Regulation Of MLH1 In Autophagy Influents The Low-dose Hyper-radiosensitivity Of Human Lung Adenocarcinoma Cells

【Objective】 To investigate the expression level of MLH1 and autophagy in lung adenocarcinoma cancer cells after low dose irradiation and the effects of suppression of MLH1 on radiosensitivity, exploring possible mechanisms for this activity.【 Methods 】 Human lung adenocarcinoma A549 and H460 cells were used. Immunofluorescent stanning,western blot and electron microscope detected MLH1 and autophagy expressions. We used RNA interference technology to silence the expression of MLH1.The expression of MLH1 was detected by real-time PCR and Western blot. Cell scratch assay, transwell invasion and migration test objected the change about invasion and migration ability of A549 cell after knockdown MLH1.Clonogenic assays were used to detect whether downregulation of MLH1 expression increased the low dose sensitivity of A549 cells to ionizing radiation. Expression of m-TOR,p-m TOR,BNIP3 and Beclin-1were assessed by and Western blot. Cell cycle were measured by flow cytometry(FCM) assays.【Results】(1) MLH1 expressed low in HRS + A549 cells l but high in HRS- H460 cells.(2)After different dose radiation the MLH1 and LC3 expression increased above 0.3 Gy in A 549 cells, but H460 cells showed no obvious difference.(3) After transfection of MLH1 si RNA the A549 cells showed increased low dose radiation sensitivity, and HRS- H460 cells began to being HRS+.(4) The A549 cells the expression level of m-TOR、BNIP3、Beclin-1 increased, but p-m TOR decreased above 0.3 Gy radiation;MLH1- A549 cells showed obvious lower level of LC3、m TOR protein and higher level of p-m TOR protein compared to MLH1+ group, and no obvious difference was found between BNIP3, Beclin 1 expression.(5) Down-regulation of MLH1 expression enhanced the ability of invasion and migration in A549 cells.(6) Down-regulation of MLH1 expression added the G2/M phase arrest after low dose irradiation.【Conclusions】(1)The change of HRS to IRR is associated with MLH1 expression levels, inhibiting MLH1 expressions could increase low dose radiation sensitivity.(2)Inhibited MLH1 expressions can inhibit cell autophagy level.(3) MLH1 may medidate m TOR signaling pathways regulating cell autophagy and participate in the occurrence and development of HRS/IRR phenomenon.