Epidermal Growth Factor Impairs the Cytochrome C/Caspase-3 Apoptotic Pathway Induced by Transforming Growth Factor β in Rat Fetal Hepatocytes Via a Phosphoinositide 3-Kinase–Dependent Pathway

Authors

  • Isabel Fabregat Ph.D.,

    Corresponding author
    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
    • Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain. fax: (34) 913941779.
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  • Blanca Herrera,

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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  • Margarita Fernández,

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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  • Alberto M. Álvarez,

    1. Centro de Citometría de Flujo y Microscopía Confocal, Universidad Complutense de Madrid, Madrid, Spain
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  • Aránzazu Sánchez,

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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  • César Roncero,

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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  • Juan-José Ventura,

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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  • Ángela M. Valverde,

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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  • Manuel Benito

    1. Departamento de Bioquímica y Biología Molecular, Facultad de Farmacia (Centro Mixto CSIC/UCM), Universidad Complutense de Madrid, Madrid, Spain
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Abstract

Transforming growth factor β (TGF-β)–mediated apoptosis is one of the major death processes in the liver. We have previously shown that epidermal growth factor (EGF) is an important survival signal for TGF-β–induced apoptosis in fetal hepatocytes (Fabregat et al., FEBS Lett 1996;384:14-18). In this work we have studied the intracellular signaling implicated in the protective effect of EGF. We show here that EGF activates p42 and p44 mitogen-activated protein kinases (MAPK). However, mitogen extracellular kinase (MEK) inhibitors do not block the survival effect of EGF. EGF also activates phosphoinositide 3-kinase (PI 3-kinase) and protein kinase B (PKB/AKT) in these cells. The presence of PI 3-kinase inhibitors blocks the protective effect of EGF on cell viability, DNA fragmentation, and caspase-3 activity. We have found that TGF-β disrupts the mitochondrial transmembrane potential (Δψm ) and activates the release of cytochrome c, this effect being blocked by EGF, via a PI 3-kinase–dependent pathway. A detailed study on bcl-2 superfamily gene expression shows that TGF-β produces a decrease in the messenger RNA (mRNA) and protein levels of bcl-xL , an antiapoptotic member of this family, capable of preventing cytochrome c release. EGF is able to maintain bcl-xL levels even in the presence of TGF-β. PI 3-kinase inhibitors completely block the protective effect of EGF on TGF-β–induced bcl-xL down-regulation. We conclude that PI 3-kinase mediates the survival effect of EGF on TGF-β–induced death by acting upstream from the mitochondrial changes, i.e., preventing bcl-xL down-regulation, cytochrome c release, and activation of caspase-3.

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