Cell configuration-related control of vimentin biosynthesis and phosphorylation in cultured mammalian cells.

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Abstract
The cell configuration-related control of a cytoskeletal protein (vimentin) expression was examined by varying cell shape between flat and spherical. Cultivation of cells [mouse embryonic fibroblast 3T3 cells, SV101 cells, melanoma B16-F1 cells, African green monkey kidney BSC-1 cells] in monolayer or in a spherical configuration on poly-2-hydroxyethylmethacrylate-coated plates revealed a preferential downregulation of vimentin synthesis during suspension culture. The mechanism(s) regulating the decrease in the expression of vimentin in spherical cells appears to be at the level of translation, because mRNA extracted from monolayer and suspension-cultured cells were equally active in directing vimentin synthesis in the rabbit reticulocyte cell-free system. When, after prolonged suspension culture, the cells were allowed to reattach and spread, vimentin synthesis recovered rapidly to the control monolayer rate. The phosphorylation of vimentin was also reduced dramatically during suspension culture. Unlike the rapid recovery of vimentin biosynthesis upon reattachment (< 6 h), the recovery in the rate of vimentin phosphorylation was much slower (> 20 h) and paralleled the recovery to the monolayer growth rate. Although the control of vimentin biosynthesis in suspension culture is a cell configuration-related process, the decrease in the rate of vimentin phosphorylation in suspension culture appears to be the result of the slower growth rate and may reflect the reported correlation between the rate of vimentin phosphorylation and the accumulation of cells in mitosis.