Relationship between Expression of p21(WAF1/CIP1) and Radio resistance in Human Gliomas

The role of p21(WAF1/CIP1) (p21) in DNA repair and apoptosis following γ‐irradiation remains controversial. In this study the influence of p21 on the radiosensitivity of human brain tumors was investigated. Resected tumors were stained immunohistochemically for p21. Expression of p21 in astrocytic tumors was high, but it was low in medulloblastomas, germinomas, and primary malignant lymphomas. Glioma and medulloblastoma cell lines were transfected with pcDNA/p21 to cause p21 overexpression, then tumor‐cell colony formation and apoptosis were assessed following γ‐irradiation of the transfected and nontransfected cells. Overexpression of p21 enhanced clono‐genic survival and suppressed apoptosis after γ‐irradiation in human brain tumor cell lines with or without p53 protein deficiency. Radioresistance was acquired when p21 was overproduced in the glioma cell lines irrespective of p53 status.