Fukuda K, Kawata S, Tamura S, Matsuda Y, Inui Y, Igura T, Inoue S, Kudara T, Matsuzawa Y
Second Department of Internal Medicine, Osaka University Medical School, Suita, Japan.
Hepatology. 1998 Sep;28(3):796-804. doi: 10.1002/hep.510280329.
Transforming growth factor betas (TGF-betas) are the potent growth inhibitors for various cell types. Certain transformed cells, however, show poor response to TGF-beta-induced growth inhibition, which contributes to their uncontrolled proliferation. Recently, we have reported that TGF-beta1 induces degradation of activated Src tyrosine kinase in rat fibroblasts. To elucidate the alteration in TGF-beta signaling pathway in tumor cells that cannot respond to the cytokine, we compared the effects of TGF-beta1 on Src kinase in two human hepatoma cell lines, TGF-beta1-insensitive Mahlavu cells and TGF-beta1-sensitive HepG2 cells. TGF-beta1 decreased Src kinase activity in HepG2 cells, but increased cellular Src levels and Src kinase activity in Mahlavu cells. Co-incubation of Mahlavu cells with TGF-beta1 and 12-O-tetradecanoyl phorbol 13-acetate (TPA) decreased Src protein levels and Src kinase activity, inducing TGF-beta1 sensitivity. TGF-beta1 induced tyrosine dephosphorylation of Ras guanosine triphosphatase-activating protein (Ras-GAP) and Ras inactivation in HepG2 cells, but induced Ras-GAP phosphorylation and Ras activation in Mahlavu cells. The Src kinase inhibitor abolished the increase of Src kinase activity in TGF-beta1-treated Mahlavu cells, and induced TGF-beta1 sensitivity. These findings suggest that regulation of Src kinase by TGF-beta1 is altered in Mahlavu cells. The altered regulation of Src may contribute to TGF-beta1 insensitivity in this cell line, at least in part through activation of Ras.
转化生长因子β（TGF-β）对多种细胞类型具有强大的生长抑制作用。然而，某些转化细胞对TGF-β诱导的生长抑制反应不佳，这导致它们不受控制地增殖。最近，我们报道了TGF-β1可诱导大鼠成纤维细胞中活化的Src酪氨酸激酶降解。为了阐明对细胞因子无反应的肿瘤细胞中TGF-β信号通路的改变，我们比较了TGF-β1对两种人肝癌细胞系（对TGF-β1不敏感的Mahlavu细胞和对TGF-β1敏感的HepG2细胞）中Src激酶的影响。TGF-β1降低了HepG2细胞中的Src激酶活性，但增加了Mahlavu细胞中的细胞Src水平和Src激酶活性。将Mahlavu细胞与TGF-β1和12-O-十四烷酰佛波醇-13-乙酸酯（TPA）共同孵育可降低Src蛋白水平和Src激酶活性，从而诱导对TGF-β1的敏感性。TGF-β1在HepG2细胞中诱导Ras鸟苷三磷酸酶激活蛋白（Ras-GAP）的酪氨酸去磷酸化和Ras失活，但在Mahlavu细胞中诱导Ras-GAP磷酸化和Ras激活。Src激酶抑制剂消除了TGF-β1处理的Mahlavu细胞中Src激酶活性的增加，并诱导了对TGF-β1的敏感性。这些发现表明，TGF-β1对Src激酶的调节在Mahlavu细胞中发生了改变。Src调节的改变可能至少部分通过Ras激活导致该细胞系对TGF-β1不敏感。
