title: Global proteome analysis identifies active immunoproteasome subunits in human platelets.
abstract: The discovery of new functions for platelets, particularly in inflammation and immunity, has expanded the role of these anucleate cell fragments beyond their primary hemostatic function. Here, four in-depth human platelet proteomic data sets were generated to explore potential new functions for platelets based on their protein content and this led to the identification of 2559 high confidence proteins. During a more detailed analysis, consistently high expression of the proteasome was discovered, and the composition and function of this complex, whose role in platelets has not been thoroughly investigated, was examined. Data set mining resulted in identification of nearly all members of the 26S proteasome in one or more data sets, except the β5 subunit. However, β5i, a component of the immunoproteasome, was identified. Biochemical analyses confirmed the presence of all catalytically active subunits of the standard 20S proteasome and immunoproteasome in human platelets, including β5, which was predominantly found in its precursor form. It was demonstrated that these components were assembled into the proteasome complex and that standard proteasome as well as immunoproteasome subunits were constitutively active in platelets. These findings suggest potential new roles for platelets in the immune system. For example, the immunoproteasome may be involved in major histocompatibility complex I (MHC I) peptide generation, as the MHC I machinery was also identified in our data sets.
authors.affiliation: From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada;
authors.forename: Cordula
authors.initials: C
authors.lastname: Klockenbusch
authors.affiliation: From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; §The Centre for Blood Research, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada;
authors.forename: Geraldine M
authors.initials: GM
authors.lastname: Walsh
authors.affiliation: From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada;
authors.forename: Lyda M
authors.initials: LM
authors.lastname: Brown
authors.affiliation: From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; ¶The Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, BC V6T 1Z1, Canada;
authors.forename: Michael D
authors.initials: MD
authors.lastname: Hoffman
authors.affiliation: ‖Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada;
authors.forename: Vladimir
authors.initials: V
authors.lastname: Ignatchenko
authors.affiliation: ‖Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 2C4, Canada; **Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 1L7, Canada.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kislinger
authors.affiliation: From the ‡The Biomedical Research Centre, 2222 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; §The Centre for Blood Research, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada; ¶The Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, BC V6T 1Z1, Canada; Kast@brc.ubc.ca.
authors.forename: Juergen
authors.initials: J
authors.lastname: Kast
mesh_terms: D001792:Blood Platelets / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D057225:Data Mining; D015870:Gene Expression; D057809:HEK293 Cells; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate; D058977:Molecular Sequence Annotation; D061251:Primary Cell Culture; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D020543:Proteome / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D015395:Histocompatibility Antigens Class I; D021122:Protein Subunits; D020543:Proteome; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease