Abstract
Gamma radiation is a well-known antiproliferative agent, yet its mechanism of inhibiting tumor cell growth is not fully understood. Human oral epidermoid carcinoma KB cells were irradiated with various doses of Co-60 gamma-rays and harvested for analysis of the phosphorylation status of retinoblastoma protein (Rb) by SDS-polyacrylamide gel electrophoresis and analysis of their DNA content by flow cytometry. Dephosphorylation of Rb, which coincided with S and G2 arrest was observed in the lethal dose range of 750-1500 cGy. Both effects could be reversed by 1 mM caffeine, an inhibitor of tyrosine kinase and DNA repair enzymes. These results suggest that gamma-radiation, like many other antiproliferative agents, induces cell cycle arrest and growth inhibition in which dephosphorylation or reactivation of Rb plays an important role.
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