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

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 (ΔΨ(m)) 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-x(L), an antiapoptotic member of this family, capable of preventing cytochrome c release. EGF is able to maintain bcl-x(L) levels even in the presence of TGF-β. PI 3-kinase inhibitors completely block the protective effect of EGF on TGF-β-induced bcl-x(L) 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-x(L) down-regulation, cytochrome c release, and activation of caspase-3.Supported by a grant from the Ministerio de Educación y Cultura (PM97/0052). B.H. and J.-J.V. were recipients of fellowships from the Ministerio de Educación y Cultura and A.S. was a recipient of a fellowship from the Comunidad de Madrid.Peer Reviewe