title: Reexpression of a cluster of silenced transgenes is associated with their rearrangement.
abstract: Irreversible inactivation or silencing of tumor suppressor genes occurs frequently in the development of cancer. A similar process of silencing can occur after the integration of transfected or microinjected genes into the genomes of recipient cells. The inactivation of transfected genes seems particularly efficient in cells with stem cell characteristics. We have been studying the inactivation of genes transfected into cultured P19 embryonal carcinoma cells and found that the CpG-rich sequence comprising the coding region of the lacZ reporter gene becomes extensively methylated after integration into the genome. 5-Aza-2'-deoxycytidine (5AdC), an inhibitor of DNA methylation, induced the reexpression of silent transgenes in one clone of P19 cells studied in detail. However, the reexpressed genes remained heavily methylated over the lacZ coding sequence. We used pulsed-field gel electrophoresis to analyze the structure of the transgenic locus in the parental and in 5AdC-treated cells and found that, in each of the cells reexpressing the transgene, the cluster of transgenes had been rearranged. Each clone had undergone a different rearrangement that appeared to involve recombination within the tandemly repeated copies of the transgene. Our data seem consistent with the idea that 5AdC induces efficient DNA recombination between tandemly repeated genes and that the reexpression of silenced genes induced by 5AdC might be triggered by the chromatin reorganization at the site of DNA recombination.
authors.affiliation: Ottawa Regional Cancer Center and Department of Medicine, University of Ottawa, Ottawa, Ontario, Canada. michael.mcburney@orcc.on.ca
authors.forename: M W
authors.initials: MW
authors.lastname: McBurney
authors.forename: S
authors.initials: S
authors.lastname: Lau
authors.forename: K
authors.initials: K
authors.lastname: Jardine
authors.forename: X
authors.initials: X
authors.lastname: Yang
authors.forename: B
authors.initials: B
authors.lastname: Davies
mesh_terms: D000818:Animals; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002999:Clone Cells; D019175:DNA Methylation / Q000187:drug effects; D000077209:Decitabine; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D015321:Gene Rearrangement / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D007763:Lac Operon / Q000235:genetics; D051379:Mice; D005810:Multigene Family / Q000187:drug effects; D010735:Phosphoglycerate Kinase / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014162:Transfection; D019076:Transgenes / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D011993:Recombinant Fusion Proteins; D000077209:Decitabine; D010735:Phosphoglycerate Kinase; D001374:Azacitidine