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

Okiyoneda, Tsukasa; Harada, Kumiko; Takeya, Motohiro; Yamahira, Kaori; Wada, Ikuo; Shuto, Tsuyoshi; Suico, Mary Ann; Hashimoto, Yoshiaki; Kai, Hirofumi

doi:10.1091/mbc.e03-06-0379

Cited by 90 publications

(89 citation statements)

References 66 publications

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“…This labeling pattern could be explained by the formation of an ␣ 1 -ATZ-calnexin complex that is not dissociated during the formation of inclusions, whereas KDEL-possessing soluble proteins are not associated with, or become dissociated from, ␣ 1 -ATZ before evolution into inclusions within the ER lumen or during movement out of the ER. These structures share some characteristics with the recently described ER quality control compartment or concentric membranous body, including membranous morphology and colocalization of ER membrane chaperone calnexin and mutant substrate proteins (38,39). Because proper function of the ER appears to be maintained while mutant proteins accumulate within these structures, they may constitute reservoirs of aberrant proteins similar to what has been attributed to aggresomes (40,41).…”

Section: Discussionmentioning

confidence: 69%

Intracellular Inclusions Containing Mutant α1-Antitrypsin Z Are Propagated in the Absence of Autophagic Activity

Kamimoto

Shoji

Hidvegi

et al. 2006

Journal of Biological Chemistry

255

261

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Mutant ␣ 1 -antitrypsin Z (␣ 1 -ATZ) protein, which has a tendency to form aggregated polymers as it accumulates within the endoplasmic reticulum of the liver cells, is associated with the development of chronic liver injury and hepatocellular carcinoma in hereditary ␣ 1 -antitrypsin (␣ 1 -AT) deficiency. Previous studies have suggested that efficient intracellular degradation of ␣ 1 -ATZ is correlated with protection from liver disease in ␣ 1 -AT deficiency and that the ubiquitin-proteasome system accounts for a major route, but not the sole route, of ␣ 1 -ATZ disposal. Yet another intracellular degradation system, autophagy, has also been implicated in the pathophysiology of ␣ 1 -AT deficiency. To provide genetic evidence for autophagy-mediated disposal of ␣ 1 -ATZ, here we used cell lines deleted for the Atg5 gene that is necessary for initiation of autophagy. In the absence of autophagy, the degradation of ␣ 1 -ATZ was retarded, and the characteristic cellular inclusions of ␣ 1 -ATZ accumulated. In wild-type cells, colocalization of the autophagosomal membrane marker GFP-LC3 and ␣ 1 -ATZ was observed, and this colocalization was enhanced when clearance of autophagosomes was prevented by inhibiting fusion between autophagosome and lysosome. By using a transgenic mouse with liver-specific inducible expression of ␣ 1 -ATZ mated to the GFP-LC3 mouse, we also found that expression of ␣ 1 -ATZ in the liver in vivo is sufficient to induce autophagy. These data provide definitive evidence that autophagy can participate in the quality control/degradative pathway for ␣ 1 -ATZ and suggest that autophagic degradation plays a fundamental role in preventing toxic accumulation of ␣ 1 -ATZ.3 a monomeric 394-amino acid glycoprotein, is synthesized and secreted primarily by liver cells. It is a prototypic member of serine protease inhibitor (serpin) superfamily proteins and the most abundant of the circulating serpins. The principal role of ␣ 1 -AT in serum is to protect lung tissues from destructive proteases (elastase, cathepsin G, and proteinase 3) released by neutrophils during inflammation. Some genetic alterations in ␣ 1 -AT are responsible for defective secretion and thus cause serum ␣ 1 -AT deficiency (1-3). The most common causal mutation found in Caucasian populations is the replacement of Glu-342 by Lys that characterizes the Z mutant of ␣ 1 -AT (␣ 1 -ATZ). This substitution is sufficient to cause an abnormality in folding early in the secretory pathway with retention of the mutant ␣ 1 -ATZ molecule in the ER of liver cells. Homozygotes for the ␣ 1 -ATZ mutation (PIZZ) are characterized by serum levels of ␣ 1 -AT that are ϳ10 -15% of those in the general population and are susceptible to two major target organ injuries. Destructive lung disease/emphysema in adults is due to a loss-of-function mechanism. Chronic liver disease often first discovered in childhood, but also affecting adults, is due to a gain-of-toxic-function mechanism in which liver cell injury results from the hepatotoxic effects of retained ␣ 1 -ATZ...

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Section: Discussionmentioning

confidence: 69%

Intracellular Inclusions Containing Mutant α1-Antitrypsin Z Are Propagated in the Absence of Autophagic Activity

Kamimoto

Shoji

Hidvegi

et al. 2006

Journal of Biological Chemistry

255

261

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“…OSER formation by these mutant proteins may in some way depend on their interaction with the ER chaperone calnexin [57][58][59]. However, the role of calnexin in OSER induction is unclear and deserves further investigation.…”

Section: Smooth Ermentioning

confidence: 99%

“…Regarding the implications for pathology, OSER has been observed to form in response to the expression of mutant, disease-causing proteins, like torsin A [56], ΔF-cystic fibrosis transmembrane conductance regulator (CFTR) [57] and mutant peripheral myelin protein-22 (PMP-22) [58], which are responsible for early onset generalized torsion dystonia, cystic fibrosis and inherited peripheral neuropathies (Dejerine Sottas syndrome and CharcotMarie-Tooth 1A), respectively. OSER formation by these mutant proteins may in some way depend on their interaction with the ER chaperone calnexin [57][58][59].…”

