scholarly journals The transmembrane domain and luminal C-terminal region independently support invariant chain trimerization and assembly with MHCII into nonamers

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Maryse Cloutier ◽  
Jean-Simon Fortin ◽  
Jacques Thibodeau
Keyword(s):  
Transmembrane Domain ◽  
Surface Expression ◽  
Terminal Region ◽  
Site Directed Mutagenesis ◽  
Cell Surface Expression ◽  
Invariant Chain ◽  
Multifunctional Protein ◽  
Hla Dr ◽  
Antigen Presenting ◽  
Order Structures

Abstract Background Invariant chain (CD74, Ii) is a multifunctional protein expressed in antigen presenting cells. It assists the ER exit of various cargos and serves as a receptor for the macrophage migration inhibitory factor. The newly translated Ii chains trimerize, a structural feature that is not readily understood in the context of its MHCII chaperoning function. Two segments of Ii, the luminal C-terminal region (TRIM) and the transmembrane domain (TM), have been shown to participate in the trimerization process but their relative importance and impact on the assembly with MHCII molecules remains debated. Here, we addressed the requirement of these domains in the trimerization of human Ii as well as in the oligomerization with MHCII molecules. We used site-directed mutagenesis to generate series of Ii and DR mutants. These were transiently transfected in HEK293T cells to test their cell surface expression and analyse their interactions by co-immunoprecipitations. Results Our results showed that the TRIM domain is not essential for Ii trimerization nor for intracellular trafficking with MHCII molecules. We also gathered evidence that in the absence of TM, TRIM allows the formation of multi-subunit complexes with HLA-DR. Similarly, in the absence of TRIM, Ii can assemble into high-order structures with MHCII molecules. Conclusions Altogether, our data show that trimerization of Ii through either TM or TRIM sustains nonameric complex formation with MHCII molecules.

scholarly journals C-terminal region regulates the functional expression of human noradrenaline transporter splice variants

2006 ◽  
Vol 401 (1) ◽  
pp. 185-195 ◽  
Author(s):  
Chiharu Sogawa ◽  
Kei Kumagai ◽  
Norio Sogawa ◽  
Katsuya Morita ◽  
Toshihiro Dohi ◽  
...  
Keyword(s):  
Amino Acids ◽  
Cell Surface ◽  
Splice Variants ◽  
Functional Expression ◽  
Surface Expression ◽  
Terminal Region ◽  
Site Directed Mutagenesis ◽  
Cell Surface Expression ◽  
C Terminus ◽  
And Function

The NET [noradrenaline (norepinephrine) transporter], an Na+/Cl−-dependent neurotransmitter transporter, has several isoforms produced by alternative splicing in the C-terminal region, each differing in expression and function. We characterized the two major isoforms of human NET, hNET1, which has seven C-terminal amino acids encoded by exon 15, and hNET2, which has 18 amino acids encoded by exon 16, by site-directed mutagenesis in combination with NE (noradrenaline) uptake assays and cell surface biotinylation. Mutants lacking one third or more of the 24 amino acids encoded by exon 14 exhibited neither cell surface expression nor NE uptake activity, with the exception of the mutant lacking the last eight amino acids of hNET2, whose expression and uptake resembled that of the WT (wild-type). A triple alanine replacement of a candidate motif (ENE) in this region mimicked the influences of the truncation. Deletion of either the last three or another four amino acids of the C-terminus encoded by exon 15 in hNET1 reduced the cell surface expression and NE uptake, whereas deletion of all seven residues reduced the transport activity but did not affect the cell surface expression. Replacement of RRR, an endoplasmic reticulum retention motif, by alanine residues in the C-terminus of hNET2 resulted in a similar expression and function compared with the WT, while partly recovering the effects of the mutation of ENE. These findings suggest that in addition to the function of the C-terminus, the common proximal region encoded by exon 14 regulates the functional expression of splice variants, such as hNET1 and hNET2.

scholarly journals Hepatitis C Virus-Mediated Inhibition of Cathepsin S Increases Invariant-Chain Expression on Hepatocyte Surface

2012 ◽  
Vol 86 (18) ◽  
pp. 9919-9928 ◽  
Author(s):  
Hangeun Kim ◽  
Budhaditya Mazumdar ◽  
Sandip K. Bose ◽  
Keith Meyer ◽  
Adrian M. Di Bisceglie ◽  
...  
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Mhc Class Ii ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Cathepsin S ◽  
Invariant Chain ◽  
Upstream Stimulatory Factor ◽  
Hla Dr ◽  
Chronic Hcv

