Hypermethylation of the p16 (Ink4a) promoter in B6C3F1 mouse primary lung adenocarcinomas and mouse lung cell lines

The Role of Lead and Cadmium in Gynecological Malignancies

Lead and cadmium are non-essential and toxic heavy metals. Their presence and elevated levels can lead to many pathologies. They disrupt the antioxidant properties of many enzymes, consume the resources of antioxidant cells, and thus participate in the generation of oxidative stress, which may result in DNA damage. In addition, they have been found to be carcinogenic through their genotoxic properties. They have been shown to be present in various types of cancer, including cancer of the female reproductive system. Both metals have been recognized as metalloestrogens, which are important in hormone-related cancers. Participation in the oncogenesis of ovarian, endometrial and cervical cancer was analysed in detail, using the available research in this field. We emphasize their role as potential biomarkers in cancer risk and diagnosis as well as advancement of gynaecological malignancies.

Lead, selenium and nickel concentrations in epithelial ovarian cancer, borderline ovarian tumor and healthy ovarian tissues

OBJECTIVE

Wide variation exists in ovarian cancer incidence rates suggesting the importance of environmental factors. Due to increasing environmental pollution, trace elements and heavy metals have drawn attention in studies defining the etiology of cancer, but scant data is available for ovarian cancer. Our aim was to compare the tissue concentrations of lead, selenium and nickel in epithelial ovarian cancer, borderline tumor and healthy ovarian tissues.

METHODS

The levels of lead, selenium and nickel were estimated using atomic absorption spectrophotometry in formalin-fixed paraffin-embedded tissue samples. Tests were carried out in 20 malignant epithelial ovarian cancer, 15 epithelial borderline tumor and 20 non-neoplastic healthy ovaries. Two samples were collected for borderline tumors, one from papillary projection and one from the smooth surface of cyst wall.

RESULTS

Pb and Ni concentrations were found to be higher both in malignant and borderline tissues than those in healthy ovaries. Concentrations of Pb and Ni in malignant tissues, borderline papillary projections and capsular tissue samples were not different. Comparison of Se concentrations of malignant, borderline and healthy ovarian tissues did not reveal statistical difference. Studied metal levels were not found to be different in either papillary projection or in cyst wall of the borderline tumors.

CONCLUSIONS

This study revealed the accumulation of lead and nickel in ovarian tissue is associated with borderline and malignant proliferation of the surface epithelium. Accumulation of these metals in epithelial ovarian cancer and borderline ovarian tumor has not been demonstrated before.

Risk factors for refractory irritable bowel syndrome-diarrhea

AIM: To investigate the risk factors for refractory irritable bowel syndrome-diarrhea (IBS-D) to provide evidence for early prevention and treatment of IBS-D.

METHODS: One hundred and twenty-one outpatients with IBS-D were divided into a refractory group (n = 56) and a non-refractory group (n = 65). The clinical data in both groups, including sex, age, body mass index (BMI), family history, smoking status, alcohol consumption, clinical symptoms, and anxiety and depression status were assessed statistically by univariate logistic regression analysis and receiver operating characteristic (ROC) curve analysis, with an attempt to find the predictors of refractory IBS-D.

RESULTS: There were no statistically significant differences in sex, age, BMI, family history, smoking status or alcohol consumption between the two groups. The univariate logistic regression analysis showed that clinical symptoms (OR = 1.010, 95%CI: 1.005-1.015), anxiety (OR = 2.810, 95%CI: 1.888-4.180) and depression (OR = 1.637, 95%CI: 1.338-2.004) status were risk factors. Their areas under the ROC curve (AUC) were 0.757, 0.919 and 0.796, respectively, and the cut-off values were 183, 9 and 6 points, respectively.

CONCLUSION: IBS is significantly associated with clinical symptoms, anxiety and depression status, which may be used as predictors of IBS-D.

ATM mediates pRB function to control DNMT1 protein stability and DNA methylation

The retinoblastoma tumor suppressor gene (RB) product has been implicated in epigenetic control of gene expression owing to its ability to physically bind to many chromatin modifiers. However, the biological and clinical significance of this activity was not well elucidated. To address this, we performed genetic and epigenetic analyses in an Rb-deficient mouse thyroid C cell tumor model. Here we report that the genetic interaction of Rb and ATM regulates DNMT1 protein stability and hence controls the DNA methylation status in the promoters of at least the Ink4a, Shc2, FoxO6, and Noggin genes. Furthermore, we demonstrate that inactivation of pRB promotes Tip60 (acetyltransferase)-dependent ATM activation; allows activated ATM to physically bind to DNMT1, forming a complex with Tip60 and UHRF1 (E3 ligase); and consequently accelerates DNMT1 ubiquitination driven by Tip60-dependent acetylation. Our results indicate that inactivation of the pRB pathway in coordination with aberration in the DNA damage response deregulates DNMT1 stability, leading to an abnormal DNA methylation pattern and malignant progression.

