Alterations in the expression of α6β4 integrin and p21/WAF1/Cip1 inN-nitrosomethylbenzylamine–induced rat esophageal tumorigenesis

Foetal rat lung epithelial (FRLE) cells: alterations in cellular homeostasis and gene expression in response to etoposide, hydrogen peroxide and sodium butyrate

Genomics technology offers a way of detecting the effects of a toxin on the expression of many genes in a single experiment. We have previously partially characterised a foetal rat lung epithelial (FRLE) cell line and shown that it is suitable for use in a pneumocytotoxicity screen. In this study, we wanted to ascertain whether we could use alterations in FRLE cell gene expression as a sensitive marker of cell stress. Sodium butyrate and etoposide were shown to arrest FRLE cell cycle at G0/G1 and G2/M phase of the cell cycle, respectively and this was associated with a decrease in the number of cells in culture. Following 24 h of culture both compounds caused a statistically significant increase in the mRNA levels of the cell cycle inhibitory protein, gadd153, whereas p21 was statistically altered by etoposide only. Hydrogen peroxide induced growth arrest at low concentrations (< or =250 microM) following 24 h of culture. We could not detect an increase in apoptosis or in the mRNA levels of the pro-apoptotic protein bax in FRLE cells following culture with hydrogen peroxide or etoposide. Thus, it was possible to correlate cellular perturbations in FRLE cells with alterations in gene expression, demonstrating that these cells are suitable for use in a toxicity screen.

Inducible nitric oxide synthase expression inN-nitrosomethylbenzylamine (NMBA)-induced rat esophageal tumorigenesis

Nitric oxide (NO), an important regulatory molecule for immune response and cytotoxicity, is endogenously generated from L-arginine by NO synthase (NOS). One mechanism for NO-induced cytotoxicity is through its interaction with superoxide to produce peroxynitrite, which causes DNA damage. Three distinct isoforms of NOS have been isolated and represent the products of three different genes. The inducible form, inducible nitric oxide synthase (iNOS), is a mediator of inflammation and a regulator of epithelial cell growth. Upregulation of iNOS has been linked to epithelial tumorigenesis in various human and animal tissues. In the current investigation, normal esophagus and N-nitrosomethylbenzylamine (NMBA)-induced preneoplastic and papillomatous lesions of the rat esophagus were characterized for expression of iNOS. F344 rats were injected subcutaneously with NMBA (0.5 mg/kg body weight) three times per week for 5 wk. At 3, 6, 9, 12, 15, 18, 21, 24, 30, and 36 wk following initiation of NMBA treatment, esophagi were collected from 12 untreated and 12 NMBA treated animals. Results of reverse transcription (RT)-polymerase chain reaction (PCR) and immunohistochemistry demonstrated a correlation between the upregulation of iNOS and neoplastic progression in the rat esophagus. The expression of iNOS mRNA in preneoplastic tissues and papillomas was significantly elevated when compared to normal tissues. Immunohistochemical analysis showed more extensive cytoplasmic staining of iNOS protein in preneoplastic tissues and papillomas than in normal tissues. Our data suggest, therefore, that the production of iNOS by the epithelium of the esophagus is associated with the development of NMBA-induced esophageal tumorigenesis in rats.

Alteration of integrin expression relates to malignant progression of human papillomavirus-immortalized esophageal keratinocytes

To investigate cellular changes related to the malignant progression of keratinocytes, we studied the serum-resistant clones from CHEK-1, a human papillomavirus type 16 E6/E7-immortalized esophageal cell line cultured in a serum-free medium. Established clones exhibited morphologic variety. Slow growing clones presented in cuboidal shapes with tight cellular adhesion and highly expressed alpha2 and alpha6beta4 integrins. Moderately proliferating clones showed loose intercellular adhesion and reduced expression of alpha2 integrin. Spindle-shaped, rapidly proliferating clones with prominent actin stress fibers demonstrated reduced alpha6 and alpha4 integrin expression in addition to alpha2 integrin and showed anchorage-independent growth. Reduced expression of alpha2 integrin was observed between 50 and 100 population doubling lengths (PDLs) during the immortalization of CHEK-1. These results suggest that the reductions of alpha2 and alpha6beta4 integrins are related to changes seen during immortalization and malignant progression.