Hepatocytes are the main source of hepatitis C virus (HCV) replication and contain the maximum viral load in an infected person. Chronic HCV infection is characterized by weak cellular immune responses to viral proteins. Cathepsin S is a lysosomal cysteine protease and controls HLA-DR–antigen complex presentation through the degradation of the invariant chain. In this study, we examined the effect of HCV proteins on cathepsin S expression and found it to be markedly decreased in dendritic cells (DCs) exposed to HCV or in hepatocytes expressing HCV proteins. The downregulation of cathepsin S was mediated by HCV core and NS5A proteins involving inhibition of the transcription factors interferon regulatory factor 1 (IRF-1) and upstream stimulatory factor 1 (USF-1) in gamma interferon (IFN-γ)-treated hepatocytes. Inhibition of cathepsin S by HCV proteins increased cell surface expression of the invariant chain. In addition, hepatocytes stably transfected with HCV core or NS5A inhibited HLA-DR expression. Together, these results suggested that HCV has an inhibitory role on cathepsin S-mediated major histocompatibility complex (MHC) class II maturation, which may contribute to weak immunogenicity of viral antigens in chronically infected humans.

scholarly journals Activation of Innate Immune Responses by Haemophilus influenzae Lipooligosaccharide

2014 ◽  
Vol 21 (5) ◽  
pp. 769-776 ◽  
Author(s):  
Joshua Choi ◽  
Andrew D. Cox ◽  
Jianjun Li ◽  
William McCready ◽  
Marina Ulanova
Keyword(s):  
Haemophilus Influenzae ◽  
Surface Expression ◽  
Innate Immune ◽  
Cell Surface Expression ◽  
Necrosis Factor Alpha ◽  
Content Type ◽  
Hla Dr ◽  
Proinflammatory Activity ◽  
Factor Alpha ◽  
Antigen Presenting

ABSTRACTA Gram-negative pathogenHaemophilus influenzaehas a truncated endotoxin known as lipooligosaccharide (LOS). Recent studies onH. influenzaeLOS highlighted its structural and compositional implications for bacterial virulence; however, the role of LOS in the activation of innate and adaptive immunity is poorly understood. THP-1 monocytes were stimulated with either lipopolysaccharide (LPS) fromEscherichia colior LOS compounds derived fromH. influenzaeEagan, Rd, and Rdlic1 lpsAstrains. Cell surface expression of key antigen-presenting, costimulatory, and adhesion molecules, as well as gene expression of some cytokines and pattern recognition receptors, were studied. Eagan and Rd LOS had a lower capacity to induce the expression of ICAM-1, CD40, CD58, tumor necrosis factor alpha (TNF-α), and interleukin-1β (IL-1β) compared to LPS. In contrast, antigen-presenting (HLA-ABC or HLA-DR) and costimulatory (CD86) molecules and NOD2 were similarly upregulated in response to LOS and LPS. LOS from a mutant Rd strain (Rdlic1 lpsA) consistently induced higher expression of innate immune molecules than the wild-type LOS, suggesting the importance of phosphorylcholine and/or oligosaccharide extension in cellular responses to LOS. An LOS compound with a strong ability to upregulate antigen-presenting and costimulatory molecules combined with a low proinflammatory activity may be considered a vaccine candidate to immunize againstH. influenzae.

scholarly journals Pleiotropic functions of the transmembrane domain 6 of human melanocortin-4 receptor

2012 ◽  
Vol 49 (3) ◽  
pp. 237-248 ◽  
Author(s):  
Hui Huang ◽  
Ya-Xiong Tao
Keyword(s):  
Cell Surface ◽  
Structure Function ◽  
Transmembrane Domain ◽  
Mapk Pathway ◽  
Surface Expression ◽  
Camp Signaling ◽  
Cell Surface Expression ◽  
Melanocortin 4 Receptor ◽  
Function Relationship ◽  
Relationship Of

The melanocortin-4 receptor (MC4R) is a critical regulator of energy homeostasis and has emerged as a premier target for obesity treatment. Numerous mutations in transmembrane domain 6 (TM6) of MC4R resulting in functional alterations have been identified in obese patients. Several mutagenesis studies also provided some data suggesting the importance of this domain in receptor function. To gain a better understanding of the structure–function relationship of the receptor, we performed alanine-scanning mutagenesis in TM6 to determine the functions of side chains. Of the 31 residues, two were important for cell surface expression, five were indispensable for α-melanocyte-stimulating hormone (α-MSH) and β-MSH binding, and six were important for signaling in the Gs–cAMP–PKA pathway. H264A, targeted normally to the plasma membrane, was undetectable by competitive binding assay and severely defective in basal and stimulated cAMP production and ERK1/2 phosphorylation. Nine mutants had decreased basal cAMP signaling. Seven mutants were constitutively active in cAMP signaling and their basal activities could be inhibited by two MC4R inverse agonists, Ipsen 5i and ML00253764. Five mutants were also constitutively active in the MAPK pathway with enhanced basal ERK1/2 phosphorylation. In summary, our study provided comprehensive data on the structure–function relationship of the TM6 of MC4R. We identified residues that are important for cell surface expression, ligand binding, cAMP generation, and residues for maintaining the WT receptor in active conformation. We also reported constitutive activation of the MAPK pathway and biased signaling. These data will be useful for rationally designing MC4R agonists and antagonists for treatment of eating disorders.

