ORGANIZATION AND REGULATORY ASPECTS OF THE HUMAN INTESTINAL MUCIN GENE (MUC2) LOCUS

The human MUC2 gene maps to chromosome 11p15, where three additional m ucin genes have been located, and encodes the most abundant gastrointe stinal mucin normally expressed in the intestinal goblet cell lineage, However, in pathological conditions, including colorectal cancer, MUC 2 can be abnormally expressed. Therefore, it is of considerable intere st to understand the regulation of the MUC2 gene and how the mechanism is altered in colon cancer, Toward this goal, we have isolated a grou p of overlapping clones (contig) spanning 85 kilobases harboring the e ntire MUC2 locus, including sequences located upstream of the gene, De tection of two DNase I-hypersensitive sites in the 5' region of the MU C2 gene suggests the presence of DNA regulatory elements. To better ch aracterize this region, we have sequenced 12 kilobases of the upstream region and analyzed it for functional activity by cloning portions of it into a luciferase reporter vector and assaying for promoter/enhanc er activity using a transient transfection assay, A fragment from the AUG translational initiation codon +1 to -848 confers maximal transcri ptional activity in several intestinal cell lines, Elements located fu rther upstream exert a negative effect on the expression of the report er gene when tested in conjunction with homologous or heterologous pro moters, The same pattern of expression is observed when the MUC2/lucif erase constructs are transfected into HeLa cells, which do not express the endogenous MUC2 gene, However, the level of activity in HeLa cell s is at least an order of magnitude higher, suggesting that additional sequences singularly or in combination are responsible for the tissue - and cell lineage-specific expression of MUC2. Finally, we have ident ified an additional mucin-like gene (MUCX), located upstream of MUC2. We show that this MUCX gene, that is transcribed in opposite orientati on to that of MUC2, is expressed with a pattern distinct from that of MUC2, yet similar to that of MUC5B and MUC6, two additional mucin gene s located at chromosome 11p15. Recent information on the order of the mucin genes at chromosome 11p15 suggests that MUCX may be MUC6, one of the already identified mucin genes, or a novel one, yet to be fully c haracterized.