Increased expression of cyclooxygenase-2 protein in rat lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine

Expression of cyclooxygenase (COX)-2 protein in preneoplastic and neoplastic lung lesions induced by the administration of 2000 ppm of N-nitrosobis(2-hydroxypropyl)amine (BHP) in the drinking water to Wistar male rats, was examined immunohistochemically. The majority of alveolar/bronchiolar adenomas (ADs) and all adenocarcinomas (ADCs) examined, stained positive or strongly positive for COX-2. In contrast, only a minority of alveolar/bronchiolar hyperplasias demonstrated immunoreactivity and half of the squamous cell carcinomas examined, were only weakly positive. Western blotting analysis also revealed expression of COX-2 protein in the resected ADs and ADCs. These results clearly indicate up-regulated expression of COX-2 in lung neoplastic lesions, particularly ADs and ADCs, induced by BHP in rats.     

Frequent mutations of Ki-ras but no mutations of Ha-ras and p53 in lung lesions induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Point mutations of the Ki-ras and p53 genes in rat lung lesions induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) were investigated by polymerase chain reaction-single-strand conformation polymorphism analysis followed by direct sequencing using paraffin-embedded tissues. Male Wistar rats 6 wk old were given 2000 ppm BHP in drinking water for 15 wk. Another group was given drinking water without BHP. The rats were killed 20–27 wk after the beginning of the experiment. Lung adenomatous and squamous lesions, including carcinomas, were induced. The frequencies of Ki-ras mutations were 40% (six of 15) in alveolar hyperplasias, 36% (five of 14) in adenomas, 72% (18 of 25) in adenocarcinomas, 20% (three of 15) in squamous metaplasias, 50% (three of six) in squamous cell carcinomas, and 50% (five of 10) in adenosquamous carcinomas. The mutations were all G → A transitions at the second position of codon 12; no other mutations were detected. However, Ha-ras mutations in exons 1 and 2 and p53 mutations in exons 5, 6, and 7 were not detected in adenocarcinomas and squamous cell carcinomas. These results indicate that Ki-ras mutation is an early genetic event in some adenomatous and squamous lung carcinogenesis and that Ki-ras mutations can cause benign lesions to convert to malignant lesions. The results also show that Ha-ras and p53 mutations are not involved in rat lung carcinogenesis induced by BHP. © 1996 Wiley-Liss, Inc.     

Global DNA methylation reflects spatial heterogeneity and molecular evolution of lung adenocarcinomas

Lung adenocarcinoma (ADC) is the most prevalent subtype of lung cancer and characterized by considerable morphological and mutational heterogeneity. However, little is known about the epigenomic intratumor variability between spatially separated histological growth patterns of ADC. In order to reconstruct the clonal evolution of histomorphological patterns, we performed global DNA methylation profiling of 27 primary tumor regions, seven matched normal tissues and six lymph node metastases from seven ADC cases. Additionally, we investigated the methylation data from 369 samples of the TCGA ADC cohort. All regions showed varying degrees of methylation changes between segments of different, but also of the same growth patterns. Similarly, copy number variations were seen between spatially distinct segments of each patient. Hierarchical clustering of promoter methylation revealed extensive heterogeneity within and between the cases. Intratumor DNA methylation heterogeneity demonstrated a branched clonal evolution of ADC regions driven by genomic instability with subclonal copy number changes. Notably, methylation profiles within tumors were not more similar to each other than to those from other individuals. In two cases, different tumor regions of the same individuals were represented in distant clusters of the TCGA cohort, illustrating the extensive epigenomic intratumor heterogeneity of ADCs. We found no evidence for the lymph node metastases to be derived from a common growth pattern. Instead, they had evolved early and separately from a particular pattern in each primary tumor. Our results suggest that extensive variation of epigenomic features contributes to the molecular and phenotypic heterogeneity of primary ADCs and lymph node metastases.     

Downregulation of connexin 26 in human lung cancer is related to promoter methylation

Cell-Cell communication via gap junctions plays a key role in carcinogenesis and in growth control. One of the gap junction proteins, Connexin 26 (Cx26) was considered as tumor suppressor in various cancers. In our study, the expression of Cx26 was analyzed in human lung cancer. The reduced mRNA expression was observed in 17 lung cancer cell lines examined by Northern blot analysis and RT-PCR. In 138 primary carcinomas comprising all subtypes analyzed by immunohistochemistry, 85 cases (62%) exhibited no expression of Cx26, whereas in other 53 cases the Cx26 staining was positive (38%). Additionally, an association between Cx26 protein expression and higher grading of tumors was found in whole tumor samples (p =0.028) but no statistically significant correlations could be observed with tumor stage, tumor size and node status. In squamous cell carcinoma, tumors with higher stage and grading were linked to higher expression of Cx26 (p = 0.015 and 0.017, respectively). To explore the mechanism responsible for the downregulation of Cx26, we treated 2 lung cancer cell lines H2170 and H226 with the demethylation agent 5-aza-2'-deoxycytidine and found the reexpression of Cx26 mRNA. Methylation status of these 2 cell lines was further analyzed by PCR amplification of bisulfite modified DNA and sequencing. A heterogeneous methylation pattern turned out. Our results suggest the inactivation of Cx26 in lung cancer may be explained by promoter methylation.     

Alkylation of rodent tissue DNA induced by N-nitrosobis(2-hydroxypropyl)amine.

