Genetic disruption of KEAP1/CUL3 E3 ubiquitin ligase complex components is a key mechanism of NF-kappaB pathway activation in lung cancer

INTRODUCTION

Inhibitor of kappa light polypeptide gene enhancer in B-cells, kinase beta (IKBKB) (IKK-β/IKK-2), which activates NF-κB, is a substrate of the KEAP1-CUL3-RBX1 E3-ubiquitin ligase complex, implicating this complex in NF-κB pathway regulation. We investigated complex component gene disruption as a novel genetic mechanism of NF-κB activation in non-small cell lung cancer.

METHODS

A total of 644 tumor- and 90 cell-line genomes were analyzed for gene dosage status of the individual complex components and IKBKB. Gene expression of these genes and NF-κB target genes were analyzed in 48 tumors. IKBKB protein levels were assessed in tumors with and without complex or IKBKB genetic disruption. Complex component knockdown was performed to assess effects of the E3-ligase complex on IKBKB and NF-κB levels, and phenotypic importance of IKBKB expression was measured by pharmacological inhibition.

RESULTS

We observed strikingly frequent genetic disruption (42%) and aberrant expression (63%) of the E3-ligase complex and IKBKB in the samples examined. Although both adenocarcinomas and squamous cell carcinomas showed complex disruption, the patterns of gene disruption differed. IKBKB levels were elevated with complex disruption, knockdown of complex components increased activated forms of IKBKB and NF-κB proteins, and IKBKB inhibition detriments cell viability, highlighting the biological significance of complex disruption. NF-κB target genes were overexpressed in samples with complex disruption, further demonstrating the effect of complex disruption on NF-κB activity.

CONCLUSIONS

Gene dosage alteration is a prominent mechanism that disrupts each component of the KEAP1-CUL3-RBX1 complex and its NF-κB stimulating substrate, IKBKB. Herein, we show that, multiple component disruption of this complex represents a novel mechanism of NF-κB activation in non-small cell lung cancer.

Abstract A14: DNA alterations to the Cullin-3/Ring box protein-1 E3 ubiquitin ligase complex represent a novel mechanism of NF-κB activation in lung cancer

Background: Nuclear factor kappa B (NF-κB) signaling is essential for lung cancer development, and therefore, may serve as a target for intervention. However, the genetic mechanisms responsible for its activation are not fully understood. Kelch-like ECH-associated protein 1 (KEAP1) binds protein substrates to the Cullin-3 (CUL3)/Ring box protein-1 (RBX1) E3 ubiquitin ligase complex where ubiquitination signals substrates for proteosomal degradation. Recently, inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ), an activator of NF-κB, was shown to be a substrate of KEAP1, implicating KEAP1's involvement in regulating NF-κB signaling. Loss of function of KEAP1 leads to IKKβ accumulation and NF-κB activation. We hypothesized that DNA deletions of the other E3 complex components (CUL3 and RBX1) are frequent alterations that disrupt complex function and contribute to NF-κB activation in lung cancer.

Methods: We screened DNA copy number profiles of 261 non-small cell lung cancer (NSCLC) tumors for DNA alterations at the KEAP1, CUL3, RBX1, and IKK loci. Profiles were generated by array comparative genomic hybridization on the SMRT array (sub-megabase resolution tiling) platform. We also analyzed mRNA expression of these genes and 9 well annotated NF-κB target genes, using gene expression profiles generated with Agilent gene expression microarrays for a subset (n=48) of the tumors.

Results: Our investigation of genetic disruption to the E3 ubiquitin ligase complex components revealed 54% of tumors harbored DNA copy number loss of at least one complex component (KEAP1, CUL3, or RBX1) or gain of IKKβ. Moreover, at the expression level, 81% of tumors analyzed had aberrant expression of one of these genes (underexpression of complex components or overexpression of IKKβ). Interestingly, the copy number alterations identified appeared to segregate with adenocarcinoma (AC) or squamous cell carcinoma (SCC) histology; KEAP1 loss was more prevalent in AC while CUL3 loss and IKKβ gain were more frequent in SCC. When NF-κB target gene expression was analyzed, we observed higher expression of 5/9 genes in tumors with underexpression of an E3 ubiquitin ligase complex component relative to matched non-malignant tissue from the same individual.

Conclusions: The presence and strikingly high frequency of genetic disruption and aberrant expression of the E3 ubiquitin ligase complex components (KEAP1, CUL3, and RBX1) revealed in this study provides evidence of its importance in lung cancer. These data suggest that DNA level alterations to this complex may represent a novel mechanism of NF-κB activation in lung cancer.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A14.

