Clinical significance of oncogenic mutations of p53 gene in oral cancen : Relationship of the mutations with radiation- and chemo-sensitivity

我们研究了来自人头颈部癌细胞系的几个突变型p53的功能多样性。将p5 3基因全长开放阅读框亚克隆到哺乳动物表达载体中，并测定其基因突变。然后，在缺乏p53基因的人骨肉瘤细胞系Saos-2细胞中检测它们的细胞内定位、转录活性和致癌功能。突变型P53(Glu17Lys，His193Leu)或截短型P53(Delta 121)不能激活含有p21waf1、bax、mdm2、p53AIP和PUMA基因应答元件的报告基因。然而，突变型p53(Asn30Ser)在所有的记者身上都显示出转录活性。另一方面，突变型p53(Asp28lHis)对p21waf1启动子有较强的激活作用，对MDM2启动子有微弱的激活作用，但对Bax启动子没有激活作用。有趣的是，这种突变型p53阻止了用DNA损伤剂阿霉素处理后的Saos-2细胞发生凋亡。突变型P53强烈诱导细胞周期停滞，但微弱地诱导细胞凋亡。另一个突变体P53(Glu17Lys，His193Leu)也可能以一种转录不依赖的方式阻止DNA损伤后的细胞凋亡。这些结果表明，某些头颈部癌细胞系存在P53基因的致癌突变，致癌的P53蛋白阻止了DNA损伤后的癌细胞发生凋亡。

We examined the functional diversity of several mutant-p53 derived from human head and neck cancer cell lines. Entire open reading frame of p53 cDNA was subcloned into a mammalian expression vector, and genetic mutations were determined. Then, their intracellular localization, transcriptional activity, and oncogenic function were examined in a human osteosarcoma cell line lacking p53 gene, Saos-2 cells. A mutant-p53 (Glu17Lys,His193Leu) or a truncated-p53 (delta 121) did not activate the reporters containing p53 responsive elements from p21waf1,BAX,MDM2,p53AIP, and PUMA genes. However, a mutant-p53 (Asn30Ser) showed the transcriptional activity on all of the reporters. On the other hand, a mutant-p53 (Asp28lHis) activated the p21waf1 promoter strongly and the MDM2 promoter faintly, but did not activate the BAX promoter. Interestingly, this mutant-p53 prevented Saos-2 cells from undergoing apoptosis after treatment with a DNA damaging agent, adriamycin. This mutant-p53 strongly induced cell cycle arrest but marginally induced apoptosis. Another mutant-p53 (Glu17Lys,His193Leu) also prevented the cells from undergoing apoptosis after DNA damage probably in a transcription-independent manner. These results suggest that some head and neck cancer cell lines contain the oncogenic mutation of p53 gene, and the oncogenic p53 protein prevents cancer cells from undergoing apoptosis after DNA damage.