POU4F3, a member of the POU family of
transcription factors, commonly causes autosomal dominant
deafness. Exome sequencing was used to identify four novel variants in POU4F3 (NM_002700.2), including c.564dupA: p.Ala189SerfsTer26, c.743T > C:p.Leu248Pro, c.879C > A:p.Phe293Leu, and c.952G > A:p.Val318Met, and diverse aspects of the molecular consequences of their
protein expression, stability, subcellular localization, and transcriptional activity were investigated. The expression of three
mutant proteins, encoded by missense variants, was reduced compared to the wild-type
protein, demonstrating that the mutants were unstable and vulnerable to degradation. Additionally, all the
mutant proteins had distinct subcellular localization patterns. A
mutant protein carrying p.Ala189SerfsTer26, in which both mono- and bi-partite
nuclear localization signals were disrupted, showed abnormal subcellular localization. Resultantly, all the
mutant proteins significantly reduced the transcriptional activity required to regulate the downstream target gene expression. Furthermore, we identified the altered expression of 14 downstream target genes associated with inner ear development using patient-derived lymphoblastoid cell lines. There was a significant correlation of the expression profile between patient-derived cells and the cochlear hair cells, which provided a breakthrough for cases where the collection of human cochlear samples for transcriptome studies was unfeasible. This study expanded the genotypic spectrum of POU4F3 in
DFNA15, and further refined the molecular mechanisms underlying POU4F3-associated
DFNA15.