The prognostic value of epigenetic silencing of p16 gene in NSCLC patients: a systematic review and meta-analysis

Background

The prognostic significance of p16 promoter hypermethylation in patients with non-small cell lung cancer (NSCLC) is still controversial. This analysis presents pooled estimates of the association to better elucidate whether p16 methylation has a prognostic role in NSCLC.

Methods

Relevant studies were identified by searching PubMed, Embase and Web of Science databases until June 2012. The association of p16 methylation with both overall survival (OS) and disease-free survival (DFS) was preformed. Studies were pooled and summary hazard ratios (HR) were calculated. Subgroup analyses, sensitivity analysis and publication bias were also conducted.

Results

A total of 18 studies containing 2432 patients met the inclusion criteria and had sufficient survival data for quantitative aggregation. The results showed that p16 methylation was an indicator of poor prognosis in NSCLC. The HR was 1.36 (95% CI: 1.08–1.73, I² = 56.7%) and 1.68 (95% CI: 1.12–2.52, I² = 38.7%) for OS and DFS, respectively. Subgroup analyses were carried out. The HRs of fresh and paraffin tissue were 1.50 (95% CI: 1.11–2.01) and 1.10 (95% CI: 0.77–1.57). The pooled HR was 1.40 (95% CI: 1.02–1.92) for methylation-specific PCR (MSP) and 1.26 (95% CI: 0.87–1.82) for quantitative MSP (Q-MSP). The combined HR of the 16 studies reporting NSCLC as a whole indicated that patients with p16 hypermethylation had poor prognosis. No significant association was found when adenocarcinoma subtype pooled. When seven studies on DFS were aggregated, the HR was 1.68 (95% CI: 1.12–2.52) without significant heterogeneity. Moreover, no obvious publication bias was detected on both OS and DFS.

Conclusion

The meta-analysis findings support the hypothesis that p16 methylation is associated with OS and DFS in NSCLC patients. Large well-designed prospective studies are now needed to confirm the clinical utility of p16 methylation as an independent prognostic marker.

Aberrant DNA methylation occurs in colon neoplasms arising in the azoxymethane colon cancer model

Mouse models of intestinal tumors have advanced our understanding of the role of gene mutations in colorectal malignancy. However, the utility of these systems for studying the role of epigenetic alterations in intestinal neoplasms remains to be defined. Consequently, we assessed the role of aberrant DNA methylation in the azoxymethane (AOM) rodent model of colon cancer. AOM induced tumors display global DNA hypomethylation, which is similar to human colorectal cancer. We next assessed the methylation status of a panel of candidate genes previously shown to be aberrantly methylated in human cancer or in mouse models of malignant neoplasms. This analysis revealed different patterns of DNA methylation that were gene specific. Zik1 and Gja9 demonstrated cancer-specific aberrant DNA methylation, whereas, Cdkn2a/p16, Igfbp3, Mgmt, Id4, and Cxcr4 were methylated in both the AOM tumors and normal colon mucosa. No aberrant methylation of Dapk1 or Mlt1 was detected in the neoplasms, but normal colon mucosa samples displayed methylation of these genes. Finally, p19(Arf), Tslc1, Hltf, and Mlh1 were unmethylated in both the AOM tumors and normal colon mucosa. Thus, aberrant DNA methylation does occur in AOM tumors, although the frequency of aberrantly methylated genes appears to be less common than in human colorectal cancer. Additional studies are necessary to further characterize the patterns of aberrantly methylated genes in AOM tumors.

Gastrointestinal hyperplasia with altered expression of DNA polymerase beta

Background

Altered expression of DNA polymerase β (Pol β) has been documented in a large percentage of human tumors. However, tumor prevalence or predisposition resulting from Pol β over-expression has not yet been evaluated in a mouse model.

Methodology/Principal Findings

We have recently developed a novel transgenic mouse model that over-expresses Pol β. These mice present with an elevated incidence of spontaneous histologic lesions, including cataracts, hyperplasia of Brunner's gland and mucosal hyperplasia in the duodenum. In addition, osteogenic tumors in mice tails, such as osteoma and osteosarcoma were detected. This is the first report of elevated tumor incidence in a mouse model of Pol β over-expression. These findings prompted an evaluation of human gastrointestinal tumors with regard to Pol β expression. We observed elevated expression of Pol β in stomach adenomas and thyroid follicular carcinomas, but reduced Pol β expression in esophageal adenocarcinomas and squamous carcinomas.

