STAT1-induced apoptosis is mediated by caspases 2, 3, and 7.
STAT1 (signal transducer and activator of transcription 1) has been implicated as a mediator of a variety of biological responses in response to stimulation by specific growth factors and cytokines. To understand better the role of STAT1 in the interferon-gamma (IFN-gamma)-induced phenotype, we generated an active form of STAT1 (STAT1C) by substituting Cys residues for both Arg-656 and Asn-658 within the C-terminal loop of the STAT1 SH2 domain. The IFN-gamma activation site element was stimulated and bound efficiently by STAT1C without IFN-gamma treatment. STAT1C was found to be tyrosine-phosphorylated in the nucleus for more than 30 h after IFN-gamma stimulation. STAT1-negative U3A cells reexpressing STAT1C showed retarded cell growth and underwent apoptosis when treated with IFN-gamma. Further analysis demonstrated that apoptosis was preceded by proteolytic cleavage of caspases 2, 3, and 7, and wild type STAT1 also induced cleavage of caspase 7 when expressed in STAT1-negative U3A cells, indicating that STAT1C augments potential activity of wild type STAT1. Studies with cycloheximide treatment showed that protein synthesis induced in the first 24 h after IFN-gamma treatment was required for apoptosis under these conditions. Finally, we found that STAT1C-induced apoptosis was, in part, mediated by caspase 2, 3, and 7 because benzyloxycarbonyl-valyl-aspartyl-valyl-alanyl-aspartic acid fluoromethyl ketone (Z-VDVAD-FMK) treatment partially blocked apoptosis. These results suggest that prolonged nuclear localization of activated STAT1 results in apoptosis involving specific regulation of caspase pathway.
Sironi
Juan J
JJ
Derald H. Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York University, New York, New York 10029, USA.
Ouchi
Toru
T
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D053143:Caspase 2; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry
D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D009842:Oligopeptides; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; C427308:benzoylcarbonyl-valyl-aspartyl-valyl-alanyl-aspartyl-fluoromethyl ketone; D014443:Tyrosine; D007371:Interferon-gamma; D004247:DNA; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053143:Caspase 2; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases