High intensity ERK signal mediates hepatocyte growth factor-induced proliferation inhibition of the human hepatocellular carcinoma cell line HepG2
High intensity ERK signal mediates hepatocyte growth factor-induced proliferation inhibition of the human hepatocellular carcinoma cell line HepG2
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DOI：
10.1074/jbc.m010890200
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发表时间：
2001-11-02
影响因子：
4.8
通讯作者：
Kitamura, N
中科院分区：
文献类型：
--
作者：
Tsukada, Y;Miyazawa, K;Kitamura, N
肝细胞生长因子(HGF)不仅能刺激多种细胞的生长，还能抑制多种肿瘤细胞的生长。HGF抑制肿瘤细胞生长的分子机制尚不清楚。我们研究了HGF抑制人肝癌细胞株HepG2增殖的细胞内信号转导途径。HGF可诱导HepG2细胞ERK的强激活。尽管MEK抑制剂PD98059呈剂量依赖性地抑制血清依赖性的细胞增殖，但10µM PD98059可将HGF诱导的ERK的强激活减弱为弱激活，从而使HGF抑制的细胞增殖完全恢复。高于或低于这个特定浓度，修复都是不完整的。Ha-RAS的表达导致ERK的强烈激活，导致了细胞的增殖抑制，正如HGF处理的HepG2细胞中观察到的那样。这种抑制作用可被MEK抑制剂抑制。此外，HGF处理和结构性激活的Ha-RAS的表达将视网膜母细胞瘤肿瘤抑制基因产物pRb的过度磷酸化形式改变为低磷酸化形式。这一变化可被抑制增殖所需的相同浓度的MEK抑制剂所抑制。这些结果表明，ERK活性是促进和抑制HepG2细胞增殖所必需的；ERK活性的水平决定了相反的增殖反应；HGF诱导的增殖抑制是由细胞周期停滞引起的，这是由于在HepG2细胞中，通过高强度的ERK信号维持了PRB的活性低磷酸化形式。
Hepatocyte growth factor (HGF) induces growth stimulation of a variety of cell types, but it also induces growth inhibition of several types of tumor cell lines. The molecular mechanism of the HGF-induced growth inhibition of tumor cells remains obscure. We have investigated the intracellular signaling pathway involved in the antiproliferative effect of HGF on the human hepatocellular carcinoma cell line HepG2. HGF induced strong activation of ERK in HepG2 cells. Although the serum-dependent proliferation of HepG2 cells was inhibited by the MEK inhibitor PD98059 in a dose-dependent manner, 10 muM PD98059 reduced the HGF-induced strong activation of ERK to a weak activation; and as a result, the proliferation inhibited by HGF was completely restored. Above or below this specific concentration, the restoration was incomplete. Expression of constitutively activated Ha-Ras, which induces strong activation of ERK, led to the proliferation inhibition of HepG2 cells, as was observed in HGF-treated HepG2 cells. This inhibition was suppressed by the MEK inhibitor. Furthermore, HGF treatment and expression of constitutively activated Ha-Ras changed the hyperphosphorylated form of the retinoblastoma tumor suppressor gene product pRb to the hypophosphorylated form. This change was inhibited by the same concentration of MEK inhibitor needed to suppress the proliferation inhibition. These results suggest that ERK activity is required for both the stimulation and inhibition of proliferation of HepG2 cells; that the level of ERK activity determines the opposing proliferation responses; and that HGF-induced proliferation inhibition is caused by cell cycle arrest, which results from pRb being maintained in its active hypophosphorylated form via a high-intensity ERK signal in HepG2 cells.