scholarly journals Regulation of the Expression, Oligomerisation and Signaling of the Inhibitory Receptor CLEC12A by Cysteine Residues in the Stalk Region

2021 ◽  
Vol 22 (19) ◽  
pp. 10207
Author(s):  
Julien Vitry ◽  
Guillaume Paré ◽  
Andréa Murru ◽  
Xavier Charest-Morin ◽  
Halim Maaroufi ◽  
...  
Keyword(s):  
Cell Surface ◽  
Cell Activation ◽  
Secretory Pathway ◽  
Surface Expression ◽  
Site Directed Mutagenesis ◽  
Cell Surface Expression ◽  
Dependent Manner ◽  
Inhibitory Receptor ◽  
Lectin Receptors ◽  
Stalk Domain

CLEC12A is a myeloid inhibitory receptor that negatively regulates inflammation in mouse models of autoimmune and autoinflammatory arthritis. Reduced CLEC12A expression enhances myeloid cell activation and inflammation in CLEC12A knock-out mice with collagen antibody-induced or gout-like arthritis. Similarly to other C-type lectin receptors, CLEC12A harbours a stalk domain between its ligand binding and transmembrane domains. While it is presumed that the cysteines in the stalk domain have multimerisation properties, their role in CLEC12A expression and/or signaling remain unknown. We thus used site-directed mutagenesis to determine whether the stalk domain cysteines play a role in CLEC12A expression, internalisation, oligomerisation, and/or signaling. Mutation of C118 blocks CLEC12A transport through the secretory pathway diminishing its cell-surface expression. In contrast, mutating C130 does not affect CLEC12A cell-surface expression but increases its oligomerisation, inducing ligand-independent phosphorylation of the receptor. Moreover, we provide evidence that CLEC12A dimerisation is regulated in a redox-dependent manner. We also show that antibody-induced CLEC12A cross-linking induces flotillin oligomerisation in insoluble membrane domains in which CLEC12A signals. Taken together, these data indicate that the stalk cysteines in CLEC12A differentially modulate this inhibitory receptor’s expression, oligomerisation and signaling, suggestive of the regulation of CLEC12A in a redox-dependent manner during inflammation.

scholarly journals Two N-Linked Glycans Differentially Control Maturation, Trafficking and Proteolysis, but not Activity of the IL-11 Receptor

2018 ◽  
Vol 45 (5) ◽  
pp. 2071-2085 ◽  
Author(s):  
Maria Agthe ◽  
Yvonne Garbers ◽  
Joachim Grötzinger ◽  
Christoph Garbers
Keyword(s):  
Cell Surface ◽  
Surface Expression ◽  
Proteolytic Processing ◽  
Biologically Active ◽  
Site Directed Mutagenesis ◽  
Cell Surface Expression ◽  
Target Cells ◽  
Post Translational Modification ◽  
Glycosylation Sites ◽  
D2 Domain

Background/Aims: The cytokine interleukin-11 (IL-11) has important pro- and anti-inflammatory functions. It activates its target cells through binding to the IL-11 receptor (IL-11R), and the IL-11/IL-11R complex recruits a homodimer of glycoprotein 130 (gp130). N-linked glycosylation, a post-translational modification where complex oligosaccharides are attached to the side chain of asparagine residues, is often important for stability, folding and biological function of cytokine receptors. Methods: We generated different IL-11R mutants via site-directed mutagenesis and analyzed them in different cell lines via Western blot, flow cytometry, confocal microscopy and proliferation assays. Results: In this study, we identified two functional N-glycosylation sites in the D2 domain of the IL-11R at N127 and N194. While mutation of N127Q only slightly affects cell surface expression of the IL-11R, mutation of N194Q broadly prevents IL-11R appearance at the plasma membrane. Accordingly, IL-11R mutants lacking N194 are retained within the ER, whereas the N127 mutant is transported through the Golgi complex to the cell surface, uncovering a differential role of the two N-glycan sequons for IL-11R maturation. Interestingly, IL-11R mutants devoid of one or both N-glycans are still biologically active. Furthermore, the IL-11RN127Q/N194Q mutant shows no inducible shedding by ADAM10, but is rather constitutively released into the supernatant. Conclusion: Our results show that the two N-glycosylation sites differentially influence stability and proteolytic processing of the IL-11R, but that N-linked glycosylation is not a prerequisite for IL-11 signaling.

scholarly journals A single N-linked oligosaccharide at either of the two normal sites is sufficient for transport of vesicular stomatitis virus G protein to the cell surface.

