Involvement of p53 mutation and mismatch repair proteins dysregulation in NNK-induced malignant transformation of human bronchial epithelial cells.

Involvement of p53 mutation and mismatch repair proteins dysregulation in NNK-induced malignant transformation of human bronchial epithelial cells.

Genome integrity is essential for normal cellular functions and cell survival. Its instability can cause genetic aberrations and is considered as a hallmark of most cancers. To investigate the carcinogenesis process induced by tobacco-specific carcinogen NNK, we studied the dynamic changes of two important protectors of genome integrity, p53 and MMR system, in malignant transformation of human bronchial epithelial cells after NNK exposure. Our results showed that the expression of MLH1, one of the important MMR proteins, was decreased early and maintained the downregulation during the transformation in a histone modification involved and DNA methylation-independent manner. Another MMR protein PMS2 also displayed a declined expression while being in a later stage of transformation. Moreover, we conducted p53 mutation analysis and revealed a mutation at codon 273 which led to the replacement of arginine by histidine. With the mutation, DNA damage-induced activation of p53 was significantly impaired. We further reintroduced the wild-type p53 into the transformed cells, and the malignant proliferation can be abrogated by inducing cell cycle arrest and apoptosis. These findings indicate that p53 and MMR system play an important role in the initiation and progression of NNK-induced transformation, and p53 could be a potential therapeutic target for tobacco-related cancers.

基因组完整性对正常细胞功能和细胞存活至关重要。其不稳定性可导致遗传畸变，并被视为大多数癌症的一个标志。为了研究烟草特异性致癌物NNK诱导的致癌过程，我们研究了基因组完整性的两个重要保护因子p53和错配修复（MMR）系统在人支气管上皮细胞经NNK暴露后发生恶性转化过程中的动态变化。我们的结果显示，重要的MMR蛋白之一MLH1的表达在转化早期下降，并在转化过程中以一种涉及组蛋白修饰且不依赖DNA甲基化的方式维持下调。另一种MMR蛋白PMS2在转化后期也表现出表达下降。此外，我们进行了p53突变分析，发现第273位密码子发生突变，导致精氨酸被组氨酸取代。由于该突变，DNA损伤诱导的p53激活显著受损。我们进一步将野生型p53重新引入转化细胞中，通过诱导细胞周期停滞和凋亡可抑制恶性增殖。这些发现表明，p53和MMR系统在NNK诱导的转化起始和进展中起重要作用，并且p53可能是烟草相关癌症的一个潜在治疗靶点。