Mutations of the Smad2 and Smad4 genes in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Mammalian models of chemically induced primary malignancies exploitable for imaging-based preclinical theragnostic research

Compared with transplanted tumor models or genetically engineered cancer models, chemically induced primary malignancies in experimental animals can mimic the clinical cancer progress from the early stage on. Cancer caused by chemical carcinogens generally develops through three phases namely initiation, promotion and progression. Based on different mechanisms, chemical carcinogens can be divided into genotoxic and non-genotoxic ones, or complete and incomplete ones, usually with an organ-specific property. Chemical carcinogens can be classified upon their origins such as environmental pollutants, cooked meat derived carcinogens, N-nitroso compounds, food additives, antineoplastic agents, naturally occurring substances and synthetic carcinogens, etc. Carcinogen-induced models of primary cancers can be used to evaluate the diagnostic/therapeutic effects of candidate drugs, investigate the biological influential factors, explore preventive measures for carcinogenicity, and better understand molecular mechanisms involved in tumor initiation, promotion and progression. Among commonly adopted cancer models, chemically induced primary malignancies in mammals have several advantages including the easy procedures, fruitful tumor generation and high analogy to clinical human primary cancers. However, in addition to the time-consuming process, the major drawback of chemical carcinogenesis for translational research is the difficulty in noninvasive tumor burden assessment in small animals. Like human cancers, tumors occur unpredictably also among animals in terms of timing, location and the number of lesions. Thanks to the availability of magnetic resonance imaging (MRI) with various advantages such as ionizing-free scanning, superb soft tissue contrast, multi-parametric information, and utility of diverse contrast agents, now a workable solution to this bottleneck problem is to apply MRI for noninvasive detection, diagnosis and therapeutic monitoring on those otherwise uncontrollable animal models with primary cancers. Moreover, it is foreseeable that the combined use of chemically induced primary cancer models and molecular imaging techniques may help to develop new anticancer diagnostics and therapeutics.

Multi-step lung carcinogenesis model induced by oral administration of N-nitrosobis(2-hydroxypropyl)amine in rats

N-Nitrosobis(2-hydroxypropyl)amine (BHP) was first synthesized by Krüger et al. (1974), and has been shown to primarily induce pancreatic duct adenocarcinomas by a subcutaneous injection in Syrian hamsters. By contrast, the carcinogenic effect of BHP has been indicated at the different target organs in rats, namely the lung. When rats are received by an oral administration of BHP in drinking water for 25 weeks, a high incidence of lung carcinomas are induced, which include adenocarcinomas, squamous cell carcinomas and combined squamous cell and adenocarcinomas. So many similarities are observed in terms of not only histological appearances but also gene alterations between human and BHP-induced rat lung cancers. Moreover, the step by step development of lung lesions, from preneoplastic lesions to cancers in rat lung carcinogenesis by BHP offers a good model to investigate the mechanisms underlying the pathogenesis of lung cancers. Because data for genetic and epigenetic alterations have indeed been accumulated during the BHP-induced rat lung carcinogenesis, we will introduce them in this review and hence demonstrate that this lung carcinogenesis model provides a useful opportunity for the research on the pathogenesis of lung cancers of both humans and rats.

No Mutations of Lysophosphatidic Acid Receptor Genes in Lung Adenocarcinomas Induced by N-Nitrosobis(2-hydroxypropyl)amine in Rats

Lysophosphatidic acid (LPA) is a bioactive phospholipid that stimulates cell proliferation and migration, and protects cells from apoptosis. It interacts with specific G protein-coupled transmembrane receptors. Recently, frequent mutations of the LPA receptor-1 (LPA1) gene were detected in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). In this study, to evaluate the involvement of other LPA receptor gene alterations during lung carcinogenesis, we investigated mutations of the LPA2, LPA3, LPA4 and LPA5 genes in lung adenocarcinomas induced by BHP in rats. Fifteen male Wistar rats, 6 weeks of age, were given 2000 ppm BHP in their drinking water for 12 weeks and then maintained without further treatment until sacrifice at 25 weeks, and 15 adenocarcinomas were obtained. Genomic DNAs were extracted from frozen tissues, and the LPA2, LPA3, LPA4 and LPA5 genes were examined for mutations, using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis. No mutations of LPA2, LPA3, LPA4 and LPA5 were detected in the 15 adenocarcinomas. These results suggest that alterations due to LPA2, LPA3, LPA4 and LPA5 gene mutations might not be involved in the development of lung adenocarcinomas induced by BHP in rats.

