Endometrial nuclear receptor co-factors SRC-1 and N-CoR are increased in human endometrium during menstruation

Steroid hormone receptor co-factors are abundantly expressed in the uterus in order to modify steroid hormone receptor action, either leading to activation or repression of transcription in the endometrium. However, the role of co-factors in remodelling of the human endometrium has not been established. We therefore endeavoured to evaluate the presence of the co-activator SRC (steroid receptor co-activator)-1 and the co-repressors N-CoR (nuclear receptor co-repressor) and steroid co-repressor SMRT (silencing mediator of retinod and thyroid) receptors in the human endometrium during the different phases of the menstrual cycle. By using a real-time RT-PCR assay, we showed that SRC-1, N-CoR and SMRT mRNA are expressed in human endometrium during all phases of the menstrual cycle, as well as in inactive endometrium. Moreover, endometrial expression of SRC-1 and N-CoR mRNA increased during menstruation when compared with the other phases of the menstrual cycle (P < 0.001). Immunohistochemistry demonstrated that SRC-1 and N-CoR stain positive in the glandular epithelium and stroma in menstrual phase endometrium. The staining was weak in proliferative and secretory endometrium and absent in inactive endometrium. Our results suggest that differential expression of endometrial steroid receptor co-factors probably play a role in the regulation of human endometrium remodelling.