Zhang B H, Ho V, Farrell G C
Storr Liver Unit, Department of Medicine and Westmead Millennium Institute, University of Sydney at Westmead Hospital, NSW 214, Westmead, Australia.
Biochem Pharmacol. 2001 Apr 15;61(8):1021-7. doi: 10.1016/s0006-2952(01)00554-8.
We have previously shown that chronic alcohol consumption inhibits liver regeneration by impairing epidermal growth factor receptor (EGFR)-operated phospholipase C-(gamma1) (PLC-(gamma1)) activation and the resultant rise in intracellular Ca(2+). In hepatocytes, activation of PLC-(gamma1) by EGFR requires involvement of a pertussis toxin-sensitive inhibitory guanine nucleotide-binding regulatory protein (G(alphai)) as an intermediate. In the present study, we first identified the G(alphai) protein isoform associated with the activated EGFR, and then examined whether the toxic effect of alcohol on EGFR signaling and liver cell proliferation was exerted on this association. In cultured hepatocytes from control rats, EGF rapidly induced association between EGFR and G(alphai2) but not other G(alphai) isoforms. In hepatocytes from rats fed alcohol for 16 weeks, EGF failed to stimulate this association of G(alphai2) with the EGFR. The impairment of EGFR-G(alphai2) complex formation caused by alcohol was associated with a decreased level of G(alphai2) in the plasma membrane fraction (approximately 50% control). Pertussis toxin, an inhibitor of G(alphai) function, produced an analogous disruption of the association between G(alphai2) and the EGFR, as well as inhibiting EGF-induced DNA synthesis. It is concluded that, in hepatocytes, G(alphai2) is specific among G(alphai) isoforms in coupling activation of the EGFR to other signaling pathways that control cell proliferation. Impaired coupling of G(alphai2) of EGFR could contribute to the mechanism by which chronic alcohol exposure inhibits liver regeneration.
我们之前已经表明，长期饮酒会通过损害表皮生长因子受体（EGFR）介导的磷脂酶C-γ1（PLC-γ1）激活以及细胞内钙离子浓度（Ca(2+)）的相应升高来抑制肝脏再生。在肝细胞中，EGFR对PLC-γ1的激活需要一种百日咳毒素敏感的抑制性鸟嘌呤核苷酸结合调节蛋白（G(alphai)）作为中间介质参与。在本研究中，我们首先鉴定了与活化的EGFR相关的G(alphai)蛋白亚型，然后研究了酒精对EGFR信号传导和肝细胞增殖的毒性作用是否作用于这种关联。在来自对照大鼠的培养肝细胞中，表皮生长因子（EGF）迅速诱导EGFR与G(alphai2)而非其他G(alphai)亚型之间的关联。在喂食酒精16周的大鼠的肝细胞中，EGF未能刺激G(alphai2)与EGFR的这种关联。酒精导致的EGFR-G(alphai2)复合物形成受损与质膜部分中G(alphai2)水平降低（约为对照的50%）有关。百日咳毒素是G(alphai)功能的抑制剂，它导致G(alphai2)与EGFR之间的关联类似地受到破坏，同时也抑制了EGF诱导的DNA合成。结论是，在肝细胞中，G(alphai2)在G(alphai)亚型中是特异性的，它将EGFR的激活与控制细胞增殖的其他信号通路偶联起来。EGFR的G(alphai2)偶联受损可能是长期酒精暴露抑制肝脏再生的机制之一。
