Abstract
Keratins are the most diverse family of intermediate filaments and are expressed in most epithelial tissues and malignancies. They form highly stable polymers that need to be cut through during cytokinesis. Previous work suggested a role of phosphorylation, but keratin regulation during cell division is not understood in detail. Depletion of Keratin 8 in an epithelial cancer cell line (HeLa) caused chromosome segregation and cytokinesis defects. Aurora B kinase localization to midzones and cleavage furrows was reduced in Keratin 8 knockouts, suggesting that Keratin 8 helps scaffold Aurora B during cytokinesis. We mapped eleven Aurora B kinase sites in Keratin 8 that were associated with cell division. Keratin 8 S34 phosphorylation occurred specifically at the cleavage furrow and persisted at the midzone until the end of cytokinesis. Inhibition of Aurora B kinase or non-phosphorylatable Keratin 8 mutant prevented the disassembly of keratin bundles at the cleavage furrow, which blocked furrow ingression. Our data reveal a functional inter-dependency between Keratin 8 and Aurora B kinase in epithelial cells. Keratin 8 promotes the translocation of Aurora B to the midzone. Aurora B kinase then generates a local zone of Keratin phosphorylation which promotes keratin filament disassembly and allows the cleavage furrow to cut through the keratin network.