Conclusions/Significance

These data support the hypothesis that balanced and proficient base excision repair protein expression and base excision repair capacity is required for genome stability and protection from hyperplasia and tumor formation.

Dynamic changes in DNA methylation during multistep rat lung carcinogenesis induced by 3-methylcholanthrene and diethylnitrosamine

3-methylcholanthrene (MCA) and diethylnitrosamine (DEN) are typical genotoxic carcinogens that can induce tumors in a variety of human and rodent tissues. However, the epigenetic mechanisms underlying their tumorigenesis are unclear. In this study we used a MCA/DEN-induced multistep lung carcinogenesis rat model to study the evolution of alterations in DNA methylation. Rats were treated with a single dose of MCA and DEN in iodized oil by left intra-bronchial instillation. The animals were killed on days 15, 35, 55, 65 and 75 and samples of various pathological phases during carcinogenesis were obtained on these days. The status of global methylation was analyzed for each sample using a monoclonal antibody specific for 5-methycytosine (5-mC) and quantified by image analysis software. We found that the degree of global methylation was, in general, higher in basal cells compared to luminal cells of normal, precancerous and tumor tissues. The combined 5-mC scores of different types of tissues decreased gradually during the progression of carcinogenesis. We also used methylation-sensitive arbitrarily primed PCR (MS-AP-PCR) to screen a total of eight differentially methylated DNA fragments in both precancerous and tumor tissues isolated using laser capture microdissection (LCM), and observed that both unique hypomethylation and hypermethylation fragments coexist after exposure to genotoxic carcinogens. Remarkably, epigenetic alterations in p16 (CDKN2A), but not in p15 (CDKN2B), were observed, and these correlated with the presence of pathologic lung lesions and loss of p16 protein expression. Moreover, defective expression of p16 in methylated primary tumor cell lines recovered markedly after treated with 5-aza-2'-deoxycytidine (5-aza-dC). These results suggest that DNA methylation alterations are an early event in tumorigenesis and play an important role during MCA/DEN-induced multistep rat lung carcinogenesis.

Epigenetics in metal carcinogenesis: nickel, arsenic, chromium and cadmium

Although carcinogenic metals have been known to disrupt a wide range of cellular processes the precise mechanism by which these exert their carcinogenic effects is not known. Over the last decade or two, studies in the field of metal carcinogenesis suggest that epigenetic mechanisms may play a role in metal-induced carcinogenesis. In this review we summarize the evidence demonstrating that exposure to carcinogenic metals such as nickel, arsenic, chromium, and cadmium can perturb DNA methylation levels as well as global and gene specific histone tail posttranslational modification marks. We also wish to emphasize the importance in understanding that gene expression can be regulated by both genetic and epigenetic mechanisms and both these must be considered when studying the mechanism underlying the toxicity and cell-transforming ability of carcinogenic metals and other toxicants, and aberrant changes in gene expression that occur during disease states such as cancer.

Genetic alterations in K-ras and p53 cancer genes in lung neoplasms from B6C3F1 mice exposed to cumene

The incidences of alveolar/bronchiolar adenomas and carcinomas in cumene-treated B6C3F1 mice were significantly greater than those of the control animals. We evaluated these lung neoplasms for point mutations in the K-ras and p53 genes that are often mutated in humans. K-ras and p53 mutations were detected by cycle sequencing of PCR-amplified DNA isolated from paraffin-embedded neoplasms. K-ras mutations were detected in 87% of cumene-induced lung neoplasms, and the predominant mutations were exon 1 codon 12 G to T transversions and exon 2 codon 61 A to G transitions. P53 protein expression was detected by immunohistochemistry in 56% of cumene-induced neoplasms, and mutations were detected in 52% of neoplasms. The predominant mutations were exon 5, codon 155 G to A transitions, and codon 133 C to T transitions. No p53 mutations and one of seven (14%) K-ras mutations were detected in spontaneous neoplasms. Cumene-induced lung carcinomas showed loss of heterozygosity (LOH) on chromosome 4 near the p16 gene (13%) and on chromosome 6 near the K-ras gene (12%). No LOH was observed in spontaneous carcinomas or normal lung tissues examined. The pattern of mutations identified in the lung tumors suggests that DNA damage and genomic instability may be contributing factors to the mutation profile and development of lung cancer in mice exposed to cumene.

