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In this paper, we examine the regulation of vimentin expression during interleukin 2-induced proliferation of the cloned helper T cell line, L2. We observe a 10-20-fold increase in steady-state vimentin RNA that is accompanied by a 14-fold increase in the rate of vimentin protein synthesis. This indicates that translation is occurring, and thus that vimentin expression is regulated, at least in part, at the level of transcription and/or RNA stability, rather than at the level of protein synthesis. In contrast to the increases in steady-state vimentin RNA and the rate of protein synthesis, steady-state vimentin protein levels increase maximally only 1.3-3-fold in proliferating L2 cells. The rate of vimentin protein turnover remains relatively constant throughout L2 cell activation, active proliferation, and return to quiescence, indicating that an increased rate of turnover does not account for the minimal increase in vimentin content. These observations are consistent with a transient increase in vimentin protein synthesis necessary to support L2 cell growth and/or vimentin network reorganization. Because cell division occurs before an equilibrium state is reached, the maximal increase in steady-state vimentin protein content is never attained. |
