title: Pathogenetic role of the deafness-related M34T mutation of Cx26.
abstract: Mutations in the GJB2 gene, which encodes the gap junction protein connexin26 (Cx26), are the major cause of genetic non-syndromic hearing loss. The role of the allelic variant M34T in causing hereditary deafness remains controversial. By combining genetic, clinical, biochemical, electrophysiological and structural modeling studies, we have re-assessed the pathogenetic role of the M34T mutation. Genetic and audiological data indicate that the majority of heterozygous carriers and all five compound heterozygotes exhibited an impaired auditory function. Functional expression in transiently transfected HeLa cells showed that, although M34T was correctly synthesized and targeted to the plasma membrane, it inefficiently formed intercellular channels that displayed an abnormal electrical behavior and retained only 11% of the unitary conductance of the wild-type protein (HCx26wt). Moreover, M34T channels failed to support the intercellular diffusion of Lucifer Yellow and the spreading of mechanically induced intercellular Ca2+ waves. When co-expressed together with HCx26wt, M34T exerted dominant-negative effects on cell-cell coupling. Our findings are consistent with a structural model, predicting that the mutation leads to a constriction of the channel pore. These data support the view that M34T is a pathological variant of Cx26 associated with hearing impairment.
authors.affiliation: Dipartimento di Biochimica, Biofisica e Chimica delle Macromolecole, University of Trieste, and Servizio di Genetica Medica, IRCCS-Ospedale Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Bicego
authors.forename: Martina
authors.initials: M
authors.lastname: Beltramello
authors.forename: Salvatore
authors.initials: S
authors.lastname: Melchionda
authors.forename: Massimo
authors.initials: M
authors.lastname: Carella
authors.forename: Valeria
authors.initials: V
authors.lastname: Piazza
authors.forename: Leopoldo
authors.initials: L
authors.lastname: Zelante
authors.forename: Feliksas F
authors.initials: FF
authors.lastname: Bukauskas
authors.forename: Edoardo
authors.initials: E
authors.lastname: Arslan
authors.forename: Elona
authors.initials: E
authors.lastname: Cama
authors.forename: Sergio
authors.initials: S
authors.lastname: Pantano
authors.forename: Roberto
authors.initials: R
authors.lastname: Bruzzone
authors.forename: Paola
authors.initials: P
authors.lastname: D'Andrea
authors.forename: Fabio
authors.initials: F
authors.lastname: Mammano
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D019943:Amino Acid Substitution; D001298:Audiology; D020013:Calcium Signaling; D002648:Child; D002675:Child, Preschool; D004396:Coloring Agents / Q000737:chemistry / Q000493:pharmacokinetics; D000072259:Connexin 26; D017630:Connexins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D003638:Deafness / Q000235:genetics*; D005260:Female; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006367:HeLa Cells; D006801:Humans; D015640:Ion Channel Gating; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: D004396:Coloring Agents; D017630:Connexins; C000607042:GJB2 protein, human; D000072259:Connexin 26