DNA methylation in liver tumorigenesis in fish from the environment

Abstract

The link between environment, alteration in DNA methylation and cancer has been well established in humans; yet, it is under-studied in unsequenced non-model organisms. The occurrence of liver tumors in the flatfish dab collected at certain UK sampling sites exceeds 20%, yet the causative agents and the molecular mechanisms of tumor formation are not known, especially regarding the balance between epigenetic and genetic factors. Methylated DNA Immunoprecipitation (MeDIP) combined with de novo high-throughput DNA sequencing were used to investigate DNA methylation changes in dab hepatocellular adenoma tumors for the first time in an unsequenced species. Novel custom-made dab gene expression arrays were designed and used to determine the relationship between DNA methylation and gene expression. In addition, the confirmatory techniques of bisulfite sequencing PCR (BSP) and RT-PCR were applied. Genes involved in pathways related to cancer, including apoptosis, wnt/β-catenin signaling and genomic and non-genomic estrogen responses, were altered both in methylation and transcription. Global methylation was statistically significantly 1.8-fold reduced in hepatocellular adenoma and non-cancerous surrounding tissues compared with liver from non-cancer bearing dab. Based on the identified changes and chemical exposure data, our study supports the epigenetic model of cancer. We hypothesize that chronic exposure to a mixture of environmental contaminants contributes to a global hypomethylation followed by further epigenetic and genomic changes. The findings suggest a link between environment, epigenetics and cancer in fish tumors in the wild and show the utility of this methodology for studies in non-model organisms.

Development and application of the adverse outcome pathway framework for understanding and predicting chronic toxicity: I. Challenges and research needs in ecotoxicology

“…The peculiar sensitivity of the early developmental time window to toxicant-caused epigenetic disruption is explained by the fact that embryo development is tightly governed by epigenetic regulation (Morgan et al, 2005;Feng et al, 2010) and epigenetic remodeling induced during this period may persist into adulthood (Szyf, 2009;Bernal and Jirtle, 2010;Faulk and Dolinoy, 2011). The epigenetic contribution is particularly well documented in the context of endocrine disruption (Crews and McLachlan, 2006;Bernal and Jirtle, 2010;Zama and Uzumcu, 2010;Greally and Jacobs, 2013;Svechnikov et al, 2014) as well as in the initiation of cancers (Newbold et al, 2000;Herath et al, 2006;Mirbahai et al, 2011). Moreover, it has also been implicated in many other dysfunctions including disruption of immune (Rodriguez-Cortez et al, 2011;Boehm et al, 2012) and nervous (Oliveira, 2012;Qureshi and Mehler, 2013) systems.…”

“…What should be used as a KE in particular cases: the change in DNA methylation patterns or only the subsequent downstream alteration of gene expression? Indeed, it appears that chemicals do have the ability to produce a characteristic change in specific methylation patterns (Bachman et al, 2006;Mirbahai et al, 2011;Thomson et al, 2012) that could be one of the KEs in a pathway leading to a detrimental outcome, however, the differences between purely adaptive or adverse changes need to be delineated in more detail. On the other hand, the earlier KE might be the metabolic pattern change that results in altered DNA methylation or modification of histones (another epigenetic mechanism), in turn leading to an AO defined as an increased susceptibility to certain diseases.…”

Comparative pathology in bivalves: Aetiological agents and disease processes

“…Methylation, in particular, comprises alterations of genic expression through mechanisms not involving alterations of DNA sequence (Baylin and Ohm, 2006). Such modifications, like hyper-methylations of promoters associated to gene silencing, are present in every step of carcinogenesis, but appears particularly predominant in the initial phase (Mirbahai et al, 2011;Jones and Baylin, 2002).…”

Synchronous giant hepatic adenoma in siblings-A case report and brief literature review

“…18 The onset of HA in fish has been reported to be associated with the environmental contamination including steroids. 19 We therefore suspect whether the environmental steroid exposure might, to some extent, contribute to the simultaneous development of HA in two siblings. Here we could not confirm this speculation with convincing evidence, and indeed it could just be a simple while extremely rare coincidence.…”