Interaction among SOX10 PAX3 and MITF, three genes altered in Waardenburg syndrome

Waardenburg syndrome (WS) is an autosomal dominant disorder with an inciden ce of 1 in 40 000 that manifests with sensorineural deafness and pigmentati on defects. It is classified into four types depending on the presence or a bsence of additional symptoms. WS1 and WS3 are due to mutations in the PAX3 gene whereas some WS2 cases are associated with mutations in the microphth almia-associated transcription factor (MITF) gene. The WS4 phenotype can re sult from mutations in the endothelin-B receptor gene (EDNRB), in the gene for its ligand, endothelin-3 (EDN3), or in the SOX10 gene. PAX3 has been sh own to regulate MITF gene expression. The recent implication of SOX10 in WS 4 prompted us to test whether this transcription factor, known to cooperate in vitro with PAX3, is also able to regulate expression from the MITF prom oter. Here we show that SOX10, in synergy with PAX3, strongly activates MIT F expression in transfection assays. Analyses revealed that PAX3 and SOX10 interact directly by binding to a proximal region of the MITF promoter cont aining binding sites for both factors. Moreover, SOX10 or PAX3 mutant prote ins fail to transactivate this promoter, providing further evidence that th e two genes act in concert to directly regulate expression of MITF, In situ hybridization experiments carried out in the dominant megacolon (Dom) mous e, confirmed that SOX10 dysfunction impairs Mitf expression as well as mela nocytic development and survival. These experiments, which demonstrate an i nteraction between three of the genes that are altered in WS, could explain the auditory-pigmentary symptoms of this disease.