Unusual degradation of α-β complexes inXenopusoocytes by β-subunits ofXenopusgastric H-K-ATPase

1998 ◽  
Vol 275 (1) ◽  
pp. C139-C145 ◽  
Author(s):  
Pei-Xian Chen ◽  
Paul M. Mathews ◽  
Peter J. Good ◽  
Bernard C. Rossier ◽  
Käthi Geering
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Xenopus Oocytes ◽  
Experimental System ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Β Subunit ◽  
Α Subunit ◽  
P Type ◽  
Α Subunits

The catalytic α-subunit of oligomeric P-type ATPases such as Na-K-ATPase and H-K-ATPase requires association with a β-subunit after synthesis in the endoplasmic reticulum (ER) to become stably expressed and functionally active. In this study, we have expressed the β-subunit of Xenopus gastric H-K-ATPase (βHK) in Xenopus oocytes together with α-subunits of H-K-ATPase (αHK) or Na-K-ATPase (αNK) and have followed the biosynthesis, assembly, and cell surface expression of functional pumps. Immunoprecipitations of Xenopus βHK from metabolically labeled oocytes show that it is well expressed and, when synthesized without α-subunits, can leave the ER and become fully glycosylated. Xenopus βHK can associate with both coexpressed αHK and αNK, but the α-β complexes formed are degraded rapidly in or close to the ER and do not produce functional pumps at the cell surface as assessed by86Rb uptake. A possible explanation of these results is that Xenopus βHK may contain a tissue-specific signal that is important in the formation or correct targeting of functional α-β complexes in the stomach but that cannot be recognized in Xenopusoocytes and in consequence leads to cellular degradation of the α-β complexes in this experimental system.

The immunogenicity of VP7, a rotavirus antigen resident in the endoplasmic reticulum, is enhanced by cell surface expression.

1990 ◽  
Vol 64 (10) ◽  
pp. 4776-4783 ◽  
Author(s):  
M E Andrew ◽  
D B Boyle ◽  
P L Whitfeld ◽  
L J Lockett ◽  
I D Anthony ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Surface Expression ◽  
Cell Surface Expression

scholarly journals Blocking intracellular degradation of the erythropoietin and asialoglycoprotein receptors by calpain inhibitors does not result in the same increase in the levels of their membrane and secreted forms

1996 ◽  
Vol 313 (2) ◽  
pp. 391-399 ◽  
Author(s):  
Drorit NEUMANN ◽  
Ming YUK HUAM ◽  
Harvey F. LODISH ◽  
Gerardo Z. LEDERKREMER
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Membrane Glycoprotein ◽  
3T3 Cells ◽  
Proteolytic Fragment ◽  
Intracellular Degradation ◽  
Nih 3T3 ◽  
Calpain Inhibitors

The erythropoietin receptor (EPO-R), a type 1 membrane glycoprotein, is degraded mainly in the lysosomes or endosomes, whereas the asialoglycoprotein receptor (ASGP-R) H2a subunit, a type 2 membrane glycoprotein, is degraded exclusively in the endoplasmic reticulum. The present study describes compounds that inhibit the intracellular degradation of these receptors in an efficient manner. However, the levels of cell-surface expression and secretion of their soluble exoplasmic domains were not enhanced to the same extent. The calpain inhibitors N-acetyl-leucyl-leucyl-norleucinal(ALLN) and N-acetyl-leucyl-leucyl-methional (ALLM) inhibited EPO-R degradation profoundly. After 3 h of chase using Ba/F3 cells and NIH 3T3 fibroblasts expressing the EPO-R, virtually all of the receptor molecules were degraded, whereas 80% of the pulse-labelled receptor remained intact in the presence of the inhibitor. EPO-R cell-surface expression was elevated 1.5-fold after 1 h of incubation with ALLN. In the absence of protein synthesis, ALLN caused the accumulation of non-degraded EPO-R molecules in endosomes and lysosomes, as determined by double immunofluorescence labelling of NIH 3T3 cells expressing EPO-Rs. In Ba/F3 cells expressing a soluble EPO-R, ALLN treatment increased secretion of the soluble exoplasmic domain of the EPO-R 2-5-fold. Similarly, in NIH 3T3 cells singly transfected with the ASGP-R H2a subunit cDNA, ALLN inhibited degradation of the ASGP-R H2a subunit precursor, as well as the degradation of the 35 kDa proteolytic fragment corresponding to the receptor ectodomain, by 3-6-fold. However, accumulation of secreted proteolytic fragment in the medium was augmented in the presence of ALLN by only 1.75-fold. In cells expressing the G78R mutant of the ASGP-R H2a subunit, which is not cleaved to the 35 kDa fragment [Yuk and Lodish (1993) J. Cell Biol. 123,1735-1749], degradation of the precursor was inhibited. Overall, our data suggest the involvement of cysteine proteinases located in the endoplasmic reticulum, as well as in post-Golgi compartments, in degradation of the EPO-R and the ASGP-R H2a subunit. The much lower effect of the inhibitory compounds on cell-surface and secreted forms of the EPO-R and ASGP-R H2a subunit illustrates the complexity and the tight regulation of the cellular localization and stability of membrane proteins.

