Isolation and characterization of additional genes influencing resistance to various mutagens in the yeast Saccharomyces cerevisiae

Summary Screening of a multi-copy vector-based yeast genomic library in haploid cells of wild-type Saccharomyces cerevisiae yielded transformants hyper-resistant to various chemical mutagens. Genetical analysis of the yeast insert DNAs revealed three genes SNG1, SNQ2, and SNQ3 that confer the phenotype hyper-resistance to MNNG, to 4-NQO and triaziquone, and to mutagens 4-NQO, MNNG, and triaziquone, respectively. Integration of the gene disruption-constructs into the haploid yeast genome yielded viable null-mutants with a mutagen-sensitive phenotype. Thus, copy number of these non-essential yeast genes determines the relative resistance to certain chemical mutagens, with zero copies yielding a phenotype of mutagen sensitivity and multiple copies one of mutagen hyper-resistance, respectively.Dedicated to Professor Dr. R. W. Kaplan on the occasion of his 80th birthday     

Spontaneous and MNNG‐induced reversion of an EGFP construct in HeLa cells: An assay for observing mutations in living cells by fluorescent microscopy

A HeLa cell line stably expressing the enhanced green fluorescence protein (EGFP) gene, interrupted by the HBB IVS2‐654 intron, was studied without treatment and after treatment with a single standard dose of 15 μM of N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG). This assay was done in order to prove that such a construct can revert by a variety of mechanisms and that it produces a visible phenotype, i.e., green fluorescence. The system permits visual detection of living mutant cells among a background of non‐mutant cells and does not require a selective medium. The results show that the construct reverts by large deletions (–62, –100, and –162 bp), small insertions (+4 bp), small rearrangements (19 bp duplication), base substitutions at purines (G₆₅₂, G₆₅₃, A₆₅₅, G₅₇₉), and a pyrimidine (T₆₅₄) between nucleotide positions 579 and 837. Splice‐site mutations were recovered, and some of the mechanisms underlying these mutations are discussed. Because of the ease of detection of revertant cells under fluorescent light and the wide variety of mutations that can be recovered, further development of this system could make it a useful new mammalian cell mutagenicity assay. Hum Mutat 18:526–534, 2001. © 2001 Wiley‐Liss, Inc.     

反义阻断hREV3基因表达对细胞生长及MNNG敏感性的影响

目的：应用反义核酸阻断技术研究ｈＲＥＶ３基因对细胞生长和ＭＮＮＧ敏感性的影响。方法：酶切法构建表达反义ｈＲＥＶ３基因片段的真核细胞表达质粒;以改良的磷酸钙－ＤＮＡ共沉淀法建立ｈＲＥＶ３基因表达被阻断的人胚肾细胞（２９３细胞）细胞系（２９３－ｈＲＥＶ３＾－）。以细胞记数方法检测核细胞系的生长速率及不同浓度的烷化剂ＭＮＮＧ对细胞的毒作用。结果：ｈＲＥＶ３基因表达被阻断的人胚肾细胞（２９３－ｈＲＥＶ３＾     

MNNG诱发大鼠腺胃癌模型的建立及p53,ras基因表达的研究

目的建立N一甲基一N’一硝基一N一亚硝基胍（N－methy1－N’－nitro－N－nitrosoguanidine，MNNG）诱发大鼠腺胃癌模型并观察p53，ras基因的表达。方法给Wistar大鼠饮用MNNG水溶液（终浓度为80μg／ml），用ABC法检测P53和P21蛋白的表达。结果MNNG成功地诱发出了胃癌、胃腺瘤、胃息肉、胃粘膜不典型增生和历上皮化生等病变。胃癌肝转移2例，淋巴结转移1例。P53蛋白在肠化及不典型增生皆阴性，胃癌阳性率为50％；P21蛋白在肠化及不典型增生中阳性率为44％，在癌组织中为23％。结论MNNG能诱发大鼠脾胃癌等病变，P53基因突变在胃癌发生发展过程中起一定作用，而ras基因激活是一个早期现象。     

人成骨细胞株HOS TE85致瘤性转化的研究

目的建立人成骨细胞株HOS TE85致瘤性转化的模型, 作为骨肉瘤癌变过程细胞分子生物学研究的模型.方法通过克隆形成率实验确定N-甲基-N′-硝基-N-亚硝基胍(N-methyl-N′-nitro-N-nitrosoguanidine, MNNG)对HOS TE85细胞转化浓度后,以MNNG作启动剂,佛波酯(12-0-Te-tradecanoyl phorbol 13-acetate, TPA)作促进剂对其进行转化,66 d后通过细胞形态、软琼脂集落形成实验和裸鼠体内致瘤实验鉴定细胞转化程度.结果经MNNG和TPA协同处理HOS TE85细胞66 d后,细胞中出现形态异常的转化灶,转化灶细胞失去接触抑制;转化细胞凝集性增强;软琼脂克隆形成率明显增加;转化细胞在裸鼠皮下成瘤,病理组织学证实为低分化骨肉瘤.结论模拟人体细胞发生恶性转化的过程,建立了HOS TE85的恶性转化模型.     

