scholarly journals Control of cystic fibrosis transmembrane conductance regulator membrane trafficking: not just from the endoplasmic reticulum to the Golgi

FEBS Journal ◽  
2013 ◽  
Vol 280 (18) ◽  
pp. 4396-4406 ◽  
Author(s):  
Carlos M. Farinha ◽  
Paulo Matos ◽  
Margarida D. Amaral
Keyword(s):  
Cystic Fibrosis ◽  
Endoplasmic Reticulum ◽  
Membrane Trafficking ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Cystic Fibrosis Transmembrane

scholarly journals ΔF508 CFTR Pool in the Endoplasmic Reticulum Is Increased by Calnexin Overexpression

2004 ◽  
Vol 15 (2) ◽  
pp. 563-574 ◽  
Author(s):  
Tsukasa Okiyoneda ◽  
Kazutsune Harada ◽  
Motohiro Takeya ◽  
Kaori Yamahira ◽  
Ikuo Wada ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Endoplasmic Reticulum ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Δf508 Cftr ◽  
Ubiquitin Proteasome ◽  
Proteasome Pathway ◽  
Cystic Fibrosis Transmembrane ◽  
Erad Pathway

The most common cystic fibrosis transmembrane conductance regulator (CFTR) mutant in cystic fibrosis patients, ΔF508 CFTR, is retained in the endoplasmic reticulum (ER) and is consequently degraded by the ubiquitin-proteasome pathway known as ER-associated degradation (ERAD). Because the prolonged interaction of ΔF508 CFTR with calnexin, an ER chaperone, results in the ERAD of ΔF508 CFTR, calnexin seems to lead it to the ERAD pathway. However, the role of calnexin in the ERAD is controversial. In this study, we found that calnexin overexpression partially attenuated the ERAD of ΔF508 CFTR. We observed the formation of concentric membranous bodies in the ER upon calnexin overexpression and that the ΔF508 CFTR but not the wild-type CFTR was retained in the concentric membranous bodies. Furthermore, we observed that calnexin overexpression moderately inhibited the formation of aggresomes accumulating the ubiquitinated ΔF508 CFTR. These findings suggest that the overexpression of calnexin may be able to create a pool of ΔF508 CFTR in the ER.

scholarly journals The endoplasmic reticulum–associated Hsp40 DNAJB12 and Hsc70 cooperate to facilitate RMA1 E3–dependent degradation of nascent CFTRΔF508

2011 ◽  
Vol 22 (3) ◽  
pp. 301-314 ◽  
Author(s):  
Diane E. Grove ◽  
Chun-Yang Fan ◽  
Hong Yu Ren ◽  
Douglas M. Cyr
Keyword(s):  
Cystic Fibrosis ◽  
Endoplasmic Reticulum ◽  
Protein Quality ◽  
Transmembrane Conductance Regulator ◽  
Folding Kinetics ◽  
Transmembrane Conductance ◽  
Life And Death ◽  
Native Proteins ◽  
Versus Protein ◽  
Cystic Fibrosis Transmembrane

Relative contributions of folding kinetics versus protein quality control (QC) activity in the partitioning of non-native proteins between life and death are not clear. Cystic fibrosis transmembrane conductance regulator (CFTR) biogenesis serves as an excellent model to study this question because folding of nascent CFTR is inefficient and deletion of F508 causes accumulation of CFTRΔF508 in a kinetically trapped, but foldable state. Herein, a novel endoplasmic reticulum (ER)-associated Hsp40, DNAJB12 (JB12) is demonstrated to play a role in control of CFTR folding efficiency. JB12 cooperates with cytosolic Hsc70 and the ubiquitin ligase RMA1 to target CFTR and CFTRΔF508 for degradation. Modest elevation of JB12 decreased nascent CFTR and CFTRΔF508 accumulation while increasing association of Hsc70 with ER forms of CFTR and the RMA1 E3 complex. Depletion of JB12 increased CFTR folding efficiency up to threefold and permitted a pool of CFTRΔF508 to fold and escape the ER. Introduction of the V510D misfolding suppressor mutation into CFTRΔF508 modestly increased folding efficiency, whereas combined inactivation of JB12 and suppression of intrinsic folding defects permitted CFTRΔF508 to fold at 50% of wild-type efficiency. Therapeutic correction of CFTRΔF508 misfolding in cystic fibrosis patients may require repair of defective folding kinetics and suppression of ER QC factors, such as JB12.

Correctors promote folding of the CFTR in the endoplasmic reticulum

2008 ◽  
Vol 413 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Tip W. Loo ◽  
M. Claire Bartlett ◽  
David M. Clarke
Keyword(s):  
Cystic Fibrosis ◽  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Cross Linking ◽  
Transmembrane Conductance Regulator ◽  
Native Structure ◽  
Transmembrane Conductance ◽  
Mutant Proteins ◽  
Regulator Protein ◽  
Cystic Fibrosis Transmembrane

Cystic fibrosis (CF) is most commonly caused by deletion of a residue (ΔF508) in the CFTR (cystic fibrosis transmembrane conductance regulator) protein. The misfolded mutant protein is retained in the ER (endoplasmic reticulum) and is not trafficked to the cell surface (misprocessed mutant). Corrector molecules such as corr-2b or corr-4a are small molecules that increase the amount of functional CFTR at the cell surface. Correctors may function by stabilizing CFTR at the cell surface or by promoting folding in the ER. To test whether correctors promoted folding of CFTR in the ER, we constructed double-cysteine CFTR mutants that would be retained in the ER and only undergo cross-linking when the protein folds into a native structure. The mature form, but not the immature forms, of M348C(TM6)/T1142C(TM12) (where TM is transmembrane segment), T351C(TM6)/T1142C(TM12) and W356C(TM6)/W1145C(TM12) mutants were efficiently cross-linked. Mutations to the COPII (coatamer protein II) exit motif (Y563KDAD567) were then made in the cross-linkable cysteine mutants to prevent the mutant proteins from leaving the ER. Membranes were prepared from the mutants expressed in the absence or presence of correctors and subjected to disulfide cross-linking analysis. The presence of correctors promoted folding of the mutants as the efficiency of cross-linking increased from approx. 2–5% to 22–35%. The results suggest that correctors interact with CFTR in the ER to promote folding of the protein into a native structure.

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