Abstract: ObjectiveTo explore the mRNA and protein expression of hMSH2 and hMLH1 gene during different stages of 16HBE cells induced by cadmium chloride(CdCl₂).MethodsReverse transcription-polymerase chain reaction(RT-PCR)and immunohistochemcial staining(SP method)were used to measure hMSH2 and hMLHI genes mRNA and protein expression levels in 16HBE cells and their different passage cells treated by cadmium chloride(the 5^th,15^th,35^th passage cells, and tumorigenic cells from nude mice's tumor tissue).ResultsThe bigger the passages times of 16HBE cells treated with cadmium chloride,the lower the expression levels of hMSH2 gene were.The hMSH2 genes mRNA and protein expression levels of the CdCl₂ transformed 35LH 16HBE cells and tumorigenic cells of nude mice significantly decreased compared with non-transformed 16HBE cells(P<0.01).There was no significant difference in mRNA and protein expression of hMLH1 gene during different stages of 16HBE cells induced by cadmium chloride(P>0.05).ConclusionThe down-regulated expression levels of hMSH2 gene may be the possible carcinogenic mechanism for cadmium chloride.