Establishment of a detection system for demethylating agents using an endogenous promoter CpG island

Disturbances of epigenetic information that result in changes in DNA methylation patterns are involved in carcinogenesis and other human disorders. Detection of agents that can cause epigenetic alterations--i.e. epimutagens--is therefore an important objective. We have developed and now describe the first detection system for demethylating agents that involves an endogenous promoter CpG island (CGI). After screening 10 promoter CGIs of genes silenced in human cancers, a CGI of the FLJ32130 gene was found to respond sensitively to a known demethylating agent, 5-aza-2'-deoxycytidine (5-aza-dC), by abundantly re-expressing its mRNA. After introducing the Hyg(r)-EGFP fusion gene into exon 3 of the FLJ32130 gene by homologous recombination, we isolated one clone that had the expected recombination outcomes and designated it F117. Two subclones (F117-47 and F117-123) of this original clone that did not share its propensity for leaky expression of the Hyg(r)-EGFP mRNA were then isolated, and methylation of their 5' CGI was confirmed. The addition of 5-aza-dC at doses of 0.1 microM or higher led to their 5' CGI being demethylated, and to Hyg(r)-EGFP being expressed; the anticipated fluorescence was readily confirmed by fluorescence microscopy. We believe that this is the first assay system that detects agents that disturb the methylated status of a CGI that regulates an endogenous promoter.     

Epigenetics and epimutagens: some new perspectives on cancer, germ line effects and endocrine disrupters

It is known that a variety of chemicals, including certain base analogues and reactive oxygen species, can alter the phenotypes of mammalian cells epigenetically, i.e., without changing their DNA sequence information in any way. The implications of such findings are not trivial, but do not seem to have been the focus of a great deal of attention amongst mutation researchers to date. In part this may be a reflection of the confused state of terminology in the chemical carcinogenesis research area and in part may signal a reluctance on the part of many of us to come to terms with the idea of heritable non-sequence changes to DNA molecules. In this review, some of the most obvious outcomes of spontaneous and induced epimutagenic change for human carcinogenesis and germ line inheritance are discussed, and an attempt is made to place the so-called endocrine disrupters in a context in which their modes of action may be more readily analysed and integrated into the broader chemical hazard framework.