Gene Mutation, Function and Cellular Localization of Endothelin-B Receptor in a Case of Hirschsprung\u27s Disease

Hirschsprung\u27s disease (HSCR) is characterized by a congenital absence of enteric ganglia in the distal colon and a failure of gastrointestinal tract innervation. Recently, one of the susceptibility loci of HSCR was mapped to human chromosome 13q22, which includes the endothelin-B (ETB) receptor gene. In analyzing the ETB receptor cDNA in patients with HSCR, a point mutation of exon 4 and a deletion of exon 5 were recognized in one of three cases studied. The wild and mutant receptor cDNA were cloned and transfected into murine fibroblast L cells, and compared in terms of binding ability and cellular localization. An [^I]-endothelin (ET)-1 binding study using intact cells showed that the mutant receptor can not bind with ET-1. By constructing a c-myc-tagged receptor, immunohistochemical analysis confirmed that the mutant receptor can be expressed as a protein. Furthermore, the immunohistochemical study showed a marked difference in cellular localization between the wild and mutant receptors; the wild type ETB receptor is localized on the cell surface whereas the mutant receptor has a diffuse intracellular distribution. These results suggest that the structural alteration of the ETB receptor observed in this HSCR case may result in changes in the cellular localization and binding capacity of the receptor, such that the mutant receptor can not transduce the ET signal. The present study illustrates one of the potential molecular genetic mechanisms underlying HSCR