Expression of osteopontin in human glioma. Its correlation with the malignancy

Osteopontin (OPN) is a phosphorylated glycoprotein that contains a functional Gly-Arg-Gly-Asp-Ser (GRGDS) cell-binding sequence. It is reported that the expression of OPN is increased in a number of transformed cell lines. This study demonstrates the expression of OPN in human glioma representative of brain tumors.

The expression of OPN in human gliomas was determined with: (a) Northern blot analysis; (b) Southern blot analysis; (c) Immunofluorescent cytochemistry; (d) Western blot analysis; (e) Cloning and sequencing of complementary DNAs (cDNAS); (f) Immunohistochemistry.

OPN mRNA was detected in all glioma cell lines examined, and Southern blot analysis showed that OPN DNA most likely exists as a single copy gene in these cell lines. Immunofluorescent cytochemistry showed strong staining mainly in the cytoplasm. These cell lines produced two major forms of OPN protein migrating at 53 and 47 kilodaltons, and two minor forms at 38 and 31 kilodaltons on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels. We also isolated and sequenced three types of splice variants in OPN from human glioma cell lines through polymerase chain reaction. In addition, Northern blot analysis was carried out on RNA from human astrocytoma tissues of various malignancy grades. Expression of OPN mRNA was high in malignant astrocytomas, but low in benign astrocytomas and non-neoplastic tissue. Immunohistochemistry also showed strong staining in malignant astrocytomas and slight staining in benign astrocytomas.

These findings indicate that OPN mRNA and proteins are expressed in human glioma cells, and that the extent of OPN expression may correlate with the malignancy grade of gliomas.