Stat1-dependent, p53-independent expression of p21(waf1) modulates oxysterol-induced apoptosis.
7-Ketocholesterol (7kchol) is prominent in atherosclerotic lesions where apoptosis occurs. Using mouse fibroblasts lacking p53, p21(waf1), or Stat1, we found that optimal 7kchol-induced apoptosis requires p21(waf1) and Stat1 but not p53. Findings were analogous in a human cell system. Apoptosis was restored in Stat1-null human cells when wild-type Stat1 was restored. Phosphorylation of Stat1 on Ser(727) but not Tyr(701) was essential for optimum apoptosis. A neutralizing antibody against beta interferon (IFN-beta) blunted Ser(727) phosphorylation and apoptosis after 7kchol treatment; cells deficient in an IFN-beta receptor subunit exhibited blunted apoptosis. IFN-beta alone did not induce apoptosis; thus, 7kchol-induced release of IFN-beta was necessary but not sufficient for optimal apoptosis. In Stat1-null cells, expression of p21(waf1) was much less than in wild-type cells; introducing transient expression of p21(waf1) restored apoptosis. Stat1 and p21(waf1) were essential for downstream apoptotic events, including cytochrome c release from mitochondria and activation of caspases 9 and 3. Our data reveal key elements of the cellular pathway through which an important oxysterol induces apoptosis. Identification of the essential signaling events that may pertain in vivo could suggest targets for therapeutic intervention.
Agrawal
Sudesh
S
Department of Cell Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Agarwal
Munna L
ML
Chatterjee-Kishore
Moitreyee
M
Stark
George R
GR
Chisolm
Guy M
GM
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D019898:Autocrine Communication / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D006801:Humans; D020287:In Situ Nick-End Labeling; D016899:Interferon-beta / Q000378:metabolism; D007653:Ketocholesterols / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D003574:Cytochrome c Group; D004268:DNA-Binding Proteins; D007653:Ketocholesterols; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; C494080:Stat1 protein, mouse; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53; C016876:SC-31769; D016899:Interferon-beta; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases