title: Topoisomerase IIβ regulates base excision repair capacity of neurons.
abstract: Topoisomerase IIβ (TopoIIβ), an enzyme involved in DNA rearrangements, is predominantly present in brain and its levels are shown to decrease with age. This study characterizes the function of TopoIIβ in regulating BER (base excision repair) activity. TopoIIβ deficient granule neurons (CGNT⁻) show greater sensitivity to N-ethyl N-nitroso urea (ENU)-mediated DNA damage. The cell-free extracts of TopoIIβ knockdown cells (ECGNT⁻) show a significant decrease in G-U BER activity during ENU-treatment as well as during recovery, suggesting that TopoIIβ promotes G-U BER activity. Since G-U BER activity is not affected in the presence of ICRF-193, catalytic inhibitor of TopoIIβ, the activity of enzyme per se may not be participating in BER activity. Further characterization of the activities of BER enzymes present in ECGNT⁻ shows that uracil DNA-glycosylase (UDG) and ligase (LIG) activities decrease significantly in both ENU treatment and recovery. Supplementation of TopoIIβ to ECGNT⁻ does not restore ligation activity and ICRF-193 does not influence the LIG activity. These results suggest a role, at least an indirect one, of TopoIIβ in the repair of ENU-mediated strand breaks via BER pathway including the activities of UDG and LIG.
authors.affiliation: Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad 500046, Andhra Pradesh, India.
authors.forename: K Preeti
authors.initials: KP
authors.lastname: Gupta
authors.forename: Umakanta
authors.initials: U
authors.lastname: Swain
authors.forename: Kalluri Subba
authors.initials: KS
authors.lastname: Rao
authors.forename: Anand K
authors.initials: AK
authors.lastname: Kondapi
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D016922:Cellular Senescence; D002531:Cerebellum / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D020552:Comet Assay; D004249:DNA Damage; D011088:DNA Ligases / Q000378:metabolism; D004260:DNA Repair; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054659:Diketopiperazines; D004305:Dose-Response Relationship, Drug; D005038:Ethylnitrosourea / Q000633:toxicity; D055785:Gene Knockdown Techniques; D009153:Mutagens / Q000633:toxicity; D009474:Neurons / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D010879:Piperazines / Q000494:pharmacology; D034622:RNA Interference; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D059005:Topoisomerase II Inhibitors / Q000494:pharmacology; D014162:Transfection; D051981:Uracil-DNA Glycosidase / Q000378:metabolism
chemical_list: D000477:Alkylating Agents; D004268:DNA-Binding Proteins; D054659:Diketopiperazines; D009153:Mutagens; D010879:Piperazines; D059005:Topoisomerase II Inhibitors; C070899:4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione; D051981:Uracil-DNA Glycosidase; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D004250:DNA Topoisomerases, Type II; D011088:DNA Ligases; D005038:Ethylnitrosourea