Study On Effect And Mechanism Of Cadmium On DNA Damage Repair Via Non-homologous End Joining

Cadmium(Cd)is a kind of heavy metal pollutant,which is widely used in industry and existed in environment(in water,air and soil).The stabilization and enrichment of Cd induced a great of harm to the health of the body through the food chain or direct exposure.Up to now,the previous studies mainly focused on the toxicity effect of Cd on organisms.In recent years,researches are more deeply and study the exact mechanism.The relationship between Cd and DSB was wildly studied.But,how Cd regulated the DNA damage repair(DDR),especially non-homologous end joining(NHEJ)-mediated DDR which is the main pathway in mammalian cells.However,the understanding of Cd on NHEJ repair is still rarely reported.In order to provide the specific theoretical basis for Cd poisoning and an important defensive strategy against Cd poisoning,this research mainly studied the mechanism of Cd influence on NHEJ-mediated DDR in human cervical cancer cells(Hela).The results of this study were shown as follows:1.After 24h exposure,Cd really was absorbed by Hela cells,and then triggered some effects(cell toxicity and genetic toxicity).In this paper,the high concentration of Cd(2.00,4.00 ?M)exposure can significantly inhibit the cell viability of Hela cells and induced DSB.But after the low concentration of Cd(0.25,0.50,1.00 ?M)exposure,the cell vitality(>80%)and cell survival(>90%)were high,and DNA damage was not caused.2.After Cd exposure,the efficiency of DDR was lower in the irradiated Hela cells.The foci of yH2AX and 53BP1(two markers for DDR)in irradiated cells with Cd treatment were significantly higher than those in irradiated cells without Cd treatment group.These results indicated that Cd can reduce the DDR efficiency in a certain time.But,after a period of time,at 24 h,the Cd can not delay the DDR efficiency.The foci of yH2AX and 53BP1 in the Cd treatment group were closed to the blank group.These results indicated that the inhibition of Cd on DDR was changed.After a certain time,cells can regulate the influence of Cd on DDR through cell's own repair mechanism.3.In the progress of NHEJ-mediated DDR,one of NHEJ-related factors Ku was not affected by Cd.But the foci of pDNA-PKcs on Thr-2609,XRCC4 and Ligase ? were significantly suppressed.Meanwhile,the level of XRCC4 and Ligase ? protein expression were also down-regulated.However,the foci of pDNA-PKcs on Ser-2056 were activated in the irradiated cells with Cd exposure.But,pATM on Ser1981,which regulated pDNA-PKcs on Thr-2609 was not changed.The same results can also find in Hela cells with NU7026 treatment.4.The irradiated cells with Cd exposure were treated with Zn.The results showed that the level of delayed DDR was removed.In the Zn treatment group,the foci of ?H2AX and 53BP1 significantly returned to normal level(the level in irradiated cells without Cd exposure).In addition,the foci of pDNA-PKcs on Thr-2609 and XRCC4 also closed to normal level.In conclusion,the study shows that Cd at the concentrations of 0.50 and 1.00 ?M did not affect the cell vitality and induced DNA damage.But Cd can delay the efficiency of NHEJ-mediated DDR by influencing the NHEJ-related factors DNA-PKcs on Thr-2609,XRCC4 and Ligase ?.Cd mainly inhibited the foci of pDNA-PKcs on Thr-2609,XRCC4 and Ligase ?formation.Cd also reduced the level of XRCC4 and Ligase ? protein expression.However,the delay of DDR can be rescued by Zn,which affected the progress of DDR by regulation pDNA-PKcs Thr2069,XRCC4 and Ligase ?.