Stiewe Thorsten, Tuve Sebastian, Peter Martin, Tannapfel Andrea, Elmaagacli Ahmet H, Pützer Brigitte M
Center for Cancer Research and Cancer Therapy, Institute of Molecular Biology, University of Essen Medical School, Essen, Germany.
Clin Cancer Res. 2004 Jan 15;10(2):626-33. doi: 10.1158/1078-0432.ccr-0153-03.
The p53 family member p73 displays significant homology to p53, but data from primary tumors demonstrating increased expression levels of p73 in the absence of any gene mutations argue against a classical tumor suppressor function. A detailed analysis of the p73 protein in tumor tissues has revealed expression of two classes of p73 isoforms. Whereas the proapoptotic, full-length, transactivation-competent p73 protein (TA-p73) has a putative tumor suppressor activity similar to p53, the antiapoptotic, NH(2)-terminally truncated, transactivation-deficient p73 protein (DeltaTA-p73) has been shown to possess oncogenic activity. The oncogenic proteins can be generated by the following two different mechanisms: (a) aberrant splicing (p73Deltaex2, p73Deltaex2/3, DeltaN'-p73) and (b) alternative promoter usage of a second intronic promoter (DeltaN-p73). The purpose of our study was to elucidate the origin of DeltaTA-p73 isoforms in hepatocellular carcinomas.
We analyzed the underlying mechanisms of p73 overexpression in cancer cells by quantification of p73 transcripts from 10 hepatocellular carcinoma patients using isoform-specific real-time reverse transcription-PCR.
Our data demonstrate that only aberrantly spliced DeltaTA-p73 transcripts from the TA promoter show significantly increased expression levels in the tumor whereas the DeltaN-p73 transcript generated from the second promoter is not significantly up-regulated.
Although we only analyzed 10 patient samples the results strongly suggest that the elevated activity of the first promoter (TA promoter) accounts for high-level expression of both full-length TA-p73 and aberrantly spliced DeltaTA-p73 isoforms in hepatocellular carcinoma tissues.
p53家族成员p73与p53显示出显著的同源性，但来自原发性肿瘤的数据表明，在没有任何基因突变的情况下p73表达水平升高，这与经典的肿瘤抑制功能相悖。对肿瘤组织中p73蛋白的详细分析揭示了两类p73亚型的表达。促凋亡的、全长的、具有反式激活能力的p73蛋白（TA-p73）具有与p53相似的假定肿瘤抑制活性，而抗凋亡的、氨基末端截短的、缺乏反式激活能力的p73蛋白（DeltaTA-p73）已被证明具有致癌活性。致癌蛋白可通过以下两种不同机制产生：（a）异常剪接（p73Deltaex2、p73Deltaex2/3、DeltaN'-p73）和（b）第二个内含子启动子的替代启动子使用（DeltaN-p73）。我们研究的目的是阐明肝细胞癌中DeltaTA-p73亚型的起源。
我们通过使用亚型特异性实时逆转录PCR对10例肝细胞癌患者的p73转录本进行定量分析，来分析癌细胞中p73过表达的潜在机制。
我们的数据表明，来自TA启动子的异常剪接的DeltaTA-p73转录本在肿瘤中的表达水平显著增加，而来自第二个启动子产生的DeltaN-p73转录本没有显著上调。
尽管我们只分析了10个患者样本，但结果强烈表明，第一个启动子（TA启动子）的活性升高是肝细胞癌组织中全长TA-p73和异常剪接的DeltaTA-p73亚型高水平表达的原因。
