ACTIVITY OF THE RAT LACTASE GENE PROMOTER IN TRANSFECTED HUMAN COLON-CANCER CELLS

The promoter activity of the upstream region of the rat intestinal lac tase-phlorizin hydrolase gene has been analysed by transfection in the human colon cancer cell line Caco-2. A 0.9 kb mRNA, corresponding to the CAT reporter gene, was synthesized from the transcription start si te of the LPH gene. The rate of expression, determined by semi-quantit ative RT-PCR, was very low, and depended on the length of the promoter fragment in front of the reporter gene. By immunocytology, we found t hat the low level of expression resulted from the low number of cells (about 1%) in which CAT was produced. The endogenous lactase was prese nt in 10-20% of the cells in culture, and evidence is provided that mo st cells that expressed CAT did not co-express the endogenous lactase. We conclude from this study that the rat small intestinal LPH gene pr omoter is active in the human Caco-2 colon cancer cells. Hence Caco-2 cells constitute an in vitro model to analyse the basic molecular mech anisms involved in the gene transcription of intestinal digestive enzy mes. Yet, the mosaic expression of the endogenous lactase and of the r eporter gene under the control of the rat LPH gene promoter suggests t hat Caco-2 cells may present specific regulatory mechanisms of express ion of small intestinal enzymes, possibly in relation to their tumouro us origin.