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
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
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DOI：
10.1053/jhep.2000.9774
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发表时间：
2000-09-01
期刊：
影响因子：
13.5
通讯作者：
Benito, M
中科院分区：
文献类型：
--
作者：
Fabregat, I;Herrera, B;Benito, M
转化生长因子β（TGF-β）介导的细胞凋亡是肝脏中的主要死亡过程之一。我们先前已经表明，表皮生长因子（EGF）是胎儿肝细胞中TGF-β诱导的细胞凋亡的重要存活信号（Fabregat等人，FEES Lett 1996;384：14-18）。在这项工作中，我们研究了EGF保护作用中涉及的细胞内信号传导，我们在这里显示EGF激活p42和p44丝裂原活化蛋白激酶（MAPK）。然而，促分裂原细胞外激酶（MEK）抑制剂并不能阻断EGF的存活作用。EGF还激活这些细胞中的磷酸肌醇3-激酶（PI 3-kinase）和蛋白激酶B（PKB/AKT）。PI 3-激酶抑制剂的存在阻断了EGF对细胞活力、DNA片段化和caspase-3活性的保护作用。我们已经发现，TGF-β破坏线粒体跨膜电位（Δ Psi（m）），并激活细胞色素c的释放，这种作用被EGF阻断，通过PI 3-激酶依赖性途径。对bcl-2超家族基因表达的详细研究表明，TGF-β使bcl-x（L）的信使RNA（mRNA）和蛋白水平降低，bcl-x（L）是该家族的抗凋亡成员，能够阻止细胞色素c的释放。EGF在TGF-β存在的情况下也能维持bcl-x（L）水平。PI 3激酶抑制剂完全阻断EGF对TGF-β诱导的bcl-xL下调的保护作用。我们的结论是PI 3-激酶介导EGF对TGF-β诱导的死亡的存活效应，其作用是在线粒体变化的上游，即，阻止bcl-x（L）下调、细胞色素c释放和半胱天冬酶-3活化。
Transforming growth factor beta (TGF-beta)-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-beta-induced apoptosis in fetal hepatocytes (Fabregat et al., FEES 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-beta disrupts the mitochondrial transmembrane potential (Delta Psi(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-beta 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-beta. PI 3-kinase inhibitors completely block the protective effect of EGF on TGF-beta-induced bcl-xL down-regulation. We conclude that PI 3-kinase mediates the survival effect of EGF on TGF-beta-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.