title: Heat-shock protein 90 associates with N-terminal extended peptides and is required for direct and indirect antigen presentation.
abstract: CD8(+) T cells recognize peptide fragments of endogenously synthesized antigens of cancers or viruses, presented by MHC I molecules. Such antigen presentation requires the generation of peptides in the cytosol, their passage to the endoplasmic reticulum, loading of MHC I with peptides, and transport of MHC I-peptide complexes to the cell surface. Heat-shock protein (hsp) 90 is a cytosolic chaperone known to associate with peptide and peptide precursors of MHC I epitopes. We report here that treatment of cells with hsp90 inhibitors leads to generation of "empty" MHC I caused by inhibited loading of MHC I with peptides. Inhibition of hsp90 does not inhibit synthesis of MHC I, nor does it affect the activity of proteasomes. Hsp90-inhibited cells, such as proteasome-inhibited cells, are poor stimulators of T lymphocytes. The role of hsp90 in presentation of an ovalbumin epitope is shown to be at a postproteasomal step: hsp90 associates with N-terminally extended precursors of the SIINFEHL epitope, and such peptides are depleted from hsp90 preparations in hsp90-inhibited cells. Inhibition of hsp90 in the antigen donor cell compromises their ability to cross-prime. Conversely, stressed cells expressing elevated hsp90 levels show a heat-shock factor-dependent, enhanced ability to cross-prime. These results demonstrate a substantial role for hsp90 in chaperoning of antigenic peptides in direct and indirect presentation. The introduction of a stress-inducible component in these pathways has significant implications for their modulation during fever and infection.
authors.affiliation: Center for Immunotherapy of Cancer and Infectious Diseases, Department of Immunology, University of Connecticut School of Medicine, Farmington, CT 06030-1601, USA.
authors.forename: Margaret K
authors.initials: MK
authors.lastname: Callahan
authors.forename: Manish
authors.initials: M
authors.lastname: Garg
authors.forename: Pramod K
authors.initials: PK
authors.lastname: Srivastava
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D002462:Cell Membrane / Q000276:immunology; D045142:Cross-Priming / Q000187:drug effects; D000939:Epitopes / Q000276:immunology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D015395:Histocompatibility Antigens Class I / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D018942:Macrolides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D010047:Ovalbumin / Q000276:immunology; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017510:Protein Folding
chemical_list: D000939:Epitopes; D018841:HSP90 Heat-Shock Proteins; D015395:Histocompatibility Antigens Class I; D018942:Macrolides; D010455:Peptides; D010047:Ovalbumin; D046988:Proteasome Endopeptidase Complex; C035359:monorden