scholarly journals Inhibiting Endoplasmic Reticulum (ER)-associated Degradation of Misfolded Yor1p Does Not Permit ER Export Despite the Presence of a Diacidic Sorting Signal

2007 ◽  
Vol 18 (9) ◽  
pp. 3398-3413 ◽  
Author(s):  
Silvere Pagant ◽  
Leslie Kung ◽  
Mariana Dorrington ◽  
Marcus C.S. Lee ◽  
Elizabeth A. Miller
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Secretory Pathway ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Er Quality Control ◽  
Er Retention ◽  
Copii Vesicles ◽  
Er Export ◽  
Cystic Fibrosis Transmembrane

Capture of newly synthesized proteins into endoplasmic reticulum (ER)-derived coat protomer type II (COPII) vesicles represents a critical juncture in the quality control of protein biogenesis within the secretory pathway. The yeast ATP-binding cassette transporter Yor1p is a pleiotropic drug pump that shows homology to the human cystic fibrosis transmembrane conductance regulator (CFTR). Deletion of a phenylalanine residue in Yor1p, equivalent to the major disease-causing mutation in CFTR, causes ER retention and degradation via ER-associated degradation. We have examined the relationship between protein folding, ERAD and forward transport during Yor1p biogenesis. Uptake of Yor1p into COPII vesicles is mediated by an N-terminal diacidic signal that likely interacts with the “B-site” cargo-recognition domain on the COPII subunit, Sec24p. Yor1p-ΔF is subjected to complex ER quality control involving multiple cytoplasmic chaperones and degradative pathways. Stabilization of Yor1p-ΔF by inhibiting its degradation does not permit access of Yor1p-ΔF to COPII vesicles. We propose that the ER quality control checkpoint engages misfolded Yor1p even after it has been stabilized by inhibition of the degradative pathway.

scholarly journals Limited ER quality control for GPI-anchored proteins

2016 ◽  
Vol 213 (6) ◽  
pp. 693-704 ◽  
Author(s):  
Natalia Sikorska ◽  
Leticia Lemus ◽  
Auxiliadora Aguilera-Romero ◽  
Javier Manzano-Lopez ◽  
Howard Riezman ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Protein Folding ◽  
Misfolded Proteins ◽  
Control Mechanisms ◽  
Gpi Anchor ◽  
Er Quality Control ◽  
Entire Class ◽  
Er Export ◽  
Export Signal

Endoplasmic reticulum (ER) quality control mechanisms target terminally misfolded proteins for ER-associated degradation (ERAD). Misfolded glycophosphatidylinositol-anchored proteins (GPI-APs) are, however, generally poor ERAD substrates and are targeted mainly to the vacuole/lysosome for degradation, leading to predictions that a GPI anchor sterically obstructs ERAD. Here we analyzed the degradation of the misfolded GPI-AP Gas1* in yeast. We could efficiently route Gas1* to Hrd1-dependent ERAD and provide evidence that it contains a GPI anchor, ruling out that a GPI anchor obstructs ERAD. Instead, we show that the normally decreased susceptibility of Gas1* to ERAD is caused by canonical remodeling of its GPI anchor, which occurs in all GPI-APs and provides a protein-independent ER export signal. Thus, GPI anchor remodeling is independent of protein folding and leads to efficient ER export of even misfolded species. Our data imply that ER quality control is limited for the entire class of GPI-APs, many of them being clinically relevant.

cAMP- but not Ca(2+)-regulated Cl- conductance is lacking in cystic fibrosis mice epididymides and seminal vesicles

1996 ◽  
Vol 271 (1) ◽  
pp. C188-C193 ◽  
Author(s):  
A. Y. Leung ◽  
P. Y. Wong ◽  
J. R. Yankaskas ◽  
R. C. Boucher
Keyword(s):  
Cystic Fibrosis ◽  
Secretory Pathway ◽  
Short Circuit ◽  
Primary Cultures ◽  
Seminal Vesicles ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Cl Secretion ◽  
Induced Changes ◽  
Cystic Fibrosis Transmembrane

Cystic fibrosis (CF) reflects the loss of adenosine 3',5'-cyclic monophosphate (cAMP)-regulated Cl- secretion consequent to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In humans, but not mice, with CF, the disease is associated with male infertility. The present study investigated the relative magnitudes of the cAMP pathways and an alternative Ca(2+)-regulated Cl- secretory pathway in primary cultures of the epididymides and the seminal vesicles of normal and CF mice. The basal equivalent short-circuit currents (Ieq) of cultures derived from the epididymides and the seminal vesicles from the CF mice were lower (6.0 +/- 0.6 and 4.0 +/- 1.0 muA/cm2, respectively) than those from normal mice (11.1 +/- 1.0 and 6.6 +/- 0.6 muA/cm2, respectively). Forskolin induced significant Ieq responses in both the epididymis (8.0 +/- 0.7 muA/cm2) and seminal vesicles (4.0 +/- 0.5 muA/cm2) from normal mice, whereas forskolin-induced changes in Ieq in CF mouse epididymis and seminal vesicles were absent, consistent with defective cAMP-CFTR-mediated Cl- secretion in CF mice. Ieq responses to agonists (ionomycin, ATP) that raise intracellular Ca2+ (Ca2+i) were larger than forskolin responses in normal animals (6.6 +/- 0.9 and 13.4 +/- 1.8 muA/cm2, respectively) and were preserved in CF (6.5 +/- 0.9 and 17.1 +/- 1.0 muA/cm2, respectively). We speculate that the fertility of male CF mice is maintained by persistent expression of the predominant alternative Ca(2+)-mediated Cl- transport system in the epididymides and seminal vesicles.

