Roland Hubaux

Molecular features in arsenic-induced lung tumors

Arsenic is a well-known human carcinogen, which potentially affects ~160 million people worldwide via exposure to unsafe levels in drinking water. Lungs are one of the main target organs for arsenic-related carcinogenesis. These tumors exhibit particular features, such as squamous cell-type specificity and high incidence among never smokers. Arsenic-induced malignant transformation is mainly related to the biotransformation process intended for the metabolic clearing of the carcinogen, which results in specific genetic and epigenetic alterations that ultimately affect key pathways in lung carcinogenesis. Based on this, lung tumors induced by arsenic exposure could be considered an additional subtype of lung cancer, especially in the case of never-smokers, where arsenic is a known etiological agent. In this article, we review the current knowledge on the various mechanisms of arsenic carcinogenicity and the specific roles of this metalloid in signaling pathways leading to lung cancer.

Unique somatic and malignant expression patterns implicate PIWI-interacting RNAs in cancer-type specific biology

Human PIWI-interacting RNAs (piRNAs) are known to be expressed in germline cells, functionally silencing LINEs and SINEs. Their expression patterns in somatic tissues are largely uncharted. We analyzed 6,260 human piRNA transcriptomes derived from non-malignant and tumour tissues from 11 organs. We discovered that only 273 of the 20,831 known piRNAs are expressed in somatic non-malignant tissues. However, expression patterns of these piRNAs were able to distinguish tissue-of-origin. A total of 522 piRNAs are expressed in corresponding tumour tissues, largely distinguishing tumour from non-malignant tissues in a cancer-type specific manner. Most expressed piRNAs mapped to known transcripts, contrary to “piRNA clusters” reported in germline cells. We showed that piRNA expression can delineate clinical features, such as histological subgroups, disease stages, and survival. PiRNAs common to many cancer types might represent a core gene-set that facilitates cancer growth, while piRNAs unique to individual cancer types likely contribute to cancer-specific biology.

EZH2 promotes E2F driven SCLC tumorigenesis through modulation of apoptosis and cell cycle regulation

Introduction: Although enhancer of zeste homolog 2 (EZH2) has been associated with both non-small cell and small-cell lung cancers (SCLCs), current observations suggest different mechanisms of EZH2 activation and overexpression in these lung cancer types. Globally, SCLC kills 200,000 people yearly. New clinical approaches for SCLC treatment are required to improve the poor survival rate. Given the therapeutic potential of EZH2 as a target, we sought to delineate the downstream consequences of EZH2 disruption to identify the cellular mechanisms by which EZH2 promotes tumorigenesis in SCLC. Methods: We generated cells with stable expression of short hairpin RNA targeting EZH2 and corresponding controls (pLKO.1) and determined the consequences of EZH2 knockdown on the cell cycle and apoptosis by means of propidium iodide staining and fluorescence-activated cell sorting, Western blot, quantitative reverse transcriptase-polymerase chain reaction as well as cell viability assessment using methylthiazol tetrazolium assays. Results: We discovered that EZH2 inhibition (1) increased apoptotic activity by up-regulating the proapoptotic factors Puma and Bad, (2) decreased the fraction of cells in S or G2/M phases, and (3) elevated p21 protein levels, implicating EZH2 in cell death and cell-cycle control in SCLC. Conclusion: Our findings present evidence for the role of EZH2 in the regulation of cell cycle and apoptosis, providing a biological mechanism to explain the tumorigenicity of EZH2 in SCLC. Our work points to the great potential of EZH2 as a therapeutic target in SCLC.

Arsenic, asbestos and radon: emerging players in lung tumorigenesis

The cause of lung cancer is generally attributed to tobacco smoking. However lung cancer in never smokers accounts for 10 to 25% of all lung cancer cases. Arsenic, asbestos and radon are three prominent non-tobacco carcinogens strongly associated with lung cancer. Exposure to these agents can lead to genetic and epigenetic alterations in tumor genomes, impacting genes and pathways involved in lung cancer development. Moreover, these agents not only exhibit unique mechanisms in causing genomic alterations, but also exert deleterious effects through common mechanisms, such as oxidative stress, commonly associated with carcinogenesis. This article provides a comprehensive review of arsenic, asbestos, and radon induced molecular mechanisms responsible for the generation of genetic and epigenetic alterations in lung cancer. A better understanding of the mode of action of these carcinogens will facilitate the prevention and management of lung cancer related to such environmental hazards.

