title: Degradation of DNA topoisomerase I by a novel trypsin-like serine protease in proliferating human T lymphocytes.
abstract: DNA topoisomerase I (Topo I) contributes to various important biological functions, and its activity is therefore likely regulated in response to different physiological conditions. Increases in both the synthesis and degradation of Topo I were previously shown to accompany phytohemagglutinin stimulation of proliferation in human peripheral T lymphocytes. The mechanism of this degradation of Topo I has now been investigated with both in vivo and in vitro assays. The activity of a nuclear protease that specifically degrades Topo I was induced in proliferating T lymphocytes. The full-length Topo I protein (100 kDa) was sequentially degraded to 97- and 82-kDa fragments both in vivo and in vitro. The initial site of proteolytic cleavage was mapped to the NH(2)-terminal region of the enzyme. The degradation of Topo I in vitro was inhibited by aprotinin or soybean trypsin inhibitor, suggesting that the enzyme responsible is a trypsin-like serine protease. Furthermore, Topo I degradation by this protease was Mg(2+)-dependent. The Topo I-specific protease activity induced during T lymphocytes proliferation was not detected in Jurkat (human T cell leukemia) cells and various other tested human cancer cell lines, possibly explaining why the abundance of Topo I is increased in tumor cells.
authors.affiliation: Institute of Biochemistry, School of Life Science, National Yang-Ming University, Taipei 112, Taiwan.
authors.forename: H J
authors.initials: HJ
authors.lastname: Chen
authors.forename: C L
authors.initials: CL
authors.lastname: Hwong
authors.forename: C H
authors.initials: CH
authors.lastname: Wang
authors.forename: J
authors.initials: J
authors.lastname: Hwang
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D001081:Apyrase / Q000494:pharmacology; D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D019169:Jurkat Cells; D008274:Magnesium / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D009124:Muscle Proteins; D010835:Phytohemagglutinins / Q000494:pharmacology; D014176:Protein Biosynthesis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism*; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology*; D013696:Temperature; D014357:Trypsin / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D015853:Cysteine Proteinase Inhibitors; D008840:Microfilament Proteins; D009124:Muscle Proteins; D010835:Phytohemagglutinins; D011993:Recombinant Fusion Proteins; C058992:Tagln protein, mouse; D016159:Tumor Suppressor Protein p53; C067713:lactacystin; D012697:Serine Endopeptidases; D014357:Trypsin; D001081:Apyrase; D004264:DNA Topoisomerases, Type I; D008274:Magnesium; D000111:Acetylcysteine