抄録
Recently, we found that the accumulation of iNOS in wtp53 cells was induced by chronic irradiation with gamma rays followed by acute irradiation with X-rays, but not by each one, resulting in an increase in nitrite concentrations of medium. It is suggested that the accumulation of iNOS may be due to the depression of acute irradiation-induced p53 functions by pre-chronic irradiation. We found that chronic irradiation with gamma rays did not inhibit the accumulation of p53 after exposure to the conditioned medium from the irradiated mp53 cells. However, the decay of accumulated p53 was stimulated by chronic irradiation with gamma rays. At the same time, the accumulation of Hdm2 was observed; suggesting that chronic irradiation with gamma rays may stimulate the degradation of p53 accumulated by NO-mediated bystander effects. Furthermore, we found that the radiosensitivity of wtp53 cells against acute irradiation with X-rays was reduced after chronic irradiation with gamma rays. This reduction of radiosensitivity of wtp53cells was nearly completely suppressed by the addition of NO scavenger, carboxy-PTIO to the medium.
This reduction of radio-sensitivity of wtp53cells is just radiation-induced adaptive response, suggesting that NO-mediated bystander effect may considerably contribute to adaptive response induced by radiation.
