Osteopontin (OPN) and
CEACAM1 have diverse biological functions in the uterus and placenta throughout the estrous cycle and pregnancy and have been shown to interact with
integrin beta3. OPN is a
glycoprotein of the extracellular matrix, which has been shown to mediate cellular migration and invasion and to contribute to
tumorigenesis in several types of
cancers. Recently we showed the expression pattern of OPN in gestational
trophoblastic tumors.
CEACAM1 is an adhesion molecule of the
carcinoembryonic antigen family that we have recently found to be expressed in
endometrial cancer and that has been shown to be down-regulated in colorectal, prostate, and
breast cancer. In this study, immunohistochemistry and immunofluorescence with specific
antibodies were performed on a series of 20 normal endometrial samples, 17
endometrial hyperplasias, and 43
endometrial carcinomas (28 endometrioid, 10 serous, and 5 clear cell
carcinomas) to investigate the expression pattern and cell-type specific localization of OPN and to correlate it with the expression of
CEACAM1. In addition, Western blot was performed on normal human endometrium and endometrial
neoplasia. Strong OPN expression with a consistent cytoplasmic localization in epithelial glandular cells was observed in the normal human endometrium in 80% of the samples of the proliferative and secretory phase (score 8-12). Similar results could be found in
endometrial hyperplasias. Strong expression of OPN could be observed in 29 (67.4%) of the 43 analyzed
endometrial carcinomas. Of the 43 analyzed
tumors, 18 (41.8%) were in the high score (8-12) category with a strong OPN expression level; 11 of 43 (25.5%) showed a moderate score (4-7) category. In
endometrioid carcinoma with increasing
malignancy grade, increasing areas with low OPN expression level or complete loss of OPN expression could be observed. In contrast, serous
tumors showed a strong OPN expression level. Similar results could be found in Western blot analysis.
CEACAM1 showed similar results and could be found to be coexpressed with OPN in normal human endometrium and in endometrial
neoplasia as we showed using immunofluorescence. In this study, the different expression patterns of OPN in endometrial
tumors could additionally support the biological diversity of endometrioid and serous
carcinomas together with other markers. We suggest that OPN might play a different role in the pathogenesis of
endometrial cancer (possibly as a functional complex with
CEACAM1) and could be relevant for invasive growth of such lesions.