Mutations of lysophosphatidic acid receptor-1 gene during progression of lung tumors in rats

Lysophosphatidic acid (LPA) is a bioactive phospholipid that stimulates cell proliferation, migration, and protects cells from apoptosis. It interacts with specific G protein-coupled transmembrane receptors. In this study, mutations of lysophosphatidic acid receptor-1 (LPA1) gene were investigated to clarify the possible molecular mechanisms underlying the development of lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats, 6 weeks of age, were given 2000ppm BHP in their drinking water for 12 weeks and then maintained without further treatment until sacrifice at 25 weeks. Genomic DNAs were extracted from paraffin-embedded tissues and exons 2-4 were examined for mutations, using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis. No LPA1 mutations were detected in 15 hyperplasias, but 2 out of 12 adenomas (16.7%) and 7 out of 17 adenocarcinomas (41.2%). These results suggest that mutations of LPA1 gene may be involved in the acquisition of growth advantage from adenomas to adenocarcinomas in lung carcinogenesis induced in rats by BHP.

Hypermethylation of the Dal-1 gene in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

DAL-1 (differentially expressed in adenocarcinoma of the lung) is an actin-binding protein that has been shown to suppress growth in lung cancer cells. Recently, inactivation of the gene encoding DAL-1 due to hypermethylation has been found in several human malignancies, including lung cancers. To assess the involvement of the Dal-1 gene in rat lung carcinogenesis, we investigated the expression of Dal1 and its methylation status in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). Six-week old male Wistar rats (n = 11) were given 2,000 ppm BHP in their drinking water for 12 wk and maintained without further treatment until they were sacrificed at 25 wk. Total RNA was extracted from 11 lung adenocarcinomas, one from each BHP treated rat, and Dal-1 gene expression was analyzed using real-time quantitative reverse transcription-polymerase chain reaction. Dal-1 expression was significantly reduced in the lung adenocarcinomas compared with three normal lung tissues (P < 0.05). For methylation analysis, bisulfite sequencing was performed using normal lung tissue and tissue from 4 tumors, all of which showed reduced expression of Dal-1. The 5' upstream region was highly methylated in all four adenocarcinomas, whereas this region was unmethylated in normal lung tissue. These results suggest that aberrant methylation of the Dal-1 gene might be involved in the development of lung adenocarcinomas induced in rats by BHP.

Numerical changes in the mitochondrial DNA displacement loop in lung lesions induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Mutations in the mitochondrial DNA (mtDNA) displacement loop (D-loop) region were investigated to clarify the possible molecular mechanisms underlying the development of lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats, 6 weeks of age, were given 2000 ppm BHP in their drinking water for 12 weeks and then maintained without further treatment until sacrifice at 25 weeks. Genomic DNA was extracted from paraffin-embedded tissues and polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis, followed by nucleotide sequencing, was performed. Eleven out of 24 hyperplasias (45.6%), 8 out of 16 adenomas (50.0%), and 14 out of 21 adenocarcinomas (66.7%) showed numerical changes, in a polymeric C-tract at positions 16,086-16,092 of the mtDNA D-loop, with a one base insertion of cytosine increasing the length of the C-tract, from the seven nucleotides observed in normal lung tissues from non-BHP treated rats, to eight. These changes were all homoplasmic and no changes were found in lung lesions when the length of the C-tract in the normal lung tissues adjacent to the lesions was seven. These results suggest that alterations in the mtDNA D-loop may occur in an early phase of lung carcinogenesis induced in rats by BHP.

Reduced expression of the Tslc1 gene and its aberrant DNA methylation in rat lung tumors

TSLC1 gene inactivation due to promoter methylation has been reported in several human cancers. Here, we investigated the expression of the Tslc1 gene and its methylation pattern in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). Six-week-old male Wistar rats were given 2000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until they were sacrificed at 25 weeks. Total RNA was extracted from a total of 11 lung adenocarcinomas and their Tslc1 gene expressions were analyzed by real-time quantitative reverse transcription-polymerase chain reaction. Tslc1 expression was significantly reduced in the lung adenocarcinomas compared with three normal lung tissues (p < 0.05). Bisulfite sequence analysis of four lung adenocarcinomas and two normal lung tissues revealed that the 5' upstream region of the Tslc1 gene was highly methylated in the four lung adenocarcinomas, but unmethylated in the two normal lung tissues. These results suggest that aberrant Tslc1 gene methylation may be involved in BHP-induced development of lung adenocarcinomas in rats.

Aberrant DNA methylation ofE-cadherin andp16 genes in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine

The study aimed to assess the involvement of aberrant DNA methylation in lung carcinogenesis by measuring expressions of E-cadherin and p16 genes, and their DNA methylation status in the 5' upstream region in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). Six-week-old male Wistar rats were given 2000 ppm BHP in their drinking water for 12 wk, and maintained without further treatment until they were sacrificed at 25 wk. A total of nine lung adenocarcinomas were collected, and total RNA from each sample was extracted for assessment of gene expression by real-time reverse transcription (RT)-polymerase chain reaction (PCR). Expressions of E-cadherin and p16 genes were significantly reduced in lung adenocarcinomas (P < 0.05 and P < 0.005, respectively) compared with normal lung tissues. For methylation analysis, bisulfite sequencing was performed using two normal lung tissues and five tumors. The two normal lung tissues were all unmethylated in regions of E-cadherin and p16. In contrast, five adenocarcinomas were highly methylated, and these aberrant methylation patterns correlated with reduced expressions of E-cadherin and p16. These results suggest that aberrant DNA methylation of E-cadherin and p16 genes may play important roles in development of lung adenocarcinomas induced by BHP in rats.

Aberrant methylation patterns of theRassf1a gene in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine

To clarify the involvement of the Rassf1a gene in lung carcinogenesis, we investigated the methylation status in the 5' upstream region of the RAS-association domain family 1, isoform A (Rassf1a) gene in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). Six-week-old male Wistar rats were given 2000 ppm BHP in their drinking water for 12 wk and maintained without further treatment until they were sacrificed at 25 wk. A total of 15 lung adenocarcinomas were obtained and total RNAs were extracted from each for assessment of expression of the Rassf1a gene by reverse transcription (RT)-polymerase chain reaction (PCR) analysis. To measure the methylation status of the Rassf1a gene, five adenocarcinomas with a marked reduction of the Rassf1a expression and two normal lung tissues were used for a bisulfite sequencing analysis. While the normal lung tissue was unmethylated, all five adenocarcinomas were highly methylated in the 5' upstream region. Genomic DNAs were also extracted from 15 adenocarcinomas, and mutation analysis of the Rassf1a was performed with PCR-single-strand conformation polymorphism (SSCP) analysis. No mutations were detected throughout exons 1-6. The present results suggest that the aberrant methylation may be involved in the inactivation of the Rassf1a gene in the development of lung adenocarcinomas induced by BHP in rats.

