title: Reduction of Cellular Expression Levels Is a Common Feature of Functionally Affected Pendrin (SLC26A4) Protein Variants.
abstract: Sequence alterations in the pendrin gene (SLC26A4) leading to functionally affected protein variants are frequently involved in the pathogenesis of syndromic and nonsyndromic deafness. Considering the high number ofSLC26A4sequence alterations reported to date, discriminating between functionally affected and unaffected pendrin protein variants is essential in contributing to determine the genetic cause of deafness in a given patient. In addition, identifying molecular features common to the functionally affected protein variants can be extremely useful to design future molecule-directed therapeutic approaches. Here we show the functional and molecular characterization of six previously uncharacterized pendrin protein variants found in a cohort of 58 Brazilian deaf patients. Two variants (p.T193I and p.L445W) were undetectable in the plasma membrane, completely retained in the endoplasmic reticulum and showed no transport function; four (p.P142L, p.G149R, p.C282Y and p.Q413R) showed reduced function and significant, although heterogeneous, expression levels in the plasma membrane. Importantly, total expression levels of all of the functionally affected protein variants were significantly reduced with respect to the wild-type and a fully functional variant (p.R776C), regardless of their subcellular localization. Interestingly, reduction of expression may also reduce the transport activity of variants with an intrinsic gain of function (p.Q413R). As reduction of overall cellular abundance was identified as a common molecular feature of pendrin variants with affected function, the identification of strategies to prevent reduction in expression levels may represent a crucial step of potential future therapeutic interventions aimed at restoring the transport activity of dysfunctional pendrin variants.
authors.affiliation: Center of Molecular Biology and Genetic Engineering (CBMEG), Molecular Biology Laboratory, State University of Campinas, UNICAMP, Campinas/São Paulo, Brazil.
authors.forename: Vanessa C S
authors.initials: VCS
authors.lastname: de Moraes
authors.affiliation: Institute of Pharmacology and Toxicology, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Bernardinelli
authors.affiliation: Center of Molecular Biology and Genetic Engineering (CBMEG), Molecular Biology Laboratory, State University of Campinas, UNICAMP, Campinas/São Paulo, Brazil.
authors.forename: Nathalia
authors.initials: N
authors.lastname: Zocal
authors.affiliation: Center of Molecular Biology and Genetic Engineering (CBMEG), Molecular Biology Laboratory, State University of Campinas, UNICAMP, Campinas/São Paulo, Brazil.
authors.forename: Jhonathan A
authors.initials: JA
authors.lastname: Fernandez
authors.affiliation: Institute of Pharmacology and Toxicology, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Charity
authors.initials: C
authors.lastname: Nofziger
authors.affiliation: Otology, Audiology and Implantable Ear Prostheses, State University of Campinas, UNICAMP, Campinas/São Paulo, Brazil.
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Castilho
authors.affiliation: Center of Molecular Biology and Genetic Engineering (CBMEG), Molecular Biology Laboratory, State University of Campinas, UNICAMP, Campinas/São Paulo, Brazil.
authors.forename: Edi L
authors.initials: EL
authors.lastname: Sartorato
authors.affiliation: Institute of Pharmacology and Toxicology, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Markus
authors.initials: M
authors.lastname: Paulmichl
authors.affiliation: Institute of Pharmacology and Toxicology, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Silvia
authors.initials: S
authors.lastname: Dossena