Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.3 (topoisomerase)
 9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In order to characterize more fully the mechanism by which casein kinase II is regulated in mammalian cells, the effect of epidermal growth factor (EGF) on the activity of the kinase in human A-431 carcinoma cells was examined. Treatment of cells with EGF prior to lysis consistently resulted in a transient 4-fold increase in the activity of cytosolic casein kinase II. Activity rose sharply between 20 and 30 min, peaked at approximately 50 min, and returned to basal levels by approximately 120 min. Similar results were obtained using the casein kinase II specific peptide substrate, Arg-Arg-Arg-Glu-Glu-Glu-Thr-Glu-Glu-Glu, or DNA topoisomerase II (which is specifically modified by the kinase in vivo and serves as a high affinity substrate in vitro) as the phosphate acceptor in assays. Identification of casein kinase II as the stimulated activity was confirmed by partial proteolytic mapping and phosphoamino acid analysis of modified topoisomerase II, by inhibition at nanomolar levels of heparin or micromolar levels of nonradioactive GTP, and by the ability to employ radioactive GTP as a direct phosphate donor. The EGF stimulation of casein kinase II was dependent on the availability of intracellular (but not extracellular) calcium. In addition, hormonal action was modulated by calcium/phospholipid-dependent protein kinase (protein kinase C). Casein kinase II stimulation did not require an increase in the concentration of the kinase, protein synthesis, the continual presence of a small effector molecule, or a direct interaction with the EGF receptor/tyrosine kinase. In contrast, hormonal activation of the kinase was dependent on the phosphorylation of casein kinase II or a terminal stimulatory factor.
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PMID:Regulation of casein kinase II activity by epidermal growth factor in human A-431 carcinoma cells. 247 67

A protein kinase activity has been identified that is tightly associated with the purified Drosophila type II DNA topoisomerase. The kinase and topoisomerase activities are not separated when the enzyme is subjected to analytical chromatography (phosphocellulose, single-strand DNA agarose, and Sephacryl S-300) and analytical glycerol gradient sedimentation. These two activities are also inactivated to the same extent by either heat or N-ethylmaleimide treatment. The evidence, however, does not rule out the possibility that the kinase activity resides in a polypeptide other than the topoisomerase polypeptide. The topoisomerase-associated protein kinase activity is not stimulated by Ca2+ or cyclic nucleotides. It shows a broad substrate range, including the DNA topoisomerase itself, casein, phosvitin, and histones. Phosphoamino acid analysis identified phosphoserine and phosphothreonine in polypeptides modified by the topoisomerase-associated protein kinase. No similar activity has been identified previously in Drosophila melanogaster.
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PMID:A protein kinase activity tightly associated with Drosophila type II DNA topoisomerase. 609 62

Topoisomerase I (Topo I) is involved in many cellular functions that involve unwinding of supercoiled DNA, such as transcription and replication. Topo I is also the target of autoimmune antibodies in progressive systemic sclerosis (scleroderma), and abnormal regulation of Topo I may influence the excessive production of collagen found in scleroderma. Topo I is phosphorylated in vivo at serine residues and, in vitro, the activity of Topo I is increased by phosphorylation by casein kinase type II (CKII) and protein kinase C (PKC). In this study, a protein kinase activity from rat liver nuclei is shown to copurify with Topo I during Bio-Rex 70 cation exchange chromatography. The kinase can phosphorylate Topo I at serine residues, resulting in a threefold increase in topoisomerase activity. A relatively tight association between this kinase and Topo I is demonstrated by the ability to coprecipitate the kinase with scleroderma autoimmune anti-Topo I antibodies. The kinase activity is similar to CKII since it is Ca2+ and cyclic nucleotide independent, it can utilize either ATP or GTP as phosphate donor, and it can phosphorylate casein and phosvitin, but not histones. However, unlike typical CKII, the Topo I-associated kinase could utilize Mn2+ almost as well as Mg2+, it is not stimulated by polyamines, and it does not appear to undergo autophosphorylation. In conclusion, we demonstrate that rat liver Topo I is relatively tightly associated with a CKII-like protein kinase that can phosphorylate and activate Topo I. These findings provide corroborative evidence that CKII, or a CKII-like protein kinase, is a physiologic regulator of Topo I.
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PMID:A casein kinase type II (CKII)-like nuclear protein kinase associates with, phosphorylates, and activates topoisomerase I. 826 Jan 98

