A distal effect of microsomal triglyceride transfer protein deficiency on the lysosomal recycling of CD1d

Microsomal triglyceride transfer protein (MTP) is an endoplasmic reticulum (ER)–resident lipid transfer protein involved in the biosynthesis and lipid loading of apolipoprotein B. MTP was recently suggested to directly regulate the biosynthesis of the MHC I–like, lipid antigen presenting molecule CD1d, based on coprecipitation experiments and lipid loading assays. However, we found that the major impact of MTP deficiency occurred distal to the ER and Golgi compartments. Thus, although the rates of CD1d biosynthesis, glycosylation maturation, and internalization from the cell surface were preserved, the late but essential stage of recycling from lysosome to plasma membrane was profoundly impaired. Likewise, functional experiments indicated defects of CD1d-mediated lipid presentation in the lysosome but not in the secretory pathway. These intriguing findings suggest a novel, unexpected role of MTP at a late stage of CD1d trafficking in the lysosomal compartment.

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Lipoprotein assembly and function in an evolutionary perspective

BioMolecular Concepts ◽

10.1515/bmc.2010.012 ◽

2010 ◽

Vol 1 (2) ◽

pp. 165-183 ◽

Cited By ~ 9

Author(s):

Dick J. Van der Horst ◽

Kees W. Rodenburg

Keyword(s):

Lipid Transfer Protein ◽

Low Density Lipoprotein ◽

Density Lipoprotein ◽

Microsomal Triglyceride Transfer Protein ◽

Lipid Binding ◽

Lipid Transfer ◽

Transfer Protein ◽

Density Lipoprotein Receptor ◽

Exchangeable Basis ◽

And Function

AbstractCirculatory fat transport in animals relies on members of the large lipid transfer protein (LLTP) superfamily, including mammalian apolipoprotein B (apoB) and insect apolipophorin II/I (apoLp-II/I). ApoB and apoLp-II/I, constituting the structural (non-exchangeable) basis for the assembly of various lipoproteins, acquire lipids through microsomal triglyceride-transfer protein, another LLTP family member, and bind them by means of amphipathic α-helical and β-sheet structural motifs. Comparative research reveals that LLTPs evolved from the earliest animals and highlights the structural adaptations in these lipid-binding proteins. Thus, in contrast to apoB, apoLp-II/I is cleaved post-translationally by a furin, resulting in the appearance of two non-exchangeable apolipoproteins in the single circulatory lipoprotein in insects, high-density lipophorin (HDLp). The remarkable structural similarities between mammalian and insect lipoproteins notwithstanding important functional differences relate to the mechanism of lipid delivery. Whereas in mammals, partial delipidation of apoB-containing lipoproteins eventually results in endocytic uptake of their remnants, mediated by members of the low-density lipoprotein receptor (LDLR) family, and degradation in lysosomes, insect HDLp functions as a reusable lipid shuttle capable of alternate unloading and reloading of lipid. Also, during muscular efforts (flight activity), an HDLp-based lipoprotein shuttle provides for the transport of lipid for energy generation. Although a lipophorin receptor – a homolog of LDLR – was identified that mediates endocytic uptake of HDLp during specific developmental periods, the endocytosed lipoprotein appears to be recycled in a transferrin-like manner. These data highlight that the functional adaptations in the lipoprotein lipid carriers in mammals and insects also emerge with regard to the functioning of their cognate receptors.

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Microsomal triglyceride transfer protein lipidation and control of CD1d on antigen-presenting cells

Journal of Experimental Medicine ◽

10.1084/jem.20050183 ◽

2005 ◽

Vol 202 (4) ◽

pp. 529-539 ◽

Cited By ~ 118

Author(s):

Stephanie K. Dougan ◽

Azucena Salas ◽

Paul Rava ◽

Amma Agyemang ◽

Arthur Kaser ◽

...

