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Stat1-dependent, p53-independent expression of p21(waf1) modulates oxysterol-induced apoptosis
Sudesh Agrawal1, Munna L Agarwal, Moitreyee Chatterjee-Kishore
1Department of Cell Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
Abstract:
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.
Insights
7-Ketocholesterol induces apoptosis via p21 and Stat1 signaling pathways, independent of p53. This process involves interferon-beta release and mitochondrial cytochrome c release, crucial for caspase activation.
Area of Science:
- Cellular biology
- Molecular mechanisms of apoptosis
- Oxysterol research
Background:
- 7-Ketocholesterol (7kchol) is implicated in atherosclerotic lesions.
- Apoptosis is a key process occurring in these lesions.
Purpose of the Study:
- To elucidate the molecular pathway of 7-ketocholesterol-induced apoptosis.
- To identify key signaling molecules involved in 7kchol-induced cell death.
Main Methods:
- Utilized mouse and human cell systems, including knockout/null cell lines for p53, p21(waf1), and Stat1.
- Investigated the role of Stat1 phosphorylation (Ser727 vs. Tyr701) and interferon-beta (IFN-beta) signaling.
- Assessed downstream apoptotic events like cytochrome c release and caspase activation.
Main Results:
- Optimal 7kchol-induced apoptosis requires p21(waf1) and Stat1, but not p53.
- Stat1 phosphorylation at Ser(727) is essential; IFN-beta release is necessary but not sufficient.
- Restoration of p21(waf1) or wild-type Stat1 rescued apoptosis in deficient cells.
- Stat1 and p21(waf1) are critical for cytochrome c release and caspase-9/3 activation.
Conclusions:
- Identified p21(waf1) and Stat1 as key mediators of 7kchol-induced apoptosis.
- The pathway involves IFN-beta signaling and mitochondrial dysfunction.
- Findings suggest potential therapeutic targets for oxysterol-related diseases.