IDENTIFICATION OF GLUCOCORTICOID RECEPTOR DOMAINS NECESSARY FOR TRANSCRIPTIONAL ACTIVATION OF THE MOUSE MAMMARY-TUMOR VIRUS PROMOTER INTEGRATED IN THE GENOME

It has previously been determined that the mouse mammary tumor virus ( MMTV) promoter when integrated in the genome assumes a defined chromat in structure which is disrupted upon addition of glucocorticoids. In c ontrast, a transiently introduced MMTV promoter has a random nucleopro tein structure. To reveal glucocorticoid receptor (GR) domains necessa ry for transcriptional activation of the MMTV promoter we compared the effects of mutations of the GR on transcriptional activation of the s tably integrated versus transiently introduced MMTV promoter. For this purpose we generated a GR-negative cell line which has an MMTV promot er/reporter construct integrated in the genome and studied the transcr iptional activation of this construct by different GR mutants introduc ed into the cells. Transcriptional activation of the integrated and tr ansiently introduced promoter was achieved by the wild-type GR or a ch imeric receptor in which the MR hormone-binding domain (HBD) replaced the GR HBD. In contrast, we found that deletion of the HBD of the GR o r replacement of this region with the equivalent domain of the estroge n receptor produced receptors that were unable to activate the MMTV pr omoter integrated in the genome although these receptors efficiently a ctivated the transiently introduced MMTV promoter. The HBD was not the sole determinant of MMTV transcriptional activation when integrated i n the genome. Chimeric receptors which harbored the MR amino terminal domain or the wildtype MR were also unable to activate the integrated MMTV promoter. Taken together, these data indicate a rigid requirement for sequences in both the GR amino and the carboxy terminal domains f or transcriptional activation of a hormone response element in the def ined chromatin context of the MMTV promoter. (C) 1998 Academic Press.