Scheving Lawrence A, Zhang Linda, Stevenson Mary C, Kwak Eun Soo, Russell William E
Division of Endocrinology, Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232-0710, USA.
Am J Physiol Gastrointest Liver Physiol. 2006 Jul;291(1):G16-25. doi: 10.1152/ajpgi.00328.2005.
The proliferative effects of EGF in liver have been extensively investigated in cultured hepatocytes. We studied the effects of EGF, insulin, and other growth regulators on the expression, interaction, and signaling of ErbB receptors in primary cultures of adult rat hepatocytes. Using immunological methods and ErbB tyrosine kinase inhibitors, we analyzed the expression and signaling patterns of the ErbB kinases over 120 h of culture. Basal and EGF-stimulated protein tyrosine phosphorylation increased as cells adapted in vitro. EGF receptor (EGFr) expression declined in the first 24 h, whereas ErbB3 expression rose. Although ErbB2 was not present in freshly isolated hepatocytes, EGF and insulin independently induced ErbB2 while suppressing ErbB3 expression. Low concentrations of EGF and insulin synergistically stimulated ErbB2 expression and DNA synthesis. The greatest increase in ErbB2, which is normally expressed by fetal and neonatal hepatocytes, occurred shortly before the onset of DNA synthesis (> 40 h). EGF promoted EGFr and ErbB2 coassociation, stimulating tyrosine phosphorylation of both proteins. In contrast, heregulin beta1 (HRG-beta1) did not promote ErbB2 and ErbB3 coassociation. A selective tyrphostin inhibitor of ErbB2 suppressed EGF-stimulated DNA synthesis, but maximum suppression required the blockade of the EGFr kinase as well. Maximal EGF stimulation of DNA synthesis in vitro depends on the induction of ErbB2 and involves an EGFr-ErbB2 heterodimer. The ability of insulin to induce ErbB2 suggests both a mechanism for the synergy between insulin and EGF and a possible metabolic control of ErbB2 in vivo.
表皮生长因子（EGF）在肝脏中的增殖作用已在培养的肝细胞中得到广泛研究。我们研究了EGF、胰岛素及其他生长调节因子对成年大鼠原代肝细胞中ErbB受体的表达、相互作用和信号传导的影响。运用免疫学方法和ErbB酪氨酸激酶抑制剂，我们分析了培养120小时内ErbB激酶的表达和信号传导模式。随着细胞在体外适应，基础及EGF刺激的蛋白酪氨酸磷酸化增加。表皮生长因子受体（EGFr）的表达在最初24小时下降，而ErbB3的表达上升。虽然新鲜分离的肝细胞中不存在ErbB2，但EGF和胰岛素可独立诱导ErbB2表达，同时抑制ErbB3表达。低浓度的EGF和胰岛素协同刺激ErbB2表达及DNA合成。通常由胎儿和新生儿肝细胞表达的ErbB2在DNA合成开始前不久（>40小时）出现最大程度的增加。EGF促进EGFr与ErbB2的共缔合，刺激两种蛋白的酪氨酸磷酸化。相反，神经调节蛋白β1（HRG-β1）不促进ErbB2与ErbB3的共缔合。一种选择性的ErbB2酪氨酸磷酸化抑制剂可抑制EGF刺激的DNA合成，但最大抑制效果还需要阻断EGFr激酶。体外最大程度的EGF刺激DNA合成取决于ErbB2的诱导，并涉及EGFr-ErbB2异二聚体。胰岛素诱导ErbB2的能力提示了胰岛素与EGF协同作用的机制以及体内对ErbB2可能的代谢调控。
