Potentiation of temozolomide cytotoxicity by inhibition of DNA polymerase beta is accentuated by BRCA2 mutation.
ABSTRACT Base excision repair (BER) plays a critical role in the repair of bases damaged by oxidative metabolism or alkylating agents, such as those commonly used in cancer therapy. Incomplete BER generates intermediates that require activation of homology-dependent DNA repair to resolve. We investigated the effects of lithocholic acid (LCA), an inhibitor of the key BER enzyme DNA polymerase beta (pol beta), in cells deficient in expression of the homology-dependent repair factor BRCA2. In vitro studies show that LCA suppresses the DNA polymerase and 5'-deoxyribose phosphate lyase activities of DNA pol beta by preventing the formation of a stable pol beta-DNA complex, reducing BER effectiveness. Cytotoxicity assays based on colony formation revealed that LCA exhibits synergism with the alkylating agent temozolomide, which engages BER through DNA methylation, and that the degree of synergism is increased in cells lacking functional BRCA2. BRCA2-deficient cells also showed heightened susceptibility to both LCA and temozolomide individually. The potentiation of temozolomide cytotoxicity by LCA owes to the conversion of single-stranded DNA breaks generated through incomplete BER of methylated nucleotides into double-stranded breaks during DNA replication, as indicated by gammaH2AX immunofluorescence. Death seems to be induced in cotreated cells through an accumulation of persistent double-stranded DNA breaks. Mutations of the BRCA2 gene have been extensively characterized and are present in various cancers, implying that inhibition of BER may offer a means to augment tumor selectivity in the use of conventional cancer therapies.
[show abstract] [hide abstract]
ABSTRACT: The fine structure of the cell walls of Gram-positive and -negative bacteria were determined by electron microscopy with the new technique of freeze substitution method, and analysed the cell wall structure of Staphylococcus aureus in detail. The surface of Staphylococcal cell wall was covered with a fuzzy coat consisting of fine fibers or electron-dence mass. This coat was completely removed after extraction of teichoic acid from the cell wall with trichloroacetic acid treatment, but was not affected by sodium dodecyl sulfate or trypsin treatment. It was suggested that many amount of teichoic acid was located on the surface of the cell wall and less inside the cell wall. The capsule of strain Smith diffuse was assumed to play the role as the barrier protected from the penetration of antibody against teichoic acid.Nippon Ishinkin Gakkai Zasshi 02/1998; 39(3):147-50.
Article: Human DNA repair genes, 2005.[show abstract] [hide abstract]
ABSTRACT: An updated inventory of about 150 human DNA repair genes is described. The compilation includes genes encoding DNA repair enzymes, some genes associated with cellular responses to DNA damage, and other genes associated with genetic instability or sensitivity to DNA damaging agents. The updated human DNA repair genes table (http://www.cgal.icnet.uk/DNA_Repair_Genes.htmlhttp://www.cgal.icnet.uk/DNA_Repair_Genes.html) is a research and reference tool that directly links to several databases: Gene Cards, Online Mendelian Inheritance in Man, the NCBI MapViewer for chromosome position, and the NCBI Entrez database for the reference nucleotide sequence. This article discusses the approximately 25 genes added, since the original version of the table was first produced in 2001, and some other revisions.Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 10/2005; 577(1-2):275-83. · 2.85 Impact Factor