Keyword(s):

Mononuclear Cells ◽

Microsomal Triglyceride Transfer Protein ◽

Antigen Presenting Cells ◽

Human Monocyte ◽

Lipid Transfer ◽

Mouse Splenocytes ◽

Transfer Protein ◽

Er Chaperone ◽

Antigen Presenting

Microsomal triglyceride transfer protein (MTP), an endoplasmic reticulum (ER) chaperone that loads lipids onto apolipoprotein B, also regulates CD1d presentation of glycolipid antigens in the liver and intestine. We show MTP RNA and protein in antigen-presenting cells (APCs) by reverse transcription–polymerase chain reaction and by immunoblotting of mouse liver mononuclear cells and mouse and human B cell lines. Functional MTP, demonstrated by specific triglyceride transfer activity, is present in both mouse splenocytes and a CD1d-positive mouse NKT hybridoma. In a novel in vitro transfer assay, purified MTP directly transfers phospholipids, but not triglycerides, to recombinant CD1d. Chemical inhibition of MTP lipid transfer does not affect major histocompatibility complex class II presentation of ovalbumin, but considerably reduces CD1d-mediated presentation of α-galactosylceramide (α-galcer) and endogenous antigens in mouse splenic and bone marrow–derived dendritic cells (DCs), as well as in human APC lines and monocyte-derived DCs. Silencing MTP expression in the human monocyte line U937 affects CD1d function, as shown by diminished presentation of α-galcer. We propose that MTP acts upstream of the saposins and functions as an ER chaperone by loading endogenous lipids onto nascent CD1d. Furthermore, our studies suggest that a small molecule inhibitor could be used to modulate the activity of NKT cells.

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MTP regulated by an alternate promoter is essential for NKT cell development

Journal of Experimental Medicine ◽

10.1084/jem.20062006 ◽

2007 ◽

Vol 204 (3) ◽

pp. 533-545 ◽

Cited By ~ 52

Author(s):

Stephanie K. Dougan ◽

Paul Rava ◽

M. Mahmood Hussain ◽

Richard S. Blumberg

Keyword(s):

Lipid Transfer Protein ◽

Microsomal Triglyceride Transfer Protein ◽

Cell Development ◽

Northern Analysis ◽

Lipid Transfer ◽

Nkt Cell ◽

Transfer Protein ◽

Phospholipid Transfer ◽

Apob Secretion

Microsomal triglyceride transfer protein (MTP), an endoplasmic reticulum lipid transfer protein critical for apolipoprotein B (apoB) secretion, regulates CD1d antigen presentation. We identified MTP variant 1 (MTPv1), a novel splice variant of mouse MTP, by polymerase chain reaction and Northern analysis in non–apoB-secreting tissues, including thymocytes and antigen-presenting cells (APCs). Edman degradation of MTPv1 isolated from transfected cells revealed three unique residues; however, recombinant MTP and MTPv1 had an equivalent protein disulfide isomerase association, subcellular localization, triglyceride transfer, phospholipid transfer, response to inhibitors, and ability to support apoB secretion. MTP and MTPv1 efficiently transferred phosphatidylethanolamine to CD1d in vitro. NKT cells fail to develop in fetal thymic organ culture (FTOC) treated with MTP antagonists. MTP-inhibited FTOCs produced negligible numbers of CD1d tetramer–positive cells and exhibited marked defects in IL-4 production upon stimulation with anti-CD3 or α-galactosylceramide–pulsed APCs. CD1d expression on CD4+CD8+ FTOC cells was unaffected by MTP inhibition. Thus, our results demonstrate that MTPv1 in thymocytes is critical to NKT cell development. We hypothesize that, when MTP is inactive, CD1d traffics to the cell surface and presents no lipid or a lipid that is incapable of mediating NKT cell selection and/or is refractory to lysosomal editing.