Global DNA hypomethylation, rather than reactive oxygen species (ROS), a potential facilitator of cadmium-stimulated K562 cell proliferation

Cell proliferation plays a critical role in the process of cadmium (Cd) carcinogenesis. Although both induction of reactive oxygen species (ROS) and alteration of DNA methylation are involved in Cd-stimulated cell proliferation, the detailed mechanism of Cd-stimulated cell proliferation remains poorly understood. In this study, K562 cells pre-treated with N-acetylcysteine (NAC) or methionine (Meth) were exposed to Cd to investigate the potential contribution of ROS and global DNA methylation pathways in Cd-induced cell proliferation. The results showed that Cd-stimulated cell proliferation, increased ROS and DNA damage levels, and induced global DNA hypomethylation. The increases of ROS and DNA damage levels were attenuated by pre-treatment with NAC. Cd-stimulated cell proliferation did not appear to be suppressed through eliminating ROS by NAC. However, methionine was shown to prevent Cd-induced global DNA hypomethylation and Cd-stimulated cell proliferation. Our results suggest that global DNA hypomethylation, rather than ROS, is a potential facilitator of Cd-stimulated K562 cell proliferation.

Molecular analysis of a multistep lung cancer model induced by chronic inflammation reveals epigenetic regulation of p16 and activation of the DNA damage response pathway

The molecular hallmarks of inflammation-mediated lung carcinogenesis have not been fully clarified, mainly due to the scarcity of appropriate animal models. We have used a silica-induced multistep lung carcinogenesis model driven by chronic inflammation to study the evolution of molecular markers and genetic alterations. We analyzed markers of DNA damage response (DDR), proliferative stress, and telomeric stress: gamma-H2AX, p16, p53, and TERT. Lung cancer-related epigenetic and genetic alterations, including promoter hypermethylation status of p16(CDKN2A), APC, CDH13, Rassf1, and Nore1A, as well as mutations of Tp53, epidermal growth factor receptor, K-ras, N-ras, and c-H-ras, have been also studied. Our results showed DDR pathway activation in preneoplastic lesions, in association with inducible nitric oxide synthase and p53 induction. p16 was also induced in early tumorigenic progression and was inactivated in bronchiolar dysplasias and tumors. Remarkably, lack of mutations of Ras and epidermal growth factor receptor, and a very low frequency of Tp53 mutations suggest that they are not required for tumorigenesis in this model. In contrast, epigenetic alterations in p16(CDKN2A), CDH13, and APC, but not in Rassf1 and Nore1A, were clearly observed. These data suggest the existence of a specific molecular signature of inflammation-driven lung carcinogenesis that shares some, but not all, of the molecular landmarks of chemically induced lung cancer.

Overview of the molecular carcinogenesis of mouse lung tumor models of human lung cancer

Lung cancer is the leading cause of cancer death worldwide, and the need to develop better diagnostic techniques and therapies is urgent. Mouse models have been utilized for studying carcinogenesis of human lung cancers, and many of the major genetic alterations detected in human lung cancers have also been identified in mouse lung tumors. The importance of mouse models for understanding human lung carcinogenic processes and in developing early diagnostic techniques, preventive measures and therapies cannot be overstated. In this report, the major known molecular alterations in lung tumorigenesis of mice are reviewed and compared to those in humans.

Silencing of genes by promoter hypermethylation: key event in rodent and human lung cancer

Transcriptional silencing by CpG island hypermethylation has become a critical component in the initiation and progression of lung cancer. The ability of pharmacologic agents to reverse promoter hypermethylation also makes it an attractive target to pursue for prevention of lung cancer. Animal models, together with studies in humans have fostered significant advances in elucidating the role of gene-specific methylation in cancer initiation and progression, the modulation of promoter methylation by carcinogen exposure and the ability to block tumor development by preventing epigenetically mediated gene silencing. These advances represent the beginning of efforts to develop a progression model for lung cancer that should aid efforts for early detection and gene targeting for therapy, and the development of preventive interventions that reverse epigenetic-mediated gene silencing.

Susceptibility to neoplastic and non-neoplastic pulmonary diseases in mice: genetic similarities

Chronic inflammation predisposes toward many types of cancer. Chronic bronchitis and asthma, for example, heighten the risk of lung cancer. Exactly which inflammatory mediators (e.g., oxidant species and growth factors) and lung wound repair processes (e.g., proangiogenic factors) enhance pulmonary neoplastic development is not clear. One approach to uncover the most relevant biochemical and physiological pathways is to identify genes underlying susceptibilities to inflammation and to cancer development at the same anatomic site. Mice develop lung adenocarcinomas similar in histology, molecular characteristics, and histogenesis to this most common human lung cancer subtype. Over two dozen loci, called Pas or pulmonary adenoma susceptibility, Par or pulmonary adenoma resistance, and Sluc or susceptibility to lung cancer genes, regulate differential lung tumor susceptibility among inbred mouse strains as assigned by QTL (quantitative trait locus) mapping. Chromosomal sites that determine responsiveness to proinflammatory pneumotoxicants such as ozone (O3), particulates, and hyperoxia have also been mapped in mice. For example, susceptibility QTLs have been identified on chromosomes 17 and 11 for O3-induced inflammation (Inf1, Inf2), O3-induced acute lung injury (Aliq3, Aliq1), and sulfate-associated particulates. Sites within the human and mouse genomes for asthma and COPD phenotypes have also been delineated. It is of great interest that several susceptibility loci for mouse lung neoplasia also contain susceptibility genes for toxicant-induced lung injury and inflammation and are homologous to several human asthma loci. These QTLs are described herein, candidate genes are suggested within these sites, and experimental evidence that inflammation enhances lung tumor development is provided.

