Sustaining Cyclin D1 Expression Renders Kidney Cancer Cells HIF2-Independent

Inactivation of theVHLtumor suppressor gene stabilizes HIF2a, which drives clear cell renal carcinoma (ccRCC). The HIF2ainhibitor belzutifan is approved for ccRCC treatment, butde novoand acquiredresistance are common. HIF2a, bound to ARNT, transcriptionally activates hundreds of genes. We performed genome-wide CRISPRa screens in HIF2a-dependent ccRCC lines treated with the belzutifan tool compound PT2399 to identify HIF2a-responsive genes that confer belzutifan resistance when not downregulated. Sustaining the expression of the HIF2atarget geneCCND1, encoding Cyclin D1, promoted HIF2a-independence/belzutifan resistance. This activity requires Cdk4/6 activation by Cyclin D1, but is not solely due to inhibitory phosphorylation of the canonical Cyclin D1 target, pRB. Indeed, ccRCC lines lacking all three pRB family members remained at least partially HIF2a-dependent. In this context. However, kinase-defective Cyclin D1 variants at least 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. Overall design: To identify candidate enhancer RNAs and profile the immediate transcriptional effects of DMSO and PT2399 drug treatment at 6 hour timepoint, PRO-seq (Precision Run-On Sequencing) was performed to investigate single nucleotide resolution of nascent RNA 3' ends.