Studies On The Effect Of Ionizing Radiation On MDM2-p53-p21 Signal Pathway Of HEK293 Cells

In the process of the cell growth, wild type p53 monitors the condition ofitself as a "molecular policeman". The p53 protein regulates the stimulationfrom the response of DNA by activating or inhibiting the expression of itsdownstream genes. P53 may interact with other proteins as a activator, anrepressor or cofactor. These downstream genes of P53 and its interacted genesmake up a large net of bioinformation. The pathway of MDM2-p53-p21 avoidsthe accumulation of damaged DNA, maintains the genetic stability and theinvision of cells by blocking the cycle of cells, inducing the apoptosis andfacilitating the repairation of DNA. In the experiment the effect of signaltransduction-pathway of MDM2-p53-p21 by ionizing radiation on the humanembryo renal cells and its mechanism of regulation are studied.1. The effect of ionizing radiation on the signal transductionof MDM2-p53-p211.1 The effect of ionizing radiation on apoptosis, necrosis and thesurvival rate of HEK293 cellsThe survival rate of HEK293 is changed by 2 Gy X-rays, the main causelies in apoptosis decrease and necrosis increase. The death of HEK293 resultsfrom necrosis caused by HDR predominantly.1.2 The effect of ionizing radiation on the progression of cellcycleIonizing radiation can induce G1 arrest of the cell line with wild-type p53gene in vitro, resulting from the mechanism that ionizing radiation couldfacilitate the expression of p53 and its activities. Ionizing radiation inhibits thesynthesis of DNA and delays the entry of the cells into M stage through G2 stage.The mechanism is still less known that ionizing radiation induces the arrest of Sstage and G2 stage. It is shown in the time-course and dose-effect results thatHEK293 cells are blocked in S stage and G2 +M stage with 2 Gy X-rays and thepercentage of G2 +M stage increases with the increasement of radiation dose.1.3 The effect of ionizing radiation on the signal transduction ofp53, p21 and MDM2Ionizing radiation as a DNA damage molecule can induce the activation ofp53 gene, its protein product can regulate transcription of its downstream gene(p21WAF1/CIP1, MDM2) and induce the expression of proteins(p21WAF1/CIP1,MDM2) as a transtription factor. The expression of P21 and MDM2 wasenhanced in HEK293 cells with 2 Gy X-rays.2. The effect of RNA interference on the signal pathway ofMDM2-p53-p21Now RNAi has successfully been applied in studying the interrelation ofgene function and signal-transduction pathway and probably provides a newstrategy for tumor gene therapy. It is shown in our results that the expression ofP53 and P21 in the HEK293 cells was decreased by p53 shRNA and theexpression of P53 and P21 increased after irradiation, but the latter is still lowerthan sham-irradiation. The expression of MDM2 increased more thansham-irradiation, which may be caused by the decrease of p53 induced byfeedback regulation of MDM2.