title: The silent codon change I507-ATC->ATT contributes to the severity of the ΔF508 CFTR channel dysfunction.
abstract: The most common disease-causing mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene is the out-of-frame deletion of 3 nucleotides (CTT). This mutation leads to the loss of phenylalanine-508 (ΔF508) and a silent codon change (SCC) for isoleucine-507 (I507-ATC→ATT). ΔF508 CFTR is misfolded and degraded by endoplasmic reticulum-associated degradation (ERAD). We have demonstrated that the I507-ATC→ATT SCC alters ΔF508 CFTR mRNA structure and translation dynamics. By comparing the biochemical and functional properties of the I507-ATT and I507-ATC ΔF508 CFTR, we establish that the I507-ATC→ATT SCC contributes to the cotranslational misfolding, ERAD, and to the functional defects associated with ΔF508 CFTR. We demonstrate that the I507-ATC ΔF508 CFTR is less susceptible to the ER quality-control machinery during translation than the I507-ATT, although 27°C correction is necessary for sufficient cell-surface expression. Whole-cell patch-clamp recordings indicate sustained, thermally stable cAMP-activated Cl(-) transport through I507-ATC and unstable function of the I507-ATT ΔF508 CFTR. Single-channel recordings reveal improved gating properties of the I507-ATC compared to I507-ATT ΔF508 CFTR (NPo=0.45±0.037 vs. NPo=0.09±0.002; P<0.001). Our results signify the role of the I507-ATC→ATT SCC in the ΔF508 CFTR defects and support the importance of synonymous codon choices in determining the function of gene products.
authors.affiliation: 2Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Blvd., MCLM 350A, Birmingham, AL 35294, USA. bebok@uab.edu.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Lazrak
authors.forename: Lianwu
authors.initials: L
authors.lastname: Fu
authors.forename: Vedrana
authors.initials: V
authors.lastname: Bali
authors.forename: Rafal
authors.initials: R
authors.lastname: Bartoszewski
authors.forename: Andras
authors.initials: A
authors.lastname: Rab
authors.forename: Viktoria
authors.initials: V
authors.lastname: Havasi
authors.forename: Steve
authors.initials: S
authors.lastname: Keiles
authors.forename: John
authors.initials: J
authors.lastname: Kappes
authors.forename: Ranjit
authors.initials: R
authors.lastname: Kumar
authors.forename: Elliot
authors.initials: E
authors.lastname: Lefkowitz
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Sorscher
authors.forename: Sadis
authors.initials: S
authors.lastname: Matalon
authors.forename: James F
authors.initials: JF
authors.lastname: Collawn
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Bebok
mesh_terms: D000200:Action Potentials; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003062:Codon; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D060746:Endoplasmic Reticulum-Associated Degradation; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D020125:Mutation, Missense; D020641:Polymorphism, Single Nucleotide; D014176:Protein Biosynthesis; D021381:Protein Transport; D059370:RNA Folding; D020871:RNA Stability; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism
chemical_list: D002712:Chlorides; D003062:Codon; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator
keywords: ABC protein; channel gating; cotranslational folding; patch-clamp; sSNP; single-nucleotide polymorphism
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