title: Chromatin remodelling at the topoisomerase II-beta promoter is associated with enhanced sensitivity to etoposide in human neuroblastoma cell lines.
abstract: Etoposide, an inhibitor of topoisomerase II, promotes DNA damage and apoptosis of cancer cells and is a component of standard therapy for neuroblastoma. Resistance to etoposide has been observed in neural tumour cells expressing lower levels of topoisomerase II. In the present study, we have examined the contribution of epigenetic modulation of gene expression in the potentiation of etoposide-mediated cytotoxicity in neuroblastoma cells. Specifically, we studied the effects of histone deacetylase inhibition with valproic acid on topoisomerase II gene expression and apoptosis in response to etoposide. Using human neuroblastoma cell lines SK-N-AS and SK-N-SH, we show that although the combination of valproic acid and etoposide promoted a reduction in growth compared to either drug alone in both cells, the effect was substantially enhanced in SK-N-AS compared to SK-N-SH cells. An increase in histone H3 acetylation and p21 expression was observed in both cell lines, however, upregulation of topoisomerase II-beta gene expression and an increase in PARP cleavage was observed in SK-N-AS cells only. Furthermore, chromatin immunoprecipitation assays revealed an increase in acetylation of histone H3 at the cognate topoisomerase II-beta gene after treatment with valproic acid in SK-N-AS cells. These results suggest a potential epigenetic mechanism of regulation of the topoisomerase II-beta gene and a possible role for its increased expression in the sensitivity of SK-N-AS neuroblastoma cells to etoposide.
authors.affiliation: Division of Pediatrics, Children’s Cancer Hospital, The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA.
authors.forename: Chandra M
authors.initials: CM
authors.lastname: Das
authors.forename: Peter E
authors.initials: PE
authors.lastname: Zage
authors.forename: Pete
authors.initials: P
authors.lastname: Taylor
authors.forename: Dolly
authors.initials: D
authors.lastname: Aguilera
authors.forename: Johannes E A
authors.initials: JE
authors.lastname: Wolff
authors.forename: Dean
authors.initials: D
authors.lastname: Lee
authors.forename: Vidya
authors.initials: V
authors.lastname: Gopalakrishnan
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000627:therapeutic use*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002470:Cell Survival; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects*; D047369:Chromatin Immunoprecipitation; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004357:Drug Synergism; D057890:Epigenomics; D005047:Etoposide / Q000627:therapeutic use*; D056572:Histone Deacetylase Inhibitors / Q000627:therapeutic use; D006801:Humans; D020128:Inhibitory Concentration 50; D009447:Neuroblastoma / Q000188:drug therapy* / Q000201:enzymology; D014635:Valproic Acid / Q000627:therapeutic use*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004268:DNA-Binding Proteins; D056572:Histone Deacetylase Inhibitors; D014635:Valproic Acid; D005047:Etoposide; D004250:DNA Topoisomerases, Type II