title: BAG-1 stabilizes mutant F508del-CFTR in a ubiquitin-like-domain-dependent manner.
abstract: BACKGROUND
  Cystic Fibrosis Transmembrane Conductance Regulator (CFTR), the dysfunctional Cl(-) channel in Cystic Fibrosis, undergoes complex biosynthesis at the endoplasmic reticulum involving several molecular chaperones including Hsp70 and many co-chaperones. Bcl-2- associated athanogenes (BAGs) constitute a protein family sharing an Hsc70-binding domain. BAG-1 possesses an ubiquitin-like domain (Ub-LD) responsible for proteasomal association and for promoting substrate release from Hsc70/Hsp70 in vitro by accelerating the chaperone ATP/ADP exchange rate.
  
  
  METHODS
  Herein, we studied the in vivo effect of BAG-1 on the turnover and processing of wild type (wt)- and F508del-CFTR, the most frequent mutation in CF patients.
  
  
  RESULTS
  Results show that BAG-1 associates with both wt- and F508del-CFTR (in higher yields with the latter) through its Ub-LD and independently of Hsc70. Moreover, the immature form of F508del-CFTR (but not of wt-CFTR) is stabilized by BAG-1 overexpression, albeit in a cell-type specific way, without detectable maturation. Data also show that BAG-1 and the proteasome inhibitor ALLN are not additive on stabilizing F508del-CFTR and this effect depends on BAG-1 Ub-LD. Moreover, under BAG-1 overexpression, a reduction in ubiquitinylated-CFTR occurs suggesting that BAG-1 competes with Ub.
  
  
  CONCLUSIONS
  Overall, data are compatible with a mechanism in which BAG-1 stabilizes F508del-CFTR by direct binding, probably competing out ubiquitin to partially avoid its proteasomal degradation.
authors.affiliation: Department of Human Genetics, National Institute of Health, Lisboa, Portugal.
authors.forename: Filipa
authors.initials: F
authors.lastname: Mendes
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Farinha
authors.forename: Verónica
authors.initials: V
authors.lastname: Felício
authors.forename: Paulo C
authors.initials: PC
authors.lastname: Alves
authors.forename: Isabel
authors.initials: I
authors.lastname: Vieira
authors.forename: Margarida D
authors.initials: MD
authors.lastname: Amaral
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C091732:BCL2-associated athanogene 1 protein; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D050505:Mutant Proteins; D014157:Transcription Factors; D025801:Ubiquitin; C093349:cystic fibrosis transmembrane conductance regulator delta F508; D019005:Cystic Fibrosis Transmembrane Conductance Regulator