Unique Pattern of Component Gene Disruption in the NRF2 Inhibitor KEAP1/CUL3/RBX1 E3-Ubiquitin Ligase Complex in Serous Ovarian Cancer

The NFE2-related factor 2 (NRF2) pathway is critical to initiate responses to oxidative stress; however, constitutive activation occurs in different cancer types, including serous ovarian carcinomas (OVCA). The KEAP1/CUL3/RBX1 E3-ubiquitin ligase complex is a regulator of NRF2 levels. Hence, we investigated the DNA-level mechanisms affecting these genes in OVCA. DNA copy-number loss (CNL), promoter hypermethylation, mRNA expression, and sequence mutation for KEAP1, CUL3, and RBX1 were assessed in a cohort of 568 OVCA from The Cancer Genome Atlas. Almost 90% of cases exhibited loss-of-function alterations in any components of the NRF2 inhibitory complex. CNL is the most prominent mechanism of component disruption, with RBX1 being the most frequently disrupted component. These alterations were associated with reduced mRNA expression of complex components, and NRF2 target gene expression was positively enriched in 90% of samples harboring altered complex components. Disruption occurs through a unique DNA-level alteration pattern in OVCA. We conclude that a remarkably high frequency of DNA and mRNA alterations affects components of the KEAP1/CUL3/RBX1 complex, through a unique pattern of genetic mechanisms. Together, these results suggest a key role for the KEAP1/CUL3/RBX1 complex and NRF2 pathway deregulation in OVCA.

Microtubule Affinity-Regulating Kinase 2 is associated with DNA damage response and cisplatin resistance in non-small cell lung cancer

Microtubule affinity‐regulating kinases (MARKs) are involved in several cellular functions but few studies have correlated MARK kinase expression with cancer, and none have explored their role in lung cancer. In this study, we identified MARK2 as frequently disrupted by DNA hypomethylation and copy gain, resulting in concordant overexpression in independent lung tumor cohorts and we demonstrate a role for MARK2 in lung tumor biology. Manipulation of MARK2 in lung cell lines revealed its involvement in cell viability and anchorage‐independent growth. Analyses of both manipulated cell lines and clinical tumor specimens identified a potential role for MARK2 in cell cycle activation and DNA repair. Associations between MARK2 and the E2F, Myc/Max and NF‐κB pathways were identified by luciferase assays and in‐depth assessment of the NF‐κB pathway suggests a negative association between MARK2 expression and NF‐κB due to activation of non‐canonical NF‐κB signaling. Finally, we show that high MARK2 expression levels correlate with resistance to cisplatin, a standard first line chemotherapy for lung cancer. Collectively, our work supports a role for MARK2 in promoting malignant phenotypes of lung cancer and potentially modulating response to the DNA damaging chemotherapeutic, cisplatin.

MicroRNAs As Biomarkers For Clinical Features Of Lung Cancer.

Each year about 1.4 million people die from lung cancer worldwide. Despite efforts in prevention, diagnosis and treatment, survival rate remains poor for this disease. This unfortunate situation is largely due to the fact that a high proportion of cases are diagnosed at advanced stages, highlighting the great need for identifying new biomarkers in order to improve early diagnosis and treatment. Recent studies on microRNAs have not only shed light on their involvement in tumor development and progression, but also suggested their potential utility as biomarkers for subtype diagnostics, staging and prediction of treatment response. This review article summarizes the impact of microRNAs on lung cancer biology, and highlights their role in the detection and classification of lung cancer as well as direct targets for drug development.

Environmental arsenic exposure: From genetic susceptibility to pathogenesis

More than 200 million people in 70 countries are exposed to arsenic through drinking water. Chronic exposure to this metalloid has been associated with the onset of many diseases, including cancer. Epidemiological evidence supports its carcinogenic potential, however, detailed molecular mechanisms remain to be elucidated. Despite the global magnitude of this problem, not all individuals face the same risk. Susceptibility to the toxic effects of arsenic is influenced by alterations in genes involved in arsenic metabolism, as well as biological factors, such as age, gender and nutrition. Moreover, chronic arsenic exposure results in several genotoxic and epigenetic alterations tightly associated with the arsenic biotransformation process, resulting in an increased cancer risk. In this review, we: 1) review the roles of inter-individual DNA-level variations influencing the susceptibility to arsenic-induced carcinogenesis; 2) discuss the contribution of arsenic biotransformation to cancer initiation; 3) provide insights into emerging research areas and the challenges in the field; and 4) compile a resource of publicly available arsenic-related DNA-level variations, transcriptome and methylation data. Understanding the molecular mechanisms of arsenic exposure and its subsequent health effects will support efforts to reduce the worldwide health burden and encourage the development of strategies for managing arsenic-related diseases in the era of personalized medicine.