Reduced expression of the Connexin26 gene and its aberrant DNA methylation in rat lung adenocarcinomas induced by N-nitrosobis(2-Hydroxypropyl)amine

Gap junctions are mediated by intercellular channels that connect adjacent cells and are composed of Connexin (Cx) proteins. A member of the Cx family, Cx26 is considered a potential tumor suppressor in several cancers. The expression of Cx26 gene and its methylation status in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) were investigated. Six-wk-old male Wistar rats were given 2,000 ppm BHP in their drinking water for 12 wk and maintained without further treatment until they were sacrificed at 25 wk. A total of nine lung adenocarcinomas were obtained and total RNA was extracted to assess expression by real-time quantitative reverse transcription (RT)-polymerase chain reaction (PCR). Five out of nine adenocarcinomas showed reduced expression compared with normal lung tissue. We next performed a bisulfite sequence analysis to measure the methylation status of the 5' upstream region of the Cx26 gene in two normal lung tissues and five lung adenocarcinomas that showed reduced expression of Cx26. All five adenocarcinomas were highly methylated in the 5' upstream region, while the two normal lung tissues were unmethylated. This suggests that aberrant methylation of the Cx26 gene may be involved in the development of lung adenocarcinomas induced by BHP in rats.

Reduced expressions of Foxp1 and Rassf1a genes in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

To clarify the involvement of the Foxp1 and Rassf1a genes in lung carcinogenesis, we investigated their expressions in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Six week old male Wistar rats were given 2000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until they were sacrificed at 25 weeks. A total of 10 lung adenocarcinomas were obtained, along with the total RNA from each for assessment of expression by reverse transcription (RT)-polymerase chain reaction (PCR). The reduced expressions of the Foxp1 and Rassf1a genes were observed in some of the lung adenocarcinomas. These analyses were also confirmed by real-time quantitative RT-PCR. These results suggest that reduced expressions of Foxp1 and Rassf1a genes may play a role in the development of lung adenocarcinomas induced by BHP in rats.

Establishment and characterization of a rat lung adenocarcinoma cell line with low malignant potential

To investigate characteristic of lung adenocarcinoma growth behavior, we have established a cell line (rat lung cancer in Nara (RLCNR)) from a tumor induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in a rat. This clone shows an epithelial cell morphology and grows as sheets in culture with an approximate doubling time of 19.2 h. Ultrastructurally, the RLCNR contains lamellar bodies in cytoplasm and the microvilli are present at the free cell surfaces. The line features well-developed desmosomes. The modal chromosome number of 42 is the same as for normal rat cells and its frequency was established to be 80.5%. To evaluate tumorigenicity, appropriate numbers of the cells were transplanted into syngeneic rats, but no tumor formation occurred. Genetic analyses revealed the RLCNR to have a GGT to GAT mutation at codon 12 of Ki-ras, but no p53 alteration. p16 gene expression was lost, associated with hypermethylation of CpG sites in the 5' upstream region of the gene. These results indicate that the present newly established cell line originated from an alveolar type II lesion of the lung. It should be useful for further investigation of in vivo growth mechanisms, especially tumor progression, of lung adenocarcinomas, since it has low malignant potential.

Alterations of the Dutt1/Robo1 gene in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Abnormalities of tumor suppressor genes (TSGs) on chromosome 3p are known to be important for the development of human lung cancers. In the present study, we investigated alterations of the Dutt1/Robo1 gene, as a possible tumor suppressor in this region, in rat lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP). Male Wistar rats, 6-wk-old, were given 2000 ppm BHP in their drinking water for 12 wk and maintained without further treatment until killed at wk 25. A total of 12 lung adenocarcinomas were obtained and total RNAs were extracted from each for assessment of aberrant transcripts of the Dutt1/Robo1 gene by reverse transcription (RT)-polymerase chain reaction (PCR) analysis. Aberrant transcripts bearing deletions of nucleotides (nt) 55-4318, 89-4346, 605-4221, and 929-4318 were detected in four of 12 adenocarcinomas (33.3%). Loss or reduced expression of the Dutt1/Robo1 gene was not found in any of the adenocarcinomas. Genomic DNAs extracted from six adenocarcinomas for Southern blot analysis did not show any evidence of deletion or gross rearrangement of the Dutt1/Robo1 gene. These results suggest that alterations of the Dutt1/Robo1 gene may be involved in the development of some lung adenocarcinomas induced by BHP in rats.

