title: Endoplasmic reticulum stress and the unfolded protein response regulate genomic cystic fibrosis transmembrane conductance regulator expression.
abstract: The unfolded protein response (UPR) is a cellular recovery mechanism activated by endoplasmic reticulum (ER) stress. The UPR is coordinated with the ER-associated degradation (ERAD) to regulate the protein load at the ER. In the present study, we tested how membrane protein biogenesis is regulated through the UPR in epithelia, using the cystic fibrosis transmembrane conductance regulator (CFTR) as a model. Pharmacological methods such as proteasome inhibition and treatment with brefeldin A and tunicamycin were used to induce ER stress and activate the UPR as monitored by increased levels of spliced XBP1 and BiP mRNA. The results indicate that activation of the UPR is followed by a significant decrease in genomic CFTR mRNA levels without significant changes in the mRNA levels of another membrane protein, the transferrin receptor. We also tested whether overexpression of a wild-type CFTR transgene in epithelia expressing endogenous wild-type CFTR activated the UPR. Although CFTR maturation is inefficient in this setting, the UPR was not activated. However, pharmacological induction of ER stress in these cells also led to decreased endogenous CFTR mRNA levels without affecting recombinant CFTR message levels. These results demonstrate that under ER stress conditions, endogenous CFTR biogenesis is regulated by the UPR through alterations in mRNA levels and posttranslationally by ERAD, whereas recombinant CFTR expression is regulated only by ERAD.
authors.affiliation: Dept. of Cell Biology, Univ. of Alabama at Birmingham, 1918 Univ. Blvd., MCLM 760, Birmingham, AL 35294-0005, USA. bebok@uab.edu
authors.forename: András
authors.initials: A
authors.lastname: Rab
authors.forename: Rafal
authors.initials: R
authors.lastname: Bartoszewski
authors.forename: Asta
authors.initials: A
authors.lastname: Jurkuvenaite
authors.forename: John
authors.initials: J
authors.lastname: Wakefield
authors.forename: James F
authors.initials: JF
authors.lastname: Collawn
authors.forename: Zsuzsa
authors.initials: Z
authors.lastname: Bebok
mesh_terms: D017398:Alternative Splicing; D020126:Brefeldin A / Q000494:pharmacology; D015687:Cell Hypoxia; D002460:Cell Line; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D005786:Gene Expression Regulation; D015894:Genome, Human; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D017510:Protein Folding; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D014415:Tunicamycin / Q000494:pharmacology; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D011994:Recombinant Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D014415:Tunicamycin; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D020126:Brefeldin A