title: Merbarone induces activation of caspase-activated DNase and excision of chromosomal DNA loops from the nuclear matrix.
abstract: Studies were carried out to address possible cellular mechanisms by which merbarone, a catalytic inhibitor of DNA topoisomerase II, can block tumor cell growth without inducing extensive DNA cleavage. Merbarone induced the release of high molecular weight DNA fragments from the nuclear matrix of HL-60 leukemia cells, which preceded the internucleosomalsize DNA fragmentation characteristic of late-stage apoptosis. The chromatin fragments were enriched in a matrix attachment region (MAR) sequence compared with a non-MAR sequence and were similar in size to DNA loops extracted from nuclear matrices. However, merbarone did not directly induce the excision of high molecular weight DNA fragments from the nuclear matrix by promoting topoisomerase II-catalyzed DNA cleavage, because the drug inhibited topoisomerase II-mediated cleavage in isolated nuclear matrix preparations. Instead, merbarone induced rapid activation of the mitochondrial apoptosis pathway, which included the following temporal sequence of events: dissipation of the mitochondrial transmembrane potential within 30 min, release of mitochondrial cytochrome c, and activation of caspase-activated DNase (CAD) by its inhibitor ICAD. The excision of high molecular weight DNA was inhibited at least 80% in merbarone-treated cells preincubated with the pan-caspase inhibitor z-VAD-fmk [Z-Val-Ala-Asp(OMe)-fluoromethyl ketone] and in caspase-resistant Jurkat cells (ICAD/double-mutated) that express a mutant form of ICAD. These results provide evidence that merbarone can induce rapid disorganization of DNA in tumor cells that have a functional mitochondrial apoptosis pathway without inducing extensive DNA cleavage.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, 173 Ashley Avenue, P.O. Box 250509, Charleston, SC 29425, USA.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Otake
authors.forename: Alice
authors.initials: A
authors.lastname: Mims
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Fernandes
mesh_terms: D002384:Catalysis; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004247:DNA / Q000187:drug effects* / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D003851:Deoxyribonucleases / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D019169:Jurkat Cells; D008928:Mitochondria / Q000201:enzymology; D008970:Molecular Weight; D015530:Nuclear Matrix / Q000187:drug effects* / Q000378:metabolism; D013858:Thiobarbiturates / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors
chemical_list: D004791:Enzyme Inhibitors; D013858:Thiobarbiturates; D059005:Topoisomerase II Inhibitors; D045304:Cytochromes c; D004247:DNA; D003851:Deoxyribonucleases; C109663:caspase-activated deoxyribonuclease; D004250:DNA Topoisomerases, Type II; C045459:merbarone