Abstract A16: Reversibly expressed and differentially methylated genes in airways of current and former smokers

Background: Smoking-related disease, including chronic obstructive pulmonary disease (COPD) and lung cancer, account for the third greatest cause of mortality and the number one cause of cancer-related death worldwide. Former smokers (FS) remain at an elevated risk for both diseases and are the fastest growing population of newly diagnosed lung cancer patients, emphasizing the need for greater understanding of molecular mechanisms associated with smoking and smoking cessation. Cigarette smoke induces DNA damage in airway and lung tissues at the genomic and epigenomic levels, where it is associated with changes to gene expression. Studies on current (CS), FS, and never smokers have identified reversible and irreversible changes in gene expression that occur upon smoking cessation. Since methylation is a reversible gene regulatory mark that is also aberrantly affected by cigarette smoke, we hypothesize that the reversible nature of genes differentially expressed in bronchial epithelial cells in the airways of CS and FS, may be due to changes in DNA methylation.

Methods: Bronchial epithelial cells were obtained from brushings of small airways (< 2mm diameter) during bronchoscopy from 12 current smokers (CS) and 6 former smokers (FS). Methylation profiles were generated for 27,579 probes corresponding to 14,575 genes, using the Illumina Infinium Human Methylation27 platform. Methylation results were aligned to the set of reversibly expressed genes described in previous studies. Genes that become either hypermethylated and underexpressed or hypomethylated and overexpressed upon smoking cessation were selected for further study.

Results: Methylation and expression analysis identified 9 genes overexpressed and hypomethylated in CS relative to FS, notably GPX2 and GSTA2 both involved in pathways previously shown to be upregulated in CS. These pathways include aryl hydrocarbon receptor signaling; a central metabolic pathway activated in response to halogenated and polycyclic aromatic hydrocarbons, and the NRF2 mediated oxidative stress response pathway, involved in the detoxification of reactive oxygen and intermediates. Additionally, 3 genes were found to be underexpressed and hypermethylated in CS relative to FS, notably SYF2 and CXCL6, involved in cell cycle regulation and inflammatory disease (including COPD) respectively.

Conclusion: Our data reveal a panel of genes whose change in gene expression upon smoking cessation may be regulated by DNA methylation, corresponding to well known genes involved in smoking metabolism and oxidative stress response. The identification of differentially methylated and expressed genes between CS and FS may provide insight into the mechanism of smoking related disease. As methylation is a reversible DNA modification, this knowledge may lead to the application of preventative epigenetic therapeutics for the growing population of FS and the immense health burden and mortality associated with cigarette smoke.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A16.

Abstract A21: Global DNA methylation analysis of bronchial epithelia of former smokers with COPD, with and without lung cancer

Introduction: Emerging evidence suggests that aberrant epigenetic regulation is involved in the development and progression of malignant and nonmalignant respiratory diseases, including chronic obstructive pulmonary disease (COPD) and lung cancer. Moreover, patients with COPD have an increased risk of developing lung cancer. Besides similar risk factors such as tobacco smoke exposure, little is known about the shared biology between COPD and lung cancer. Smoking causes aberrations in airway and lung parenchyma at both the genomic and epigenomic levels, resulting in global changes to gene expression. In this study, we hypothesize that alterations at the level of DNA methylation in airway epithelia of former smokers (FS) with COPD with and without non-small cell lung cancer (NSCLC) may be used to identify genes involved in the pathogenesis of these respiratory diseases, independent of the effects of active smoking.

Methods: Bronchial epithelial cells were obtained from brushings of small airways (< 2 mm diameter) during bronchoscopy from FS with COPD (n=22), without COPD (n=22) and patients with COPD as well as previous surgical resection of Stage I NSCLC (n=6). Illumina's Infinium Methylation (HM27) assay was used to assess DNA methylation status of 27,578 CpG sites associated with 14,475 genes.

Results: COPD patients are distinguished from non-COPD patients based on airway methylation profiles. Genes differentially methylated in airways between COPD and non-COPD patients include several modulators of aryl hydrocarbon receptor and IL6 signaling, as well as genes previously implicated in COPD, including immune chemotaxis regulators (CXCL11, CCR8) and GABA receptor signaling (GABRA5). Airway epithelial DNA from COPD patients with NSCLC compared to those without NSCLC was differentially methylated at sites encoding multiple key regulators of xenobiotic metabolism, regulators of free radical savaging/detoxification and retinol metabolic pathway components including several alcohol dehydrogenase, glutathione S transferase, and UDP glucoronosyltransferase genes.

