Cyclin mRNA and protein expression in recombinant interleukin 2‐stimulated cloned murine T lymphocytes

Expression of cyclin, a non‐histone nuclear protein, during recombinant interleukin 2 (rIL2)‐driven cell‐cycle progression of cloned T lymphocytes has been assessed. We found that expression of cyclin protein, as detected by immunofluorescence, is tightly associated with proliferation, and not merely S‐phase, of L2 cells stimulated with rIL2. Cyclin immunofluorescence was detected in all cell‐cycle phases (G₁/S/G₂/M, as detected by flow cytometry) of proliferating L2 cells. Accumulation of cyclin mRNA levels was induced as early as 1 h after stimulation, was maximal at 25–49 h, and remained elevated throughout stimulation, as detected by Northern blot analysis. A cDNA‐encoding murine cyclin was cloned from a cDNA library prepared from IL2‐stimulated cloned T cells. The sequence of the 5′ end of the murine cyclin cDNA was determined and found to be 88% and 82% similar to the sequences of cDNA clones encoding rat and human cyclin, respectively. The present studies demonstrate that cyclin protein and mRNA accumulation are highly regulated during IL2‐induced proliferation of a cloned T cell. These data provide a framework for addressing the molecular mechanisms regulating cyclin gene expression during cellular proliferation.