Functional characterization of three mutations of the endothelin B receptor gene in patients with Hirschsprung's disease: evidence for selective loss of Gi coupling.

BACKGROUND Hirschsprung's disease (HSCR) is one the most common congenital intestinal disease. It leads to aganglionic megacolon in the early childhood. Several susceptibility genes have been identified : RET protooncogene and its ligand, glial cell derived neutrophic factor (GDNF), Sox 10, Endothelin-3 (EDN3) and its receptor B (EDNRB). EDNRB mutations are found in 5% of familial or sporadic HSCR. Only few EDNRB mutations found in HSCR have been explored and some of them seem to be non fonctional variants. MATERIALS AND METHODS The properties of three mutant human endothelin B receptor (hETB) (G57S, R319W and P383L) in isolated HSCR were analyzed. Stable recombinant cells expressing the three mutants and the wild-type (WT) were established. The hETB receptors were characterized for 125I ET-1 binding, ET-1 induced signaling: calcium transient, AP-1 transcriptional factor activation and cAMP accumulation. RESULTS Immunofluorescence experiments showed normal cellular distributions of the mutant G57S, R319W and WT hETB receptors. In contrast, the P383L hETB mutant receptor was concentrated near the nucleus and essentially no ET-1 binding was detected. The two other mutants (G57S and R319W) bound ET-1 normally, induced calcium transients and activated the AP-1 pathway in the same way as wild type, but did not inhibit adenylate cyclase. The G57S hETB mutant even stimulated cAMP accumulation which was blocked by pertussis toxin. CONCLUSION The absence of the P383L mutant receptor from the membrane clearly indicates that this mutation could be involved in HSCR. The G57S and R319W mutant receptors, despite their normal coupling to Gaq, have a defect in the Galphai signaling pathway and the G57S mutation couples to Galphas. These observations allow us to hypothesize that cAMP signaling might be involved in the differenciation of neural cells in the bowel.