Interferon- Induces X-linked Inhibitor of Apoptosis-associated Factor-1 and Noxa Expression and Potentiates Human Vascular Smooth Muscle Cell Apoptosis by STAT3 Activation

Yale University, New Haven, Connecticut, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2008; 283(11):6832-42. DOI: 10.1074/jbc.M706021200
Source: PubMed


Interferon (IFN)-gamma actions on the vessel wall play an important role in the pathogenesis of arteriosclerosis, yet the contribution of different IFN-gamma signaling pathways to the phenotypic modulation of vascular smooth muscle cells (VSMCs) are poorly understood. We investigated the effects of IFN-gamma on VSMCs and arteries through interactions involving signal transducer and activator of transcription (STAT) proteins. In addition to STAT1 activation, IFN-gamma consistently phosphorylated STAT3 in human VSMCs but weakly or not at all in human endothelial cells or mouse VSMCs. STAT3 activation resulted in nuclear translocation of this transcription factor. By selectively inhibiting STAT3 and not STAT1 signaling, we identified a number of candidate IFN-gamma-inducible, STAT3-dependent gene products by microarray analysis. Results for selected genes, including the pro-apoptotic molecules X-linked inhibitor of apoptosis associated factor-1 (XAF1) and Noxa, were verified by real time quantitative reverse transcription-PCR and immunoblot analyses. IFN-gamma-induced STAT3 and STAT1 signaling in VSMCs demonstrated reciprocal inhibition. STAT3 activation by IFN-gamma sensitized VSMCs to apoptosis triggered by both death receptor- and mitochondrial-mediated pathways. Knock down of XAF1 and Noxa expression inhibited the priming of VSMCs to apoptotic stimuli by IFN-gamma. Finally, we confirmed the in vivo relevance of our observations using a chimeric animal model of immunodeficient mice bearing human coronary artery grafts in which the expression of XAF1 and Noxa as well as the pro-apoptotic effects induced by IFN-gamma were dependent on STAT3. The data suggest STAT1-independent signaling by IFN-gamma via STAT3 that promotes the death of human VSMCs.

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    • "(Peilot et al., 2000; Qing and Stark, 2004; Ramana et al., 2005; Shen et al., 2001). However, it may also induce the expression of proapoptotic genes in VSMC, sensitizing these cells to the effects of death-inducing signals such as TRAIL (Bai et al., 2008). Our recent analysis of IFN-γ signaling in both mouse and human cultured VSMC, using gene knock out or siRNA knock down approaches, respectively, has revealed that AIP1 functions as a novel negative regulator of IFN-γ/ JAK1,2/STAT1/3 signaling in this cell type (Yu et al., 2011). "
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    • "Of particular interest was our identification of the cell death-associated gene network U2, whose core contains PML, signal transducer and activator of transcription 3 (acute-phase response factor) (STAT3), and LYN (Fig. 5). Interestingly, all of the genes in U2 have been reported to participate in apoptosis in a wide variety of cells; that is, retinoblastoma 1 (RB1) (Day et al., 1997), PML (Xu et al., 2004), LYN (Yoshida et al., 2000), STAT3 (Bai et al., 2008), caspase 1, apoptosis-related cysteine peptidase (interleukin 1, beta, convertase) (CASP1) (Yamanaka et al., 2000) and caspase 4, apoptosis-related cysteine peptidase (CASP4) (Pelletier et al., 2006) all increase apoptosis of cells. The activation of caspase family members plays an important role in apoptosis, and CASP4 protein is necessary for activation of CASP1 protein (Earnshaw et al., 1999). "
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    • "and high STAT3 protein levels were detected in SM-like phospho-S6-positive cells of LAM lung and in the xenographic tumors. STAT3 participates in normal cellular events, such as differentiation, proliferation, and cell survival under cytokine, growth factor, and hormone signaling (Calò et al., 2003), and its expression is detected in normal cells and tissues, including airway and pulmonary vascular human SM cells (Simon et al., 2002; Bai et al., 2008) and human lungs (El-Hashemite and Kwiatkowski, 2005). However , both STAT3 expression and Tyr705 STAT3 phosphorylation are persistently elevated in a variety of human tumors (Al Zaid Siddiquee and Turkson, 2008), which contributed to tumor cell growth and survival (Al Zaid Siddiquee and Turkson , 2008). "
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    ABSTRACT: Tumor suppressor complex TSC1/TSC2 represents a key negative regulator of mammalian target of rapamycin (mTOR)-S6 kinase 1 signaling. Mutational inactivation of TSC1 or TSC2, linked to a rare lung disease, lymphangioleiomyomatosis (LAM), manifests as neoplastic growth of smooth-muscle (SM)-like cells and cystic destruction of the lungs that induces loss of pulmonary function. However, the precise mechanisms of abnormal cell growth in LAM remain uncertain. Here, we demonstrate increased signal transducer and activator of transcription (STAT) 3 expression, phosphorylation, and nuclear localization in SM-like cells in LAM lungs and in TSC2-null xenographic tumors. Treatment of TSC2-null tumors with mTOR inhibitor rapamycin attenuated STAT3 expression and phosphorylation. Increased STAT3 level and activation were also observed in LAM-dissociated (LAMD) cell cultures compared with normal human bronchus fibroblasts (HBFs) from LAM patients. Although interferon (IFN)-gamma inhibited proliferation of HBFs, IFN-gamma treatment had little effect on proliferation of LAMD and TSC2-null cells. Re-expression of TSC2 or treatment with rapamycin inhibited IFN-gamma-induced STAT3 phosphorylation and synergized with IFN-gamma in inhibiting TSC2-null and LAMD cell proliferation. Reduction of STAT3 protein levels or activity using specific small interfering RNA or inhibitory peptide, respectively, decreased proliferation and induced apoptosis in TSC2-null and LAMD cells and sensitized cells to growth-inhibitory and proapoptotic effects of IFN-gamma. Collectively, our data demonstrate that STAT3 activation is required for proliferation and survival of cells with TSC2 dysfunction, that STAT3 impedes growth-inhibitory and proapoptotic effects of IFN-gamma, and that TSC2- and rapamycin-dependent inhibition of STAT3 restores antiproliferative effects of IFN-gamma. Thus, STAT3 may provide a novel therapeutic target for diseases associated with TSC1/TSC2 dysfunction.
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