Regulation of the T cell receptor-alpha mRNA expression in the human lymphoblastic T cell line CEM. 
We analyzed the transcriptional events involved in the T cell receptor (TcR)-alpha mRNA expression in a human lymphoblastic T-cell line CEM.  CD3-negative and CD3-positive CEM subclones that either lack mature TcR-alpha mRNA or express TcR-alpha mRNA were used.  Exposure of the TcR-alpha mRNA negative subclones to phorbol 12-myristate 13-acetate (PMA) was followed by 2- to 3-fold increase of transcription, indicating that PMA acts on a transcriptional level.  No increase of transcription was observed after blocking protein synthesis with cycloheximide (CHX) or after sequential stimulation with CHX followed by PMA.  On the posttranscriptional level, CHX as well as PMA induced a progressive stabilization of TcR-alpha mRNA in the nuclear compartment, which was independent of ongoing transcription.  The half-life of the TcR-alpha mRNA upon stimulation was about 6 hours.  The accumulation of mature TcR-alpha mRNA seemed to be controlled by nuclear events on a transcriptional as well as posttranscriptional level.  The data imply that alterations of TcR-alpha gene transcription are dependent on protein synthesis.  DNA-binding proteins enhance transcription and labile nuclear proteins target TcR-alpha mRNA for rapid turnover.