Alterations of the M6p/Igf2 receptor gene in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Alterations of the mannose 6-phosphate/insulin-like growth factor II receptor (M6p/lgf2r) gene were investigated in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Male Wistar rats, 6 wk old, were given 2000 ppm BHP in their drinking water for 12 wk and maintained without further treatment until killed at week 25. A total of 12 lung adenocarcinomas were obtained, and total RNAs were extracted from each for assessment of mutations and levels of aberrant transcripts of the M6p/Igf2r gene by reverse transcription (RT)-polymerase chain reaction (PCR) single-strand conformation polymorphism analysis and RT-PCR analysis, respectively. No mutations were found in exons 27, 28, 31, 33, and 34. Aberrant transcripts bearing deletions of nt 3698 to 4902, 3366 to 4902, and 3817 to 4697 were detected in three of 12 adenocarcinomas (25%). These results suggest that alterations of the M6p/Igf2r gene may be involved in the development of lung adenocarcinomas induced by BHP in rats.

Alterations of the retinoblastoma-related gene RB2/p130 in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Alteration of the retinoblastoma-related gene RB2/p130 was investigated in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in male Wistar rats. At 6 wk of age, 21 animals were given 2000 ppm of BHP in their drinking water for 12 wk and then maintained without further treatment until they were killed at the end of week 25. A total of 21 lung adenocarcinomas were obtained, and total RNAs were extracted from each for mutation analysis of RB2/p130 by the reverse transcription-polymerase chain reaction-single-strand comformation polymorphism approach. No mutations were found in exons 19-22. However, examination of the expression of the RB2/p130 gene by Northern blot analysis showed mRNA levels to be significantly lower than those of normal lung tissues. Western blot analysis showed reduction of the pRb2/p130 protein in all of the adenocarcinomas examined. These results suggest that alteration of the RB2/p130 gene may play important roles in the development of lung adenocarcinomas induced by BHP in rats.

FHIT alterations in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Alteration of the FHIT gene was investigated in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl) amine (BHP) in male Wistar rats. Animals at 6 weeks of age were given 2000 p.p.m. of BHP in drinking water for 12 weeks, then maintained without further treatment until killed at the end of week 25. A total of 25 lung adenocarcinomas were obtained and total RNAs were extracted from each for assessment of aberrant transcription of the FHIT gene by reverse transcription (RT)-polymerase chain reaction (PCR) analysis. Aberrant transcripts were detected in 15 adenocarcinomas (60%) as absence in the regions of nucleotides (nt) -9 to 279, -98 to 279, -98 to 348 or -98 to 447. Genomic DNAs were also extracted from all 25 adenocarcinomas and exons 5-9 were examined for mutations, using PCR-single strand conformation polymorphism (SSCP) analysis and sequencing. A mutation was detected in only one adenocarcinoma (4%), an ACC to ATC (Thr to IIe) transition at codon 76. Southern blot analysis of eight tumors did not show any evidence of gross rearrangement or deletion of the FHIT gene. Western blot analysis revealed reduced expression of Fhit protein in six out of 10 adenocarcinomas (60%). These results suggest that alteration of the FHIT gene may be involved in the development of lung adenocarcinomas induced by BHP in rats.

Elevated expression of transforming growth factor betas and the tumor necrosis factor family in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Expression of transforming growth factor betas (TGF betas), tumor necrosis factor (TNF) family members, interferons (IFNs), macrophage migration inhibitory factor (MIF) and granulocyte macrophage colony stimulating factor (GM-CSF) 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 of age, were given 2,000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until killed at week 25. Total RNAs were extracted from 15 adenocarcinomas. Four samples of normal lung tissue from untreated rats served as controls. The expression of TGFbeta1, TGFbeta2, TGFbeta3, TNFalpha, TNFbeta and lymphotoxin beta (Ltbeta) was significantly higher in adenocarcinomas than in normal lung tissues. In contrast, MIF was expressed at the same level in neoplasms and normal tissue and no expression of IFNbeta, IFNgamma and GM-CSF was apparent in either adenocarcinomas or normal lung tissues. These results suggest that elevated expression of TGFbetas and TNF family members may contribute to the development and progression of lung adenocarcinomas induced by BHP in rats.

