The regulation of interleukin-2-induced vimentin gene expression in a cloned T lymphocyte

Abstract

Nucleotide sequencing of a 1748 base pair murine vimentin cDNA demonstrates that the 466 amino acid murine vimentin monomer possesses structural features characteristic of intermediate filament chains. Vimentin gene expression is growth- associated in the murine helper T cell clone, L2, with steady-state vimentin mRNA levels increasing 7- to 20-fold following interleukin 2 (IL2) stimulation. Accompanying a 7-fold increase in vimentin mRNA levels is a 3-fold increase in vimentin mRNA half-life, indicating that mRNA stabilization is one of several mechanisms responsible for this induction of vimentin mRNA expression. Steady-state vimentin precursor RNA levels increase 3- to 4-fold following IL2 stimulation, while vimentin precursor RNA half-life remains constant. These results indicate that precursor RNA stabilization does not contribute to the upregulation of vimentin precursor RNA expression, and suggest that IL2 induces an increase in the rate of vimentin gene transcription. The 7 to 20-fold increase in vimentin mRNA levels is paralleled by a 14-fold increase in the rate of vimentin protein synthesis. This suggests that translation is occurring, and thus that vimentin expression is regulated at least in part, by the abundance of vimentin mRNA present. In contrast to the increases in steady-state vimentin mRNA and the rate of vimentin protein synthesis, steady-state vimentin protein levels increase maximally only 1.3- to 3-fold in proliferating L2 cells. This increase in vimentin protein content is associated with recently activated and actively proliferating cells, with protein levels accumulating as the cells progress through the cell cycle. The rate of vimentin protein degradation remains relatively constant throughout L2 cell activation, active proliferation and return to quiescence, indicating that an increased rate of degradation does not account for the minimal increase in vimentin protein content. These observations may be accounted for by a transient increase in vimentin protein synthesis necessary to support L2 cell growth and/or vimentin network reorganization. Due to the transient nature of this increase, and the fact that cell division occurs every 34 h, equilibrium at this increased rate of synthesis is never reached