title: Characterization of promoter elements involved in the down-regulation of topoisomerase IIalpha expression in a drug-resistant cell line.
abstract: Reduced expression of topoisomerase II is one of the mechanisms observed in cell lines and clinical samples that are resistant to topoisomerase II-targeting agents. The Chinese hamster lung cell line DC-3F/9-OH-E made resistant to 9-OH ellipticine and cross-resistant to other topoisomerase II inhibitors has previously been shown to express lower level of topoisomerase IIalpha isoform, than the parental DC-3F cell line. We have shown here that topoisomerase IIalpha promoter activity is lower in the resistant cell line. The promoter sequence responsible for the differential expression of Chinese hamster topoisomerase IIalpha gene was localized in a small promoter region, which harbors three inverted CAAT elements (ICEs) that bind transcription factor NF-Y, two GC boxes that bind Sp1 and a TATA-like element that binds unknown factors. Immunoblot analysis of cell lysates showed that the resistant line expressed reduced levels of NF-Y subunits and attenuated level of p53. Although p53 has been reported being involved in the regulation of topoisomerase II expression, it is not responsible for the reduced topoisomerase IIalpha expression in the drug resistant line. Mutational analysis of individual elements suggested that the resistant cell line has relaxed responses to ICE mutations, and the TATA-like element plays a predominant role in the regulation of topoisomerase IIalpha. Furthermore, gel mobility shift assays showed that the resistant line has a differential binding to the novel TATA-like element, which may be responsible for the down-regulation of topoisomerase IIalpha gene.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Biology, Brigham and Women's Hospital, 221 Longwood Avenue, BLI 449A, Boston, Massachusettes 02115, USA.
authors.forename: Deepa
authors.initials: D
authors.lastname: Saxena
authors.forename: Gary K
authors.initials: GK
authors.lastname: Yiu
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Ni
authors.forename: Kuan-Chun
authors.initials: KC
authors.lastname: Huang
authors.forename: Roberto
authors.initials: R
authors.lastname: Mantovani
authors.forename: Alain G
authors.initials: AG
authors.lastname: Jacquemin-Sablon
authors.forename: Shu-Wing
authors.initials: SW
authors.lastname: Ng
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004268:DNA-Binding Proteins; D015536:Down-Regulation / Q000235:genetics; D004351:Drug Resistance; D024202:Electrophoretic Mobility Shift Assay; D004611:Ellipticines / Q000494:pharmacology; D005786:Gene Expression Regulation; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009841:Oligonucleotides / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D004611:Ellipticines; D009841:Oligonucleotides; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; C034192:ellipticine; D008156:Luciferases; D015500:Chloramphenicol O-Acetyltransferase; D004250:DNA Topoisomerases, Type II