The objectives of this study were to assess the immunolocalization of human osteopontin (OPN) in oral lesions and to identify human cell lines of oral squamous cell carcinoma (OSCC) origin that express OPN mRNA. OPN was localized using immunohistochemistry in the following oral specimens: normal epithelium (n=6), epithelial hyperplasia (n=4), epithelial dysplasia (n=28), carcinoma in situ (n=11) and squamous cell carcinoma (n=43). Cell lines UMSCC‐1, MDA TU 138, MDA 686LN, SCC4, SCC9, SCC25, CAL 27 and MDA 1483 were characterized for OPN mRNA expression using Northern blotting. OPN was not detected in normal oral epithelium. Intracellular and intercellular immunore‐activity was seen in 75% of hyperplasias, 57% of dysplasias, 54% of carcinoma in situ and 67% of squamous cell carcinomas. UMSCC‐1 expressed high levels of OPN mRNA. We conclude that OPN protein is detectable in premalignant and malignant lesions arising from oral epithelium. UMSCC‐1 may be a useful cell line in which to conduct in vitro studies designed to clarify the role of OPN in OSCC.
Studies to assess osteopontin (OPN) localization in adult human bone using immunochemical techniques produce conflicting results due to variations in tissue processing or antibody immunoreactivity. The present study was designed to resolve these discrepancies using well-characterized antibodies and improved antigen detection. An anti-osteopontin (alpha-OPN) antiserum was developed that recognizes various soluble molecular weight forms of human OPN, including monomeric, cleaved, and dimerized products. An affinity column of full length recombinant human OPN (rOPN) coupled to support was used to purify alpha-OPN antibodies. Western analysis showed that the affinity-purified antibodies recognized numerous molecular weight forms of OPN. These antibodies were used to study the distribution of OPN in adult human bone using immunohistochemical techniques combined with an antigen retrieval protocol utilizing a newly developed antigen retrieval solution, Retriev-Alltrade mark (Bronco Technologies Inc, Pasadena, TX). Immunolocalization of OPN in archival bone specimens prior to antigen retrieval produced no demonstrable immunostaining even at high concentrations of alpha-OPN. Use of the antigen retrieval protocol restored OPN immunoreactivity, with strong staining apparent in cement lines, osteoblasts, osteocytes, canaliculi, osteoid, and bone matrix. We conclude that antigen retrieval restores immunochemical recognition of OPN in archival specimens containing bone without increasing nonspecific binding.
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