Expression and signalling characteristics of the corticotrophin-releasing hormone receptors during the implantation phase in the human endometrium.
Corticotrophin-releasing hormone (CRH) has been identified in several peripheral tissues, including the female reproductive organs. CRH is expressed in the placenta, myometrium, epithelial endometrium and the endometrial stromal cells at all phases of the menstrual cycle. Similarly, CRH receptors are present in pregnant and non-pregnant myometrium, placenta and endometrium. Putative roles of CRH in the endometrium include involvement in implantation, decidualisation and maintenance of pregnancy. In this study we sought to investigate in detail the CRH receptor repertoire expressed in the human endometrium and their signalling characteristics. Using RT-PCR we were able to demonstrate the expression of CRH receptor 1alpha (CRH-R1alpha) and CRH-R2alpha in the human endometrium. CRH-R1beta was present in 40% of endometrial cDNAs examined. No apparent expression of CRH-R2beta, CRH-R2gamma or any other CRH-R1 splice variants was detected. Chemical cross-linking studies with 125I-ovine CRH revealed that the endometrial CRH receptor has a molecular weight of 45 kDa. Using the non-hydrolysable photoreactive analogue [alpha-32P]GTP-azidoanilide and peptide antisera raised against G-protein alpha-subunits, we then studied coupling of endometrial CRH receptors to G proteins. Treatment of endometrial membranes with human CRH (100 nM) increased the labelling of Gq and Gs, but not Gi or Go. These results were supported by experiments in epithelial cells of the non-pregnant human endometrium in the secretory phase which showed that CRH induced increases in both cAMP and inositol trisphosphate levels. These results suggested that CRH may exert multiple effects in the human endometrium via distinct signalling cascades. These events are possibly mediated via different receptor subtypes.