scholarly journals Modulation of Transporter Associated with Antigen Processing (TAP)-Mediated Peptide Import into the Endoplasmic Reticulum by Flavivirus Infection

2001 ◽  
Vol 75 (12) ◽  
pp. 5663-5671 ◽  
Author(s):  
Frank Momburg ◽  
Arno Müllbacher ◽  
Mario Lobigs
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Mhc Class I ◽  
Antigen Processing ◽  
Surface Expression ◽  
Class I ◽  
Peptide Transport ◽  
Cell Surface Expression ◽  
Flavivirus Infection ◽  
Mhc Class I Molecules

ABSTRACT In contrast to many other viruses that escape the cellular immune response by downregulating major histocompatibility complex (MHC) class I molecules, flavivirus infection can upregulate their cell surface expression. Previously we have presented evidence that during flavivirus infection, peptide supply to the endoplasmic reticulum is increased (A. Müllbacher and M. Lobigs, Immunity 3:207–214, 1995). Here we show that during the early phase of infection with different flaviviruses, the transport activity of the peptide transporter associated with antigen processing (TAP) is augmented by up to 50%. TAP expression is unaltered during infection, and viral but not host macromolecular synthesis is required for enhanced peptide transport. This study is the first demonstration of transient enhancement of TAP-dependent peptide import into the lumen of the endoplasmic reticulum as a consequence of a viral infection. We suggest that the increased supply of peptides for assembly with MHC class I molecules in flavivirus-infected cells accounts for the upregulation of MHC class I cell surface expression with the biological consequence of viral evasion of natural killer cell recognition.

scholarly journals A Highly Conserved Motif at the COOH Terminus Dictates Endoplasmic Reticulum Exit and Cell Surface Expression of NKCC2

2009 ◽  
Vol 284 (32) ◽  
pp. 21752-21764 ◽  
Author(s):  
Nancy Zaarour ◽  
Sylvie Demaretz ◽  
Nadia Defontaine ◽  
David Mordasini ◽  
Kamel Laghmani
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Conserved Motif

scholarly journals Cell Surface Expression of Calnexin, a Molecular Chaperone in the Endoplasmic Reticulum

2000 ◽  
Vol 275 (46) ◽  
pp. 35751-35758 ◽  
Author(s):  
Yasushi Okazaki ◽  
Hiroshi Ohno ◽  
Kan Takase ◽  
Takenori Ochiai ◽  
Takashi Saito
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Molecular Chaperone ◽  
Surface Expression ◽  
Cell Surface Expression

scholarly journals Human epithelial Na+ channel missense variants identified in the GenSalt study alter channel activity

