Akt Phosphorylation of Deleted in Liver Cancer 1 Abrogates Its Suppression of Liver Cancer Tumorigenesis and Metastasis
Akt Phosphorylation of Deleted in Liver Cancer 1 Abrogates Its Suppression of Liver Cancer Tumorigenesis and Metastasis
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DOI：
10.1053/j.gastro.2010.06.051
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发表时间：
2010-10-01
期刊：
影响因子：
29.4
通讯作者：
Yam, Judy Wai Ping
中科院分区：
文献类型：
--
作者：
Ko, Frankie Chi Fat;Chan, Lo-Kong;Yam, Judy Wai Ping
背景与目的：肝癌中缺失1 （dcl1）编码Rho GTPase激活蛋白，是肝细胞癌中真正的肿瘤抑制因子。dcl1在癌症中的低表达归因于基因组缺失和表观遗传沉默。然而，dcl1抑制肿瘤活性的调控机制尚不明确。在这项研究中，我们阐明了一种新的翻译后修饰，通过这种修饰，dcl1的活性在功能上受到调节。方法：采用分子和生化方法研究Akt磷酸化dcl1的作用。通过体外和体内功能实验来阐明Akt磷酸化dcl1的功能意义。结果：在胰岛素诱导或Akt表达的情况下，肝癌细胞系中外源性和内源性dcl1的磷酸化增强。相反，添加磷脂酰肌醇3-激酶/Akt通路抑制剂或沉默Akt可减弱DLC1的磷酸化水平。采用定点突变的方法，用丙氨酸取代dcl1中Akt底物基序的丝氨酸残基。dcl1的S567被确定为Akt磷酸化的唯一靶点。S567在所有DLC家族成员中都有很好的保守性。Akt在相应残基处磷酸化DLC2。功能分析表明，在小鼠模型中，S567D拟磷dcl1突变体失去了对癌性转化肝细胞的肿瘤发生和转移的抑制活性。结论：这项研究揭示了一种新的翻译后修饰，可以在功能上解除dcl1的生物活性。Akt磷酸化DLC c1和DLC c2的保守残基指向了DLC肿瘤抑制家族的共同调控机制。
BACKGROUND & AIMS: Deleted in liver cancer 1 (DLC1), which encodes a Rho GTPase activating protein, is a bona fide tumor suppressor in hepatocellular carcinoma. Underexpression of DLC1 in cancer has been attributed to genomic deletion and epigenetic silencing. However, the regulatory mechanism of the tumor suppressive activity of DLC1 remains elusive. In this study, we elucidated a novel post-translational modification by which the activity of DLC1 is functionally regulated. METHODS: Molecular and biochemical approaches were employed to study Akt phosphorylation of DLC1. In vitro and in vivo functional assays were performed to elucidate the functional significance of Akt phosphorylation of DLC1. RESULTS: Phosphorylation of ectopically expressed and endogenous DLC1 was enhanced upon insulin induction or with Akt expression in liver cancer cell lines. Conversely, addition of a phosphatidylinositol 3-kinase/Akt pathway inhibitor or silencing of Akt attenuated the phosphorylation level of DLC1. Site-directed mutagenesis was employed to replace the serine residue of the consensus Akt substrate motifs of DLC1 with alanine. S567 of DLC1 was identified as the only target of Akt phosphorylation. S567 is well conserved in all DLC family members. DLC2 was phosphorylated by Akt at the corresponding residue. Functional assays demonstrated that the S567D phosphomimetic DLC1 mutant lost its inhibitory activities in tumorigenesis and metastasis of oncogenically transformed hepatoblasts in a mouse model. CONCLUSIONS: This study has revealed a novel post-translational modification that functionally deregulates the biologic activities of DLC1. Phosphorylation of DLC1 and DLC2 by Akt at the conserved residue points to a common regulatory mechanism of the DLC tumor suppressor family.