title: Microsomal triglyceride transfer protein lipidation and control of CD1d on antigen-presenting cells.
abstract: 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 alpha-galactosylceramide (alpha-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 alpha-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.
authors.affiliation: Gastroenterology Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Stephanie K
authors.initials: SK
authors.lastname: Dougan
authors.forename: Azucena
authors.initials: A
authors.lastname: Salas
authors.forename: Paul
authors.initials: P
authors.lastname: Rava
authors.forename: Amma
authors.initials: A
authors.lastname: Agyemang
authors.forename: Arthur
authors.initials: A
authors.lastname: Kaser
authors.forename: Jamin
authors.initials: J
authors.lastname: Morrison
authors.forename: Archana
authors.initials: A
authors.lastname: Khurana
authors.forename: Mitchell
authors.initials: M
authors.lastname: Kronenberg
authors.forename: Caroline
authors.initials: C
authors.lastname: Johnson
authors.forename: Mark
authors.initials: M
authors.lastname: Exley
authors.forename: M Mahmood
authors.initials: MM
authors.lastname: Hussain
authors.forename: Richard S
authors.initials: RS
authors.lastname: Blumberg
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D000938:Antigen-Presenting Cells / Q000276:immunology*; D018949:Antigens, CD1 / Q000276:immunology*; D055610:Antigens, CD1d; D001692:Biological Transport / Q000276:immunology; D001854:Bone Marrow Cells / Q000276:immunology; D002352:Carrier Proteins / Q000276:immunology*; D004721:Endoplasmic Reticulum / Q000276:immunology*; D005699:Galactosylceramides / Q000276:immunology*; D006801:Humans; D006825:Hybridomas; D007422:Intestines / Q000166:cytology / Q000276:immunology; D008099:Liver / Q000166:cytology / Q000276:immunology; D008214:Lymphocytes / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D013154:Spleen / Q000166:cytology / Q000276:immunology; D020298:U937 Cells
chemical_list: D018949:Antigens, CD1; D055610:Antigens, CD1d; C526877:CD1D protein, human; D002352:Carrier Proteins; D005699:Galactosylceramides; C493154:alpha-galactosylceramide; C106092:microsomal triglyceride transfer protein