GROWTH SUPPRESSION MEDIATED BY TRANSFECTION OF WILD-TYPE HMLH1 IN HUMAN CANCER-CELLS EXPRESSING ENDOGENOUS TRUNCATED HMLH1 PROTEIN

Many genes that are frequently mutated in human cancer are known to be involved in the control of normal cellular proliferation. One of the genes involved in DNA mismatch repair is hMLH1, defective mutations of which are found in some familial and various sporadic cancers. Althou gh the DNA mismatch repair activity of hMLH1 has been identified, othe r biological functions of hMLH1 have not been well investigated. To in vestigate the effect of wild-type hMLH1 in cellular proliferation, wil d-type hMLH1 cDNA was introduced into human colorectal carcinoma cell line HCT116 and human gastric carcinoma cell line SNU-1, each containi ng a homozygous non-sense mutation at codon 252 and 226 in hMLH1, repe ctively. The hMLH1-transfected stable clones showed mRNA and protein e xpression of transfected hMLH1. Three in vitro cell growth experiments demonstrated that compared with parental and vector-transfected contr ol counterparts, both hMLH1-transfected HCTI16 and SNU-1 clones displa yed: i) decreased cellular proliferation; ii) a significant decrease i n the rate of DNA synthesis and iii) a dramatic reduction of anchorage -independence and the size of colonies in semisolid medium. In additio n to DNA repair activity, these results suggest that hMLH1 may play a role in the negative regulation of HCT116 and SNU-1 cell growth.