Cross-talk between CDK4/6 and SMYD2 regulates gene transcription, tubulin methylation, and ciliogenesis

Area of Science:

• Cell Biology
• Epigenetics
• Molecular Oncology

Background:

• Dysregulation of cyclin-dependent kinases 4 and 6 (CDK4/6) is implicated in various human diseases, with underlying mechanisms often unclear.
• CDK4/6 kinases play critical roles in cell cycle progression and are frequently dysregulated in cancers.

Purpose of the Study:

• To elucidate the mechanisms underlying CDK4/6 dysregulation.
• To identify novel substrates and signaling pathways involving CDK4/6.
• To explore the therapeutic potential of targeting the CDK4/6-SMYD2 axis in disease.

Main Methods:

• Phosphorylation assays to determine SMYD2 as a CDK4/6 substrate.
• Western blotting and quantitative PCR to assess protein and gene expression.
• siRNA-mediated depletion and pharmacological inhibition of CDK4/6 and SMYD2.
• Immunofluorescence microscopy to analyze cilia assembly and microtubule dynamics.
• Analysis of patient-derived samples from breast cancer and ADPKD.

Main Results:

• Identified SMYD2, a histone/lysine methyltransferase, as a direct substrate of CDK4/6.
• Demonstrated a positive feedback loop where CDK4/6 phosphorylates and activates SMYD2, and SMYD2 enhances CDK4/6 expression.
• Established SMYD2 as an alpha-tubulin methyltransferase, linking CDK4/6-SMYD2 signaling to microtubule dynamics.
• Showed that inhibiting CDK4/6 or SMYD2 promotes cilia assembly by stabilizing microtubules and upregulating IFT20.
• Observed restoration of primary cilia in breast cancer and ADPKD cells upon CDK4/6 and SMYD2 inhibition.

Conclusions:

• CDK4/6 directly cross-talks with the epigenome via SMYD2, influencing microtubule dynamics and ciliogenesis.
• The CDK4/6-SMYD2 pathway is a critical regulator of primary cilia.
• Targeting CDK4/6 and SMYD2 with inhibitors offers a potential therapeutic strategy to restore primary cilia function in diseases characterized by its loss, such as cancer and ADPKD.