Increased DNA methylation in the HoxA5 promoter region correlates with decreased expression of the gene during tumor promotion

Promoter-region DNA methylation inhibits transcription. A two-stage SENCAR (sensitive to mouse carcinogenesis) mouse skin carcinogenicity model was used to examine gene-specific changes in methylation during skin tumor promotion. Analysis was performed on 7,12-dimethylbenz[a]anthracene (DMBA)-initiated skin promoted with 9, 18, 27, or 36 mg cigarette smoke condensate (CSC) for 9 wk, or 27 mg CSC for 9 wk and sacrificed 6 wk afterwards (recovery group). Additionally, tumors arising following promotion with 27 mg CSC for 29 wk were assessed. Gene array analysis identified differentially expressed genes. Expression of HoxA5, a tumor suppressor gene, was decreased following 9 wk of treatment with 27 mg CSC, and returned to control levels during recovery. HoxA5 promoter methylation was measured with the enzymatic regional methylation assay (ERMA). DNA was bisulfite-modified, PCR-amplified with primers containing dam sites, incubated with [14C-methyl] S-adenosyl-L-methionine (SAM) and dam methyltransferase for DNA quantification, then incubated with [3H-methyl] SAM and SssI methylase to quantify methylation status. Higher 3H/14C ratios indicate increased methylation. The 3H/14C ratios of animals promoted with 27 or 36 mg CSC (48.2 +/- 6.9 and 24.2 +/- 6.1, respectively) were higher than the control or recovery group ratios (12.3 +/- 0.1 and 12.6 +/- 0.3, respectively); sequence analysis supported these findings. Increased methylation of p16 or O6 methylguanine methyltranferase (MGMT) was detected in 4/8 (50%) of the tumor samples from mice promoted with 27 mg CSC. These data suggest that increased DNA methylation contributes to the downregulation of HoxA5, and combined with hypermethylation of p16 or MGMT, this might facilitate the clonal expansion of increasingly aberrant cells during promotion.

Aberrant promoter hypermethylation of the death-associated protein kinase gene is early and frequent in murine lung tumors induced by cigarette smoke and tobacco carcinogens

Loss of expression of the death-associated protein (DAP)-kinase gene by aberrant promoter methylation may play an important role in cancer development and progression. The purpose of this investigation was to determine the commonality for inactivation of the DAP-kinase gene in adenocarcinomas induced in mice by chronic exposure to mainstream cigarette smoke, the tobacco carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and vinyl carbamate, and the occupational carcinogen methylene chloride. The timing for inactivation was also determined in alveolar hyperplasias that arise in lung cancer induced in the A/J mouse by NNK. The DAP-kinase gene was not expressed in three of five NNK-induced lung tumor-derived cell lines or in a spontaneously arising lung tumor-derived cell line. Treatment with 5-aza-2'-deoxycytidine restored expression; dense methylation throughout the DAP-kinase CpG island detected by bisulfite sequencing supported methylation as the inactivating event in these cell lines. Methylation-specific PCR detected inactivation of the DAP-kinase gene in 43% of tumors associated with cigarette smoke, a frequency similar to those reported in human non-small cell lung cancer. In addition, DAP-kinase methylation was detected in 52%, 60%, and 50% of tumors associated with NNK, vinyl carbamate, and methylene chloride, respectively. Methylation was observed at similar prevalence in both NNK-induced hyperplasias and adenocarcinomas (46% versus 52%), suggesting that inactivation of this gene is one pathway for tumor development in the mouse lung. Bisulfite sequencing of both premalignant and malignant lesions revealed dense methylation, substantiating that this gene is functionally inactivated at the earliest histological stages of adenocarcinoma development. This study is the first to use a murine model of cigarette smoke-induced lung cancer and demonstrate commonality for inactivation by promoter hypermethylation of a gene implicated in the development of this disease in humans.