Conclusion: Our preliminary results suggest a role for DNA methylation in the deregulation of previously identified COPD-related genes, and specifically highlight differences in airways of COPD patients with/without NSCLC corresponding to well-known smoking-related metabolomic processes. Knowledge of DNA methylation disruption will further our understanding of the etiological role of COPD in the development of lung cancer, and contribute to the development of chemo-prevention strategies targeting the biology of both COPD and NSCLC. Supported by CIHR.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):A21.

A sequence-based approach to identify reference genes for gene expression analysis

BACKGROUND

An important consideration when analyzing both microarray and quantitative PCR expression data is the selection of appropriate genes as endogenous controls or reference genes. This step is especially critical when identifying genes differentially expressed between datasets. Moreover, reference genes suitable in one context (e.g. lung cancer) may not be suitable in another (e.g. breast cancer). Currently, the main approach to identify reference genes involves the mining of expression microarray data for highly expressed and relatively constant transcripts across a sample set. A caveat here is the requirement for transcript normalization prior to analysis, and measurements obtained are relative, not absolute. Alternatively, as sequencing-based technologies provide digital quantitative output, absolute quantification ensues, and reference gene identification becomes more accurate.

METHODS

Serial analysis of gene expression (SAGE) profiles of non-malignant and malignant lung samples were compared using a permutation test to identify the most stably expressed genes across all samples. Subsequently, the specificity of the reference genes was evaluated across multiple tissue types, their constancy of expression was assessed using quantitative RT-PCR (qPCR), and their impact on differential expression analysis of microarray data was evaluated.

RESULTS

We show that (i) conventional references genes such as ACTB and GAPDH are highly variable between cancerous and non-cancerous samples, (ii) reference genes identified for lung cancer do not perform well for other cancer types (breast and brain), (iii) reference genes identified through SAGE show low variability using qPCR in a different cohort of samples, and (iv) normalization of a lung cancer gene expression microarray dataset with or without our reference genes, yields different results for differential gene expression and subsequent analyses. Specifically, key established pathways in lung cancer exhibit higher statistical significance using a dataset normalized with our reference genes relative to normalization without using our reference genes.

CONCLUSIONS

Our analyses found NDUFA1, RPL19, RAB5C, and RPS18 to occupy the top ranking positions among 15 suitable reference genes optimal for normalization of lung tissue expression data. Significantly, the approach used in this study can be applied to data generated using new generation sequencing platforms for the identification of reference genes optimal within diverse contexts.

FACADE: a fast and sensitive algorithm for the segmentation and calling of high resolution array CGH data

The availability of high resolution array comparative genomic hybridization (CGH) platforms has led to increasing complexities in data analysis. Specifically, defining contiguous regions of alterations or segmentation can be computationally intensive and popular algorithms can take hours to days for the processing of arrays comprised of hundreds of thousands to millions of elements. Additionally, tumors tend to demonstrate subtle copy number alterations due to heterogeneity, ploidy and hybridization effects. Thus, there is a need for fast, sensitive array CGH segmentation and alteration calling algorithms. Here, we describe Fast Algorithm for Calling After Detection of Edges (FACADE), a highly sensitive and easy to use algorithm designed to rapidly segment and call high resolution array data.

An integrative multi-dimensional genetic and epigenetic strategy to identify aberrant genes and pathways in cancer

Background

Genomics has substantially changed our approach to cancer research. Gene expression profiling, for example, has been utilized to delineate subtypes of cancer, and facilitated derivation of predictive and prognostic signatures. The emergence of technologies for the high resolution and genome-wide description of genetic and epigenetic features has enabled the identification of a multitude of causal DNA events in tumors. This has afforded the potential for large scale integration of genome and transcriptome data generated from a variety of technology platforms to acquire a better understanding of cancer.

Results

Here we show how multi-dimensional genomics data analysis would enable the deciphering of mechanisms that disrupt regulatory/signaling cascades and downstream effects. Since not all gene expression changes observed in a tumor are causal to cancer development, we demonstrate an approach based on multiple concerted disruption (MCD) analysis of genes that facilitates the rational deduction of aberrant genes and pathways, which otherwise would be overlooked in single genomic dimension investigations.

