title: N-Alpha-Acetyltransferases and Regulation of CFTR Expression.
abstract: The majority of cystic fibrosis (CF)-causing mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) lead to the misfolding, mistrafficking, and degradation of the mutant protein. Inhibition of degradation does not effectively increase the amount of trafficking competent CFTR, but typically leads to increased ER retention of misfolded forms. Thus, the initial off pathway steps occur early in the processing of the protein. To identify proteins that interact with these early forms of CFTR, in vitro crosslink experiments identified cotranslational partners of the nascent chain of the severe misfolded mutant, G85E CFTR. The mutant preferentially interacts with a subunit of an N-alpha-acetyltransferase A. Based on recent reports that acetylation of the N-termini of some N-end rule substrates control their ubiquitination and subsequent degradation, a potential role for this modification in regulation of CFTR expression was assessed. Knockdown experiments identified two complexes, which affect G85E CFTR proteins levels, NatA and NatB. Effects of the knockdowns on mRNA levels, translation rates, and degradation rates established that the two complexes regulate G85E CFTR through two separate mechanisms. NatA acts indirectly by regulating transcription levels and NatB acts through a previously identified, but incompletely understood posttranslational mechanism. This regulation did not effect trafficking of G85E CFTR, which remains retained in the ER, nor did it alter the degradation rate of CFTR. A mutation predicted to inhibit N-terminal acetylation of CFTR, Q2P, was without effect, suggesting neither system acts directly on CFTR. These results contradict the prediction that N-terminal acetylation of CFTR determines its fitness as a proteasome substrate, but rather NatB plays a role in the conformational maturation of CFTR in the ER through actions on an unidentified protein.
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
authors.forename: Ali J
authors.initials: AJ
authors.lastname: Vetter
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
authors.forename: Andrey L
authors.initials: AL
authors.lastname: Karamyshev
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
authors.forename: Anna E
authors.initials: AE
authors.lastname: Patrick
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
authors.forename: Henry
authors.initials: H
authors.lastname: Hudson
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Thomas
mesh_terms: D003550:Cystic Fibrosis / Q000235:genetics / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D005786:Gene Expression Regulation; D046912:Multiprotein Complexes / Q000378:metabolism; D009154:Mutation; D063206:N-Terminal Acetyltransferases / Q000378:metabolism*; D011485:Protein Binding; D014176:Protein Biosynthesis; D054730:Protein Interaction Domains and Motifs; D011499:Protein Processing, Post-Translational; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D046912:Multiprotein Complexes; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D063206:N-Terminal Acetyltransferases