Wnt signaling pathway involvement in genotypic and phenotypic variations in Waardenburg syndrome type 2 with MITF mutations

Abstract

Mutation in the gene encoding microphthalmia-associated transcription factor (MITF) lead to Waardenburg syndrome 2 (WS2), an autosomal dominantly inherited syndrome with auditory-pigmentary abnormalities, which is clinically and genetically heterogeneous. Haploinsufficiency may be the underlying mechanism for WS2. However, the mechanisms explaining the genotypic and phenotypic variations in WS2 caused by MITF mutations are unclear. A previous study revealed that MITF interacts with LEF-1, an important factor in the Wnt signaling pathway, to regulate its own transcription through LEF-1-binding sites on the MITF promoter. In this study, four different WS2-associated MITF mutations (p.R217I, p.R217G, p.R255X, p.R217del) that are associated with highly variable clinical features were chosen. According to the results, LEF-1 can activate the expression of MITF on its own, but MITF proteins inhibited the activation. This inhibition weakens when the dosage of MITF is reduced. Except for p.R217I, p.R255X, p.R217G, and p.R217del lose the ability to activate TYR completely and do not inhibit the LEF-1-mediated activation of the MITF-M promoter, and the haploinsufficiency created by mutant MITF can be overcome; correspondingly, the mutants’ associated phenotypes are less severe than that of p.R217I. The dominant negative of p.R217del made it have a second-most severe phenotype. This study’s data imply that MITF has a negative feedback loop of regulation to stabilize MITF gene dosage that involves the Wnt signaling pathway and that the interaction of MITF mutants with this pathway drives the genotypic and phenotypic differences observed in Waardenburg syndrome type 2 associated with MITF mutations.

Biology of human melanocyte development, Piebaldism, and Waardenburg syndrome

“…Wnt signaling (not show) is critical for melanocyte development by promoting the interaction between ß‐catenin with LEF 1/ TCF , which induces the MITF ‐M promotor . Furthermore, the b‐ HLH ‐Zip domain of MITF interacts with LEF ‐1, functioning as a nuclear mediator to attenuate MITF expression and regulating gene dosage (not shown) . PAX 3 and SOX 10 trans‐activate the MITF promoter, synergistically upregulating expression .…”

“…The primary mechanism of WS2 associated with MITF and SOX10 pathogenic variants appears to be related to haploinsufficiency, and the degree of phenotype severity may also be related to Wnt signaling. MITF pathogenic variants that do not effect LEF‐1 mediated activation of the M‐promotor appear to be associated with a mild phenotype . The most severe auditory‐pigmentary phenotype, represented by Tietz syndrome, are associated with dominant‐negative mutations in MITF or pathogenic variants that prevent LEF‐1 site activation (eg, MITF p.R217I) .…”

“…MITF pathogenic variants that do not effect LEF‐1 mediated activation of the M‐promotor appear to be associated with a mild phenotype . The most severe auditory‐pigmentary phenotype, represented by Tietz syndrome, are associated with dominant‐negative mutations in MITF or pathogenic variants that prevent LEF‐1 site activation (eg, MITF p.R217I) . Homozygous mutations in MITF also result in a severe phenotype characterized by coloboma, osteopetrosis, microphthalmia, macrocephaly, global hypopigmentation, and deafness (COMMAD) .…”

“…MITF pathogenic variants that do not effect LEF-1 mediated activation of the M-promotor appear to be associated with a mild phenotype. 103 result in a severe phenotype characterized by coloboma, osteopetrosis, microphthalmia, macrocephaly, global hypopigmentation, and deafness (COMMAD). 106 Similarly, the most severe phenotype associated with pathogenic variants of SOX10, characterized by the presence of neuropathy, result from truncated mutations neighboring or involving the last exon.…”

“…10,101 Furthermore, the b-HLH-Zip domain of MITF interacts with LEF-1, functioning as a nuclear mediator to attenuate MITF expression and regulating gene dosage (not shown). 103 PAX3 and SOX10 trans-activate the MITF promoter, synergistically upregulating expression. 2,113 MITF effector genes, including SNAI2, Bcl2, p16, and proteins of melanogenesis.…”