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 Regulation of Ubiquitin-Proteasome System–mediated Degradation by Cytosolic Stress

2007 ◽  
Vol 18 (11) ◽  
pp. 4279-4291 ◽  
Author(s):  
Sean M. Kelly ◽  
Judy K. VanSlyke ◽  
Linda S. Musil
Keyword(s):  
Heat Shock ◽  
Secretory Pathway ◽  
Proteasome Inhibitors ◽  
Ubiquitin Proteasome System ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Junction Protein ◽  
Ubiquitin Proteasome ◽  
Gap Junction Protein ◽  
Cystic Fibrosis Transmembrane

ER-associated, ubiquitin-proteasome system (UPS)-mediated degradation of the wild-type (WT) gap junction protein connexin32 (Cx32) is inhibited by mild forms of cytosolic stress at a step before its dislocation into the cytosol. We show that the same conditions (a 30-min, 42°C heat shock or oxidative stress induced by arsenite) also reduce the endoplasmic reticulum (ER)-associated turnover of disease-causing mutants of Cx32 and the cystic fibrosis transmembrane conductance regulator (CFTR), as well as that of WT CFTR and unassembled Ig light chain. Stress-stabilized WT Cx32 and CFTR, but not the mutant/unassembled proteins examined, could traverse the secretory pathway. Heat shock also slowed the otherwise rapid UPS-mediated turnover of the cytosolic proteins myoD and GFPu, but not the degradation of an ubiquitination-independent construct (GFP-ODC) closely related to the latter. Analysis of mutant Cx32 from cells exposed to proteasome inhibitors and/or cytosolic stress indicated that stress reduces degradation at the level of substrate polyubiquitination. These findings reveal a new link between the cytosolic stress-induced heat shock response, ER-associated degradation, and polyubiquitination. Stress-denatured proteins may titer a limiting component of the ubiquitination machinery away from pre-existing UPS substrates, thereby sparing the latter from degradation.

Biosynthesis and Degradation of CFTR

1999 ◽  
Vol 79 (1) ◽  
pp. S167-S173 ◽  
Author(s):  
RON R. KOPITO
Keyword(s):  
Cystic Fibrosis ◽  
Secretory Pathway ◽  
Covalent Modification ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Binding Domains ◽  
The Common ◽  
Effects Of Temperature ◽  
Cystic Fibrosis Transmembrane

Kopito, Ron R. Biosynthesis and Degradation of CFTR. Physiol. Rev. 79, Suppl.: S167–S173, 1999. — Many of the mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that cause cystic fibrosis interfere with the folding and biosynthetic processing of nascent CFTR molecules in the endoplasmic reticulum. Mutations in the cytoplasmic nucleotide binding domains, including the common allele ΔF508, decrease the efficiency of CFTR folding, reduce the probability of its dissociation from molecular chaperones, and largely prevent its maturation through the secretory pathway to the plasma membrane. These mutant CFTR molecules are rapidly degraded by cytoplasmic proteasomes by a process that requires covalent modification by multiubiquitination. The effects of temperature and chemical chaperones on the intracellular processing of mutant CFTR molecules suggest that strategies aimed at increasing the folding yield of this protein in vivo may eventually lead to the development of novel therapies for cystic fibrosis.

scholarly journals The Cochaperone HspBP1 Inhibits the CHIP Ubiquitin Ligase and Stimulates the Maturation of the Cystic Fibrosis Transmembrane Conductance Regulator

2004 ◽  
Vol 15 (9) ◽  
pp. 4003-4010 ◽  
Author(s):  
Simon Alberti ◽  
Karsten Böhse ◽  
Verena Arndt ◽  
Anton Schmitz ◽  
Jörg Höhfeld
Keyword(s):  
Cystic Fibrosis ◽  
Quality Control ◽  
Ubiquitin Ligase ◽  
Molecular Chaperones ◽  
Protein Quality ◽  
Regulatory Mechanism ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Ubiquitin Ligase Activity ◽  
Cystic Fibrosis Transmembrane

The CHIP ubiquitin ligase turns molecular chaperones into protein degradation factors. CHIP associates with the chaperones Hsc70 and Hsp90 during the regulation of signaling pathways and during protein quality control, and directs chaperone-bound clients to the proteasome for degradation. Obviously, this destructive activity should be carefully controlled. Here, we identify the cochaperone HspBP1 as an inhibitor of CHIP. HspBP1 attenuates the ubiquitin ligase activity of CHIP when complexed with Hsc70. As a consequence, HspBP1 interferes with the CHIP-induced degradation of immature forms of the cystic fibrosis transmembrane conductance regulator (CFTR) and stimulates CFTR maturation. Our data reveal a novel regulatory mechanism that determines folding and degradation activities of molecular chaperones.

Sign in / Sign up

Export Citation Format

Share Document