Progesterone-action in the murine uterus and mammary gland requires steroid receptor coactivator 2: Relevance to the human

The importance of the progesterone receptor (PR) in female reproductive and mammary gland biology is well recognized; however, the coregulators selectively enlisted by PR have yet to be comprehensively defined in vivo. To evaluate the involvement of steroid receptor coactivator (SRC)/p160 family members in these physiological systems, a mouse model (PR^Cre/+SRC-2 ^flox/flox) was generated in which SRC-2 function was ablated specifically in cell-types that express the PR. Although PR^Cre/+SRC- 2^flox/flox ovarian activity was normal, uterine function was severely compromised. Absence of SRC-2 in PR positive uterine cells led to an early block in embryo implantation, a defect not ascribed to SRC-1 or-3 knockouts. While the PR^Cre/+SRC-2^flox/flox uterus can display a partial decidual response, removal of SRC-1 in the PR^Cre/+SRC-2 ^flox/flox uterus results in a block in decidualization, confirming that uterine SRC-2 and-1 are both necessary for PR-mediated transcriptional responses which lead to complete decidualization. The absence of significant branching and alveolar morphogenesis in the hormone-treated PR ^Cre/+SRC-2^flox/flox mammary gland establishes an important role for mammary SRC-2 in cellular proliferative programs that require PR. Finally, the observation that SRC-2 is also expressed in many of the same cell-types in the human, underscores the importance of further study of this coregulator's role in both peri-implantation biology and mammary development.