MYO3A Causes Human Dominant Deafness and Interacts with Protocadherin 15-CD2 Isoform

Abstract

Hereditary hearing loss is characterized by both allelic and locus genetic heterogeneity. Both recessive and dominant forms of hearing loss may be caused by different mutations in the same deafness gene. In a family with post-lingual progressive non-syndromic deafness, whole exome sequencing of genomic DNA from five hearing-impaired relatives revealed a single variant, p.Gly488Glu (rs145970949:G>A) in MYO3A, co-segregating with hearing loss as an autosomal dominant trait. This amino acid change, predicted to be pathogenic, alters a highly conserved residue in the motor domain of MYO3A. The mutation severely alters the ATPase activity and motility of the protein in vitro, and the mutant protein fails to accumulate in the filopodia tips in COS7 cells. However, the mutant MYO3A was able to reach the tips of organotypic inner ear culture hair cell stereocilia, raising the possibility of a local effect on positioning of the mechano-electrical transduction (MET) complex at the stereocilia tips. To address this hypothesis, we investigated the interaction of MYO3A with the cytosolic tail of the integral tip-link protein protocadherin 15 (PCDH15), a core component of MET complex. Interestingly, we uncovered a novel interaction between MYO3A and PCDH15 shedding new light on the function of myosin IIIA at stereocilia tips.

Impact of the Motor and Tail Domains of Class III Myosins on Regulating the Formation and Elongation of Actin Protrusions

“…MYO3 are not anticipated to function as dimers because they lack a predicted coiled-coil domain, and thus MYO3A is the first monomeric myosin determined to be capable of enhancing the formation of protrusions. The deafness-associated G488E MYO3A mutant, which does not tip localize in filopodia (COS7 cells), is not rescued in the presence of WT MYO3A and ESPN1 (25), supporting the idea that MYO3A is monomeric.…”

“…The findings from recent MYO3 studies (25,27,32,34) and an overall growing interest in the function of myosins in actinbased protrusions (8,39,46) demanded a systematic study of the functional differences of MYO3 motor and tail domains. Our results highlight the enhanced motor activity of human MYO3A compared with MYO3B, which correlates with its enhanced ability to localize to actin protrusion tips as well as induce the formation and elongation of actin protrusions.…”

“…Calycal processes are parallel actin-based microvillus-like protrusions in vertebrate photoreceptors. Mutations in human MYO3A are associated with non-syndromic hearing loss (DFNB30) (24,25).MYO3 isoforms contain an N-terminal kinase domain, a conserved motor domain, a neck region, and a class specific C-terminal tail domain (Fig. 1, A and B) (20).…”

“…Calycal processes are parallel actin-based microvillus-like protrusions in vertebrate photoreceptors. Mutations in human MYO3A are associated with non-syndromic hearing loss (DFNB30) (24,25).…”

Plasma Membrane Targeting of Protocadherin 15 Is Regulated by the Golgi-Associated Chaperone Protein PIST

“…PCDH15-CD1 also interacts with Myosin VIIA, and the stereociliary localization of PCDH15 is perturbed in myosin VIIA mutant mice [25]. Recently, PCDH15-CD2 was shown to interact with Myosin 3A, which might regulate the transportation of PCDH15 to stereociliary tips [26]. In the present work, we show that PCDH15-CD3, but not PCDH15-CD1 or PCDH15-CD2, interacts with PDZ domain-containing protein PIST, which might play an important role in the intracellular trafficking and plasma membrane targeting of PCDH15-CD3.…”