RESUMEN
TET proteins, by converting 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), are hypothesized, but not directly shown, to protect promoter CpG islands (CGIs) against abnormal DNA methylation (DNAm) in cancer. We define such a protective role linked to DNA damage from oxidative stress (OS) known to induce this abnormality. TET2 removes aberrant DNAm during OS through interacting with DNA methyltransferases (DNMTs) in a "Yin-Yang" complex targeted to chromatin and enhanced by p300 mediated TET2 acetylation. Abnormal gains of DNAm and 5hmC occur simultaneously in OS, and knocking down TET2 dynamically alters this balance by enhancing 5mC and reducing 5hmC. TET2 reduction results in hypermethylation of promoter CGIs and enhancers in loci largely overlapping with those induced by OS. Thus, TET2 indeed may protect against abnormal, cancer DNAm in a manner linked to DNA damage.
Asunto(s)
Cromatina/metabolismo , Metilación de ADN , ADN de Neoplasias/metabolismo , Proteínas de Unión al ADN/metabolismo , Neoplasias/metabolismo , Estrés Oxidativo , Procesamiento Proteico-Postraduccional , Proteínas Proto-Oncogénicas/metabolismo , 5-Metilcitosina/análogos & derivados , 5-Metilcitosina/metabolismo , Acetilación , Cromatina/genética , ADN (Citosina-5-)-Metiltransferasa 1 , ADN (Citosina-5-)-Metiltransferasas/metabolismo , ADN de Neoplasias/genética , Proteínas de Unión al ADN/genética , Dioxigenasas , Proteína p300 Asociada a E1A/metabolismo , Células HCT116 , Histona Desacetilasa 1/metabolismo , Histona Desacetilasa 2/metabolismo , Humanos , Neoplasias/genética , Unión Proteica , Estabilidad Proteica , Proteínas Proto-Oncogénicas/genética , Interferencia de ARN , Factores de Tiempo , Transfección , UbiquitinaciónRESUMEN
Recent clinical data in lung cancer suggests that epigenetically targeted therapy may selectively enhance chemotherapeutic sensitivity. There have been few if any studies rigorously evaluating this hypothesized priming effect. Here we describe a series of investigations testing whether epigenetic priming with azacitidine and entinostat increases sensitivity of NSCLC to cytotoxic agents. We noted no differences in chemosensitivity following treatment with epigenetic therapy in in vitro assays of viability and colony growth. Using cell line and patient derived xenograft (PDX) models, we also observed no change in responsiveness to cisplatin in vivo. In select models, we noted differential responses to irinotecan treatment in vivo. In vitro epigenetic therapy prior to tumor implantation abrogated response of H460 xenografts to irinotecan. Conversely, in vitro epigenetic therapy appeared to sensitize A549 xenografts (tumor growth inhibition 51%, vs. 22% in mock-pretreated control). In vivo epigenetic therapy enhanced the response of adenocarcinoma PDX to irinotecan. Taken together, these data do not support broadly applicable epigenetic priming in NSCLC. Priming effects may be context-specific, dependent on both tumor and host factors. Further preclinical study is necessary to determine whether, and in which contexts, priming with epigenetic therapy has potential to enhance chemotherapeutic efficacy in NSCLC patients.