Section: Smooth Ermentioning

confidence: 99%

Endoplasmic reticulum architecture: structures in flux

Borgese

Francolini

Snapp

2006

Current Opinion in Cell Biology

206

147

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The endoplasmic reticulum (ER) is a dynamic pleiomorphic organelle containing continuous but distinct subdomains. The diversity of ER structures parallels its many functions, including secretory protein biogenesis, lipid synthesis, drug metabolism and Ca 2+ signaling. Recent studies are revealing how elaborate ER structures arise in response to subtle changes in protein levels, dynamics, and interactions as well as in response to alterations in cytosolic ion concentrations. Subdomain formation appears to be governed by principles of self-organization. Once formed, ER subdomains remain malleable and can be rapidly transformed into alternative structures in response to altered conditions. The mechanisms that modulate ER structure are likely to be important for the generation of the characteristic shapes of other organelles.

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“…In addition, analysis of calnexin's role in degradation of misfolded CFTR and CFTR⌬F508 has provided mixed results. Overexpression of calnexin results in the accumulation of ⌬F508 CFTR in the ER (Okiyoneda et al, 2004), but RNA interference (RNAi)-mediated decrease of calnexin levels or deletion of the calnexin gene does not inhibit degradation of wild-type (WT) or ⌬F508 CFTR (Farinha and Amaral, 2005;Okiyoneda et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Assembly and Misassembly of Cystic Fibrosis Transmembrane Conductance Regulator: Folding Defects Caused by Deletion of F508 Occur Before and After the Calnexin-dependent Association of Membrane Spanning Domain (MSD) 1 and MSD2

Rosser

Grove

Chen

et al. 2008

MBoC

115

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Cystic fibrosis transmembrane conductance regulator (CFTR) is a polytopic membrane protein that functions as a Cl ؊ channel and consists of two membrane spanning domains (MSDs), two cytosolic nucleotide binding domains (NBDs), and a cytosolic regulatory domain. Cytosolic 70-kDa heat shock protein (Hsp70), and endoplasmic reticulum-localized calnexin are chaperones that facilitate CFTR biogenesis. Hsp70 functions in both the cotranslational folding and posttranslational degradation of CFTR. Yet, the mechanism for calnexin action in folding and quality control of CFTR is not clear. Investigation of this question revealed that calnexin is not essential for CFTR or CFTR⌬F508 degradation. We identified a dependence on calnexin for proper assembly of CFTR's membrane spanning domains. Interestingly, efficient folding of NBD2 was also found to be dependent upon calnexin binding to CFTR. Furthermore, we identified folding defects caused by deletion of F508 that occurred before and after the calnexin-dependent association of MSD1 and MSD2. Early folding defects are evident upon translation of the NBD1 and R-domain and are sensed by the RMA-1 ubiquitin ligase complex. INTRODUCTIONCystic fibrosis transmembrane conductance regulator (CFTR) is a membrane glycoprotein that is localized to the apical surface of epithelial cells that line ducts of glands and airways. CFTR functions as an ATP-gated Cl Ϫ channel that is critical for proper hydration of the mucosal layer that lines lung airways (Welsh and Smith, 1993). Individuals who inherit two mutant forms of CFTR have exceedingly viscous mucous and, due to chronic lung infections, develop cystic fibrosis and often die from lung failure. CFTR is a member of the ATP-binding cassette (ABC) transporter superfamily (Hyde et al., 1990) and is a 1480-amino acid protein that contains two membrane spanning domains (MSDs), MSD1 and MSD2; two cytosolic nucleotide binding domains (NBDs), NBD1 and NBD2; and a regulatory (R) domain (Riordan et al., 1989). The proper folding and assembly of CFTR subdomains in the endoplasmic reticulum (ER) is required for CFTR to engage the COPII machinery and be packaged into vesicles for transport to the plasma membrane (Kopito, 1999;Wang et al., 2004). The folding pathway of this complex polytopic membrane protein has been a topic of great interest, because misfolding results in premature recognition of CFTR by the ER quality control system (ERQC) and degradation by the ubiquitin proteasome system (Skach, 2000). In fact, the most common disease-causing mutation of CFTR, ⌬F508CFTR, results in almost complete degradation of the protein by the ERQC system, which gives rise to a loss of function phenotype and lung disease (Ward and Kopito, 1994).The assembly of CFTR into an ion channel is complicated because it requires the coordinated folding and assembly of its membrane and cytoplasmic domains into a functional unit (Du et al., 2005;Riordan, 2005;Cui et al., 2007). CFTR is a modular protein, and its domains can collapse to a protease-resistant conformation i...

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

Cited by 90 publications

References 66 publications

Intracellular Inclusions Containing Mutant α1-Antitrypsin Z Are Propagated in the Absence of Autophagic Activity

Intracellular Inclusions Containing Mutant α1-Antitrypsin Z Are Propagated in the Absence of Autophagic Activity

Endoplasmic reticulum architecture: structures in flux

Assembly and Misassembly of Cystic Fibrosis Transmembrane Conductance Regulator: Folding Defects Caused by Deletion of F508 Occur Before and After the Calnexin-dependent Association of Membrane Spanning Domain (MSD) 1 and MSD2

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