Osteopontin and its receptor alpha v beta 3 integrin are coexpressed in the human endometrium during the menstrual cycle but regulated differentially

Osteopontin is an arginine-glycine-aspartic acid-containing acidic glycopro tein component of the extracellular matrix that is postulated to bind to in tegrin receptors at the cell surface to mediate cellular adhesion and migra tion during embryo implantation. The primary aim of this study was to exami ne the uterine expression of osteopontin throughout the menstrual cycle in normal fertile controls sampled prospectively based on urinary LH surge det ection. Expression of osteopontin was documented using Northern blot analys is, in situ hybridization, and immunohistochemistry. Furthermore, the tempo ral pattern of osteopontin expression was compared with that of its recepto r, the alphav beta3 integrin. Using Ishikawa cells, a well differentiated e ndometrial adenocarcinoma cell line, the in vitro regulation of osteopontin and its receptor alphav beta3 integrin was studied. By Northern blot analy sis, osteopontin mRNA appears during the early secretory phase, with maxima l expression occurring in mid to late secretory-phase endometrium. The in s itu hybridization analyses showed that osteopontin mRNA specifically locali zed in epithelial cells within the endometrium. Immunostaining of osteopont in was detected in the glandular secretions and on the apical portions of s urface (luminal) epithelium. The patterns of expression of osteopontin by N orthern blotting, in situ hybridization, and immunohistochemistry are remar kably similar to the pattern for the alphav beta3 integrin. Despite these s imilarities in distribution, in vitro studies demonstrate that osteopontin and beta3 integrin subunit expression are differentially regulated. The exp ression of osteopontin was primarily induced in response to progesterone, w hereas the beta3 integrin subunit was up-regulated by epidermal growth fact or or heparin-binding epidermal growth factor. The differential regulation of these two endometrial proteins suggests the existence of two separate pa thways regulating epithelial gene expression in human endometrium. during t he window of implantation. In adhesion assays using Ishikawa cells, alphav beta3 but not alphav beta5 or beta1 integrins appear to be the primary rece ptors for osteopontin. These findings may better define the factors that fa vor the development of a receptive endometrium.