1985 ◽  
Vol 5 (11) ◽  
pp. 3074-3083 ◽  
Author(s):  
C E Machamer ◽  
R Z Florkiewicz ◽  
J K Rose
Keyword(s):  
Cell Surface ◽  
G Protein ◽  
Vesicular Stomatitis Virus ◽  
Intracellular Transport ◽  
Surface Expression ◽  
Site Directed Mutagenesis ◽  
Cell Surface Expression ◽  
Glycosylation Sites ◽  
Vesicular Stomatitis ◽  
The Individual

We investigated the role of glycosylation in intracellular transport and cell surface expression of the vesicular stomatitis virus glycoprotein (G) in cells expressing G protein from cloned cDNA. The individual contributions of the two asparagine-linked glycans of G protein to cell surface expression were assessed by site-directed mutagenesis of the coding sequence to eliminate one or the other or both of the glycosylation sites. One oligosaccharide at either position was sufficient for cell surface expression of G protein in transfected cells, and the rates of oligosaccharide processing were similar to the rate observed for wild-type protein. However, the nonglycosylated G protein synthesized when both glycosylation sites were eliminated did not reach the cell surface. This protein did appear to reach a Golgi-like region, as determined by indirect immunofluorescence microscopy, however, and was modified with palmitic acid. It was also apparently not subject to increased proteolytic breakdown.

CD39/NTPDase1 Variants Identified in Human Neutrophils Regulate Antithrombotic Activity.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 3088-3088 ◽  
Author(s):  
Kim E. Olson ◽  
Dianne Pulte ◽  
Marinus Johan Broekman ◽  
Ashley E. Olson ◽  
Joan Drosopoulos ◽  
...  
Keyword(s):  
Cell Surface ◽  
Atpase Activity ◽  
Western Blot ◽  
Transmembrane Domain ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Human Neutrophils ◽  
Platelet Activity ◽  
Total Rna ◽  
Cos Cells

Abstract Blood-borne cellular elements expressing ectonucleotidase activity have been shown to regulate platelet activation and recruitment in response to agonists. In particular, exposure of a platelet releasate to isolated neutrophils (PMN) results in loss of its platelet activating activity in a subsequent assay (Valles et al, J Clin Invest1993, 92:1357–1365). Whereas expression of CD39 on vascular endothelial cells has been well characterized, expression on leukocytes has been less well studied. Freshly prepared lymphocyte and PMN cell populations were evaluated for both cell surface expression of CD39 and ectonucleotidase activity. FACS analysis showed that 98% of PMN were positive for CD39 compared to only 20% of lymphocytes. In addition, neutrophils stained more intensely, indicating the presence of a higher quantity of cell surface-expressed CD39. Interestingly, neutrophils exhibited only 1/3 of the ATPase and 1/2 of the ADPase activities of the same number of lymphocytes, although the latter are thought to have greater antithrombotic capacity. RT-PCR products from total RNA isolated from lymphocytes and PMN were sequenced. This revealed alternately spliced CD39 mRNA species present in PMN at levels equal to that of CD39 mRNA. In contrast, lymphocytes, which showed much higher levels of CD39 mRNA, expressed these variants at much lower levels. RACE analyses of cDNAs generated from total RNA demonstrated two CD39 gene-derived mRNAs. Each was comprised of an alternate 3′ segment lacking the C-terminal transmembrane domain, and distinguished by an internal deletion. Myc- and Flag-tagged constructs expressed in COS cells resulted in cell surface expression of the respectively tagged variants (immunocytochemistry, western blot analyses of plasma membrane preparations). Membrane preparations assayed for enzyme activity revealed no apyrase activity for either molecule expressed alone or together. Co-transfection of CD39 with equal amounts of either construct singly or in combination resulted in a 30-50% decrease in ATPase activity compared to CD39 alone. Similarly, CD39 co-expressed with either construct alone lost 75–90% of its ADPase activity. Unexpectedly, co-transfection of CD39 with both variants together resulted in a 20–40% increase in ADPase activity. Glutaraldehyde cross-linking of membrane preparations from triply transfected COS cells followed by immunoprecipitation and western blot analyses demonstrated the presence of all three species in higher order complexes. Thus, both variants can simultaneously associate with CD39, generating hetero-multimers with altered substrate preference and catalytic efficiency compared to CD39 tetramers. These observations add to our understanding of the regulation of ectonucleotidase activity at the cell surface. The balanced expression of CD39 and its two identified variants may underlie the anti-platelet activity of neutrophils previously reported. The finding that association of CD39 with either construct alone results in near complete loss of ADPase activity with only partial diminution of ATPase activity suggests a possible etiology for a pro-thrombotic phenotype.

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