HIF2α inhibits glutaminase clustering in mitochondria to sustain growth of clear cell renal cell carcinoma

Abstract

Clear cell renal cell carcinomas (ccRCCs) are largely driven by HIF2α and are avid consumers of glutamine. However, inhibitors of glutaminase 1 (CLS1), the first step in glutaminolysis, have not shown benefit in phase III trials, and HIF2α inhibition, recently FDA approved for treatment of ccRCC, shows significant but incomplete benefits. This highlights the need to better understand the Interplay between glutamine metabolism and HIF2α In ccRCC. Here, we report that glutamine deprivation rapidly redistributed CLS1 into isolated clusters within mitochondria in diverse cell types, but not in ccRCC. CLS1 clustering occurred rapidly within 1–3 hours, was reversible, was specifically triggered by reduced intracellular glutamate, and was dependent on mitochondrial fission. Clustered CLS1 markedly enhanced glutaminase activity and promoted cell death under glutamine-deprived conditions. HIF2α prevented CL51 clustering, independently of its transcriptional activity, thereby maintaining low CLS activity and protecting ccRCC cells from glutamine-deprivation-induced cell death. Forced clustering of CLS1, using constitutively clustering mutants, restored high CLS activity, promoted apoptosis, and suppressed ccRCC tumor growth in vivo. These findings reveal multiple insights into cellular glutamine handling, including a previously unrecognized process by which HIF2α promotes ccRCC: by suppressing CLS1 clustering and maintaining low CLS activity. This mechanism provides a potential explanation for the lack of clinical efficacy of CLS inhibitors in ccRCC and suggests a therapeutic avenue to combine HIF2α inhibition with strategies that restore CLS1 clustering.