The hepatitis B virus-X protein activates a phosphatidylinositol 3-kinase-dependent survival signaling cascade
The hepatitis B virus-X protein activates a phosphatidylinositol 3-kinase-dependent survival signaling cascade
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DOI：
10.1074/jbc.m011263200
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发表时间：
2001-05-18
影响因子：
4.8
通讯作者：
Lee, YI
中科院分区：
文献类型：
--
作者：
Lee, YI;Kang-Park, S;Lee, YI
乙肝病毒X蛋白(HBx)是一种多功能蛋白，它不仅能协同激活L；病毒和细胞基因的转录，而且通过诱导或阻断细胞凋亡来协调增殖和细胞程序性死亡之间的平衡。HBx可减轻血清剥夺和促凋亡性刺激诱导的常肝细胞凋亡。1-D-3-脱氧-3-氟-肌醇(1-D-3-deoxy-3-flo-myo-inositol，1-D-3-deoxy-3-flo-myo-inositol)可阻断HBX(CHL-X)转化的CHL细胞中3‘-磷酸化磷脂酰肌醇的形成，但不能阻断正常CHL细胞中3’-磷酸化磷脂酰肌醇的形成。在HBx转化的CHL(CHL-X)细胞中，依赖于PI3K的生存信号下游效应因子之一的丝氨酸47苏氨酸激酶Akt是CHL细胞的2倍，HBx可诱导丝氨酸473位Akt和丝氨酸136位Bad的磷酸化，而这两种作用分别被Wortmannin和显性负突变Akt和Bad所特异性地阻断。我们还发现HBx抑制caspase 3活性，PI3K抑制剂阻断HBx对caspase 3活性的下调。HBx蛋白上PI3K磷酸化所需的区域与已知的反式激活结构域重叠。HBx以非P53依赖的方式阻断血清撤除诱导的CHL细胞的凋亡。结果表明，与其他DNA肿瘤病毒通过灭活P53来阻止细胞凋亡不同，乙肝病毒通过HBx-PI3K-Akt-Bad途径和灭活肝细胞中至少部分不依赖于P53的caspase3活性来实现对凋亡性死亡的保护。此外，这些数据表明，PI3K活性的调节可能代表着一种潜在的治疗策略，以对抗人肝细胞癌中细胞凋亡的发生。
The hepatitis B virus-X (HBx) protein is known as a multifunctional protein that not only coactivates l;tanscription of viral and cellular genes but coordinates the balance between proliferation and programmed cell death, by inducing or blocking apoptosis, In this study the role of the HBx protein in activation of phosphatidylinositol 3-kinase (PI3K) was investigated as a possible cause of anti-apoptosis in liver cells. HBx relieved serum deprivation-induced and pro-apoptic stimuli-induced apoptosis in Chang liver (CHL) cells. Treatment with 1-D-3-deoxy-3-fluoro-myo-inositol, an antagonist to PI3K, which blocks the formation of 3'-phosphorylated phosphatidyl inositol in CHL cells transformed by HBx (CHL-X) but not normal Chang liver (CHL) cells, showed a marked loss of viability with evidence of apoptosis, Similarly, treatment with wortmannin, an inhibitor of PI3K, stimulated apoptosis in HBx-transformed CHL cells but not in normal cells, confirming that HBx blocks apoptosis through the PI3K pathway. The serine 47 threonine kinase, Akt, one of the downstream effecters of PI3K-dependent survival signaling was 2-fold higher in HBx-transformed CHL (CHL-X) cells than CHL cells, Phosphorylation of Akt at serine 473 and Bad at serine 136 were induced by HBx, which were specifically blocked by wortmannin and dominant negative mutants of Akt and Bad, respectively. We also demonstrated that HBx inhibits caspase 3 activity and HBx down-regulation of caspase 3 activity was blocked by the PI3K inhibitor. Regions required for PI3K phosphorylation on the HBx protein overlap with the known transactivation domains. HBx blocks apoptosis induced by serum withdrawal in CHL cells in a p53-independent manner. The results indicate that, unlike other DNA tumor viruses that block apoptosis by inactivating p53, the hepatitis B virus achieves protection from apoptotic death through a HBx-PI3K-Akt-Bad pathway and by inactivating caspase 3 activity that is at least partially p53-independent in liver cells. Moreover, these data suggest that modulation of the PI3K activity may represent a potential therapeutic strategy to counteract the occurrence of apoptosis in human hepatocellular carcinoma.