Small-insert metagenomic libraries from four samples were constructed by a topoisomerase-based and a T4 DNA ligase-based approach. Direct comparison of both approaches revealed that application of the topoisomerase-based method resulted in a higher number of insert-containing clones per microg of environmental DNA used for cloning and a larger average insert size. Subsequently, the constructed libraries were partially screened for the presence of genes conferring proteolytic activity. The function-driven screen was based on the ability of the library-containing Escherichia coli clones to form halos on skim milk-containing agar plates. The screening of 80,000 E. coli clones yielded four positive clones. Two of the plasmids (pTW2 and pTW3) recovered from positive clones conferred strong proteolytic activity and were studied further. Analysis of the entire insert sequences of pTW2 (28,113 bp) and pTW3 (19,956 bp) suggested that the DNA fragments were derived from members of the genus Xanthomonas. Each of the plasmids harbored one gene (2,589 bp) encoding a metalloprotease (mprA, pTW2; mprB, pTW3). Sequence and biochemical analyses revealed that MprA and MprB are similar extracellular proteases belonging to the M4 family of metallopeptidases (thermolysin-like family). Both enzymes possessed a unique modular structure and consisted of four regions: the signal sequence, the N-terminal proregion, the protease region, and the C-terminal extension. The architecture of the latter region, which was characterized by the presence of two prepeptidase C-terminal domains and one proprotein convertase P domain, is novel for bacterial metalloproteases. Studies with derivatives of MprA and MprB revealed that the C-terminal extension is not essential for protease activity. The optimum pH and temperature of both proteases were 8.0 and 65 degrees C, respectively, when casein was used as substrate.
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PMID:Isolation and characterization of metalloproteases with a novel domain structure by construction and screening of metagenomic libraries. 1921 12

Although it is well established that Cdc2 kinase phosphorylates the DNA damage checkpoint protein Crb2(53BP1) in mitosis, the full impact of this modification is still unclear. The Tudor-BRCT domain protein Crb2 binds to modified histones at DNA lesions to mediate the activation of Chk1 by Rad3ATR kinase. We demonstrate here that fission yeast cells harbouring a hyperactive Cdc2CDK1 mutation (cdc2.1w) are specifically sensitive to the topoisomerase 1 inhibitor camptothecin (CPT) which breaks DNA replication forks. Unlike wild-type cells, which delay only briefly in CPT medium by activating Chk1 kinase, cdc2.1w cells bypass Chk1 to enter an extended cell-cycle arrest which depends on Cds1 kinase. Intriguingly, the ability to bypass Chk1 requires the mitotic Cdc2 phosphorylation site Crb2-T215. This implies that the presence of the mitotic phosphorylation at Crb2-T215 channels Rad3 activity towards Cds1 instead of Chk1 when forks break in S phase. We also provide evidence that hyperactive Cdc2.1w locks cells in a G1-like DNA repair mode which favours non-homologous end joining over interchromosomal recombination. Taken together, our data support a model such that elevated Cdc2 activity delays the transition of Crb2 from its G1 to its G2 mode by blocking Srs2 DNA helicase and Casein Kinase 1 (Hhp1).
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PMID:Hyperactive Cdc2 kinase interferes with the response to broken replication forks by trapping S.pombe Crb2 in its mitotic T215 phosphorylated state. 2486 25

The heterogeneity of tumor cells and the potential existence of rare cells with reduced chemotherapeutic response is expected to play a pivotal role in the development of drug resistant cancers. Herein, we utilized the colon cancer cell lines, Caco2 and DLD1, to investigate heterogeneity of topoisomerase 1 (TOP1) activity in different cell subpopulations, and the consequences for the chemotherapeutic response towards the TOP1 targeting drug, camptothecin. The cell lines consisted of two subpopulations: one (the stem-cell-like cells) divided asymmetrically, was camptothecin resistant, had a differently phosphorylated TOP1 and a lower Casein Kinase II (CKII) activity than the camptothecin sensitive non-stem-cell-like cells. The tumor suppressor p14ARF had a different effect in the two cell subpopulations. In the stem-cell-like cells, p14ARF suppressed TOP1 activity and downregulation of this factor increased the sensitivity towards camptothecin. It had the opposite effect in non-stem-cell-like cells. Since it is only the stem-cell-like cells that have tumorigenic activity our results point towards new considerations for future cancer therapy. Moreover, the data underscore the importance of considering cell-to-cell variations in the analysis of molecular processes in cell lines.
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PMID:Different Camptothecin Sensitivities in Subpopulations of Colon Cancer Cells Correlate with Expression of Different Phospho-Isoforms of Topoisomerase I with Different Activities. 3242 58