Steroid receptor coactivator expression throughout the menstrual cycle in normal and abnormal endometrium

The endometrium of reproductive aged women undergoes cyclic developmental changes in preparation for implantation in response to estrogen and progesterone. These steroids and their receptors are tightly regulated throughout the menstrual cycle, and their actions are facilitated by the presence of steroid receptor coactivators of the p160 family. In this study using immunohistochemistry and Western blot analysis, we characterize the expression patterns of three coactivators, steroid receptor coactivator-1, amplified in breast cancer-1 (AIB1), and transcriptional intermediary factor-2 in human endometrium obtained prospectively from normal fertile women throughout the menstrual cycle. With the exception of glandular AIB1, which increased in the late secretory phase, none of the coactivators changed significantly during the menstrual cycle. We compared coactivator expression patterns in fertile endometrium to the endometrium of anovulatory (proliferative; n = 3) and clomiphene-induced ovulatory (secretory; n = 13) women with polycystic ovarian syndrome (PCOS), a group that have a higher likelihood of developing estrogen-induced endometrial hyperplasia and cancer. To control for the effect of clomiphene citrate, an additional group was included consisting of ovulatory women treated with clomiphene citrate for "male factor" infertility. Compared with both fertile and infertile controls, PCOS women exhibited elevated levels of AIB1 and transcriptional intermediary factor-2 expression in both epithelial and stromal cells. We postulate that increased coactivator expression may render the endometrium more sensitive to estrogen. In support of this, we describe an increased expression of ERalpha (an estrogen-induced gene product) during the menstrual cycle in PCOS endometrium compared with fertile controls. In summary, we demonstrate that the expression of p160 coactivators are regulated in endometrium during the menstrual cycle in normal fertile women but are overexpressed in the endometrium of women with PCOS. Based on these findings, we suggest a possible mechanism to explain the poor reproductive performance observed in PCOS and the increased incidence of endometrial hyperplasia and cancer noted in this group of women.