After ovulation, progesterone stimulates a temporally regulated secretory transformation in human endometrial epithelium. Using a combination of immunohistochemistry, and Western and Northern blotting, we demonstrate that 1) the polymorphic epithelial mucin MUC1 is secreted by human endometrial epithelium; 2) low levels of both mRNA and core protein are present in the preovulatory phase of the menstrual cycle; 3) mRNA levels increase several-fold after ovulation, consistent with transcriptional regulation by progesterone; 4) there is an increase in translation product in postovulatory endometrium; and 5) the tandem repeat domain of the MUC-1 polypeptide is glycosylated in endometrium.

Endometrial epithelial cells express MUC1 with increased abundance in the secretory phase of the menstrual cycle, when embryo implantation occurs. MUC1 is associated with the apical surface of epithelial cells and is also secreted, being detectable in uterine fluid at elevated levels in the implantation phase. However, its physiological role is uncertain; it may either inhibit intercellular adhesion by steric hindrance or carry carbohydrate recognition structures capable of mediating cell-cell interaction. Here we show that endometrial epithelium expresses both Sialyl-Lewis x (SLex) and Sialyl-Lewis a (SLea), with a distribution and pattern of menstrual cycle regulation similar to that of MUC1. Using Western blotting and double determinant ELISA of uterine flushings, we demonstrate that SLex is associated with MUC1 core protein. The endometrial carcinoma cell lines HEC1A and HEC1B are shown to express MUC1 in a mosaic pattern, while three other cell lines express much lower amounts. HEC1A expresses both SLex and SLea while HEC1B expresses SLea only. Immunoprecipitation has been used to demonstrate that SLea is associated with MUC1 in HEC1B cells, and both SLex and SLea are associated with MUC1 in HEC1A cells.

After ovulation, progesterone stimulates a temporally regulated secretory transformation in human endometrial epithelium. Using a combination of immunohistochemistry, and Western and Northern blotting, we demonstrate that 1) the polymorphic epithelial mucin MUC1 is secreted by human endometrial epithelium; 2) low levels of both mRNA and core protein are present in the preovulatory phase of the menstrual cycle; 3) mRNA levels increase several-fold after ovulation, consistent with transcriptional regulation by progesterone; 4) there is an increase in translation product in postovulatory endometrium; and 5) the tandem repeat domain of the MUC-1 polypeptide is glycosylated in endometrium.

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