Quantification of the C-myc Oncoprotein in Human Glioblastoma Cells and Tumor Tissue

The identification of a quantifiable oncoprotein marker in glial cells could lead to its use as an aid in the diagnosis, grading, and treatment of tumours of glial origin. In this study, monoclonal antibodies to the c-myc oncoprotein were used in conjunction with immunofluorescence microscopy, flow cytometry, and immunoblot analysis to quantitate and characterize the expression of this oncoprotein in neoplastic and benign cultured glial cells and brain-tumor tissue. Flow cytometric analysis revealed that the c-myc oncoprotein was highly expressed in neoplastic cell lines and in glioblastoma tumor specimens. In contrast, anti-c-myc oncoprotein staining was not present in a non-neoplastic glial cell line or in a benign brain tissue specimen. Immunoblot analysis revealed two distinct c-myc oncoprotein bands, having molecular weights of 64 and 75 kD. Densitometric determinations of the relative levels of the 64-kD protein were in good agreement with the determinations made by flow cytometry. Flow cytometry was also used to relate the quantity of the c-myc oncoprotein present in the cells to their cell cycle phase. In the malignant cultured cells, the protein underwent an approximate twofold increase as the cells progressed from G1/G0 to G2/M in the cell cycle. The present results suggest that the c-myc oncoprotein may prove to be a useful marker for the proliferation status and/or malignancy of glial cells.