Expression pattern of osteopontin (OPN) in human adrenal tissues and in NCI259R cells

Objectives: Osteopontin (OPN) is a glycoprotein of the extracellular matrix, which we previously found to be expressed in benign and malignant endocrine tissues of the utero-placental system, and which was shown to mediate cellular migration and invasion and to contribute to tumorigenesis in several types of cancers. Recently, expression profiling of adrenal neoplasms revealed OPN mRNA to be expressed in these tumors. The present study was designed to analyze the expression profiling of OPN protein in normal and tumorous adrenal tissues.

Methods: Immunohistochemistry and immunofluorescence with specific anti-OPN antibodies were performed in normal adrenal tissue as well as in benign and malignant adrenocortical tumors. In addition, we studied OPN protein expression in these tissues and in the human adrenocortical cancer cell line NCI-259R cell line using Western blot analysis.

Results: In the normal human adrenal gland, OPN protein was found to be expressed strictly in the cortex, with the staining intensity decreasing in a centripetal fashion. Expression in adrenocortical hyperplasia was more intense than in normal adrenal cortex. Expression of OPN could also be observed in the analyzed adrenocortical adenomas and carcinomas, even though with a slightly reduced staining intensity. These results were confirmed by Western blot analysis. OPN protein expression could also be found in the human adrenocortical cell line NCI259R.

Conclusion: In this study we show for the first time, that OPN protein is expressed in the human adrenal gland. Furthermore, we demonstrate that OPN expression is strictly confined to the cortex, making it, thus, a potential diagnostic marker to distinguish between adrenal cortex and medulla. Our ongoing studies aim to clarify the role of OPN in adrenal tumorigenesis.