ccRCCs that sustain tumorigenic and metastatic programs via both HIF-dependent and independent mechanisms. Methods Using an in vivo positive selection ORF screen in poorly tumorigenic pVHL-proficient cells and cell-based mechanistic studies in pVHL-deficient cells, we discovered that the aspartate (Asp) and glutamate (Glu) transporter, SLC1A1/EAAT3, is a metabolic oncogenic dependency in ccRCC. Results pVHL loss promotes HIF-independent SLC1A1 expression via H3K27ac dysregulation. SLC1A1 inactivation, using either genetic or pharmacological approaches, depletes Asp/Glu-derived metabolites eg, Tricarboxylic acid (TCA) cycle and nucleotide intermediates, impedes ccRCC growth, and sensitizes ccRCCs to anti-metabolite drugs (eg, glutaminase blockers). In human tumors, higher SLC1A1 expression is associated with reduced immune infiltration, oncogenic metabolic programs, and advanced stage/metastatic disease. Finally, in ccRCC animal models, SLC1A1 inactivation diminishes lung metastasis and the outgrowth of established renal tumors. Conclusions Altogether, our studies credential SLC1A1 as a novel, actionable, HIF-independent, metabolic dependency in pVHL-deficient ccRCCs.