Abstract: Abstract: Objectinve To explored the ralations between expression of MLH1 gene and microsatillites stability in human embryonic kidney cell line 293t. Methods A plasmid vector encoding shRNA targeting hMLH1 (pGPU6/GFP/Neo-shMLH1) was constructed to knock down hMLH1 gene in 293t cell line，and evaluated the microsatallite stability before and after Knocked down. Results the expression of MLH1 in knocked down group was obviously knocked down in 293t cell, and the microsatallite states was changed from microsatallite stability into microsatallite instability conpared with control group. Conclusion The results showed that the expression of MLH1 gene was intimately associated with the microsatallite stability， knocked down hMLH1 protein could lead to microsatallite instability in cell line 293t.

Key words: MMR gene, hMLH1, microsatallite instability, RNA interference