The DFNA5 gene, responsible for hearing loss and involved in cancer, encodes a novel apoptosis-inducing protein

Abstract

DFNA5 was first identified as a gene causing autosomal dominant hearing loss (HL). Different mutations have been found, all exerting a highly specific gain-of-function effect, in which skipping of exon 8 causes the HL. Later reports revealed the involvement of the gene in different types of cancer. Epigenetic silencing of DFNA5 in a large percentage of gastric, colorectal and breast tumors and p53-dependent transcriptional activity have been reported, concluding that DFNA5 acts as a tumor suppressor gene in different frequent types of cancer. Despite these data, the molecular function of DFNA5 has not been investigated properly. Previous transfection studies with mutant DFNA5 in yeast and in mammalian cells showed a toxic effect of the mutant protein, which was not seen after transfection of the wild-type protein. Here, we demonstrate that DFNA5 is composed of two domains, separated by a hinge region. The first region induces apoptosis when transfected in HEK293T cells, the second region masks and probably regulates this apoptosis inducing capability. Moreover, the involvement of DFNA5 in apoptosis-related pathways in a physiological setting was demonstrated through gene expression microarray analysis using Dfna5 knockout mice. In view of its important role in carcinogenesis, this finding is expected to lead to new insights on the role of apoptosis in many types of cancer. In addition, it provides a new line of evidence supporting an important role for apoptosis in monogenic and complex forms of HL. Keywords: tumor suppressor; hearing loss; apoptosis; dfna5; cancer; GSEA INTRODUCTION DFNA5 first was discovered in a Dutch family with autosomal dominant hearing loss (HL). 1 Not much was known concerning its cellular function and how its function was related to HL. Recently, a novel mutation in DFNA5 has been identified in a Korean family, totaling five families with DFNA5 HL. 2 These families all have different genomic DFNA5 mutations, but in each case the DFNA5 mRNA transcript skips exon 8, resulting in a frameshift and a premature truncation of the protein. [1][2][3][4][5] These findings have led to the hypothesis that DFNA5-associated HL is attributable to a highly specific gain-of-function mutation, in which skipping of one exon causes disease while mutations in other parts of this gene may not result in HL at all. Further experimental evidence for this hypothesis was provided by the finding that transfection of mutant DFNA5 causes cell death in both yeast 6 and mammalian 7 cells and by the discovery of a new DFNA5 mutation. 8 The latter mutation truncated the protein in the fifth exon, but did not segregate with HL and was present in family members with normal hearing. The hypothesis was further corroborated by a mouse that lacked the Dfna5 protein. This knockout (KO) mouse did not display any HL and, as a consequence, was not a suitable animal model to study DFNA5-associated HL. 9 To date, little information is available on the physiological function of DFNA5. However, since its identification, the small num...

Loss of conserved Gsdma3 self-regulation causes autophagy and cell death

“…Another homologue, deafness autosomal dominant non-syndromic sensorineural 5 (DFNA5) and GSDM share the conserved DFNA5-GSDM domain region (the N-terminal domain). Previous reports suggest that DFNA5 consists of two globular domains separated by a hinge region; the N-terminal domains display cell death induction activity, whereas the second domain might serve as a regulatory domain [44,45]. That report and the results presented in the present study ascribe a similar structure and conserved function to the GSDM family.…”

GSDMD membrane pore formation constitutes the mechanism of pyroptotic cell death

“…All gasdermins (GSDMA, GSDMB, GSDMC, and GSDMD in humans; GSDMA1‐3, GSDMC1‐4, and GSDMD in mice) are composed of a distinct N‐terminal and C‐terminal domain (Tanaka et al , 2013), a feature shared by the extended gasdermin family members DFNA5 and DFNB59 (deafness, autosomal‐dominant 5/autosomal‐recessive 59). Several lines of evidence suggest that the N‐terminal domain of other gasdermin family members is intrinsically cytotoxic (Saeki et al , 2007; Op de Beeck et al , 2011; Shi et al , 2015). Given the functional and sequence similarity between gasdermin N‐terminal domains, it is not surprising that all gasdermins induce membrane permeability pores and subsequent cell death (Ding et al, 2016).…”

Inflammasomes: mechanism of assembly, regulation and signalling

“…These dominant mutations map to the C-terminal domain, and Shi et al 4 recently demonstrated that they abrogate the interaction between the C-and N-terminal domains of GSDMA3, and that the N-terminal domain of this protein also induces pyroptosis. Interestingly, mutations in DFNA5 that result in exon skipping and premature truncation of the protein are associated with autosomal dominant hearing loss 128 . How truncated DFNA5 causes this pathology is unknown, but it might be linked to the induction of programmed cell death, as the truncated isoform (which contains the entire N-terminal domain) was shown to be cytotoxic 128 .…”

“…Interestingly, mutations in DFNA5 that result in exon skipping and premature truncation of the protein are associated with autosomal dominant hearing loss 128 . How truncated DFNA5 causes this pathology is unknown, but it might be linked to the induction of programmed cell death, as the truncated isoform (which contains the entire N-terminal domain) was shown to be cytotoxic 128 .…”