Murine pancreatic tumor cell line TD2 bears the characteristic pattern of genetic changes with two independently amplified gene loci

TGFalpha/p53(+/-) transgenic mice represent a genetically engineered mouse model for pancreatic adenocarcinoma. The tumors develop a characteristic pattern of secondary genetic changes. From one of these tumors, the permanent cell line TD2 was established. Here, we describe in detail the genetic changes by molecular-cytogenetic techniques. The original tumor-specific CGH profile has been retained unchanged. The most characteristic aberration pattern bears chromosome 11. Egfr, localized on proximal chromosome 11, is amplified two to three times and leads to an easily identifiable, stable marker chromosome with a large amplification unit, which is present in each metaphase. The wild-type p53 gene on distal chromosome 11 is lost. The p16Ink4a locus on chromosome 4 is hypermethylated. For c-Myc a 15-fold amplification, present in a 1.65 Mb amplification unit, is detected on chromosome 15. Transition between presence in the form of several double minutes, DMs, or a single homogeneously staining region, HSR, was observed for c-Myc. Molecular-cytogenetic analysis of both amplification units show that Egfr amplification and c-Myc amplification represent two alternative modes by which genes get amplified in tumor cells. The expression level of the respective genes was proven by Northern blot analysis. The cell line TD2 represents a valuable in vitro model for pancreatic adenocarcinoma.

Both products of the mouse Ink4a/Arf locus suppress melanoma formation in vivo

Deletion of the INK4a/ARF locus at 9p21 is detected with high frequency in human melanoma. Within a short genomic distance, this locus encodes several proteins with established tumor-suppressor roles in a broad spectrum of cancer types. Several lines of evidence support the view that p16INK4a and p19ARF exert the tumor-suppressor activities of this locus, although their relative importance in specific cancer types such as melanoma has been less rigorously documented on the genetic level. Here, we exploit a well-defined mouse model of RAS-induced melanomas to examine the impact of germline p16INK4a or p19ARF nullizygosity on melanoma formation. We demonstrate that loss of either Ink4a/Arf product can cooperate with RAS activation to produce clinically indistinguishable melanomas. In line with the common phenotypic end point, we further show that RAS+ p16INK4a-/- melanomas sustain somatic inactivation of p19ARF-p53 and, correspondingly, that RAS+ p19ARF-/- melanomas experience high-frequency loss of p16INK4a. These genetic studies provide definitive proof that p16INK4a and p19ARF cooperate to suppress the development of melanoma in vivo.

Analysis of specific lysine histone H3 and H4 acetylation and methylation status in clones of cells with a gene silenced by nickel exposure

We have previously reported that the gpt transgene in G12 Chinese hamster cells could be silenced by water-insoluble nickel compounds nickel sulfide (NiS) or nickel subsulfide (Ni(3)S(2)) and showed that the transgene was silenced by de novo DNA methylation and chromatin condensation. To further understand the nature of this silencing, we used the chromatin immunoprecipitation assay to elucidate the chromatin structure in nickel-induced silenced G12 clones. We also analyzed the effects of the DNA methyltransferase inhibitor 5-azacytidine (5-AzaC) and a histone deacetylase inhibitor trichostatin A (TSA) on histone H3 and H4 acetylation and gpt gene expression in selected nickel-silenced clones. We observed that both histone H3 and H4 were hypoacetylated and a methyl DNA-binding protein MeCP2 was targeted to the gpt gene locus, resulting in a localized inactive chromatin configuration in nickel-silenced cell clones. The histone H3K9 was also found methylated in three of four nickel- silenced cell clones, whereas the histone H3K9 was deacetylated in all four cell clones, indicating that the H3K9 methylation was involved in nickel-induced gene silencing. The acetylation of the gpt gene could be increased by a combination of 5-AzaC and TSA treatment, but not by either 5-AzaC or TSA alone. The gpt transcript was studied by either Northern blot or by semiquantitative RT-PCR following treatment of the silenced clones with TSA or 5-AzaC. An increase in gpt mRNA could be detected by RT-PCR in the clones that regained acetylation of H3 and H4. These data show that gene silencing induced by nickel in the gpt transgenic cell line involved a loss of histone acetylation and an activation of histone methylation. Both H4 and H3 histone acetylation were lost in the silenced clones and these clones exhibited an increase in the methylation of the lysine 9 in histone H3.

