title: A role for heat shock protein 27 in CTL-mediated cell death.
abstract: CTL exocytosis of granules containing perforin and granzyme proteases induces apoptotic cell death. Either granzyme A or B can act with perforin to trigger apoptosis. Granzyme B activates a ubiquitous apoptotic cascade induced by caspase cleavage, but the granzyme A pathway is largely unknown. Using affinity chromatography with recombinant mutant inactive granzyme A, we previously isolated two granzyme A-binding proteins, PHAP (putative HLA-associated protein) I and II. PHAP II, a substrate of granzyme A, is degraded within minutes of CTL attack. Two additional cytoplasmic proteins of 27 and 53 kDa bind strongly to the mutant granzyme A column, requiring 6 M urea to elute. Sequencing identified these as the monomer and dimer of hsp27, a small heat shock protein up-regulated by stress and cellular activation. Hsp27 coprecipitates with granzyme A from cytoplasmic lysates and is not a substrate of the enzyme. Hsp27 translocates to the detergent-insoluble fraction of target cells and relocalizes from diffuse cytoplasmic staining to long filamentous fibers, especially concentrated in a perinuclear region, within minutes of CTL attack. Hsp27 may participate in morphologic changes during granule-mediated lysis. Low or absent levels of hsp27 expression in T lymphocytes, even after heat shock, may play a role in CTL resistance to granule-mediated lysis.
authors.affiliation: The Center for Blood Research, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Beresford
authors.forename: M
authors.initials: M
authors.lastname: Jaju
authors.forename: R S
authors.initials: RS
authors.lastname: Friedman
authors.forename: M J
authors.initials: MJ
authors.lastname: Yoon
authors.forename: J
authors.initials: J
authors.lastname: Lieberman
mesh_terms: D016923:Cell Death / Q000276:immunology; D002458:Cell Fractionation; D011232:Chemical Precipitation; D003593:Cytoplasm / Q000201:enzymology; D003602:Cytotoxicity, Immunologic; D004789:Enzyme Activation; D053804:Granzymes; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000276:immunology* / Q000302:isolation & purification / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D011485:Protein Binding / Q000276:immunology; D011994:Recombinant Proteins / Q000302:isolation & purification; D012697:Serine Endopeptidases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D013312:Stress, Physiological; D013379:Substrate Specificity; D013602:T-Lymphocytes, Cytotoxic / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D006360:Heat-Shock Proteins; D011994:Recombinant Proteins; D053804:Granzymes; D012697:Serine Endopeptidases; C509212:GZMA protein, human