Granzyme B is a novel interleukin-18 converting enzyme.
BACKGROUND
Granzyme B (GrB) is recognized to induce apoptosis; however, little is known about its possible role in other biological events. IL-18, a potent inflammatory cytokine, is produced as an inactive precursor (proIL-18). Several cells, including monocytes/macrophage lineage and non-hematopoietic cells such as keratinocytes, produce proIL-18. ProIL-18 requires appropriate processing to become active. Caspase-1 is the authentic IL-18 processing enzyme and is essential for IL-18 release from monocyte/macrophage lineage cells. However, caspase-1 is absent in non-hematopoietic cells, suggesting that there is another candidate to cleave proIL-18 except for caspase-1.


OBJECTIVE
GrB can invade and be active in cytoplasm of non-hematopoietic cells via perforin, therefore we investigated whether GrB converts proIL-18 into the biologically active form.


METHODS
Recombinant proIL-18 (rproIL-18) was produced and purified for protease reaction with GrB; this incubate was evaluated by immunoblotting. Biological activity of the proteolytic fragment cleaved by GrB was determined by IFN-gamma assay using KG-1 cells. IFN-gamma induction was also analyzed between extracts from GrB(+)/caspase-1(-) human CD8+ T cells and proIL-18 from normal human keratinocytes (NHK).


RESULTS
The proteolytic fragment that GrB cleaved proIL-18 had the same sequence and biological activity compared with mature IL-18 cleaved by caspase-1. Culture extracts from CD8+ T cells was able to cleave proIL-18 into authentic mature IL-18. IFN-gamma induction was also detected in NHK treated with CD8+ T cells.


CONCLUSIONS
GrB is a potent IL-18 converting enzyme and suggest that GrB secreted by CTLs and/or NK cells may initiate IL-18 release from target cells, leading to the development of inflammation.
Omoto
Youichi
Y
Department of Dermatology, Mie University, Graduate School of Medicine, Tsu, Mie 514-8507, Japan.
Yamanaka
Keiichi
K
Tokime
Kazuya
K
Kitano
Shigehisa
S
Kakeda
Masato
M
Akeda
Tomoko
T
Kurokawa
Ichiro
I
Gabazza
Esteban C
EC
Tsutsui
Hiroko
H
Katayama
Naoyuki
N
Yamanishi
Kiyofumi
K
Nakanishi
Kenji
K
Mizutani
Hitoshi
H
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020170:Caspase 1 / Q000494:pharmacology; D002478:Cells, Cultured; D053804:Granzymes / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007249:Inflammation / Q000503:physiopathology; D007371:Interferon-gamma / Q000378:metabolism; D020382:Interleukin-18 / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data
D020382:Interleukin-18; D007371:Interferon-gamma; D053804:Granzymes; D020170:Caspase 1