Promoter-hypermethylation is causing functional relevant downregulation of methylthioadenosine phosphorylase (MTAP) expression in hepatocellular carcinoma
Promoter-hypermethylation is causing functional relevant downregulation of methylthioadenosine phosphorylase (MTAP) expression in hepatocellular carcinoma
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DOI：
10.1093/carcin/bgi201
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发表时间：
2006-01-01
期刊：
影响因子：
4.7
通讯作者：
Bosserhoff, AK
中科院分区：
文献类型：
--
作者：
Hellerbrand, C;Mühlbauer, M;Bosserhoff, AK
甲硫腺苷磷酸化酶(MTAP)基因定位于染色体9p21区。在这里，几种癌症中经常发生纯合缺失，这与肿瘤抑制基因p16和p15的丢失有关。本研究的目的是分析MTAP在肝细胞癌中的表达，探讨MTAP在肝细胞癌发生中的调控和功能作用。与原代人肝细胞相比，实时定量聚合酶链式反应和Western blotting检测到MTAP在三种不同的肝癌细胞系中的表达明显下调。这不是由于基因组的丢失或突变，而是由于启动子的超甲基化。与非癌肝组织相比，肝细胞癌组织中MTAP-1的表达在mRNA和蛋白水平上均显著降低。为了研究下调的MTAP在肝癌细胞中表达的功能相关性，通过稳定转染法重新诱导肝癌细胞系中MTAP的表达。在这些再表达MTAP的细胞克隆中，侵袭能力显著降低，而对细胞增殖的影响与假手术组相比无明显差异。此外，在MTAP再表达细胞中，干扰素-α和干扰素-γ对细胞增殖的抑制作用明显强于假手术组。综上所述，我们的结果提示MTAP失活在肝细胞癌的发展和侵袭性中起着重要的作用。此外，鉴于最近的一份报告揭示了MTAP活性与干扰素敏感性之间的关联，我们的发现可能对治疗策略具有临床意义。
The methylthioadenosine phosphorylase (MTAP) gene is localized in the chromosomal region 9p21. Here, frequently homozygous deletions occur in several kinds of cancer associated with the loss of tumour suppressor genes as p16 and p15. The aim of this study was to analyse MTAP expression in hepatocellular carcinoma (HCC) and to get an insight into the regulation and functional role of MTAP in hepatocancerogenesis. Compared with primary human hepatocytes MTAP expression was markedly downregulated in three different HCC cell lines as determined by real-time PCR and western blotting. This was not due to genomic losses or mutations but to promoter-hypermethylation. Reduced MTAP-expression was confirmed in vivo in HCC compared with non-cancerous liver tissue on both mRNA and protein levels. To study the functional relevance of the downregulated MTAP expression in HCC, MTAP expression was re-induced in HCC cell lines by stable transfection. In these MTAP re-expressing cell clones the invasive potential was strongly reduced, whereas no effects on cell proliferation were observed in comparison with mock transfected cell clones. Furthermore, in MTAP re-expressing cells interferon (IFN)-alpha and IFN-gamma induced a significantly stronger inhibition of cell proliferation than in mock transfected cells. In conclusion, our results suggest a functional role of MTAP inactivation in HCC development and invasiveness. Furthermore, in the light of a recent report revealing an association between MTAP activity and IFN sensitivity, our findings may have clinical significance for therapeutic strategies.