Thoresen G Hege, Guren Tormod K, Christoffersen Thoralf
Department of Pharmacology, Faculty of Medicine, University of Oslo.
Cell Physiol Biochem. 2003;13(4):229-38. doi: 10.1159/000072426.
Previous data disagree as to the role of extracellular signal-regulated kinase (ERK) in the EGF receptor-mediated stimulation of proliferation in hepatocytes. Using cultured rat hepatocytes, we here show that EGF receptor stimulation in mid/late G(1) phase caused a sustained ERK activation that lasted for at least 48 h. Inhibition of the early part of this activity by a single addition of the MEK inhibitor PD98059 did not affect the DNA synthesis. However, inhibition of both the early and the sustained phase of ERK activation by wash-out and repeated administrations of PD98059 abolished the DNA synthesis induced by EGF and TGFalpha. EGF receptor stimulation also transiently activated p38, and inhibition of p38 by SB203580 markedly decreased the DNA synthesis. Furthermore, EGF and TGFalpha stimulated phosphorylation of Akt, a downstream target of the PI3-kinase pathway, and the PI3-kinase inhibitors wortmannin and LY294002 blocked the EGF-induced DNA synthesis. These results support a mechanism for EGF receptor-mediated mitogenic signalling in hepatocytes where ERK has an obligatory role, acting in concert with PI3-kinase, and augmented by p38. Furthermore, the data suggest that to perform this role ERK has to be activated for a prolonged period.
关于细胞外信号调节激酶（ERK）在表皮生长因子（EGF）受体介导的肝细胞增殖刺激中的作用，以往的数据存在分歧。利用培养的大鼠肝细胞，我们在此表明，在G（1）期中期/后期刺激EGF受体可导致ERK持续激活，持续至少48小时。单次添加MEK抑制剂PD98059抑制该活性的早期部分并不影响DNA合成。然而，通过洗脱和重复给予PD98059抑制ERK激活的早期和持续阶段，可消除EGF和转化生长因子α（TGFα）诱导的DNA合成。EGF受体刺激还可短暂激活p38，用SB203580抑制p38可显著降低DNA合成。此外，EGF和TGFα刺激PI3激酶途径的下游靶点Akt的磷酸化，PI3激酶抑制剂渥曼青霉素和LY294002可阻断EGF诱导的DNA合成。这些结果支持了一种EGF受体介导的肝细胞有丝分裂信号传导机制，其中ERK起着必不可少的作用，与PI3激酶协同作用，并由p38增强。此外，数据表明，ERK要发挥这一作用，必须被长时间激活。