Levels of methyl and hydroxypropyl adducts induced by single s.c. injections of various doses of tritium-labeled N-nitrosobis(2-hydroxypropyl)amine ([1-3H]BHP) were determined in the liver, pancreas, kidney and lung of hamsters and rats. At doses of BHP used in carcinogenesis studies (100-500 mg/kg), methylation of DNA was more extensive than its hydroxypropylation; however, it did not increase proportionally with the dose and gradually became secondary to hydroxypropylation at higher doses of the carcinogen. Ratios of hydroxypropyl versus methyl adducts also varied significantly depending on the tissue and species. In both species ratios of N7-hydroxypropylguanine (N7-HpG) versus N7-methylguanine (N7-MeG) were greater in kidney and pancreas than in liver or lung. Due to apparent differences in the repair of O6-methylguanine (O6-MeG) and O6-hydroxypropylguanine (O6-HpG), and the propensity of 2-hydroxypropylating as compared to methylating agents to yield a greater percentage of oxygen adducts, ratios of O6-HpG versus O6-MeG were markedly greater than those of N7-HpG versus N7-MeG. Levels of O6-HpG were greater than those of O6-MeG in rat liver, pancreas and kidney and also in hamster kidney, while such levels were similar in rat lung and also in hamster liver, pancreas and lung. Like N-nitrosobis(2-oxopropyl)amine (BOP) and N-nitroso(2-hydroxypropyl) (2-oxopropyl)amine (HPOP), BHP was activated primarily in the liver and induced substantially greater DNA damage in this than in any other tissue examined. However, unlike BOP and HPOP, which induced similar levels of hepatic DNA damage in the above two species, BHP methylated and hydroxypropylated hamster liver DNA more extensively than that of the rat. Differences between BOP and BHP were also observed regarding levels and distribution of DNA adducts in extrahepatic tissues. In rats, BHP induced greater levels of methylation and hydroxypropylation in lung than in kidney, while the reverse was observed with BOP. Apparently reduction of the beta-carbon of pancreas-specific nitrosamine carcinogens results in a shift of alkylation from kidney to the lung. Excretion of HPOP in the urine of BHP-treated animals and the observed saturation of DNA methylation at high doses of BHP, supported the hypothesis that the BHP-induced methylation of DNA proceeded via the intermediate formation of HPOP. This was further supported by the observation that both excretion of HPOP and levels of methyl adducts were greater in hamsters than in rats.(ABSTRACT TRUNCATED AT 400 WORDS)     

Elevated expression of interleukins in lung adenocarcinomas induced by N-Nitrosobis(2-hydroxypropyl)amine in rats.

The expression of interleukins (ILs) in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats was investigated using a multiprobe RNase protection assay (RPA) followed by densitometric quantification. Male Wistar rats, 6 weeks old, were given 2000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until they were killed at week 25. Total RNAs were extracted from 14 individual adenocarcinomas and 2 specimens of normal lung tissue of untreated rats. In adenocarcinomas, elevated expression of IL-1alpha (6 / 14), IL-1beta (14 / 14), IL-3 (7 / 14), IL-4 (11 / 14), IL-5 (9 / 14), IL-6 (11 / 14) and IL-10 (8 / 14) was observed, compared with normal lung tissues. In contrast, no expression of IL-2 was detected in any case. The results suggest that preferential expression of these ILs and their complex networks may contribute to the development and progression of lung adenocarcinomas induced by BHP in rats.     

Mutations and reduced expression of the transforming growth factor-beta receptor II gene in rat lung adenocarcinomas induced by N-nitrosobis-(2-hydroxypropyl)amine.

Mutations and expression of the transforming growth factor-beta receptor type II (TGF-beta RII) gene were investigated in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Males of the Wistar strain, 6 weeks old, were given 2000 ppm of BHP in their drinking water for 12 weeks and then maintained without further treatment until killed at week 25. Total RNA was extracted from 12 adenocarcinomas and mutations in TGF-beta RII were investigated by RT-PCR-restriction-SSCP analysis followed by sequencing analysis. Two out of 12 adenocarcinomas showed band shifts, indicative of mutations (16.7%). One was a CTG-to-TTG (Leu to Leu) transition at codon 308 without amino acid alteration and the other a frameshift deletion of one of two guanines at nucleotides 1434 to 1435 (codon 477 to 478). Semi-quantitative RT-PCR analysis demonstrated significantly reduced TGF-beta RII expression in adenocarcinomas, as compared with normal lung tissue. These results suggest that TGF-beta RII alterations may play a role in the acquisition of growth advantage by lung adenocarcinomas induced by BHP in rats.     

Prostatic cancer induced in MRC rats by N-nitrosobis(2-oxopropyl)-amine and N-nitrosobis(2-hydroxypropyl)amine

Weekly intragastric treatment with N-nitrosobis(2-oxo-propyl)amineor N-nitrosobis(2-hydroxypropyl)amine induced hyperplastic,preneoplastic and neoplastic prostatic changes in >80% ofMRC rats. The lesions initially appeared as focal or multifocalproliferations of alveolar epithelium in a cribriform patternwhich, in all but one case, underwent progressive changes, oftentending toward squamous cell formation. Tumors, found primarilyin the ventral prostate, demonstrated various degrees of differentiationand invasive growth. A few neoplasms developed in the seminalvesicles; however all were of a glandular type. The sequentialalteration of induced lesions is described and the possiblereasons for the squamous cell character of most tumors discussed.Prostatic cancer induction by systemic application of specificnitrosamines could provide a unique tool for investigating importantaspects of the disease.