Increased expression of cyclin D1, cyclin E and p21(Cip1) associated with decreased expression of p27(Kip1) in chemically induced rat mammary carcinogenesis

We induced rat mammary tumors in 7-week-old female Sprague-Dawley rats by intragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA), and analyzed by immunohistochemistry the expression of cyclin D1, cyclin E, p21(Cip1), and p27(Kip1) in carcinomas, atypical tumors, and benign tumors as well as normal mammary glands from the control group. Proliferation status was assessed by immunohistochemistry using bromodeoxyuridine (BrdU). A sequential increase in cyclin D1-, cyclin E-, and p21(Cip1)-positive epithelial cells was observed from normal mammary glands, to atypical tumors, to carcinomas. In contrast, carcinomas showed a significantly lower number of epithelial cells immunoreactive to p27(Kip1) when compared with atypical tumors, benign tumors and normal mammary glands. The immunoreactivities of BrdU, cyclin D1, cyclin E, and p21(Cip1) were positively correlated, whereas that of p27(Kip1) appeared inversely correlated to those of the others. Reverse transcriptase-polymerase chain reaction (RT-PCR) and western blot analysis were also performed to determine the mRNA and protein levels of cyclins and cyclin-dependent kinase inhibitors in tumors and normal mammary glands. The protein levels for cyclin D1, cyclin E and p21(Cip1) in carcinomas and atypical tumors were significantly higher than those in benign tumors, while normal mammary glands showed negligible expression. On RT-PCR, tumors showed higher mRNA levels of cyclin D1 and cyclin E than those of normal mammary glands. Our results suggest that rat mammary carcinogenesis involves increased expression of cyclin D1, cyclin E, and p21(Cip1), associated with decreased expression of p27(Kip1).

Absence of p16, p21 and p53 gene alterations in hepatocellular carcinomas induced by N-nitrosodiethylamine or a choline-deficient L-amino acid-defined diet in rats

To clarify the involvement of tumor suppressor genes in exogenous and endogenous liver carcinogenesis, alterations of p16, p21 and p53 in hepatocellular carcinomas (HCCs) induced by N-nitrosodiethylamine (DEN) and a choline deficient L-amino acid-defined (CDAA) diet in rats were investigated. Male Fischer 344 rats received DEN at 6-week of age followed by partial hepatectomy (PH), with colchicine to induce cell cycle disturbance, and a selection pressure regimen. Sacrifice was after 42 weeks. Other animals continuously received a CDAA diet for 75 weeks and were then killed. Eleven and 15 HCCs were obtained, respectively. Total RNA was extracted from and cDNA was synthesized with reverse transcriptase to allow investigation of mutations in p16, p21 and p53 by polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) analysis. Expression of p16 and p21 mRNA was also analyzed by reverse transcription (RT)-PCR. The results showed no mutations or deletions of p16, p21 and p53 in any of the HCCs induced by DEN or CDAA. Loss or decrease of p16 and p21 expression were also not found, suggesting that p16, p21 and p53 alteration may not be necessary for either exogenous or endogenous liver carcinogenesis in rats.

Suppression of N-nitrosomethylbenzylamine-induced rat esophageal tumorigenesis by dietary feeding of 1'-acetoxychavicol acetate

The modifying effects of 1'-acetoxychavicol acetate (ACA) on N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis were investigated in male F344 rats. At 5 weeks of age, all test animals, except those given the test chemical alone, and the control rats received s.c. injections of NMBA (0.5 mg/kg body weight/injection, three times per week) for 5 weeks. At the termination of the study (20 weeks), 75% of rats treated with NMBA alone had esophageal neoplasms (papillomas). However, the groups given a dose of 500 ppm ACA during the initiation phase developed a significantly reduced incidence of tumors (29%; P<0.01). Exposure to ACA (500 ppm) during the post-initiation phase also decreased the frequency of the tumors (38%; P<0.05). A reduction of the incidence of preneoplastic lesions (hyperplasia or dysplasia) was obtained when ACA was administered in the initiation phase (P<0.01). Cell proliferation in the esophageal epithelium, determined by assay of proliferating cell nuclear antigen (PCNA), was lowered by ACA (P<0.05). Blood polyamine contents in rats given NMBA and the test compound were also smaller than those of rats given the carcinogen (P<0.05). These findings suggest that dietary ACA is effective in inhibiting the development of esophageal tumors by NMBA when given during the initiation or post-initiation phase, and such inhibition is related to suppression of cell proliferation in the esophageal epithelium.

The beta4 integrin subunit rescues A431 cells from apoptosis through a PI3K/Akt kinase signaling pathway

To study whether alpha6beta4 integrin regulates apoptosis, human A431 cells were plated on bacteria plates in the presence or absence of mAb beta4. In the absence of mAb beta4, A431 cells demonstrated morphological characteristics of apoptosis by 24 h and most cells died by 48 h. In contrast, in the presence of mAb beta4, cells remained viable, and at the end of 48 h, 70-80% of cells survived. Treatment of A431 cells with mAb beta4 resulted in tyrosine phosphorylation of the p85 subunit of PI3 kinase; PI3 kinase activity increased within 15 min and peaked at 60 min. Stimulation of beta4 in A431 cells resulted in a time-dependent phosphorylation of Akt with a concomitant and parallel phosphorylation of Bad. Inactivation of PI3 kinase with inhibitors blocked the anti-apoptotic effect induced by mAb beta4. These are the first results to suggest that ligation of alpha6beta4 integrin protects cells from apoptosis through a PI3K/Akt kinase signaling pathway.