2016 ◽  
Vol 311 (5) ◽  
pp. F908-F914 ◽  
Author(s):  
Evan C. Ray ◽  
Jingxin Chen ◽  
Tanika N. Kelly ◽  
Jiang He ◽  
L. Lee Hamm ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Cell Surface ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Channel Activity ◽  
Dietary Salt ◽  
Α Subunit ◽  
Γ Subunit ◽  
Genes Encoding ◽  
Altered Sensitivity

Mutations in genes encoding subunits of the epithelial Na+ channel (ENaC) can cause early onset familial hypertension, demonstrating the importance of this channel in modulating blood pressure. It remains unclear whether other genetic variants resulting in subtler alterations of channel function result in hypertension or altered sensitivity of blood pressure to dietary salt. This study sought to identify functional human ENaC variants to examine how these variants alter channel activity and to explore whether these variants are associated with altered sensitivity of blood pressure to dietary salt. Six-hundred participants of the Genetic Epidemiology Network of Salt Sensitivity (GenSalt) study with salt-sensitive or salt-resistant blood pressure underwent sequencing of the genes encoding ENaC subunits. Functional effects of identified variants were examined in a Xenopus oocyte expression system. Variants that increased channel activity included three in the gene encoding the α-subunit (αS115N, αR476W, and αV481M), one in the β-subunit (βS635N), and one in the γ-subunit (γL438Q). One α-subunit variant (αA334T) and one γ-subunit variant (βD31N) decreased channel activity. Several α-subunit extracellular domain variants altered channel inhibition by extracellular Na+ (Na+ self-inhibition). One variant (αA334T) decreased and one (αV481M) increased cell surface expression. Association between these variants and salt sensitivity did not reach statistical significance. This study identifies novel functional human ENaC variants and demonstrates that some variants alter channel cell surface expression and/or Na+ self-inhibition.

scholarly journals Obesity-Linked Variants of Melanocortin-4 Receptor Are Misfolded in the Endoplasmic Reticulum and Can Be Rescued to the Cell Surface by a Chemical Chaperone

2010 ◽  
Vol 31 (4) ◽  
pp. 605-605
Author(s):  
Susana Granell ◽  
Sameer Mohammad ◽  
Ramanagouda Ramanagoudr-Bhojappa ◽  
Giulia Baldini
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Er Stress ◽  
Binding Protein ◽  
Intracellular Localization ◽  
Specific Inhibitor ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Chemical Chaperone ◽  
Melanocortin 4 Receptor

Abstract Melanocortin-4 receptor (MC4R) is a G protein-coupled receptor expressed in the brain where it controls food intake. Many obesity-linked MC4R variants are poorly expressed at the plasma membrane and are retained intracellularly. We have studied the intracellular localization of four obesity-linked MC4R variants, P78L, R165W, I316S, and I317T, in immortalized neurons. We find that these variants are all retained in the endoplasmic reticulum (ER), are ubiquitinated to a greater extent than the wild-type (wt) receptor, and induce ER stress with increased levels of ER chaperones as compared with wt-MC4R and appearance of CCAAT/enhancer-binding protein homologous protein. Expression of the X-box-binding-protein-1 with selective activation of a protective branch of the unfolded protein response did not have any effect on the cell surface expression of MC4R-I316S. Conversely, the pharmacological chaperone 4-phenyl butyric acid (PBA) increased the cell surface expression of wt-MC4R, MC4R-I316S, and I317T by more than 40%. PBA decreased ubiquitination of MC4R-I316S and prevented ER stress induced by expression of the mutant, suggesting that the drug functions to promote MC4R folding. MC4R-I316S rescued to the cell surface is functional, with a 52% increase in agonist-induced cAMP production, as compared with untreated cells. Also direct inhibition of wt-MC4R and MC4R-I316S ubiquitination by a specific inhibitor of the ubiquitin-activating enzyme 1 increased by approximately 40% the expression of the receptors at the cell surface, and the effects of PBA and ubiquitin-activating enzyme 1 were additive. These data offer a cell-based rationale that drugs that improve MC4R folding or decrease ER-associated degradation of the receptor may function to treat some forms of hereditary obesity.

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