CIS-ACTING ELEMENTS REQUIRED FOR EXPRESSION OF THE NONSPECIFIC CROSS-REACTING ANTIGEN GENE IN COLORECTAL-CARCINOMA

Background & Aims: The nonspecific cross-reacting antigen (NCA) is a c ell adhesion molecule, and the messenger RNA for NCA is overexpressed in 92% of colorectal carcinomas. The aim of this study was to determin e the cis-acting elements that may be responsible for the expression o f NCA. Methods: Deletion mutants of the 5' flanking sequence and first intron were ligated into chloramphenicol acetyltransferase expression vectors, transfected into Chinese hamster ovary (CHO), DiFi, and HT-2 9 human colorectal carcinoma cells, and BxPC-3 and MDAPanc-28 human pa ncreatic carcinoma cells. The amount of acetylated chloramphenicol was determined to show the presence and activity of cis-acting sequences. Results: The 5' flanking sequence functions as a promoter in all of c ell lines and contains negative regulatory and enhancer sequences. The minimal promoter is active in Chinese hamster ovary and HT-29, though not in MDAPanc-28 cells. The first intron contains a silencer capable of suppressing a heterologous promoter. Conclusions: The results show cis-acting sequences within and 5' to the NCA gene, which appear to p lay a role in the expression of this gene in malignant tissues. Some o f these sequences function in a cell type-specific manner. Further stu dies of these elements may provide insight into the mechanisms of the abnormal growth patterns of malignant cells.