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Isolation of a cDNA Clone for Spinach Lipid Transfer Protein and Evidence that the Protein Is Synthesized by the Secretory Pathway

PLANT PHYSIOLOGY ◽

10.1104/pp.95.1.164 ◽

1991 ◽

Vol 95 (1) ◽

pp. 164-170 ◽

Cited By ~ 85

Author(s):

Werner R. Bernhard ◽

Sharon Thoma ◽

Jose Botella ◽

Chris R. Somerville

Keyword(s):

Cdna Clone ◽

Secretory Pathway ◽

Lipid Transfer Protein ◽

Lipid Transfer ◽

Transfer Protein

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The Oxysterol-Binding Protein Cycle: Burning Off PI(4)P to Transport Cholesterol

Annual Review of Biochemistry ◽

10.1146/annurev-biochem-061516-044924 ◽

2018 ◽

Vol 87 (1) ◽

pp. 809-837 ◽

Cited By ~ 51

Author(s):

Bruno Antonny ◽

Joëlle Bigay ◽

Bruno Mesmin

Keyword(s):

Secretory Pathway ◽

Lipid Transfer Protein ◽

Binding Protein ◽

Asymmetric Distribution ◽

Lipid Transfer ◽

Oxysterol Binding Protein ◽

Transfer Protein ◽

Lipid Exchange ◽

Opposite Process ◽

Phosphatidylinositol 4

To maintain an asymmetric distribution of ions across membranes, protein pumps displace ions against their concentration gradient by using chemical energy. Here, we describe a functionally analogous but topologically opposite process that applies to the lipid transfer protein (LTP) oxysterol-binding protein (OSBP). This multidomain protein exchanges cholesterol for the phosphoinositide phosphatidylinositol 4-phosphate [PI(4)P] between two apposed membranes. Because of the subsequent hydrolysis of PI(4)P, this counterexchange is irreversible and contributes to the establishment of a cholesterol gradient along organelles of the secretory pathway. The facts that some natural anti-cancer molecules block OSBP and that many viruses hijack the OSBP cycle for the formation of intracellular replication organelles highlight the importance and potency of OSBP-mediated lipid exchange. The architecture of some LTPs is similar to that of OSBP, suggesting that the principles of the OSBP cycle—burning PI(4)P for the vectorial transfer of another lipid—might be general.

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Miro recruits VPS13D to mitochondria

10.1101/2020.10.07.328906 ◽

2020 ◽

Author(s):

Andrés Guillén-Samander ◽

Marianna Leonzino ◽

Pietro De Camilli

Keyword(s):

Secretory Pathway ◽

Lipid Transfer Protein ◽

Transport Proteins ◽

Lipid Transport ◽

Eukaryotic Cells ◽

Lipid Transfer ◽

Transfer Protein ◽

Accessory Factor ◽

Mitochondrial Motility ◽

Higher Eukaryotes

AbstractMitochondria, which are excluded from the secretory pathway, depend on lipid transport proteins for their lipid supply from the ER, where most lipids are synthesized. In yeast, the outer membrane GTPase Gem1 is an accessory factor of ERMES, an ER-mitochondria tethering complex that contains lipid transport domains and plays a function, partially redundant with VPS13, in lipid transfer between the two organelles. In metazoa, where VPS13, but not ERMES, is present, the Gem1 orthologue Miro has been linked to mitochondrial motility but not to lipid transport. Here we show that Miro recruits to mitochondria the lipid transport protein VPS13D which, like Miro, is an essential protein in mammals, and whose localization had remained elusive. We also show that VPS13D can tether mitochondria to the ER in a Miro- and VAP-dependent way. These findings reveal a so far missing link between function(s) of Gem1/Miro in yeast and higher eukaryotes, where Miro is a Parkin substrate, with potential implications for Parkinson’s disease pathogenesis.SummaryProtein-mediated ER-mitochondria lipid transfer is critical for eukaryotic cells. However, the underlying machinery is not well conserved. Guillén-Samander et al, show that Gem1/Miro is an evolutionary conserved link between the yeast ERMES complex and the mammalian lipid transfer protein VPS13D.

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