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Requirement for Cyclin D1 Underlies Cell-Autonomous HIF2 Dependence in Kidney Cancer
Nitin H Shirole1,2, Devishi Kesar2, Yenarae Lee2
1Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts.
Abstract:
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.
Insights
Sustaining Cyclin D1 expression confers resistance to belzutifan, a treatment for clear cell renal carcinoma (ccRCC). This resistance involves both kinase-dependent and independent activities of Cyclin D1.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Clear cell renal carcinoma (ccRCC) is driven by HIF2a stabilization due to VHL gene inactivation.
- Belzutifan, a HIF2a inhibitor, treats ccRCC but faces challenges with de novo and acquired resistance.
- HIF2a, complexed with ARNT, regulates gene transcription crucial for ccRCC progression.
Purpose of the Study:
- To identify HIF2a-responsive genes conferring resistance to belzutifan in ccRCC.
- To elucidate the mechanisms by which CCND1 (Cyclin D1) promotes resistance.
- To investigate the roles of Cdk4/6, pRB, and its paralogs in Cyclin D1-mediated resistance.
Main Methods:
- CRISPR activation (CRISPRa) screens in ccRCC cell lines resistant to a belzutifan analog.
- Analysis of CCND1 expression and its impact on HIF2a-dependency.
- Assessment of Cyclin D1's role in resistance using wild-type and kinase-defective variants, and cell lines with depleted pRB family members.
Main Results:
- Sustained expression of the HIF2a target gene CCND1 confers HIF2a-independence and belzutifan resistance.
- Cyclin D1's resistance-promoting activity requires Cdk4/6 activation but extends beyond pRB phosphorylation.
- A kinase-defective Cyclin D1 variant partially overcame belzutifan's effects, indicating kinase-independent roles.
Conclusions:
- CCND1 is a key mediator of belzutifan resistance in ccRCC.
- Cyclin D1 promotes ccRCC growth through both Cdk4/6-dependent phosphorylation of pRB paralogs and kinase-independent mechanisms.
- Targeting CCND1 or its associated pathways may overcome belzutifan resistance in ccRCC.
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