MNNG亚慢性暴露致大鼠食管损伤及炎性反应机制研究

目的 观察MNNG亚慢性暴露对大鼠血清肿瘤坏死因子-α(TNF-α)、白细胞介素6(IL-6)、白介素1β(IL-1β)含量及食管组织结构的影响.方法 65只SPF级雄性Wistar大鼠随机分为生理盐水对照组、80、120、160和200 μg/ml MNNG染毒组,每组13只.对照组大鼠采用等量生理盐水灌胃,实验组大...     

Protective effect of Lactobacillus rhamnosus 231 against N-Methyl-N′-nitro-N-nitrosoguanidine in animal model

The protective effect of Lactobacillus rhamnosus 231 (Lr 231) against potent carcinogen N-Methyl-N'-Nitro-N-Nitrosoguanidine (MNNG) in the rat model is studied. Daily feeding with Lr 231 improved the body weight of male Wistar rats compared with control groups. Fecal azoreductase (p < 0.001) and nitroreductase (p < 0.01) enzyme activity decreased significantly in Lr 231 group in comparison with control groups that received only phosphate buffer or MNNG. Oral administration of MNNG led to a significant increase in Glutathione transferase (GST) while Glutathione reductase (GSH) showed decreased activity. Conversely, feeding Lr 231 showed significantly increased GSH and decreased GST activity in comparison to the MNNG group, emphasizing the protection provided by Lr 231 against MNNG. Histopathological analysis of liver, spleen and colon showed decreased signs of inflammation in the Lr 231 group. The present study highlights that inclusion of active Lr 231 in regular diets could be used to prevent MNNG induced colon carcinoma.     

HP感染蒙古沙土鼠致Barrett食管及胃癌的实验研究

目的 通过建立幽门螺杆菌(HP)感染蒙古沙土鼠的动物模型,观察HP及HP与N-甲基-N′-硝基-N-亚甲基胍(MNNG)共同作用后食管和胃黏膜的组织学改变.方法 96只SPF级蒙古沙土鼠随机分为4组,每组24只.A组单用HP菌液灌胃;B组在接种HP后4周,摄入MNNG水(20μg/ml),连续30周;C组单用MNNG水(20μg/ml),连续30周;D组为对照组.各组分别在实验后12、24和48周3个时相点各处死8只,取食管和胃黏膜行组织学检查,用Warthin-Starry银染、PCR和快速尿素酶法检测HP.结果 累计至48周,萎缩、肠化生和异型增生的发生率A组(62.5%,33.3%,37.5%)、B组(62.5%,20.8%,54.2%)显著高于C组(37.5%,4.2%,8.3%)、D组(0),差异有统计学意义(P＜0.01).A组有1例发生胃癌,2例出现Barrett食管.结论 HP感染可以直接导致胃癌发生,同时也能诱发出Barrett食管.     

高剂量富硒植物硒对胃癌模型大鼠的安全性研究

目的:对比研究长期摄入高剂量不同富硒植物硒对大鼠重要肝指标的影响,为安全合理利用不同植物硒源提供科学依据。方法:采用N-甲基-N’-硝基-N-亚硝基胍(MNNG)诱发大鼠胃癌模型,连续灌喂四种高剂量不同富硒植物硒17w,于18w末测定大鼠肝脏硒累积、丙二醛(MDA)含量和谷胱甘肽过氧化物酶(GPx)活性。结果:摄入富硒青花菜、富硒红羽、富硒绿羽的大鼠肝硒水平显著高于摄入富硒大蒜。补充植物硒显著降低了大鼠的肝MDA水平,提高了肝GPx活性。富硒大蒜高、低剂量组大鼠肝MDA含量差异显著,而GPx活性差异不显著。结论:长期摄入高剂量富硒大蒜后,动物肝组织低硒累积可作为富硒大蒜高安全性的重要依据。植物硒可通过GPx清除肝组织MDA,防止肝氧化损伤。     

Progesterone Enhancement of Stomach Tumor Development in SD Rats Treated with N-Methyl-N'-nitro-N-nitrosoguanidine

The effects of chronic progesterone treatment on gastric tumorigenesis were examined in 6-week-old male SD rats. The rats were castrated, progesterone or testosterone pellets were implanted, and, starting one week after the operation, 100 mg/liter of N -methyl- N -nitro- N '-nitrosoguanidine (MNNG) was administered in the drinking water for 16 weeks. Every 2 months the pellets were changed. Group 1 animals received castration plus MNNG while Groups 2 and 3 also received progesterone and testosterone, respectively. In the Group 4 case, progesterone and testosterone were administered alternately for 2-month periods and in Group 5 MNNG was given to intact animals. All survivors were killed one year after the start of MNNG treatment. In Group 1 the incidence of gastric tumors was significantly decreased as compared with the Group 5 value. The Group 2 incidence, in contrast, was similar to that in Group 5, and the size of the observed gastric tumors was massively increased. The area of the pyloric gland mucosa was also greater than in other groups. Testosterone treatment was associated with a less pronounced increase in tumor size and a recovery in incidence. The results indicate that progesterone may exert a promoting influence on gastric tumor development.