Requirement for Cyclin D1 Underlies Cell-Autonomous HIF2 Dependence in Kidney Cancer.

Inactivation of the VHL gene stabilizes HIF2α, which drives clear-cell renal cell carcinoma (ccRCC). The HIF2α inhibitor belzutifan is approved for ccRCC treatment, but de novo and acquired resistance are common. HIF2α, bound to ARNT, transcriptionally activates many genes. We performed CRISPR-mediated gene activation screens in HIF2α-dependent ccRCC lines treated with a belzutifan analog to identify HIF2α-responsive genes that confer cell-autonomous belzutifan resistance when not downregulated. Sustaining the expression of the HIF2α target gene CCND1, encoding cyclin D1, promoted HIF2α independence/belzutifan resistance. This activity requires CDK4/6 activation by cyclin D1 but is not solely due to phosphorylation of the canonical cyclin D1 target, pRB. Indeed, ccRCC lines lacking all three pRB family members remained at least partially HIF2α-dependent. In this context, however, a kinase-defective cyclin D1 variant partially overrode belzutifan's antiproliferative effects, suggesting that ccRCC promotion by cyclin D1 requires the phosphorylation of pRB paralogs and one or more kinase-independent cyclin D1 activities. SIGNIFICANCE: We discovered that cyclin D1 is the key target of HIF2 driving the cell-autonomous proliferation of VHL-mutant kidney cancers and that cyclin D1 has targets beyond pRB in this setting. These findings have implications for treating kidney cancer with HIF2 inhibitors, alone or in combination with CDK4/6 inhibitors.