STABILIZATION OF CYCLIN-E AND CDK2 MESSENGER-RNAS AT G1 S TRANSITION IN RAT-1A CELLS EMERGING FROM THE G0 STATE/

mRNAs for cyclin E and Cdk2 have a role in the commitment to DNA repli cation in the cell cycle, and are induced in Rat-1A cells by serum sti mulation. Cyclin E and cdk2 genes are transcribed in quiescent cells, but their transcripts rapidly turn over and levels are kept low. The r ate of transcription of the cdk2 gene is slightly increased after seru m stimulation, while that of cyclin E is fairly constant. At the G1/S transition of serum-stimulated cells, transient stabilization of the t wo types of mRNAs occurs, an event which may lead to induction of each mRNA. Artificial expression of an immediate-early protein Delta FosB results in proliferation of quiescent Rat-1A cells, and this is accomp anied by an efficient induction of cyclin E and cdk2 mRNAs. In Delta F osB-expressing cells, two types of mRNAs are stabilized to the same ex tent seen in serum-stimulated cells. The expression of cyclin E and cd k2 genes is upregulated by stabilization of their transcripts, at leas t in part. We propose that Delta FosB may have a role in regulation of progression of the cell cycle in serum-stimulated Rat-1A cells by tri ggering stabilization of mRNAs for cyclin E and Cdk2.