title: MHC class II-associated proteins in B-cell exosomes and potential functional implications for exosome biogenesis.
abstract: Professional antigen-presenting cells secrete major histocompatibility complex class II (MHC II) carrying exosomes with unclear physiological function(s). Exosomes are first generated as the intraluminal vesicles (ILVs) of a specific type of multivesicular body, and are then secreted by fusion of this compartment with the plasma membrane. We have previously shown that in contrast to the sorting of MHC II at lysosomally targeted multivesicular bodies, sorting of MHC II into exosomes does not rely on MHC II ubiquitination. In search for proteins that drive the incorporation of MHC II into exosomes or functionally discriminate exosomal from plasma membrane MHC II, we first analyzed the total proteome of highly purified B cell-derived exosomes using sensitive and accurate mass spectrometry (MS), and identified 539 proteins, including known and not previously identified constituents. Using quantitative MS, we then identified a small subset of proteins that were specifically co-immunoprecipitated with MHC II from detergent-solubilized exosomes. These include HSC71, HSP90, 14-3-3ɛ, CD20 and pyruvate kinase type M2 (PKM2), and we speculate on the functionality of their interaction with exosomal MHC II.
authors.affiliation: Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands.
authors.forename: Sonja I
authors.initials: SI
authors.lastname: Buschow
authors.forename: Bas W M
authors.initials: BW
authors.lastname: van Balkom
authors.forename: Marian
authors.initials: M
authors.lastname: Aalberts
authors.forename: Albert J R
authors.initials: AJ
authors.lastname: Heck
authors.forename: Marca
authors.initials: M
authors.lastname: Wauben
authors.forename: Willem
authors.initials: W
authors.lastname: Stoorvogel
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D018951:Antigens, CD20 / Q000378:metabolism; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D002458:Cell Fractionation; D002461:Cell Line, Transformed; D005089:Exocytosis / Q000276:immunology; D055354:Exosomes / Q000378:metabolism*; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D013058:Mass Spectrometry; D057146:Multivesicular Bodies / Q000378:metabolism*; D011770:Pyruvate Kinase / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; D018951:Antigens, CD20; D050883:HSC70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; C494371:HSPA8 protein, human; D000949:Histocompatibility Antigens Class II; D011770:Pyruvate Kinase