PLK1 Regulates MicroRNA Biogenesis through Drosha Phosphorylation

Area of Science:

• Molecular Biology
• Cancer Biology
• Biochemistry

Background:

• Polo-Like Kinase 1 (PLK1) is a crucial cell-cycle regulator and a therapeutic target in various cancers.
• Drosha, the catalytic core of the microprocessor complex, is essential for microRNA (miR) biogenesis.
• Several kinases are known to phosphorylate miR biogenesis machinery components, affecting their activity and localization.

Purpose of the Study:

• To investigate the hypothesis that PLK1 regulates miR biogenesis through direct phosphorylation of Drosha.
• To elucidate the functional consequences of PLK1-mediated Drosha phosphorylation on the miR biogenesis pathway.
• To identify specific miRs regulated by PLK1 and assess their potential as biomarkers for kinase inhibitor response.

Main Methods:

• In vitro kinase assays to confirm PLK1 phosphorylation of Drosha at specific serine residues (S300/S302).
• Western blotting and co-immunoprecipitation to assess Drosha phosphorylation, DGCR8 association, and subcellular localization.
• Small RNA sequencing and qPCR to identify PLK1-regulated miRs and analyze pre-miR and pri-miR levels.

Main Results:

• PLK1 directly phosphorylates Drosha at S300 and/or S302, affecting Drosha-DGCR8 complex formation and subcellular localization.
• PLK1 inhibition leads to decreased Drosha phosphorylation, altered Drosha:DGCR8 localization (increased cytosolic, decreased nuclear), and reduced miR biogenesis.
• Ten specific miRs were identified as significantly downregulated by PLK1 inhibition, with regulation occurring at the pri-miR to pre-miR processing step.

Conclusions:

• PLK1-mediated Drosha phosphorylation is a key regulatory mechanism for miR biogenesis, independent of PLK1's cell-cycle role.
• Drosha S300 and S302 serve as integration sites for multiple kinase signals, influencing the biogenesis efficiency of distinct miR subsets.
• The identified kinase-regulated miRs hold promise as predictive biomarkers for assessing response to kinase inhibitor therapies in cancer and other diseases.