To assess the role of expression of the retinoblastoma (RB) gene on the sensitivity of cells to the cytotoxic effects of ionizing radiation, we transfected a normal RB gene into cells of <tex-math>${\rm RB}^{+}$</tex-math> and <tex-math>${\rm RB}^{-}$</tex-math> osteosarcoma cell lines and an <tex-math>${\rm RB}^{-}$</tex-math> prostate carcinoma line and studied the radiosensitivity of the cells before and after transfection. Four transfected clones were isolated from the two <tex-math>${\rm RB}^{-}$</tex-math> tumor cell lines that expressed the product of the transfected normal RB gene and contained no mutations in the pocket and C-terminal regions by sequencing. A small increase in radiosensitivity was observed in cell lines transfected with the pDOL plasmid vector alone, containing the neo gene and a long terminal repeat (LTR) promoter. However, no significant change in radiosensitivity occurred in transfected cells expressing the normal RB gene compared to controls transfected with an <tex-math>${\rm RB}^{-}$</tex-math> plasmid. Based on this and other information, we conclude that RB gene function is not involved in the response of these human tumor cells to the cytotoxic effects of radiation.

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