Research Instructor Vanderbilt University Medical Center Nashville, TN, United States
Background: Clear cell renal cell carcinoma (ccRCC) is an aggressive kidney cancer driven by VHL loss and aberrant HIF-2α signaling. Identifying alternative means to regulate HIF-2α has potential therapeutic benefit. Recently, acetyl-CoA synthetase 2 (ACSS2), which converts acetate to acetyl-CoA, has been associated with poor patient prognosis in ccRCC. While other studies have linked acetate metabolism to HIF-2α, none have investigated this connection in a setting driven by HIF-2α. Our study aimed to elucidate the effects of modulating ACSS2 on HIF-2α, metabolism, and growth in clinically relevant ccRCC models.
Methods: Immunoblotting, immunoprecipitation, qPCR, Nanostring and ATAC-seq were used to monitor target expression and signaling changes. Multiple growth assays were used to study the effects of altering ACSS2 in-vitro using various cell line models. Additional growth studies were performed using in-vivo subcutaneous xenografts and ex-vivo patient-derived cell cultures. Functional characterization was performed with enzymatic assays, mass spectrometry, and electron microscopy. All in-vitro experiments were performed with a minimum n=3 biological replicates and n=5 for in-vivo studies.
Results: ACSS2 inhibition reduced HIF-2α levels and suppressed ccRCC growth in vitro, in vivo, and in ccRCC patient-derived cell cultures. This treatment resulted in reduced glycolytic signaling, cholesterol metabolism, and mitochondrial integrity. Mechanistically, ACSS2 inhibition decreased chromatin accessibility and HIF-2α transcription, while also reducing HIF-2α protein stability. Here, we identify a potential secondary pathway of degradation that acts in the absence of VHL and show the E3 ligase MUL1 can directly interact with HIF-2α, and that overexpression of MUL1 decreased HIF-2α levels.
Conclusions: This study demonstrates that targeting ACSS2 is effective at suppressing HIF-2α expression and signaling in clinically relevant models, including those resistant to HIF-2α targeted therapies. These findings highlight ACSS2 inhibition as a strategy to complement HIF-2α targeted therapies and deplete pathogenically stabilized HIF-2α preventing resistance.
