Abstract PR008: The SLC1A1/EAAT3 dicarboxylic amino acid transporter: An actionable, HIF-independent, hub that links epigenetic dysregulation to nucleotide metabolism in kidney cancer
Authors: Chakraborty Abhishek A. 
Published: August 2023

Abstract
Significance: The clear cell renal cell carcinomas (ccRCCs), which harbor the hallmark inactivation of the von Hippel Lindau tumor suppressor protein (pVHL), represent the majority of adult kidney cancers. Although, early stage/localized ccRCC is effectively managed by surgery and surveillance, therapeutic options for advanced stage disease are limited, highlighting the unmet need for novel therapies. Chromatin dysregulation is routinely observed in ccRCC and our previous work identified a distinct histone modification signature associated with pVHL-deficient ccRCCs, versus the pVHL-proficient chromophobe and papillary sub-types, which included elevated levels of bulk Histone H3 K27 acetylation (H3K27ac). H3K27ac marks transcriptionally activated regions in the genome. We hypothesized that, as in other biological contexts, H3K27ac accumulation in pVHL-deficient ccRCCs drives the expression of key oncogenes. Here, we functionally probed this dysregulated epigenetic program to identify actionable targets in kidney cancer. Experimental Approach and Results: We identified genes marked by elevated H3K27ac (ChIP-Seq) and higher expression (RNA-Seq), specifically in pVHL-deficient cells and prioritized the top 100 genes that encoded druggable products. Using a library representing these ORFs, we did an in vivo ‘sufficiency’ screen, to identify candidates whose expression promoted tumor growth in otherwise poorly tumorigenic pVHL-proficient cells. Our screen (and downstream validation studies) identified SLC1A1, which encodes an Asp/Glu transporter named EAAT3, as an oncogenic driver in ccRCC. Results: SLC1A1 expression was elevated in pVHL-deficient cells – but in a HIF-independent manner. Inactivation of SLC1A1 (using CRISPR/Cas9) led to fitness defects in a panel of ccRCC cell lines, along with a notable depletion of nucleotide biosynthesis precursors, likely because of the importance of the Asp carbon skeleton in this pathway. Consistent with this, esterified-Asp rescued the fitness defects associated with SLC1A1 loss. Moreover, SLC1A1 upregulation (high Asp/Glu) diminished dependency on Glutaminase; whereas, SLC1A1 loss (low Asp/Glu) increased Glutaminase dependency and promoted sensitivity to Glutaminase blockade. Finally, using clinical cohorts and cell-based studies, we found that SLC1A1 can impact its own transcriptional expression, but also the expression of certain other metabolic transporters involved in Asp/Glu metabolism (e.g. SLC22A11) and nucleotide metabolism (e.g SLC28A1). We speculate, these transcriptional alterations are driven by the conversion of Glu into a-ketoglutarate, a key cofactor for KDMs. Our ongoing studies are addressing the mechanistic basis of this transcriptional regulation and exploring the feasibility of pharmacologically targeting SLC1A1 in ccRCC. Altogether, we show that ccRCCs hijack nutrient reabsorption mechanisms (e.g. SLC1A1) to drive oncogenic programs. SLC1A1 thus links epigenetic dysregulation to a HIF-independent metabolic program regulating nucleotide biosynthesis/uptake.
Citation Format: Abhishek A. Chakraborty. The SLC1A1/EAAT3 dicarboxylic amino acid transporter: An actionable, HIF-independent, hub that links epigenetic dysregulation to nucleotide metabolism in kidney cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr PR008.