182 CALBINDIN-D28k IS PREDOMINANTLY EXPRESSED AND REGULATED BY ESTROGEN IN HUMAN ENDOMETRIUM DURING MENSTRUAL CYCLE

Abstract

The human endometrium resists embryo implantation except during the window of receptivity. A change in endometrial gene expression is required for the development of receptivity. Uterine calbindin-D28k (CaBP-28k) has been shown to be involved in the regulation of endometrial receptivity by intracellular Ca²⁺. Nowadays, this protein has been mainly linked to the brain, kidneys, and pancreas, but potential role(s) of CaBP-28k remain to be clarified in the uterus of humans during the menstrual cycle. Thus, we demonstrated in this study that the expression of CaBP-28k in the human endometrium in more divided in the menstrual phases. During the menstrual cycle of humans, uterine expression levels of CaBP-28k mRNA and protein increased at the proliferative phase and fluctuated in these tissues, compared with other phases. We assessed the effects of the sex-steroid hormones E₂ and P₄ on the expression of CaBP-28k in the Ishikawa cell line. A significant increase in the expression of CaBP-9k mRNA was observed at the concentration of 17β-oestradiol (E₂; 10^–9 to 10^–7 M). In addition, spatial expression of CaBP-28k was detected by immunohistochemistry. CaBP-28k is abundantly localised in the cytoplasm of the luminal and glandular epithelial cells during the menstrual cycle. Taken together, these results indicate that CaBP-28k, a uterine calcium-binding protein, is abundantly expressed in the human uterus, suggesting that uterine expression of CaBP-28k may be involved in reproductive functions during the menstrual cycle of humans.