Heat‐resistant variants of the Chinese hamster ovary cell: Alteration of cellular structure and expression of vimentin

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Abstract
Three heat‐resistant mutant cell lines (78‐1, 78‐2, 78‐3) were previously selected from Chinese hamster ovary cells. In this study, we investigated whether the differences in intrinsic thermal sensitivity result from alteration of stress protein levels or cellular structural changes. Although there was no significant difference in the levels of stress proteins, i.e., constitutive HSP70 in wild type and three heat‐resistant mutant strains, there were marked differences in the amounts of vimentin among the cell lines. Two‐dimensional gel electrophoresis and Western blot showed a 2.3–2.9‐fold increase in the level of vimentin in the mutant cells under normal growth conditions. Northern blot also revealed higher amounts of vimentin mRNA in the mutant cells. Electron microscopy and immunofluorescence suggest that increased amounts of the vimentin‐containing intermediate filaments are correlated with the heat‐resistant phenotypes.