title: The intracellular granzyme B inhibitor, proteinase inhibitor 9, is up-regulated during accessory cell maturation and effector cell degranulation, and its overexpression enhances CTL potency.
abstract: Granzyme B (grB) is a serine proteinase released by cytotoxic lymphocytes (CLs) to kill abnormal cells. GrB-mediated apoptotic pathways are conserved in nucleated cells; hence, CLs require mechanisms to protect against ectopic or misdirected grB. The nucleocytoplasmic serpin, proteinase inhibitor 9 (PI-9), is a potent inhibitor of grB that protects cells from grB-mediated apoptosis in model systems. Here we show that PI-9 is present in CD4(+) cells, CD8(+) T cells, NK cells, and at lower levels in B cells and myeloid cells. PI-9 is up-regulated in response to grB production and degranulation, and associates with grB-containing granules in activated CTLs and NK cells. Intracellular complexes of PI-9 and grB are evident in NK cells, and overexpression of PI-9 enhances CTL potency, suggesting that cytoplasmic grB, which may threaten CL viability, is rapidly inactivated by PI-9. Because dendritic cells (DCs) acquire characteristics similar to those of target cells to activate naive CD8(+) T cells and therefore may also require protection against grB, we investigated the expression of PI-9 in DCs. PI-9 is evident in thymic DCs (CD3(-), CD4(+), CD8(-), CD45(+)), tonsillar DCs, and DC subsets purified from peripheral blood (CD16(+) monocytes and CD123(+) plasmacytoid DCs). Furthermore, PI-9 is expressed in monocyte-derived DCs and is up-regulated upon TNF-alpha-induced maturation of monocyte-derived DCs. In conclusion, the presence and subcellular localization of PI-9 in leukocytes and DCs are consistent with a protective role against ectopic or misdirected grB during an immune response.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Australia.
authors.forename: Claire E
authors.initials: CE
authors.lastname: Hirst
authors.forename: Marguerite S
authors.initials: MS
authors.lastname: Buzza
authors.forename: Catherina H
authors.initials: CH
authors.lastname: Bird
authors.forename: Hilary S
authors.initials: HS
authors.lastname: Warren
authors.forename: Paul U
authors.initials: PU
authors.lastname: Cameron
authors.forename: Manling
authors.initials: M
authors.lastname: Zhang
authors.forename: Philip G
authors.initials: PG
authors.lastname: Ashton-Rickardt
authors.forename: Phillip I
authors.initials: PI
authors.lastname: Bird
mesh_terms: D000276:Adjuvants, Immunologic / Q000096:biosynthesis / Q000097:blood / Q000235:genetics / Q000502:physiology; D000938:Antigen-Presenting Cells / Q000166:cytology* / Q000378:metabolism; D015550:Cell Degranulation / Q000276:immunology*; D002454:Cell Differentiation / Q000276:immunology; D002460:Cell Line; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000235:genetics; D003713:Dendritic Cells / Q000145:classification / Q000378:metabolism; D053804:Granzymes; D006801:Humans; D007424:Intracellular Fluid / Q000201:enzymology / Q000378:metabolism; D007962:Leukocytes / Q000378:metabolism; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000378:metabolism*; D015842:Serine Proteinase Inhibitors / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics / Q000502:physiology; D015843:Serpins / Q000096:biosynthesis* / Q000097:blood / Q000235:genetics / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism*; D013602:T-Lymphocytes, Cytotoxic / Q000201:enzymology / Q000276:immunology*; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology*
chemical_list: D000276:Adjuvants, Immunologic; C102316:SERPINB9 protein, human; D015842:Serine Proteinase Inhibitors; D015843:Serpins; C509213:GZMB protein, human; D053804:Granzymes; D012697:Serine Endopeptidases