Department of Clinical Hematology, Third Military Medical University, Chongqing, China.
PLoS One. 2012;7(4):e35754. doi: 10.1371/journal.pone.0035754. Epub 2012 Apr 23.
Abnormal activation of the canonical Wnt signaling pathway has been implicated in carcinogenesis. Transcription of Wnt target genes is regulated by nuclear β-catenin, whose over-expression is observed in Hepatocellular Carcinoma (HCC) tissue. Cyr61, a member of the CCN complex family of multifunctional proteins, is also found over-expressed in many types of tumor and plays dramatically different roles in tumorigenesis. In this study, we investigated the relationship between Cyr61 and β-catenin in HCC. We found that while Cyr61 protein was not expressed at a detectable level in the liver tissue of healthy individuals, its expression level was elevated in the HCC and HCC adjacent tissues and was markedly increased in cancer-adjacent hepatic cirrhosis tissue. Over-expression of Cyr61 was positively correlated with increased levels of β-catenin in human HCC samples. Activation of β-catenin signaling elevated the mRNA level of Cyr61 in HepG2 cells, while inhibition of β-catenin signaling reduced both mRNA and protein levels of Cyr61. We identified two TCF4-binding elements in the promoter region of human Cyr61 gene and demonstrated that β-catenin/TCF4 complex specifically bound to the Cyr61 promoter in vivo and directly regulated its promoter activity. Furthermore, we found that over-expression of Cyr61 in HepG2 cells promoted the progression of HCC xenografts in SCID mice. These findings indicate that Cyr61 is a direct target of β-catenin signaling in HCC and may play an important role in the progression of HCC.
经典 Wnt 信号通路的异常激活与致癌作用有关。Wnt 靶基因的转录受核 β-catenin 调控,在肝癌 (HCC) 组织中观察到其过表达。Cyr61 是多功能蛋白 CCN 家族的成员,在许多类型的肿瘤中也发现过表达,并在肿瘤发生中发挥截然不同的作用。在本研究中,我们研究了 Cyr61 和 β-catenin 在 HCC 中的关系。我们发现,尽管 Cyr61 蛋白在健康个体的肝组织中无法检测到表达,但在 HCC 和 HCC 相邻组织中的表达水平升高,在癌旁肝硬化组织中明显增加。Cyr61 的过表达与人类 HCC 样本中β-catenin 水平的升高呈正相关。β-catenin 信号的激活可上调 HepG2 细胞中 Cyr61 的 mRNA 水平,而抑制β-catenin 信号可降低 Cyr61 的 mRNA 和蛋白水平。我们在人 Cyr61 基因的启动子区域鉴定出两个 TCF4 结合元件,并证明 β-catenin/TCF4 复合物可特异性结合 Cyr61 启动子,直接调节其启动子活性。此外,我们发现 HepG2 细胞中 Cyr61 的过表达可促进 HCC 异种移植物在 SCID 小鼠中的进展。这些发现表明 Cyr61 是 HCC 中 β-catenin 信号的直接靶标,可能在 HCC 的进展中发挥重要作用。