Evidence for modulation of a 24K protein in human endometrium during the menstrual cycle

The presence and distribution of a protein with a molecular weight of 24,000 (24K) was determined in endometrial biopsies from regularly cycling women. This protein, of as yet unknown function and originally found in a breast cancer cell line, was detected by immunohistochemistry using a monoclonal antibody. In the glandular epithelium, the 24K protein began to appear during the late proliferative phase and decreased after ovulation. In contrast, the strongest immunostaining was observed in the superficial epithelium during the secretory phase. In these cells, the 24K immunoactivity reached the maximum around day 21 of the cycle and was clearly seen in the bulbous projections of the apical cytoplasm. These results suggest that the 24K protein may be a marker for hormonal events during the menstrual cycle.