An alteration in the phosphorylation of vimentin-type intermediate filaments is associated with mitosis in cultured mammalian cells.

Analysis of cultured Chinese hamster ovary (CHO) cells has shown that vimentin exists primarily as two 57,000 dalton isoelectric variants, a nonphosphorylated form and a slightly more acidic phosphorylated form. Similar analyses of CHO cells that were treated with colcemid show the presence of at least two to three additional, more acidic, phosphorylated vimentin isoelectric variants. An increasing 32P-specific activity of these variants suggests that this alteration involves increased phosphorylation. Analysis of 32P-labeled vimentin from colcemid-treated cells indicates that the amount of the additional phosphorylated variants correlates with the accumulation of cells in mitosis. CHO cells enriched in mitotic cells without antimitotic drugs demonstrate the same alteration in the isoelectric focusing pattern of phosphorylated vimentin. When mitotic cells are replated, the amount of additional phosphorylated variants is reduced within 30 min. The data suggest that an alteration in phosphorylated vimentin is temporally related to the alteration in the organization of intermediate filaments in mitotic cells.