Conclusions

Notably, this is the first comprehensive study of breast cancer cells by parallel integrative genome wide analyses of DNA copy number, LOH, and DNA methylation status to interpret changes in gene expression pattern. Our findings demonstrate the power of a multi-dimensional approach to elucidate events which would escape conventional single dimensional analysis and as such, reduce the cohort sample size for cancer gene discovery.

Integrating the multiple dimensions of genomic and epigenomic landscapes of cancer

Advances in high-throughput, genome-wide profiling technologies have allowed for an unprecedented view of the cancer genome landscape. Specifically, high-density microarrays and sequencing-based strategies have been widely utilized to identify genetic (such as gene dosage, allelic status, and mutations in gene sequence) and epigenetic (such as DNA methylation, histone modification, and microRNA) aberrations in cancer. Although the application of these profiling technologies in unidimensional analyses has been instrumental in cancer gene discovery, genes affected by low-frequency events are often overlooked. The integrative approach of analyzing parallel dimensions has enabled the identification of (a) genes that are often disrupted by multiple mechanisms but at low frequencies by any one mechanism and (b) pathways that are often disrupted at multiple components but at low frequencies at individual components. These benefits of using an integrative approach illustrate the concept that the whole is greater than the sum of its parts. As efforts have now turned toward parallel and integrative multidimensional approaches for studying the cancer genome landscape in hopes of obtaining a more insightful understanding of the key genes and pathways driving cancer cells, this review describes key findings disseminating from such high-throughput, integrative analyses, including contributions to our understanding of causative genetic events in cancer cell biology.

Abstract 1133: Inactivation of BRG1 in non-small cell lung cancer (NSCLC) cell lines

Purpose: To study the frequency and gene expression profile of BRG1 inactivation in NSCLC cell lines. Background: BRG1 is the catalytic subunit of SWI/SNF chromatin remodeling complex and provides ATPase activity necessary for transcriptional regulation of many genes. BRG1 is frequently inactivated in lung cancers and loss of BRG1 correlated with poor prognosis. Methods: Forty NSCLC cell lines containing various gene mutations were analyzed. BRG1 cDNA was sequenced and SNP analysis was used to confirm the large deletion mutants. Gene expression profile was determined by Illumina human WG-6 V3 beadchip (detecting ∼ 48,000 transcripts, ∼25,000 genes). BRG1 mRNA levels were determined by both RNA microarray and qPCR methods. BRG1 protein expression was analyzed by immuno-blotting. Results: Thirteen of forty (33%) NSCLC cell lines had no BRG1 protein expression (n =11) or expressed abnormal size of BRG1 (n =2). BRG1 cDNA was sequenced in these cell lines as well as control cell lines. While 10 control cell lines with normal BRG1 protein expression were not found to contain mutations, eleven cell lines without BRG1 protein expression and one containing abnormal size BRG1 protein were found to have mutations, including deletions, point mutations and insertion. The deletions and point mutations of BRG1 are homozygous. Mutant BRG1 expressed either no or lower than normal levels of BRG1 mRNA. BRG1 inactivation was found more frequent in smokers (50%) than non-smokers (15%), and coexisted with KRAS mutation, but was mutually exclusive to EGFR mutation. Furthermore, inactivation of BRG1 and LKB1, a tumor suppressor gene also located on chromosome 19p and adjacent to BRG1, showed 73% concordance (P=0.03). Finally, RNA microarray analysis showed nearly 800 transcripts (False Discovery Rate <5%) down or up regulated in NSCLC cell lines with BRG1 inactivation compared to cell lines with wild type BRG1. Conclusions: 1) BRG1 is frequently mutated in NSCLC cell lines by deletions or point mutations. 2) There is excellent concordance (98 %) between mutation status and loss of protein expression. 3) Inactivation of BRG1 shows concordance with smoking history and LKB1 mutation, and is negatively correlated with EGFR mutation. 4) Inactivation of BRG1 has a major impact on gene expression profile of NSCLC cell lines. These data indicate that BRG1 may play an important role in lung tumorigenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1133.

Abstract LB-346: A novel lung tumor suppressor implicated in somatic and familial cancers

Background: Lung cancer (LC) is the most common cause of cancer death worldwide. Previous familial linkage studies have identified a tumor suppressor locus on 6q23-25. However, no single gene has yet been implicated within this 30 Mb region. Discovering the genetic and epigenetic events that affect LC risk and development will lead to better methods for risk assessment, early detection and treatment.

