Nuclear Cyclin D1/CDK4 Kinase Regulates CUL4 Expression and Triggers Neoplastic Growth via Activation of the PRMT5 Methyltransferase

Cyclin D1 elicits transcriptional effects through inactivation of the retinoblastoma protein and direct association with transcriptional regulators. The current work reveals a molecular relationship between cyclin D1/CDK4 kinase and protein arginine methyltransferase 5 (PRMT5), an enzyme associated with histone methylation and transcriptional repression. Primary tumors of a mouse lymphoma model exhibit increased PRMT5 methyltransferase activity and histone arginine methylation. Analyses demonstrate that MEP50, a PRMT5 coregulatory factor, is a CDK4 substrate, and phosphorylation increases PRMT5/MEP50 activity. Increased PRMT5 activity mediates key events associated with cyclin D1-dependent neoplastic growth, including CUL4 repression, CDT1 overexpression, and DNA rereplication. Importantly, human cancers harboring mutations in Fbx4, the cyclin D1 E3 ligase, exhibit nuclear cyclin D1 accumulation and increased PRMT5 activity.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (116 K)Download as PowerPoint slideHighlights► Nuclear cyclin D1 accumulation promotes increased PRMT5 methyltransferase activity ► Cyclin D1/CDK4 phosphorylates the PRMT5 cofactor MEP50 ► PRMT5 mediates cyclin D1-dependent transcriptional repression of CUL4A/B ► PRMT5 inhibition reduces survival of cyclin D1-driven lymphoma cells