RESUMO
The down-regulated in adenoma (DRA) gene is significantly down-regulated in adenomas and adenocarcinomas of the colon as well as in colon cancer cell lines. It is also mutated in the disease congenital chloride diarrhea, which is characterized by loss of chloride transport and diarrhea. We now show a second function for DRA relevant to colon tumorigenesis, i.e., growth suppression. Transfection of full-length DRA into various cell lines (DLD-1, HT-29, HCT-15, SW837, SW480, MCF-7, NIH3T3, CaSki, and HeLa) that lack endogenous DRA expression results in a reduced number of drug-resistant colonies compared with vector control, suggesting growth suppression by DRA. In addition, expression of DRA under the control of an inducible promoter reduced the growth rate of DLD-1 cells compared with cells not expressing DRA. The COOH-terminal cytoplasmic domain of DRA is required for growth suppression, but an in-frame deletion (DeltaVal317) that causes congenital chloride diarrhea and results in a loss of anion transport had no effect on growth suppression, indicating that anion transport and growth suppression are independent functions of DRA. One cell line, adenovirus-transformed HEK293, exhibited significant resistance to DRA-induced growth suppression, whereas the human papillomavirus-transformed cell lines, CaSki and HeLa, did not. E1A is an adenoviral protein required to transform HEK293 cells. DLD-1 cells that stably express 12S E1A are resistant to growth suppression by DRA, similar to HEK293 cells.