Alteration in the retinoblastoma gene associated with immortalization of human fibroblasts treated with 60Co gamma rays.

Genetic analysis was carried out in human fibroblasts (KMST-6) immortalized by treatment with 60Co gamma rays in order to determine if any genetic change was involved in the immortal transformation of human cells. Analysis by restriction fragment length polymorphism revealed an alteration in chromosome 13q12-14, in which the retinoblastoma (RB) gene locus (13q14) is located. Then the RB gene itself was examined. Structural abnormalities in the RB gene were detected by Southern blot analysis. Furthermore, abnormal RB protein (pRB) was expressed in immortalized KMST-6 cells, as shown by in vitro phosphorylation, whereas normal KMS-6 cells expressed the intact pRB. These findings indicated that inactivation of the RB gene is one of the key events of the immortalization of human cells.