Methods: Genome-wide genes disrupted by two-hit inactivation were identified by combining gene dosage, DNA methylation, and gene expression assays for a group of lung adenocarcinomas (AC) and adjacent non-malignant tissues. Gene expression, DNA hypermethylation and/or copy number aberrations were validated in data from AC, squamous cell carcinoma (SqCC), and pre-malignant lesions by querying other cohorts using gene-specific and whole-genome approaches. The role of DNA methylation in gene silencing was assessed using inhibition of DNMT by 5′-azacytidine. The association of allelic variants with LC risk was investigated in 193 familial LC cases and 213 controls collected by the Genetic Epidemiology of Lung Cancer Consortium (GELCC) using a Cochrane-Armitage trend test. The association of gene expression with prognosis was performed on public data using a Mantel-Cox log test. Stable mRNA knock-downs were generated using lentiviral delivery of a gene-specific shRNA, and apoptotic cells were counted using Annexin5/propidium iodide staining.

Results: Integration of AC gene dosage, DNA methylation and mRNA expression showed EYA4 to be frequently affected by two-hits and significantly down-regulated. Quantitative PCR techniques confirmed that EYA4 was hypermethylated (46%) and down-regulated (72%), validating our microarray results. A direct link between EYA4 methylation and expression was verified by restoration of expression after 5′-azacytidine treatment in methylated cell lines. Congruent with EYA family member function, in vitro assays revealed that EYA4 knock-down cells displayed a decrease in the number of apoptotic cells - a hallmark of cancer. Further investigations led to the discovery of frequent EYA4 disruption in SqCC and pre-neoplastic tissue. The GELCC dataset was examined to assess EYA4 allelotype association with familial risk. Doing so revealed that numerous EYA4 variants are associated with increased risk. Finally, the association of EYA4 expression with survival was investigated along with other somatically altered genes at 6q23-25. Of these genes, low EYA4 expression was found to be the most significantly associated with poor prognosis.

Conclusions: EYA4 is a frequently disrupted gene that maps to a locus previously associated with cancer risk. It is implicated in somatic as well as familial cancers, and is likely a tumor suppressor gene with apoptotic functions. The direct association of EYA4 with risk and survival underscores its relevance on a clinical level.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-346.

Transcriptome profiles of carcinoma-in-situ and invasive non-small cell lung cancer as revealed by SAGE

Background

Non-small cell lung cancer (NSCLC) presents as a progressive disease spanning precancerous, preinvasive, locally invasive, and metastatic lesions. Identification of biological pathways reflective of these progressive stages, and aberrantly expressed genes associated with these pathways, would conceivably enhance therapeutic approaches to this devastating disease.

Methodology/Principal Findings

Through the construction and analysis of SAGE libraries, we have determined transcriptome profiles for preinvasive carcinoma-in-situ (CIS) and invasive squamous cell carcinoma (SCC) of the lung, and compared these with expression profiles generated from both bronchial epithelium, and precancerous metaplastic and dysplastic lesions using Ingenuity Pathway Analysis. Expression of genes associated with epidermal development, and loss of expression of genes associated with mucociliary biology, are predominant features of CIS, largely shared with precancerous lesions. Additionally, expression of genes associated with xenobiotic metabolism/detoxification is a notable feature of CIS, and is largely maintained in invasive cancer. Genes related to tissue fibrosis and acute phase immune response are characteristic of the invasive SCC phenotype. Moreover, the data presented here suggests that tissue remodeling/fibrosis is initiated at the early stages of CIS. Additionally, this study indicates that alteration in copy-number status represents a plausible mechanism for differential gene expression in CIS and invasive SCC.

Conclusions/Significance

This study is the first report of large-scale expression profiling of CIS of the lung. Unbiased expression profiling of these preinvasive and invasive lesions provides a platform for further investigations into the molecular genetic events relevant to early stages of squamous NSCLC development. Additionally, up-regulated genes detected at extreme differences between CIS and invasive cancer may have potential to serve as biomarkers for early detection.

Oncogene mutations, copy number gains and mutant allele specific imbalance (MASI) frequently occur together in tumor cells

BACKGROUND

Activating mutations in one allele of an oncogene (heterozygous mutations) are widely believed to be sufficient for tumorigenesis. However, mutant allele specific imbalance (MASI) has been observed in tumors and cell lines harboring mutations of oncogenes.

