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Mao L, Wang Y, An L, Zeng B, Wang Y, Frishman D, Liu M, Chen Y, Tang W, Xu H. Molecular Mechanisms and Clinical Phenotypes of GJB2 Missense Variants. BIOLOGY 2023; 12:biology12040505. [PMID: 37106706 PMCID: PMC10135792 DOI: 10.3390/biology12040505] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 01/19/2023] [Accepted: 01/20/2023] [Indexed: 03/29/2023]
Abstract
The GJB2 gene is the most common gene responsible for hearing loss (HL) worldwide, and missense variants are the most abundant type. GJB2 pathogenic missense variants cause nonsyndromic HL (autosomal recessive and dominant) and syndromic HL combined with skin diseases. However, the mechanism by which these different missense variants cause the different phenotypes is unknown. Over 2/3 of the GJB2 missense variants have yet to be functionally studied and are currently classified as variants of uncertain significance (VUS). Based on these functionally determined missense variants, we reviewed the clinical phenotypes and investigated the molecular mechanisms that affected hemichannel and gap junction functions, including connexin biosynthesis, trafficking, oligomerization into connexons, permeability, and interactions between other coexpressed connexins. We predict that all possible GJB2 missense variants will be described in the future by deep mutational scanning technology and optimizing computational models. Therefore, the mechanisms by which different missense variants cause different phenotypes will be fully elucidated.
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Affiliation(s)
- Lu Mao
- Precision Medicine Center, Academy of Medical Science, Zhengzhou University, Zhengzhou 450052, China
| | - Yueqiang Wang
- Basecare Medical Device Co., Ltd., Suzhou 215000, China
| | - Lei An
- Translational Medicine Center, Huaihe Hospital of Henan University, Kaifeng 475000, China
| | - Beiping Zeng
- Precision Medicine Center, Academy of Medical Science, Zhengzhou University, Zhengzhou 450052, China
| | - Yanyan Wang
- The Research and Application Center of Precision Medicine, The Second Affiliated Hospital of Zhengzhou University, Zhengzhou 450014, China
| | - Dmitrij Frishman
- Wissenschaftszentrum Weihenstephan, Technische Universitaet Muenchen, Am Staudengarten 2, 85354 Freising, Germany
| | - Mengli Liu
- Precision Medicine Center, Academy of Medical Science, Zhengzhou University, Zhengzhou 450052, China
| | - Yanyu Chen
- Precision Medicine Center, Academy of Medical Science, Zhengzhou University, Zhengzhou 450052, China
| | - Wenxue Tang
- The Research and Application Center of Precision Medicine, The Second Affiliated Hospital of Zhengzhou University, Zhengzhou 450014, China
| | - Hongen Xu
- Precision Medicine Center, Academy of Medical Science, Zhengzhou University, Zhengzhou 450052, China
- The Research and Application Center of Precision Medicine, The Second Affiliated Hospital of Zhengzhou University, Zhengzhou 450014, China
- Correspondence:
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Ambrosi C, Walker AE, DePriest AD, Cone AC, Lu C, Badger J, Skerrett IM, Sosinsky GE. Analysis of trafficking, stability and function of human connexin 26 gap junction channels with deafness-causing mutations in the fourth transmembrane helix. PLoS One 2013; 8:e70916. [PMID: 23967136 PMCID: PMC3744544 DOI: 10.1371/journal.pone.0070916] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Accepted: 06/25/2013] [Indexed: 01/24/2023] Open
Abstract
Human Connexin26 gene mutations cause hearing loss. These hereditary mutations are the leading cause of childhood deafness worldwide. Mutations in gap junction proteins (connexins) can impair intercellular communication by eliminating protein synthesis, mis-trafficking, or inducing channels that fail to dock or have aberrant function. We previously identified a new class of mutants that form non-functional gap junction channels and hemichannels (connexons) by disrupting packing and inter-helix interactions. Here we analyzed fourteen point mutations in the fourth transmembrane helix of connexin26 (Cx26) that cause non-syndromic hearing loss. Eight mutations caused mis-trafficking (K188R, F191L, V198M, S199F, G200R, I203K, L205P, T208P). Of the remaining six that formed gap junctions in mammalian cells, M195T and A197S formed stable hemichannels after isolation with a baculovirus/Sf9 protein purification system, while C202F, I203T, L205V and N206S formed hemichannels with varying degrees of instability. The function of all six gap junction-forming mutants was further assessed through measurement of dye coupling in mammalian cells and junctional conductance in paired Xenopus oocytes. Dye coupling between cell pairs was reduced by varying degrees for all six mutants. In homotypic oocyte pairings, only A197S induced measurable conductance. In heterotypic pairings with wild-type Cx26, five of the six mutants formed functional gap junction channels, albeit with reduced efficiency. None of the mutants displayed significant alterations in sensitivity to transjunctional voltage or induced conductive hemichannels in single oocytes. Intra-hemichannel interactions between mutant and wild-type proteins were assessed in rescue experiments using baculovirus expression in Sf9 insect cells. Of the four unstable mutations (C202F, I203T, L205V, N206S) only C202F and N206S formed stable hemichannels when co-expressed with wild-type Cx26. Stable M195T hemichannels displayed an increased tendency to aggregate. Thus, mutations in TM4 cause a range of phenotypes of dysfunctional gap junction channels that are discussed within the context of the X-ray crystallographic structure.
