Huynh H, Do P T, Nguyen T H, Chow P, Tan P H, Quach T H, Van T, Soo K C, Tran E
Laboratory of Molecular Endocrinology, Division of Cellular and Molecular Research, National Cancer Centre of Singapore, 169610, Singapore.
Int J Oncol. 2004 Dec;25(6):1839-47. doi: 10.3892/ijo.25.6.1839.
Hepatocellular carcinoma (HCC) is one of the most common malignancies in Southeast Asia. Hyperphosphorylation of retinoblastoma (pRB) by cyclin/CDKs in G1/S transition is required for its inactivation and cell cycle progression. In the present study, we report that phosphorylation of pRB at Ser780 and Ser795 was detected in 71% (33 of 46) and 63% (29 of 46) of HCCs examined respectively. pRB protein was undetectable in 13% (6 of 46) of HCCs examined. Phosphorylated pRB was localized in the nuclei of hepatocarcinoma cells. Benign hepatocytes exhibited very weakly or no nuclear staining for phosphorylated pRB. Over-expression of E2F-1, cyclin D1, Cdk-2, Cdk-4 and cyclin A was found in 64% (30 of 46), 43% (26 of 46), 28% (11 of 46), 71% (33 of 46) and 63% (29 of 46) of HCCs examined respectively and this was correlated with elevation of ERK. Treatment of HepG2 cells with MEK1/2 inhibitor U0126 resulted in cell cycle arrest, downregulation of cyclin D1 and Cdk-2 expression and inhibition of pRB phosphorylation at Ser780 and Ser795. Ectopic expression of activated MEK1 in HepG2 cells increased cyclin D1 and Cdk-2 expression, phosphorylation of pRB at Ser780 and Ser795, and percentage of cells in S phase. Our data indicate that activated ERK plays an important role in cyclin D1 and Cdk-2 expression and phosphorylation of pRB at Ser780 and Ser795 in liver cancer cells.
肝细胞癌（HCC）是东南亚最常见的恶性肿瘤之一。在G1/S期转换过程中，细胞周期蛋白/周期蛋白依赖性激酶（CDKs）对视网膜母细胞瘤（pRB）的过度磷酸化是其失活和细胞周期进展所必需的。在本研究中，我们报告在分别检测的46例HCC中，71%（33/46）和63%（29/46）检测到pRB在Ser780和Ser795位点的磷酸化。在检测的46例HCC中，13%（6/46）未检测到pRB蛋白。磷酸化的pRB定位于肝癌细胞核中。良性肝细胞对磷酸化pRB的核染色非常弱或无染色。在分别检测的46例HCC中，64%（30/46）、43%（26/46）、28%（11/46）、71%（33/46）和63%（29/46）中发现E2F-1、细胞周期蛋白D1、细胞周期蛋白依赖性激酶2（Cdk-2）、细胞周期蛋白依赖性激酶4（Cdk-4）和细胞周期蛋白A的过表达，这与细胞外信号调节激酶（ERK）升高相关。用MEK1/2抑制剂U0126处理HepG2细胞导致细胞周期停滞、细胞周期蛋白D1和Cdk-2表达下调以及Ser780和Ser795位点pRB磷酸化的抑制。在HepG2细胞中异位表达活化的MEK1增加了细胞周期蛋白D1和Cdk-2的表达、Ser780和Ser795位点pRB的磷酸化以及S期细胞百分比。我们的数据表明，活化的ERK在肝癌细胞中细胞周期蛋白D1和Cdk-2的表达以及Ser780和Ser795位点pRB的磷酸化中起重要作用。
