In attempts to identify genetic alterations occurring in glioma pathogenesis and progression, we screened for genes that were differentially expressed between normal brain and glioblastoma tissues. We have identified one gene, which we designated GDOX (Glioma Derived Oncogene on X). This gene was expressed in glioblastoma, as confirmed by Northern blot analysis, in situ hybridization, and Western blot. Except in testes and kidney, the mRNA of this gene was not expressed in any other normal tissue, including brain. Transfection of a murine glial cell line with GDOX cDNA resulted in an increase of cell proliferation, while transfection of a human glioblastoma cell line with antisense GDOX cDNA resulted in growth arrest. To further investigate the role of GDOX in glioma progression, we have used siRNA to suppress GDOX expression in glioblastoma cell lines. Transfection of U87, a human glioblastoma cell line, with siRNA targeting GDOX substantially reduced the expression of GDOX mRNA, as judged by RT-PCR analysis. The reduction of GDOX mRNA expression in U87 that were transfected with GDOX siRNA was verified by real-time quantitative RT-PCR. We have transfected other glioblastoma cell lines, such as U251, and obtained similar results. To test the hypothesis that the inhibition of GDOX expression by GDOX siRNA suppresses cell proliferation, U87 that were transfected with GDOX siRNA was subjected to 3H-thymidine incorporation assay. The amount of 3H-thymidine incorporation in U87 that were transfected with GDOX siRNA was reduced compared to untransfected U87 several days after transfection, indicating a decrease in the rate of cell proliferation in transfected cells. To assess the long-term effect of GDOX suppression in glioblastoma cell line, we have transfected U87 with a vector encoding the GDOX siRNA. U87 that were stably transfected with the vector exhibited a slower growth rate in culture and underwent morphological changes. Our evidence so far strongly suggests that GDOX is an oncogene and it has an important role in glioma development and progression.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]