Regulation of progesterone receptor gene expression.

The levels of progesterone receptor (PR) mRNA, PR protein, and [3H]R5020 binding activity were measured in parallel experiments conducted on a T47D subline expressing the estrogen receptor. A significant increase of PR mRNA levels could be detected within 6 h of exposure of the cells to estradiol (10(-8) M). The changes in mRNA, however, did not lead to any variation of PR protein levels of [3H]R5020 binding activity. A parallel analysis of PR mRNA and [3H]R5020 binding was then performed in a series of tumor biopsies. In estrogen receptor-positive and PR-positive tissues a correlation among the two values was found. It is postulated that the above mentioned data could reflect the existence of a difference in the mechanisms controlling the numerous steps of the PR synthesis in the various hormone-responsive tissues. This variability could allow an organ-specific response to the cyclic changes of circulating hormone.