FOXO3 Modulates Endothelial Gene Expression and Function by Classical and Alternative Mechanisms

Department of Dermatology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2010; 285(14):10163-78. DOI: 10.1074/jbc.M109.056663
Source: PubMed


FOXO transcription factors represent targets of the phosphatidylinositol 3-kinase/protein kinase B survival pathway controlling important biological processes, such as cell cycle progression, apoptosis, vascular remodeling, stress responses, and metabolism. Recent studies suggested the existence of alternative mechanisms of FOXO-dependent gene expression beyond classical binding to a FOXO-responsive DNA-binding element (FRE). Here we analyzed the relative contribution of those mechanisms to vascular function by comparing the transcriptional and cellular responses to conditional activation of FOXO3 and a corresponding FRE-binding mutant in human primary endothelial cells. We demonstrate that FOXO3 controls expression of vascular remodeling genes in an FRE-dependent manner. In contrast, FOXO3-induced cell cycle arrest and apoptosis occurs independently of FRE binding, albeit FRE-dependent gene expression augments the proapoptotic response. These findings are supported by bioinformatical analysis, which revealed a statistical overrepresentation of cell cycle regulators and apoptosis-related genes in the group of co-regulated genes. Molecular analysis of FOXO3-induced endothelial apoptosis excluded modulators of the extrinsic death receptor pathway and demonstrated important roles for the BCL-2 family members BIM and NOXA in this process. Although NOXA essentially contributed to FRE-dependent apoptosis, BIM was effectively induced in the absence of FRE-binding, and small interfering RNA-mediated BIM depletion could rescue apoptosis induced by both FOXO3 mutants. These data suggest BIM as a critical cell type-specific mediator of FOXO3-induced endothelial apoptosis, whereas NOXA functions as an amplifying factor. Our study provides the first comprehensive analysis of alternatively regulated FOXO3 targets in relevant primary cells and underscores the importance of such genes for endothelial function and integrity.

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    • "It is therefore likely that the FOXO-interference activity of PAX3-FOXO1 is due to the FOXO1 moiety of PAX3-FOXO1. Non-classical gene-regulation exerted by a non-DNA-binding FOXO mutant has been described [46,47,48]. These surprising effects were shown on genes without FOXO DNA-binding elements (IRS) in their promoter and were explained by FOXO's capacity (and also mutant FOXO lacking DNA-binding capacity) to bind gene promoters indirectly by making complexes with other DNA-binding proteins targeted to these promoters. "
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    • "In addition, up-regulation of SMAD2 and IGFBP-3 by PAX3 knock-down could mediate proliferation inhibition and apoptosis via mediating TGF-b, p53 and BCL2 family-dependent apoptosis [28, 29]. Up-regulation of FOXO3 by PAX3 knock-down could also induce BIM expression and lead to apoptosis [30]. Taken together, PAX3 silencing activates multiple apoptotic signalling pathways, while simultaneously inhibiting anti-apoptotic signalling pathways, thereby inducing apoptosis in neuroblastoma cells. "
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    • "These findings indicate that, at early or mild stages of stress, FoxO3a is required to initiate a proliferative cellular program, but that, upon onset of severe or prolonged stress, FoxO3a may contribute to a proapoptotic program shift. Interestingly, a recent report suggested that direct binding of FoxO3a to FHRE may enhance transcriptional activation of genes involved in vascular remodeling in endothelial cells, whereas the proapoptotic functions of FoxO3a appeared to be mediated independently of FHRE binding (Czymai et al., 2010). Our findings that FoxO3a selectively increases MMP2 expression via binding to an FIGURE 7: FoxO3a is required for vascular outgrowth. "
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