Assistant Professor of Molecular Medicine Cleveland Clinic's Lerner College of Medicine - CWRU Cleveland, OH, United States
Background: The clear cell renal cell carcinomas (ccRCC), which harbor the signature inactivation of the pVHL tumor suppressor protein, represent ~75% of kidney cancers. Inactivating mutations in histone-modifying enzymes occur recurrently in ccRCC. Consistent with this, we found differences in histone modifications in pVHL-null ccRCCs [relative to the pVHL-proficient (papillary and chromophobe) RCCs], including elevated levels of acetylated lysine 27 on Histone H3 (H3K27ac), which is associated with transcriptionally active enhancer regions. We hypothesized, therefore, that elevated H3K27ac controls genes that are essential for tumorigenesis in pVHL-deficient cells.
Methods: Our histone profiling in human tumors was done using a multiplexed Mass Spectrometry method. The genomic localization of H3K27ac was performed using ChIP-Seq and these profiles were integrated with gene expression data, measured using RNA-Seq. The SLC1A1 transporter was identified as a ccRCC oncogene using an unbiased genetic screen in vivo. These findings were validated using cell-based studies where SLC1A1 was inactivated genetically (using CRISPR/Cas9) or pharmacologically. The mechanistic basis for SLC1A1's oncogenic function was interrogated using LC-MS/MS based targeted metabolomics studies.
Results: Relying on genomics studies (e.g. integrating H3K27ac marking with transcriptional output) and an in vivo “up” screen, seeking genes that were sufficient to promote tumorigenesis in pVHL-proficient cells, we identified the Asp/Glu transporter SLC1A1 as a novel oncogene in ccRCC. SLC1A1 expression is regulated by pVHL status in an HIF-independent manner. Furthermore, SLC1A1 loss promotes anti-proliferative effects in ccRCCs. Metabolomics studies indicate that Asp uptake underlies SLC1A1's oncogenic function. Finally, SLC1A1 status directly impacts Glutaminase dependence.
Conclusions: Our studies identify the Asp/Glu dicarboxylic amino acid transporter SLC1A1 as a novel actionable target in ccRCC, define the metabolic basis for this dependence, and establish SLC1A1's role as a predictor of Glutaminase dependence in ccRCC.
