Simpson D J, Clayton R N, Farrell W E
Centre for Cell and Molecular Medicine, School of Postgraduate Medicine, Keele University, North Staffordshire Hospital, Stoke-on-Trent, ST4 7QB, UK.
Oncogene. 2002 Feb 14;21(8):1217-24. doi: 10.1038/sj.onc.1205195.
Death Associated Protein kinase (DAP kinase) a novel calmodulin-dependent serine/threonine kinase was first identified as a positive mediator of programmed cell death. Loss of DAP kinase expression was first demonstrated in highly metastatic cells, whilst re-expression of the protein resulted in delayed local tumour growth and a decreased incidence of metastasis. Although loss of DAP kinase expression has been reported in several cell lines derived from human malignancies the mechanisms responsible have not been defined. In this study we have examined 32 sporadic pituitary tumours for expression of the DAP kinase protein and transcript. In addition, we examined the methylation and deletion status of the DAP kinase CpG island as possible mechanisms for the inactivation of the DAP kinase gene. Eleven of 32 (34%) tumours had undetectable DAP kinase expression, by Western blot and/or RT-PCR analysis. Loss of DAP kinase expression was significantly (P=0.004) associated with invasive tumours (10 of 17; 59%) compared to their non-invasive (1 of 15; 7%) counterparts. Of 11 tumours that failed to express DAP kinase, five (45%) showed de novo methylation of the CpG island contained within the promoter region, while four (36%) had evidence of homozygous deletion of this region. Statistical analysis showed that loss of DAP kinase expression was significantly (P=<0.001) associated with methylation or deletion of the DAP kinase CpG island. With two exceptions, none of the remaining tumours or five histologically normal post-mortem pituitaries examined had evidence of methylation or deletion within this region. To our knowledge this is the first report that describes two mutually exclusive mechanisms associated with loss of DAP kinase gene expression. In addition, we also show that loss of the DAP kinase protein and associated genetic aberrations preferentially segregates with tumours that show an invasive phenotype.
死亡相关蛋白激酶（DAP激酶）是一种新型的钙调蛋白依赖性丝氨酸/苏氨酸激酶，最初被鉴定为程序性细胞死亡的正向调节因子。DAP激酶表达缺失首次在高转移性细胞中得到证实，而该蛋白的重新表达则导致局部肿瘤生长延迟和转移发生率降低。尽管在源自人类恶性肿瘤的几种细胞系中已报道了DAP激酶表达缺失，但其相关机制尚未明确。在本研究中，我们检测了32例散发性垂体肿瘤中DAP激酶蛋白和转录本的表达。此外，我们还检测了DAP激酶CpG岛的甲基化和缺失状态，将其作为DAP激酶基因失活的可能机制。通过蛋白质印迹法和/或逆转录-聚合酶链反应分析，32例肿瘤中有11例（34%）未检测到DAP激酶表达。与非侵袭性肿瘤（15例中的1例；7%）相比，DAP激酶表达缺失与侵袭性肿瘤（17例中的10例；59%）显著相关（P = 0.004）。在11例未表达DAP激酶的肿瘤中，5例（45%）显示启动子区域内CpG岛的从头甲基化，而4例（36%）有该区域纯合缺失的证据。统计分析表明，DAP激酶表达缺失与DAP激酶CpG岛的甲基化或缺失显著相关（P < 0.001）。除两例外，其余肿瘤或所检测的5例组织学正常的尸检垂体均无该区域甲基化或缺失的证据。据我们所知，这是第一份描述与DAP激酶基因表达缺失相关的两种相互排斥机制的报告。此外，我们还表明，DAP激酶蛋白的缺失及相关基因畸变优先与具有侵袭性表型的肿瘤相关。