METHODOLOGY/PRINCIPAL FINDINGS

We determined 1) mutational status, 2) copy number gains (CNGs) and 3) relative ratio between mutant and wild type alleles of KRAS, BRAF, PIK3CA and EGFR genes by direct sequencing and quantitative PCR assay in over 400 human tumors, cell lines, and xenografts of lung, colorectal, and pancreatic cancers. Examination of a public database indicated that homozygous mutations of five oncogenes were frequent (20%) in 833 cell lines of 12 tumor types. Our data indicated two major forms of MASI: 1) MASI with CNG, either complete or partial; and 2) MASI without CNG (uniparental disomy; UPD), due to complete loss of wild type allele. MASI was a frequent event in mutant EGFR (75%) and was due mainly to CNGs, while MASI, also frequent in mutant KRAS (58%), was mainly due to UPD. Mutant: wild type allelic ratios at the genomic level were precisely maintained after transcription. KRAS mutations or CNGs were significantly associated with increased ras GTPase activity, as measured by ELISA, and the two molecular changes were synergistic. Of 237 lung adenocarcinoma tumors, the small number with both KRAS mutation and CNG were associated with shortened survival.

CONCLUSIONS

MASI is frequently present in mutant EGFR and KRAS tumor cells, and is associated with increased mutant allele transcription and gene activity. The frequent finding of mutations, CNGs and MASI occurring together in tumor cells indicates that these three genetic alterations, acting together, may have a greater role in the development or maintenance of the malignant phenotype than any individual alteration.

Genomic imbalances in precancerous tissues signal oral cancer risk

Oral cancer develops through a series of histopathological stages: through mild (low grade), moderate, and severe (high grade) dysplasia to carcinoma in situ and then invasive disease. Early detection of those oral premalignant lesions (OPLs) that will develop into invasive tumors is necessary to improve the poor prognosis of oral cancer. Because no tools exist for delineating progression risk in low grade oral lesions, we cannot determine which of these cases require aggressive intervention. We undertook whole genome analysis by tiling-path array comparative genomic hybridization for a rare panel of early and late stage OPLs (n = 62), all of which had extensive longitudinal follow up (>10 years). Genome profiles for oral squamous cell carcinomas (n = 24) were generated for comparison. Parallel analysis of genome alterations and clinical parameters was performed to identify features associated with disease progression. Genome alterations in low grade dysplasias progressing to invasive disease more closely resembled those observed for later stage disease than they did those observed for non-progressing low grade dysplasias. This was despite the histopathological similarity between progressing and non-progressing cases. Strikingly, unbiased computational analysis of genomic alteration data correctly classified nearly all progressing low grade dysplasia cases. Our data demonstrate that high resolution genomic analysis can be used to evaluate progression risk in low grade OPLs, a marked improvement over present histopathological approaches which cannot delineate progression risk. Taken together, our data suggest that whole genome technologies could be used in management strategies for patients presenting with precancerous oral lesions.

Integrative genomic and gene expression analysis of chromosome 7 identified novel oncogene loci in non-small cell lung cancer

Lung cancer accounts for over a quarter of cancer deaths, with non-small cell lung cancer (NSCLC) accounting for approximately 80% of cases. Several genome studies have been undertaken in both cell models of NSCLC and clinical samples to identify alterations underlying disease behaviour, and many have identified recurring aberrations of chromosome 7. The presence of recurring chromosome 7 alterations that do not span the well-studied oncogenes EGFR (at 7p11.2) and MET (at 7q31.2) has raised the hypothesis of additional genes on this chromosome that contribute to tumourigenesis. In this study, we demonstrated that multiple loci on chromosome 7 are indeed amplified in NSCLC, and through integrative analysis of gene dosage alterations and parallel gene expression changes, we identified new lung cancer oncogene candidates, including FTSJ2, NUDT1, TAF6, and POLR2J. Activation of these key genes was confirmed in panels of clinical lung tumour tissue as compared with matched normal lung tissue. The detection of gene activation in multiple cohorts of samples strongly supports the presence of key genes involved in lung cancer that are distinct from the EGFR and MET loci on chromosome 7.

