We have utilized a series of glioma cell lines to study the effects of ionizing radiation on the regulation of proteins that contribute to cell cycle progression. While no alterations of cyclin E or cdk4 were detected, a high percentage of glioma cell lines exhibited constitutive overexpression of cdk2 protein and aberrant patterns of cyclin D1 protein. The fraction of glioma cells expressing cdk2 was similar to that observed in normal astrocytes, but individual glioma cells overexpressed cdk2. In response to ionizing radiation, both cyclin D1 and cdk2 accumulated in control cells but not in gliomas with overexpressed cdk2 or aberrant cyclin D1. These novel findings provide the first evidence of altered cyclin-cdk regulation in gliomas in response to ionizing radiation.

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