SRC-MEDIATED ACTIVATION OF THE HUMAN NEUROTENSIN NEUROMEDIN N PROMOTER

Background. Expression of the gene encoding the neurotensin/neuromedin N (NT/N) is developmentally tally regulated in the gut in a distincti ve temporal and spatial fashion. Src kinase, a nonreceptor tyrosine ki nase, has been implicated in the growth and differentiation of various tissues; its role in gut differentiation is not known. The purpose of this study was to determine whether the Src signaling pathway plays a role in the activation of the human NT/N promoter. Methods. Caco-2 ce lls, a human colon cancer cell line that can differentiate to a small bowel phenotype, were transiently transfected with human NT/N promoter fragments linked to luciferase and various amounts of Src expression plasmids or dominant negative Raf; luciferase and beta-galactosidase a ctivities were measured after 48 hours. Results. Cotransfection of Src resulted in an approximate eightfold increase of NT/N promoter activi ty; mutation of a proximal activating protein-1/cyclic adenosine monop hosphate responsive element site resulted in a dramatic decrease of Sr c-mediated NT/N induction. Cotransfection with a dominant negative Raf plasmid partially blocked Src-mediated NT/N activation. Conclusions. Src increases NT/N promoter activity In Caco-2 cells acting, in part, through a proximal AP-1/CRE promoter element. In addition, Src regulat ion of the NT/N promoter appears to be mediated through a Raf-dependen t pathway. We propose that Src may play a role in tissue-specific gene expression in the gut.