Expression of two isoforms of CD44 in human endometrium

The distribution of the cell-surface adhesion glycoprotein CD44 in human endometrium was examined by immunofluorescence using six monoclonal antibodies to epitopes common to all forms of the molecule, and by reverse transcription-polymerase chain reaction (RT-PCR). Immunoreactivity was observed throughout the menstrual cycle in stroma, vessels, glandular, and luminal epithelium. Variations in staining intensity were observed, especially in the epithelial compartment. CD44 was also expressed strongly by decidualized stromal cells of first-trimester pregnancy. No systematic variation of immunoreactivity was observed with stages of the normal cycle, but a fraction (25%) of the specimens lacked reactivity in the epithelium. To determine the molecular size of the epithelial isoform, an immunoprecipitation technique was developed using surface-radioiodinated, detergent-extracted glands. This indicated the presence at the cell surface of a single dominant CD44E species with an approximate molecular mass of 130 kDa. RT-PCR was used to investigate the isoforms present in whole endometrial tissue, isolated gland fragments, and Ishikawa endometrial carcinoma cells. Complementary DNA produced from total endometrial mRNA was PCR-amplified across the splice junction between exons 5 and 15. Transcripts corresponding to the hyaluronate receptor CD44H as well as a larger isoform were identified. CD44H was absent, or very scarce, in cDNA from purified gland epithelium. In contrast, Ishikawa cells expressed this form abundantly. The glands and Ishikawa cells also expressed CD44E containing sequences encoded by exons 12, 13, and 14. These data demonstrate the presence of CD44 in human endometrium and decidua, and show that different isoforms of CD44 are associated with tissue compartments in which different functional roles can be anticipated.