Two distinct mutations of the RET receptor causing Hirschsprung's disease impair the binding of signalling effectors to a multifunctional docking site

Abstract

The RET gene codes for a transmembrane tyrosine kinase which is a subunit of a multimeric complex that acts as a receptor for four structurally related molecules: the glial cell line-derived neurotrophic factor (GDNF), neurturin, artemin and persephin. Germline mutations of RET cause a dominantly inherited dysgenesis of the enteric nervous system known as Hirschsprung's disease (HSCR; aganglionosis megacolon). The majority of HSCR mutations results either in a reduction of dosage of the RET protein or in the loss of RET function. Two novel distinct mutations of RET that led either to the deletion of codon 1059 (denoted Delta1059) or to the substitution of a Pro for Leu1061 have been identified in five HSCR families. In one large pedigree, two children born from asymptomatic consanguineous parents presented a severe form of HSCR and were found to carry the mutation at codon 1061 in the homozygous state. A tyrosine residue at position 1062 is an intracytoplasmic docking site that enables RET to recruit several signalling molecules, including the Shc adaptor protein. We now report that both HSCR mutations impair the fixation of Shc to RET and consequently prevent its phosphorylation. In addition, quantitative analysis in PC12 cells reveals that mutation Delta1059 inactivates the ability of RET to transduce a downstream signal whereas mutation L1061P only partially inhibits the signalling of RET. Finally, we provide evidence that these effects are partly mediated via the disruption of the RET/Shc interaction. Collectively, these results demonstrate that HSCR can be ascribed to mutations of RET which interfere with the binding of transduction effectors, such as Shc, and further provide a biochemical explanation for the phenotype of patients carrying a homozygous mutation at codon 1061. Finally, these data indicate that Y1062 is a multifunctional docking site that confers to RET the capacity to engage downstream signalling pathways which exert a crucial role during enteric neurogenesis.