Dynamic regulation of progesterone receptor activity in female reproductive tissues.

The progesterone receptor (PR) in cooperation with coregulator complexes coordinates crucial processes in female reproduction. To investigate the dynamic regulation of PR activity in vivo, a new transgenic mouse model utilizing a PR activity indicator (PRAI) system was generated. Studies utilizing the PRAI mouse have revealed that progesterone temporally regulates PR activity in female reproductive tissues. Specifically, progesterone rapidly enhances PR activity immediately after administration. However, chronic progesterone stimulation represses PR activity in female reproductive organs. Like progesterone, RU486 also temporally regulates PR activity in female reproductive organs. However, the temporal regulation of PR activity by RU486 is the inverse of progesterone's activity. RU486 acutely represses PR activity after injection but increases PR activity after chronic treatment in female reproductive tissues. Treatment with a mixed antagonist/agonist of PR, when compared to natural hormone, results in dramatically different tissue-specific patterns of intracellular PR activity, coregulator levels, and kinase activity. Transcriptional regulation of gene expression by PR is facilitated by coordinate interactions with the steroid receptor coactivators (SRCs). Bigenic PRAI-SRC knockout mouse models enabled us to draw a tissue-specific coactivator atlas for PR activity in vivo. Based on this atlas, we conclude that the endogenous physiological function of PR in distinct tissues is modulated by different SRCs. SRC-3 is the primary coactivator for PR in the breast and SRC-1 is the primary coactivator for PR in the uterus.