Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
Hepatology. 2010 Dec;52(6):2023-33. doi: 10.1002/hep.23939. Epub 2010 Oct 26.
The A kinase anchor protein 12 (AKAP12) is a central mediator of protein kinase A and protein kinase C signaling. Although AKAP12 has been described to act as a tumor suppressor and its expression is frequently down-regulated in several human malignancies, the underlying molecular mechanisms responsible for the AKAP12 reduction are poorly understood. We therefore analyzed the expression of AKAP12 and its genetic and epigenetic regulatory mechanisms in human hepatocarcinogenesis. Based on tissue microarray analyses (n = 388) and western immunoblotting, we observed a significant reduction of AKAP12 in cirrhotic liver (CL), premalignant lesions (DN), and hepatocellular carcinomas (HCCs) compared to histologically normal liver specimens (NL). Analyses of array comparative genomic hybridization data (aCGH) from human HCCs revealed chromosomal losses of AKAP12 in 36% of cases but suggested additional mechanisms underlying the observed reduction of AKAP12 expression in hepatocarcinogenesis. Quantitative methylation analysis by MassARRAY of NL, CL, DN, and HCC tissues, as well as of various tumorigenic and nontumorigenic liver cell lines revealed specific hypermethylation of the AKAP12α promoter but not of the AKAP12β promoter in HCC specimens and in HCC cell lines. Consequently, restoration experiments performed with 5-aza-2'deoxycytidine drastically increased AKAP12α mRNA levels in a HCC cell line (AKN1) paralleled by AKAP12α promoter demethylation. As hypermethylation is not observed in CL and DN, we investigated microRNA-mediated posttranscriptional regulation as an additional mechanism to explain reduced AKAP12 expression. We found that miR-183 and miR-186 are up-regulated in CL and DN and are able to target AKAP12.
In addition to genetic alterations, epigenetic mechanisms are responsible for the reduction of the tumor suppressor gene AKAP12 in human hepatocarcinogenesis.
蛋白激酶 A 和蛋白激酶 C 信号的一个中央介质是蛋白激酶锚定蛋白 12（AKAP12）。尽管已经描述 AKAP12 作为肿瘤抑制因子起作用并且其表达在几种人类恶性肿瘤中经常下调，但是负责 AKAP12 减少的潜在分子机制知之甚少。因此，我们分析了 AKAP12 的表达及其遗传和表观遗传调节机制在人类肝癌发生中。基于组织微阵列分析（n = 388）和western 免疫印迹，我们观察到与组织学正常肝标本（NL）相比，肝硬化肝（CL）、前恶性病变（DN）和肝细胞癌（HCC）中 AKAP12 显著减少。来自人类 HCC 的阵列比较基因组杂交数据分析（aCGH）显示 AKAP12 的染色体丢失在 36%的病例中，但表明在肝癌发生中观察到的 AKAP12 表达减少的其他机制。NL、CL、DN 和 HCC 组织以及各种肿瘤发生和非肿瘤发生的肝细胞系的定量甲基化分析通过 MassARRAY 显示 HCC 标本和 HCC 细胞系中 AKAP12α 启动子的特异性高甲基化，但 AKAP12β 启动子没有高甲基化。因此，用 5-aza-2'-脱氧胞苷进行的恢复实验在 HCC 细胞系（AKN1）中极大地增加了 AKAP12α mRNA 水平，伴随着 AKAP12α 启动子去甲基化。由于 CL 和 DN 中不观察到高甲基化，我们研究了 microRNA 介导的转录后调节作为解释 AKAP12 表达减少的另一种机制。我们发现 miR-183 和 miR-186 在 CL 和 DN 中上调并且能够靶向 AKAP12。
除了遗传改变，表观遗传机制负责人类肝癌发生中肿瘤抑制基因 AKAP12 的减少。
