Selective regulation of apoptosis: the cytotoxic lymphocyte serpin proteinase inhibitor 9 protects against granzyme B-mediated apoptosis without perturbing the Fas cell death pathway.
Cytotoxic lymphocytes (CLs) induce caspase activation and apoptosis of target cells either through Fas activation or through release of granule cytotoxins, particularly granzyme B. CLs themselves resist granule-mediated apoptosis but are eventually cleared via Fas-mediated apoptosis. Here we show that the CL cytoplasmic serpin proteinase inhibitor 9 (PI-9) can protect transfected cells against apoptosis induced by either purified granzyme B and perforin or intact CLs. A PI-9 P1 mutant (Glu to Asp) is a 100-fold-less-efficient granzyme B inhibitor that no longer protects against granzyme B-mediated apoptosis. PI-9 is highly specific for granzyme B because it does not inhibit eight of the nine caspases tested or protect transfected cells against Fas-mediated apoptosis. In contrast, the P1(Asp) mutant is an effective caspase inhibitor that protects against Fas-mediated apoptosis. We propose that PI-9 shields CLs specifically against misdirected granzyme B to prevent autolysis or fratricide, but it does not interfere with homeostatic deletion via Fas-mediated apoptosis.
Department of Medicine, Monash Medical School, Box Hill Hospital, Box Hill 3128, Australia.
C H
CH
Bird
V R
VR
Sutton
J
J
Sun
C E
CE
Hirst
A
A
Novak
S
S
Kumar
J A
JA
Trapani
P I
PI
Bird
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology*; D061945:Caspase Inhibitors; D005434:Flow Cytometry; D006801:Humans; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000378:metabolism; D015843:Serpins / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology*; D013602:T-Lymphocytes, Cytotoxic / Q000502:physiology*; D014162:Transfection / Q000235:genetics; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000502:physiology
D061945:Caspase Inhibitors; D011994:Recombinant Proteins; C102316:SERPINB9 protein, human; D015843:Serpins; D019014:fas Receptor