Essential contribution of intron sequences to Ca2+-dependent activation ofc-fos transcription in pituitary cells

In pituitary cells, c-fos transcription induced by releasing hormones and g rowth factors results from enhanced initiation of transcription, and sustai ned elongation of transcripts beyond the first intron. We studied the regul atory role of the first intron of the mouse c-fos gene for the control of i ts transcription in rat pituitary cells. We showed that the intron contains a block to elongation which is relieved by physiological activators TRH an d EGF. By expressing luciferase under the control of the c-fos promoter inc luding the first intron in reporter gene constructs, we demonstrate enhance ment of TRH and EGF transcriptional stimulation by intron sequences. Furthe r analysis of Ca2+ signalling-depending transcription showed that the intro n contains control elements in addition to the block to elongation, and tha t sequences in the first intron can mediate Ca2+-stimulated transcription a lso with a minimal or the SV40 promoter, irrespective of the presence or ab sence of the intronic block site. Within the c-fos promoter the serum respo nse element and the cAMP response element play a permissive role in Ca2+-an d cAMP-enhanced transcription of intron containing reporter genes. Specific binding of nuclear proteins to a consensus enhancer binding site (Spl) wit hin the first intron of c-fos was demonstrated, which might reflect one of the mechanisms that link Ca2+ and intron sequences to c-fos expression. The se findings point towards important functions of intronic sequences in gene transcription control. Copyright (C) 2000 S. Karger AG,Basel.