Ephemerally expressed wild-type and mutant steroid hormone receptors are equally able to influence expression of transient or resident templates.

We have tested transiently expressed mutant and chimeric glucocorticoid receptors (GR) for their ability to influence transcription of either a co-transfected or a stably integrated reporter gene. To the latter purpose we have generated a cell line harbouring 2 chromosomally anchored copies of the well-characterized mouse mammary tumor virus (MMTV) promoter/enhancer region fused to the bacterial beta-galactosidase gene (LacZ). We were particularly interested in verifying whether some earlier characterized dominant negative GR mutants would still act the same way on chromosomal targets. We show that trans-regulation (activation/-repression) of the chromosomally anchored reporter is qualitatively and quantitatively indistinguishable from trans-regulation obtained with transient co-transfection. In parallel, we also tested ephemerally expressed wild-type progesterone receptor (PR) and androgen receptor (AR) for their capacity of acting on either transient or resident MMTV reporter templates. Also in this case we show that activation of chromosomally anchored or transiently co-transfected reporter by both these steroid hormone receptors is qualitatively and quantitatively indistinguishable. These results outline that newly expressed trans-effectors may exert their specific function independently of the precise structural organization of their responsive genes.