Transfection of oocytes and other types of ovarian cells in rabbits after direct injection into uterine arteries of adenoviruses and plasmid/liposomes

Transfection of oocytes should be avoided in somatic gene therapy. However, several viral vectors including adenoviruses can transfect zona-pellucida-free eggs in vitro. During early stages of development, oocytes of postnatal ovaries lack the zona pellucida. Therefore, they may be susceptible to gene transfer and unintended toxic effects. The purpose of this study was to see whether the injection of adenoviruses (1 x 10(10) PFU) or plasmid (500 microg)/DOTMA:DOPE (1:2) liposomes directly into uterine arteries in pregnant rabbits leads to transfection of oocytes and other types of ovarian cells. LacZ and herpes simplex virus thymidine kinase (HSV-TK) were used as transgenes. It was found that both adenovirus and plasmid vectors transfected oocytes at the primordial and primary follicle stage when they were not protected by the zona pellucida, whereas no transfection was seen in oocytes surrounded by the zona pellucida. Efficient transfection of corpus luteum and granulosa cells was also detected by adenoviral and plasmid vectors. Transfection of oocytes and other ovarian cells was verified by X-gal staining and laser microdissection, followed by PCR analysis. HSV-TK gene transfer, followed by ganciclovir treatment, led to destruction of a significant number of oocytes, whereas HSV-TK gene transfer alone did not lead to toxic effects. It is concluded that the presence of a high concentration of adenovirus or plasmid vectors via the uterine artery may lead to transfection of zona-pellucida-free oocytes and other ovarian cells.

Novel approaches to the treatment of non-small cell lung cancer

Prognosis of non-small cell lung carcinomas (NSCLC) remains poor, especially in advanced disease. The introduction of new cytotoxic agents in the past decade did only attain minor improvements in survival. It is rather clear that chemotherapy may have reached a plateau, and that it will be difficult to obtain better results in advanced NSCLC by chemotherapy alone. Novel treatment modalities are urgently needed in advanced NSCLC. Backed-up by advances in the understanding of tumor cell biology, a new generation of anticancer agents specifically directed at targets such as tyrosine kinases, farnesyl transferase, angiogenesis factors, matrixmetalloproteinases and oncogenes has been developed in recent years. In this review, we give a brief summary of the state-of-the-art treatment of NSCLC, highlighting its limitations. Novel systemic approaches are then discussed in detail with focus on their mechanistic rationale, stage of clinical development and possible drawbacks. Finally, perspectives of future applications and impact on the treatment of NSCLC are also discussed.

Obligate roles for p16(Ink4a) and p19(Arf)-p53 in the suppression of murine pancreatic neoplasia

Epithelial tumors of the pancreas exhibit a wide spectrum of histologies with varying propensities for metastasis and tissue invasion. The histogenic relationship among these tumor types is not well established; moreover, the specific role of genetic lesions in the progression of these malignancies is largely undefined. Transgenic mice with ectopic expression of transforming growth factor alpha (TGF-alpha) in the pancreatic acinar cells develop tubular metaplasia, a potential premalignant lesion of the pancreatic ductal epithelium. To evaluate the cooperative interactions between TGF-alpha and signature mutations in pancreatic tumor genesis and progression, TGFalpha transgenic mice were crossed onto Ink4a/Arf and/or p53 mutant backgrounds. These compound mutant mice developed a novel pancreatic neoplasm, serous cystadenoma (SCA), presenting as large epithelial tumors bearing conspicuous gross and histological resemblances to their human counterpart. TGFalpha animals heterozygous for both the Ink4a/Arf and the p53 mutation showed a dramatically increased incidence of SCA, indicating synergistic interaction of these alleles. Inactivation of p16(Ink4a) by loss of heterozygosity, intragenic mutation, or promoter hypermethylation was a common feature in these SCAs, and correspondingly, none of the tumors expressed wild-type p16(Ink4a). All tumors sustained loss of p53 or Arf, generally in a mutually exclusive fashion. The tumor incidence data and molecular profiles establish a pathogenic role for the dual inactivation of p16(Ink4a) and p19(Arf)-p53 in the development of SCA in mice, demonstrating that p16(Ink4a) is a murine tumor suppressor. This genetically defined model provides insights into the molecular pathogenesis of SCA and serves as a platform for dissection of cell-specific programs of epithelial tumor suppression.

Dmp1 is haplo-insufficient for tumor suppression and modifies the frequencies of Arf and p53 mutations in Myc-induced lymphomas

Loss of Dmp1, an Arf transcriptional activator, leads to spontaneous tumorigenesis in mice, causing death from various forms of cancer by two years of age. Retention and expression of the wild-type Dmp1 allele in tumors arising in Dmp1(+/-) mice demonstrate that Dmp1 can be haplo-insufficient for tumor suppression. The mean latency of E(mu)-Myc-induced B-cell lymphomas is halved on a Dmp1(-/-) or Dmp1(+/-) genetic background. Although p53 mutations or Arf deletion normally occur in approximately 50% of E(mu)-Myc-induced lymphomas, Dmp1 loss obviates selection for such mutations, indicating that Dmp1 is a potent genetic modifier of the Arf-p53 pathway in vivo.

