Dep. Bioquímica y Biología Molecular II, Facultad de Farmacia, Universidad Complutense, Madrid, Spain.
Laboratori d´Oncologia Molecular and Departament de Ciències Fisiològiques II, Universitat de Barcelona, Institut d´Investigació Biomèdica de Bellvitge, L'Hospitalet de Llobregat, Barcelona, Spain.
Cell Signal. 2012 Feb;24(2):505-513. doi: 10.1016/j.cellsig.2011.09.031. Epub 2011 Oct 7.
Liver progenitor cells rise as potential critical players in hepatic regeneration but also carcinogenesis. It is therefore mandatory to define the signals controlling their activation and expansion. Recently, by using a novel in vitro model of oval cell lines expressing a mutant tyrosine kinase-inactive form of c-Met we demonstrated that autocrine c-Met signalling plays an essential role in promoting oval cell survival. Here, we investigated the significance of the epidermal growth factor receptor (EGFR) signalling in oval cell proliferation and survival, as well as a potential functional crosstalk between the c-Met and the EGFR pathways. We found an autocrine activation of the EGFR-triggered pathway in Met(flx/flx) and Met(-/-) oval cells as judged by constitutive expression of the EGFR ligands, transforming growth factor-alpha (TGF-α) and heparin-binding EGF like growth factor (HB-EGF), and activation of EGFR. On the other hand, treatment with AG1478, a specific inhibitor of EGFR, effectively blocked endogenous and EGF-induced proliferation, while increased serum withdrawal and transforming growth factor-beta (TGF-β)-induced apoptosis. These results suggest that constitutively activated EGFR might promote oval cell proliferation and survival. We found that hepatocyte growth factor (HGF) does not transactivate EGFR nor EGF transactivates c-Met. Furthermore, treatment with AG1478 or EGFR gene silencing did not interfere with HGF-mediated activation of target signals, such as protein kinase B (AKT/PKB), and extracellular signal-regulated kinases 1/2 (ERK 1/2), nor did it have any effect on HGF-induced proliferative and antiapoptotic activities in Met(flx/flx) cells, showing that HGF does not require EGFR activation to mediate such responses. EGF induced proliferation and survival equally in Met(flx/flx) and Met(-/-) oval cells, proving that EGFR signalling does not depend on c-Met tyrosine kinase activity. Together, our results provide strong evidence that in normal, untransformed oval cells, c-Met and EGFR represent critical molecular players to control proliferation and survival that function independent of one another.
肝祖细胞作为肝再生和癌变的潜在关键因子而备受关注。因此，有必要明确控制其激活和扩增的信号。最近，我们使用一种新型的体外模型，即表达突变型酪氨酸激酶失活型 c-Met 的卵圆细胞系，证明了自分泌 c-Met 信号在促进卵圆细胞存活方面发挥着至关重要的作用。在此，我们研究了表皮生长因子受体（EGFR）信号在卵圆细胞增殖和存活中的意义，以及 c-Met 和 EGFR 途径之间可能存在的功能串扰。我们发现，在 Met(flx/flx)和 Met(-/-)卵圆细胞中，EGFR 信号通路被自分泌激活，这可以通过 EGFR 配体转化生长因子-α（TGF-α）和肝素结合表皮生长因子样生长因子（HB-EGF）的组成性表达以及 EGFR 的激活来判断。另一方面，特异性 EGFR 抑制剂 AG1478 的处理可有效阻断内源性和 EGF 诱导的增殖，同时增加血清撤离和转化生长因子-β（TGF-β）诱导的细胞凋亡。这些结果表明，持续激活的 EGFR 可能促进卵圆细胞的增殖和存活。我们发现，肝细胞生长因子（HGF）不能转激活 EGFR，EGF 也不能转激活 c-Met。此外，AG1478 处理或 EGFR 基因沉默并不干扰 HGF 介导的靶信号激活，如蛋白激酶 B（AKT/PKB）和细胞外信号调节激酶 1/2（ERK 1/2），也不会对 HGF 诱导的 Met(flx/flx)细胞的增殖和抗凋亡活性产生任何影响，表明 HGF 不需要 EGFR 激活来介导这些反应。EGF 可在 Met(flx/flx)和 Met(-/-)卵圆细胞中同样诱导增殖和存活，证明 EGFR 信号不依赖于 c-Met 酪氨酸激酶活性。总之，我们的研究结果为 c-Met 和 EGFR 在正常未转化的卵圆细胞中作为控制增殖和存活的关键分子提供了有力证据，它们彼此独立发挥作用。