Re: The Wnt Signaling Pathway in Non-Small Cell Lung Cancer

We read with great interest the article by Stewart (1) in the December issue of the Journal. The author gives a useful update of genomic alterations affecting Wnt signaling components that are frequently observed in non-small cell lung cancer (NSCLC) and reminds us that Wnt component mutations seen in other cancers such as colon are uncommon in NSCLC. We believe it is necessary to bring further attention to the fact that Wnt pathway disruption in lung cancer differs greatly from what is observed in other malignancies. As described by Stewart, numerous Wnt pathway components are disrupted in lung adenocarcinoma (LUAD). The alterations summarized in Table 1 from Stewart (1) are also prominent in our own LUAD cohort (n = 77; Figure 1). Further investigation of our tumor set revealed that when considering gene expression signatures associated with canonical Wnt pathway transcription, up to 30% of tumors showed signatures consistent with active Wnt signaling (TCF1 13–30%, TCF4 4%, LEF1 2%; gene set enrichment analysis [GSEA], P < .01). These results agree with other studies assessing Wnt pathway activation in lung cancer, indicating Wnt/TCF is active in a significant fraction of lung tumors. For example, a recent study demonstrated that 45% of 309 NSCLCs stained positive for nuclear β-catenin, which is often associated with Wnt/TCF activity (2). However, despite the occurrence of component disruption and the apparent Wnt activity across lung tumor datasets, we found no correlation between Wnt/TCF activity (defined using GSEA) and disruption status of the Wnt pathway component genes (Table 1 from Stewart [1]). The frequencies of component alteration do not differ between tumors classified as Wnt/TCF active vs inactive for CoRReSPoNdeNCe Figure 1. Comparison of DNA and mRNA expression alterations affecting Wnt components between lung adenocarcinoma (LUAD) classified as Wnt active and inactive. Genetic alterations (over-and underexpres-sion, DNA hyper-and hypomethylation, and copy gain and loss) in 77 LUAD tumors were defined relative to patient-matched nonmalignant tissue using the following thresholds: expression fold change >2, percent difference in DNA methylation >20%, copy number gain > 2.3 copies and loss < 1.7 copies. Details on sample acquisition, processing, clinical information, and data analyses are described elsewhere (7). Copy number data was generated using Affymetrix SNP 6 arrays, methylation by Illumina HM27 arrays and expression by Illumina Human WG6v3.0 arrays. TCF activation status was assessed using preranked gene set enrichment analysis on all genes in a given tumor with a minimum …

Germline copy number variations are associated with breast cancer risk and prognosis

Breast cancer is one of the most common cancers among women, and susceptibility is explained by genetic, lifestyle and environmental components. Copy Number Variants (CNVs) are structural DNA variations that contribute to diverse phenotypes via gene-dosage effects or cis-regulation. In this study, we aimed to identify germline CNVs associated with breast cancer susceptibility and their relevance to prognosis. We performed whole genome CNV genotyping in 422 cases and 348 controls using Human Affymetrix SNP 6 array. Principal component analysis for population stratification revealed 84 outliers leaving 366 cases and 320 controls of Caucasian ancestry for association analysis; CNVs with frequency > 10% and overlapping with protein coding genes were considered for breast cancer risk and prognostic relevance. Coding genes within the CNVs identified were interrogated for gene- dosage effects by correlating copy number status with gene expression profiles in breast tumor tissue. We identified 200 CNVs associated with breast cancer (q-value < 0.05). Of these, 21 CNV regions (overlapping with 22 genes) also showed association with prognosis. We validated representative CNVs overlapping with APOBEC3B and GSTM1 genes using the TaqMan assay. Germline CNVs conferred dosage effects on gene expression in breast tissue. The candidate CNVs identified in this study warrant independent replication.