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Affiliation(s)
- Cinzia Ambrosi
- National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, University of California San Diego, La Jolla, California, United States of America
| | - Amy E. Walker
- National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, University of California San Diego, La Jolla, California, United States of America
| | - Adam D. DePriest
- Biology Department, State University of New York Buffalo State, Buffalo, New York, United States of America
| | - Angela C. Cone
- National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, University of California San Diego, La Jolla, California, United States of America
| | - Connie Lu
- National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, University of California San Diego, La Jolla, California, United States of America
| | - John Badger
- DeltaG Technologies, San Diego, California, United States of America
| | - I. Martha Skerrett
- Biology Department, State University of New York Buffalo State, Buffalo, New York, United States of America
| | - Gina E. Sosinsky
- National Center for Microscopy and Imaging Research, Center for Research in Biological Systems, University of California San Diego, La Jolla, California, United States of America
- Department of Neurosciences, University of California San Diego, La Jolla, California, United States of America
- * E-mail:
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Yilmaz A, Menevse S, Bayazit Y, Karamert R, Ergin V, Menevse A. Two Novel Missense Mutations in the Connexin 26 Gene in Turkish Patients with Nonsyndromic Hearing Loss. Biochem Genet 2009; 48:248-56. [DOI: 10.1007/s10528-009-9314-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Accepted: 08/21/2009] [Indexed: 11/28/2022]
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Hoang Dinh E, Ahmad S, Chang Q, Tang W, Stong B, Lin X. Diverse deafness mechanisms of connexin mutations revealed by studies using in vitro approaches and mouse models. Brain Res 2009; 1277:52-69. [PMID: 19230829 DOI: 10.1016/j.brainres.2009.02.008] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2009] [Revised: 02/01/2009] [Accepted: 02/04/2009] [Indexed: 12/12/2022]
Abstract
Mutations in connexins (Cxs), the constitutive protein subunits of gap junction (GJ) intercellular channels, are one of the most common human genetic defects that cause severe prelingual non-syndromic hearing impairments. Many subtypes of Cxs (e.g., Cxs 26, 29, 30, 31, 43) and pannexins (Panxs) are expressed in the cochlea where they contribute to the formation of a GJ-based intercellular communication network. Cx26 and Cx30 are the predominant cochlear Cxs and they co-assemble in most GJ plaques to form hybrid GJs. The cellular localization of specific Cx subtypes provides a basis for understanding the molecular structure of GJs and hemichannels in the cochlea. Information about the interactions among the various co-assembled Cx partners is critical to appreciate the functional consequences of various types of genetic mutations. In vitro studies of reconstituted GJs in cell lines have yielded surprisingly heterogeneous mechanisms of dysfunction caused by various Cx mutations. Availability of multiple lines of Cx-mutant mouse models has provided some insight into the pathogenesis processes in the cochlea of deaf mice. Here we summarize recent advances in understanding the structure and function of cochlear GJs and give a critical review of current findings obtained from both in vitro studies and mouse models on the mechanisms of Cx mutations that lead to cell death in the cochlea and hearing loss.
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Affiliation(s)
- Emilie Hoang Dinh
- Department of Otolaryngology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322-3030, USA
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