Overexpression of Smad2 reveals its concerted action with Smad4 in regulating TGF-beta-mediated epidermal homeostasis

Members of the transforming growth factor-beta (TGF-beta) superfamily are critical regulators for epithelial growth and can alter the differentiation of keratinocytes. Transduction of TGF-beta signaling depends on the phosphorylation and activation of Smad proteins by heteromeric complexes of ligand-specific type I and II receptors. To understand the function of TGF-beta and activin-specific Smad, we generated transgenic mice that overexpress Smad2 in epidermis under the control of keratin 14 promoter. Overexpression of Smad2 increases endogenous Smad4 and TGF-beta 1 expression while heterozygous loss of Smad2 reduces their expression levels, suggesting a concerted action of Smad2 and -4 in regulating TGF-beta signaling during skin development. These transgenic mice have delayed hair growth, underdeveloped ears, and shorter tails. In their skin, there is severe thickening of the epidermis with disorganized epidermal architecture, indistinguishable basement membrane, and dermal fibrosis. These abnormal phenotypes are due to increased proliferation of the basal epidermal cells and abnormalities in the program of keratinocyte differentiation. The ectodermally derived enamel structure is also abnormal. Collectively, our study presents the first in vivo evidence that, by providing an auto-feedback in TGF-beta signaling, Smad2 plays a pivotal role in regulating TGF-beta-mediated epidermal homeostasis.

Absence of PTEN/MMAC1 gene mutations in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats

Mutations of the phosphatase and tensin homolog deleted on chromosome ten/mutated in multiple advanced cancers 1 (PTEN/MMAC1) gene were investigated in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. 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 RNA was extracted from 15 adenocarcinomas and mutations of the PTEN/MMAC1 gene were investigated by reverse transcription-polymerase chain reaction-restriction-single-strand conformation polymorphism analysis. No mutations were detected, and loss or decrease of expression of PTEN/MMAC1 mRNA was also not found in any of the cases. These results suggest that alterations of the PTEN/MMAC1 gene may not be involved in the development of adenocarcinomas induced by BHP in rats.

Alterations of the transforming growth factor-beta signaling pathway in hepatocellular carcinomas induced endogenously and exogenously in rats

To elucidate involvement of the transforming growth factor-beta (TGF-beta) signaling pathway in endogenous and exogenous liver carcinogenesis, we investigated mutations of TGF-beta receptor type II (TGF-betaRII), Smad2 and Smad4 genes, and expression of TGF-betaRII in hepatocellular carcinomas (HCCs) induced by a choline-deficient L-amino acid-defined (CDAA) diet and by N-nitrosodiethylamine (DEN). Male Fischer 344 rats received a CDAA diet continuously and HCCs were sampled after 75 weeks. Administration of DEN was followed by partial hepatectomy (PH), with colchicine to induce cell cycle disturbance and a selection pressure regimen, HCCs being obtained after 42 weeks. Total RNAs were extracted from individual HCCs and mutations in TGF-betaRII, Smad2 and Smad4 were investigated by reverse transcription (RT)-polymerase chain reaction (PCR)-restriction-single-strand conformation polymorphism (SSCP) analysis followed by sequencing analysis. Mutations of Smad2 were detected in 2 out of 12 HCCs (16.7%) induced by the CDAA diet, a GGT-to-GGC transition (Gly to Gly) at codon 30 and a TCT-to-GCT (Ser to Ala) transversion at codon 118, without any TGF-betaRII or Smad4 alterations. No mutations of TGF-betaRII, Smad2 and Smad4 were encountered in eleven HCCs induced by the exogenous carcinogen. Semi-quantitative RT-PCR revealed reduced expression of TGF-betaRII in 2 HCCs (16.7%) without Smad2 mutations out of 12 HCCs induced by the CDAA diet and none of 11 induced by DEN. These results suggest that the TGF-beta signaling pathway may be disturbed in endogenous liver carcinogenesis 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.