Comparative genomic hybridization on BAC arrays

Alterations in genomic DNA are a key feature of many constitutional disorders and cancer. The discovery of the underlying regions of gene dosage has thus been essential in dissecting complex disease phenotypes and identifying targets for therapeutic intervention and diagnostic testing. The development of array comparative genomic hybridization (aCGH) using bacterial artificial chromosomes (BACs) as hybridization targets has facilitated the discovery and fine mapping of novel genomic alterations allowing rapid identification of target genes. In BAC aCGH, DNA samples are first labeled with fluorescent dyes through a random priming reaction with 100-400 ng of genomic DNA. This probe is then co-hybridized to an array consisting of BAC clones, either tiling the genome (approximately 50 kbp resolution) or spaced at intervals (e.g., 1 Mbp resolution). The resulting arrays are then imaged and the signal at each locus is compared between a reference and test sample to determine the copy number status. The DNA samples to be analyzed may be derived from either fresh, frozen, or formalin-fixed paraffin-embedded material, and sample requirements are currently significantly lower than those for oligonucleotide platforms due to the high probe-binding capacity of BAC clone targets (approximately 150 kbp) compared to oligonucleotides (25-80 bp). In this chapter, we describe in detail the technical procedure required to perform copy number analysis of genomes with BAC aCGH.

Abstract A27: Contribution of DNA methylation in development of lung cancer in former smokers

A27

Background

Lung cancer is the most common cause of cancer death worldwide with more than 1.2 million people dying of the disease each year. Half of newly diagnosed lung cancer patients are former smokers. Understanding why former smokers develop lung cancer is clearly important to the development of early detection, prevention and treatment strategies for these people. The effects of cigarette smoke on the epigenome are widespread as both global DNA methylation and local DNA methylation have been identified, associated with genomic instability and tumour suppressor gene (TSG) silencing, respectively. In a cancer-specific context, upregulation of oncogenes and silencing of tumour suppressor genes both occur as a result of tobacco smoke exposure. Therefore, molecular studies examining tumors at genomic and epigenomic levels will likely identify causal genetic events involved in cancer development in former smokers.

Objective

The objective of this study is to determine the contribution of DNA methylation as a mechanism to lung cancer development in former smokers.

Hypothesis

As smoking induces methylation changes in bronchioepithelial cells, we hypothesize that this constitutes the first hit to TSG inactivation. In order to inactivate both alleles, these methylation changes would be maintained in tumors where a second hit would be found at the same gene loci.

Materials and Methods

Epithelial cells from former smokers (those with >10 years of smoking cessation) were collected from peripheral airways during routine bronchoscopy. Half of the cells were fixed in Cytolyt and the other half in RNAlater for DNA and RNA extraction, respectively. Copy number profiling was performed by array comparative genomic hybridization (aCGH) using whole-genome tiling path SMRT v2 BAC array. Methylation analysis was performed by coupling affinity based enrichment of methylated sequences with hybridization to the same aCGH platform described above. Expression status of genes was determined by gene expression microarray analysis using Agilent 44K expression arrays. RESULTS: Preliminary MeDIP aCGH of bronchial brush cells from eight former smokers who had previous surgical removal of Stage I NSCLC, and eight former smokers without NSCLC, of similar age (68±7 versus 62±6), revealed distinct differences in frequency of DNA methylation between cancer and non-cancer groups. For example, at 11p13 the cancer group shows hypermethylation at the WT1 locus, a known TSG. Analysis in 62 NSCLC tumors for gene dosage, showed a high frequency of loss at the WT1 locus. To examine downstream effects of these events in tumours, expression of WT1 was assessed and found to be significantly underexpressed in the majority of NSCLC tumours compared to a normal lung reference. Collection of more samples and further integrative analysis is currently underway.

Conclusion

Differences in methylation between these two groups may explain why some former smokers develop cancer while others remain cancer free despite similar lifestyle changes. As methylation is a reversible DNA modification, this knowledge would prompt the development and application of DNA demethylation chemopreventative agents and unique therapeutic strategies.

Citation Information: Cancer Prev Res 2008;1(7 Suppl):A27.

Evolving strategies for global gene expression analysis of cancer

The advent of high throughput gene expression profiling, from microarrays to sequence based assays has yielded vast insight into the biology of tumors. New technologies are constantly being unveiled which promise to generate more accurate maps of tumor gene deregulation, and demand the development of new strategies in data analysis. This review details the challenges faced in profiling tumor transcriptomes, and highlights the emerging strategies to utilize global profiling approaches to advance our understanding of causal genetic and epigenetic events and their impact on gene expression and tumor phenotype and behavior, through high throughput profiling, and integration of multiple dimensions of genomic data.

