Relationship between the expression of cyclins/cyclin-dependent kinases and sex-steroid receptors/Ki67 in normal human endometrial glands and stroma during the menstrual cycle

Cell cycle regulatory molecules were analysed in normal human endometrial tissue using antibodies against cyclins D1, E, A, and B1 and cyclin-dependent kinases (CDKs) cdk4, cdk2, and cdc2. The expression of these regulatory molecules in gland cells and stromal cells was compared with the expression of oestrogen receptors (ER), progesterone receptors (PR), and Ki67 (a growth-related molecule). In general, a substantially higher percentage of the gland cells stained positive for cyclins and CDKs during the proliferative phase of the menstrual cycle. Cyclin E, cdk2 and/or cdk4 were especially apparent in the cytoplasm of most of the gland cells as well as in the stromal cells. In contrast, most of the regulatory molecules were undetectable in the gland cells by the end of the secretory phase of the cycle, but they did not decline in the stromal cells. The data also revealed that ER, PR, and Ki67 in both gland cells and stromal cells follow the same basic pattern of expression as the cyclins and CDKs. These results suggest that cyclins and CDKs are functionally involved in the rhythmic proliferation of normal human endometrial tissue, and the action of these agents may be related to the endometrial levels of sex steroids and Ki67.