Clinical and molecular characterizations of novelPOU3F4mutations reveal that DFN3 is due to null function of POU3F4 protein

Abstract

UK. Clinical and molecular characterizations of novel POU3F4 mutations reveal that DFN3 is due to null function of POU3F4 protein. Physiol Genomics 39: 195-201, 2009. First published August 11, 2009 doi:10.1152/physiolgenomics.00100.2009.-X-linked deafness type 3 (DFN3), the most prevalent X-linked form of hereditary deafness, is caused by mutations in the POU3F4 locus, which encodes a member of the POU family of transcription factors. Despite numerous reports on clinical evaluations and genetic analyses describing novel POU3F4 mutations, little is known about how such mutations affect normal functions of the POU3F4 protein and cause inner ear malformations and deafness. Here we describe three novel mutations of the POU3F4 gene and their clinical characterizations in three Korean families carrying deafness segregating at the DFN3 locus. The three mutations cause a substitution (p.Arg329Pro) or a deletion (p.Ser310del) of highly conserved amino acid residues in the POU homeodomain or a truncation that eliminates both DNA-binding domains (p.Ala116fs). In an attempt to better understand the molecular mechanisms underlying their inner ear defects, we examined the behavior of the normal and mutant forms of the POU3F4 protein in C3H/10T1/2 mesodermal cells. Protein modeling as well as in vitro assays demonstrated that these mutations are detrimental to the tertiary structure of the POU3F4 protein and severely affect its ability to bind DNA. All three mutated POU3F4 proteins failed to transactivate expression of a reporter gene. In addition, all three failed to inhibit the transcriptional activity of wild-type proteins when both wildtype and mutant proteins were coexpressed. Since most of the mutations reported for DFN3 thus far are associated with regions that encode the DNA binding domains of POU3F4, our results strongly suggest that the deafness in DFN3 patients is largely due to the null function of POU3F4. hearing loss; X-linked deafness type 3; inner ear CONGENITAL HEARING LOSS IS one of the most common sensory disorders in humans, affecting approximately one in 1,000 newborns (24). More than 50% of the congenital hearing loss is due to genetic causes, and the majority of these hereditary cases are nonsyndromic. While most genetic nonsyndromic hearing loss is caused by mutations in autosomal genes, X-linked cases are estimated to comprise between 1 and 5% of these (26). Thus far, four different X-linked nonsyndromic hearing loss loci (DFN2, DFN3, DFN4, and DFN6) have been mapped, but the causative gene has been identified only for the DFN3 locus (33).X-linked deafness type 3 (DFN3) accounts for ϳ50% of all families carrying X-linked nonsyndromic hearing loss (26). Clinical characteristics of DFN3 in affected males include temporal bone abnormalities, stapes fixation, and, in most cases, a mixed type of hearing loss, which is often progressive (7,8,10). Anatomical anomalies of the temporal bone revealed by computer-assisted tomography (CT) include dilatation of the lateral end of the internal acoustic canal (IAC...

Octamer-binding transcription factors: genomics and functions

“…Strong evidence has linked mutations of Oct9 to DFN3, the most prevalent and hereditary X chromosome-linked hearing loss, which is characterized by conductive hearing loss and progressive sensorineural deafness (94-96, 190). These mutations include substitutions (e.g., Gly216Glu, Arg329Pro, Arg330Ser, and Arg323Gly), deletions (e.g., Ser310del) or truncations (e.g., Ala116fs).…”

A POU3F4 Mutation Causes Nonsyndromic Hearing Loss in a Chinese X-linked Recessive Family

“…The supposed improvement in bone conduction sensitivity could be concealed by a true sensorineural deafness following the disorder. [1526]…”

Novel and De Novo Mutations Extend Association of POU3F4 with Distinct Clinical and Radiological Phenotype of Hearing Loss

“…All but one of the identified POU3F4 mutations are predicted to truncate the protein and thus abolish or considerably impair its function. Most of them result in the loss of at least one POU homeodomain, an important part for protein-DNA interactions, with two NLS [23], while the p.Val324Asp mutation affects the NLS site at the carboxy terminus (Fig 3). In the whole analyzed group we didn’t find any deletions involving a part or the whole POU3F4 gene.…”