SIGMA2: a system for the integrative genomic multi-dimensional analysis of cancer genomes, epigenomes, and transcriptomes

Background

High throughput microarray technologies have afforded the investigation of genomes, epigenomes, and transcriptomes at unprecedented resolution. However, software packages to handle, analyze, and visualize data from these multiple 'omics disciplines have not been adequately developed.

Results

Here, we present SIGMA², a system for the integrative genomic multi-dimensional analysis of cancer genomes, epigenomes, and transcriptomes. Multi-dimensional datasets can be simultaneously visualized and analyzed with respect to each dimension, allowing combinatorial integration of the different assays belonging to the different 'omics.

Conclusion

The identification of genes altered at multiple levels such as copy number, loss of heterozygosity (LOH), DNA methylation and the detection of consequential changes in gene expression can be concertedly performed, establishing SIGMA² as a novel tool to facilitate the high throughput systems biology analysis of cancer.

DNA amplification is a ubiquitous mechanism of oncogene activation in lung and other cancers

Chromosomal translocation is the best-characterized genetic mechanism for oncogene activation. However, there are documented examples of activation by alternate mechanisms, for example gene dosage increase, though its prevalence is unclear. Here, we answered the fundamental question of the contribution of DNA amplification as a molecular mechanism driving oncogenesis. Comparing 104 cancer lines representing diverse tissue origins identified genes residing in amplification 'hotspots' and discovered an unexpected frequency of genes activated by this mechanism. The 3431 amplicons identified represent approximately 10 per hematological and approximately 36 per epithelial cancer genome. Many recurrently amplified oncogenes were previously known to be activated only by disease-specific translocations. The 135 hotspots identified contain 538 unique genes and are enriched for proliferation, apoptosis and linage-dependency genes, reflecting functions advantageous to tumor growth. Integrating gene dosage with expression data validated the downstream impact of the novel amplification events in both cell lines and clinical samples. For example, multiple downstream components of the EGFR-family-signaling pathway, including CDK5, AKT1 and SHC1, are overexpressed as a direct result of gene amplification in lung cancer. Our findings suggest that amplification is far more common a mechanism of oncogene activation than previously believed and that specific regions of the genome are hotspots of amplification.

Disruption of the Non-Canonical WNT Pathway in Lung Squamous Cell Carcinoma

Disruptions of beta-catenin and the canonical Wnt pathway are well documented in cancer. However, little is known of the non-canonical branch of the Wnt pathway. In this study, we investigate the transcript level patterns of genes in the Wnt pathway in squamous cell lung cancer using reverse-transcriptase (RT)-PCR. It was found that over half of the samples examined exhibited dysregulated gene expression of multiple components of the non-canonical branch of the WNT pathway. In the cases where beta catenin ( CTNNB1) was not over-expressed, we identified strong relationships of expression between wingless-type MMTV integration site family member 5A ( WNT5A)/ frizzled homolog 2 ( FZD2), frizzled homolog 3 ( FZD3)/ dishevelled 2 ( DVL2), and low density lipoprotein receptor-related protein 5 ( LRP5)/ secreted frizzled-related protein 4 ( SFRP4). This is one of the first studies to demonstrate expression of genes in the non-canonical pathway in normal lung tissue and its disruption in lung squamous cell carcinoma. These findings suggest that the non-canonical pathway may have a more prominent role in lung cancer than previously reported.

Disruption of the non-canonical WNT pathway in lung squamous cell carcinoma

Disruptions of beta-catenin and the canonical Wnt pathway are well documented in cancer. However, little is known of the non-canonical branch of the Wnt pathway. In this study, we investigate the transcript level patterns of genes in the Wnt pathway in squamous cell lung cancer using reverse-transcriptase (RT)-PCR. It was found that over half of the samples examined exhibited dysregulated gene expression of multiple components of the non-canonical branch of the WNT pathway. In the cases where beta catenin (CTNNB1) was not over-expressed, we identified strong relationships of expression between wingless-type MMTV integration site family member 5A (WNT5A)/ frizzled homolog 2 (FZD2), frizzled homolog 3 (FZD3) / dishevelled 2 (DVL2), and low density lipoprotein receptor-related protein 5 (LRP5)/ secreted frizzled-related protein 4 (SFRP4). This is one of the first studies to demonstrate expression of genes in the non-canonical pathway in normal lung tissue and its disruption in lung squamous cell carcinoma. These findings suggest that the non-canonical pathway may have a more prominent role in lung cancer than previously reported.