A heterozygous mutation in GJB2 (Cx26F142L) associated with deafness and recurrent skin rashes results in connexin assembly deficiencies
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Background: Mutations in GJB2 encoding Connexin26 (CX26) are associated with hearing loss and hyperproliferative skin disorders of differing severity including Keratitis Ichthyosis Deafness (KID) and Vohwinkel syndrome. A 6-year-old Caucasian girl who presented with recurrent skin rashes and sensorineural hearing loss harbored a heterozygous point mutation in GJB2 (c.424T>C; p.F142L).
Objectives: To characterise the impact of CX26F142L on cellular events.
Methods: Plasmids CX26WT, CX26F142L, CX26G12R (KID) or CX26D66H (Vohwinkel) were transfected into HeLa cells expressing Cx26 or Cx43, or into HaCaT cells, a model keratinocyte cell line. Confocal microscopy determined protein localisation. MTT assays assessed cell viability in the presence or absence of Carbenoxolone, a connexin-channel blocker. Co-immunoprecipitation/western blot analysis determined Cx43:Cx26 interactions. Quantitative Real-Time-Polymerase Chain Reaction assessed changes in gene expression of ER stress markers. Dye uptake assays determined Connexin-channel functionality.
Results: F142L and G12R were restricted to perinuclear areas. Collapse of the microtubule network, rescued by co-treatment with Paclitaxel, occurred. ER stress was not involved. Cell viability was reduced in cells expressing F142L and G12R but not D66H. Unlike G12R that forms 'leaky' hemichannels F142L had restricted permeability. Cell viability of F142L and G12R transfected cells was greater in HeLa cells expressing Cx43 than in native Cx-free HeLa cells. Co-immunoprecipitation suggested a possible interaction between Cx43 and the three mutations.
Conclusion: Expression of CX26F142L and G12R result in microtubule collapse, rescued by interaction with Cx43. The GJB2 mutations interacted with Cx43 suggesting that unique Cx43:Cx26 channels are central to the diverse phenotype of CX26 skin-related channelopathies.
Keywords: Connexin channelopathy; GJB2 mutation; hyperproliferative skin disorder; keratitis ichthyosis deafness.
