Regulatory mechanisms of cytoskeletal proteins by phosphorylation and their cellular functions

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We found that Cdk1 phosphorylates vimentin-Ser55 from prometaphase to metaphase, leading to the recruitment of Plk-1 to vimentin. Upon binding to Phospho-Ser55 of vimentin, Plk1 is activated, and then phosphorylates vimentin-Ser82. During cytokinesis, Rho-kinase and Aurora-B specifically phosphorylate IFs at the cleavage furrow. The IF phosphorylation by Cdk1, Plk1, Rho-kinase, and Aurora-B plays an important role in the local IF breakdown, and is essential for the efficient segregation of IF networks into daughter cells. We also. found that Cdk1 phosphorylates Thr59 and Thr388 on inner centromere protein (lNCENP). INCENP phosphorylation by Cdk1 is necessary for the recruitment of Plk1 to the kinetochore, and the complex formation of Plk1 and Aurora-B on INCENP may play crucial roles in the regulation of chromosome dynamics. We identified Trichoplein and Fas binding factor-1 (Fbf-I) as novel keratin-binding proteins. Trichoplein and Fbf-1 have a domain that shows a low degree of sequence similarity between trichohyalin and plectin, designated, as trichohyalin/plectin homology domain (TPHD). These proteins co-localized with keratin, and also localized at cell-cell adhesion.