Alterations at the Ink4a locus in transplacentally induced murine lung tumors

The malignant phenotype results from multiple genetic alterations, including the activation of oncogenes and inactivation of tumor suppressor genes. Activation of the Ki-ras oncogene has been implicated as an early event in the pathogenesis of lung adenocarcinomas in humans and experimental animal models. Previous studies from this laboratory have shown that, following treatment of pregnant [D2 x B6D2F(1)]F(2) or Balb/c mice with the polycyclic aromatic hydrocarbon, 3-methylcholanthrene (MC), lung tumors from the transplacentally exposed offspring exhibited a high incidence of mutations in the Ki-ras gene. The role of genetic alterations at other oncogenic or tumor suppressor loci that can mediate lung tumor initiation and/or progression have not been well characterized in either human or murine models. Using the transplacental carcinogenesis model, which results in the induction of both lung and liver tumors following in utero exposure to MC, the results of this and our previous studies show that alterations in the Ink4a locus occur in only 15 and 27% of the lung and liver tumors, respectively. Preliminary data also suggests that the type of mutation induced in the Ki-ras gene following the initial exposure to MC may influence lung tumor progression. These results imply that damage to the Ink4a gene is not a frequent pathway to malignant progression in mouse lung and liver tumors following in utero exposure to environmental carcinogens.

Loss of p16Ink4a with retention of p19Arf predisposes mice to tumorigenesis

The cyclin-dependent kinase inhibitor p16INK4a can induce senescence of human cells, and its loss by deletion, mutation or epigenetic silencing is among the most frequently observed molecular lesions in human cancer. Overlapping reading frames in the INK4A/ARF gene encode p16INK4a and a distinct tumour-suppressor protein, p19ARF (ref. 3). Here we describe the generation and characterization of a p16Ink4a-specific knockout mouse that retains normal p19Arf function. Mice lacking p16Ink4a were born with the expected mendelian distribution and exhibited normal development except for thymic hyperplasia. T cells deficient in p16Ink4a exhibited enhanced mitogenic responsiveness, consistent with the established role of p16Ink4a in constraining cellular proliferation. In contrast to mouse embryo fibroblasts (MEFs) deficient in p19Arf (ref. 4), p16Ink4a-null MEFs possessed normal growth characteristics and remained susceptible to Ras-induced senescence. Compared with wild-type MEFs, p16Ink4a-null MEFs exhibited an increased rate of immortalization, although this rate was less than that observed previously for cells null for Ink4a/Arf, p19Arf or p53 (refs 4, 5). Furthermore, p16Ink4a deficiency was associated with an increased incidence of spontaneous and carcinogen-induced cancers. These data establish that p16Ink4a, along with p19Arf, functions as a tumour suppressor in mice.

Use of laser capture microdissection, cDNA microarrays, and tissue microarrays in advancing our understanding of prostate cancer

One difficulty in studying epithelial tumors has been the inability to isolate pure samples for DNA and RNA analysis. Prostate cancer, with its infiltrative nature, is particularly challenging. The Combination of several new technologies should help overcome these hurdles. Laser capture microdissection uses a laser beam to achieve transfer of pure cell populations for isolation of DNA, RNA, and protein. High-throughput analysis of these samples can be achieved by using cDNA expression microarrays. High-density tissue microarrays should allow for validation of differentially expressed genes. This review will concentrate on the application of laser capture microdissection, cDNA microarrays, and tissue microarrays in the area of prostate cancer research.

Reduced latency but no increased brain tumor penetrance in mice with astrocyte specific expression of a human p53 mutant

p53-germline mutations located in the core DNA-binding domain have been associated with a more dominant tumor penetrance especially for breast cancer and brain tumors. We previously reported an unusual accumulation of CNS tumors associated with a unique p53 germline mutation, Y236delta (deletion of codon 236). To test whether this tissue-specific tumor predisposition reflects a gain-of-function activity of Y236delta, we generated transgenic mice expressing Y236delta in astrocytes using the regulatory elements of the glial fibrillary acidic protein (GFAP) gene. After transplacental exposure to N-ethyl-N-nitrosourea (25 mg/kg BW) brain tumors developed in 18% (7/39) of GFAP-Y236delta transgenic p53-/- mice, while in p53+/- mice the incidence was 28% (11/40) (P>0.3). However, the mean tumor latency for GFAP-Y236delta/p53+/- mice was significantly shorter than for p53+/- mice, with 19.9 weeks vs 31.6 weeks (P=0.039), respectively. Taken together, cell specific expression of Y236delta results in an acceleration of tumor progression but does not confer a higher tumor penetrance. Conceivably, the transdominant effect of Y236delta provided a growth advantage early in the progression of neoplastic cells, since the endogenous p53 wild-type allele was lost in all brain tumors independent of the genotype. This reflects well observations from human astrocytic neoplasms with p53 mutations.