Hypophosphorylation of topoisomerase II in etoposide (VP-16)-resistant human leukemia K562 cells associated with reduced levels of beta II protein kinase C. 1995

M K Ritke, and N R Murray, and W P Allan, and A P Fields, and J C Yalowich
Department of Pharmacology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.

We selected and characterized a 30-fold etoposide (VP-16)-resistant subline of K562 human leukemia cells (K/VP.5) that exhibits quantitative and qualitative changes in topoisomerase II, including hypophosphorylation of this drug target. The initial rate of topoisomerase II phosphorylation was reduced 3-fold in K/VP.5 compared with K562 cells, but the rate of dephosphorylation was similar. Analysis of potential topoisomerase II protein kinases revealed a 3-fold reduction in the level of the beta II protein kinase C (PKC) in K/VP.5 cells, whereas levels of alpha- and epsilon PKC, casein kinase II, p42map kinase, and p34cdc2 kinase were comparable for both cell lines. The PKC activator, bryostatin 1, together with K562 nuclear extracts potentiated VP-16-induced topoisomerase II/DNA covalent complex formation in nuclei isolated from K/VP.5 cells but not from K562 cells. Bryostatin 1 effects were blocked by the PKC inhibitor 7-O-methyl-hydroxy-staurosporine. Bryostatin 1 also up-regulated topoisomerase II phosphorylation and potentiated VP-16 activity in intact K/VP.5 cells but had no enhancing effect in K562 cells. 4 beta-Phorbol-12,13-dibutyrate and 12-O-tetradecanoylphorbol-13-acetate did not potentiate VP-16-induced topoisomerase II/DNA complex formation in intact cells or in isolated K/VP.5 nuclei. Together, our results indicate that beta II PKC plays a role in modulating the VP-16-induced DNA binding activity of topoisomerase II in resistant K/VP.5 cells through a mechanism linked to phosphorylation of topoisomerase II.

UI MeSH Term Description Entries
D007938 Leukemia A progressive, malignant disease of the blood-forming organs, characterized by distorted proliferation and development of leukocytes and their precursors in the blood and bone marrow. Leukemias were originally termed acute or chronic based on life expectancy but now are classified according to cellular maturity. Acute leukemias consist of predominately immature cells; chronic leukemias are composed of more mature cells. (From The Merck Manual, 2006) Leucocythaemia,Leucocythemia,Leucocythaemias,Leucocythemias,Leukemias
D010766 Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Phosphorylations
D011493 Protein Kinase C An serine-threonine protein kinase that requires the presence of physiological concentrations of CALCIUM and membrane PHOSPHOLIPIDS. The additional presence of DIACYLGLYCEROLS markedly increases its sensitivity to both calcium and phospholipids. The sensitivity of the enzyme can also be increased by PHORBOL ESTERS and it is believed that protein kinase C is the receptor protein of tumor-promoting phorbol esters. Calcium Phospholipid-Dependent Protein Kinase,Calcium-Activated Phospholipid-Dependent Kinase,PKC Serine-Threonine Kinase,Phospholipid-Sensitive Calcium-Dependent Protein Kinase,Protein Kinase M,Calcium Activated Phospholipid Dependent Kinase,Calcium Phospholipid Dependent Protein Kinase,PKC Serine Threonine Kinase,Phospholipid Sensitive Calcium Dependent Protein Kinase,Phospholipid-Dependent Kinase, Calcium-Activated,Serine-Threonine Kinase, PKC
D004247 DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA, Double-Stranded,Deoxyribonucleic Acid,ds-DNA,DNA, Double Stranded,Double-Stranded DNA,ds DNA
D004249 DNA Damage Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a MUTATION or a block of DNA REPLICATION. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (PYRIMIDINE DIMERS) or interstrand crosslinking. Damage can often be repaired (DNA REPAIR). If the damage is extensive, it can induce APOPTOSIS. DNA Injury,DNA Lesion,DNA Lesions,Genotoxic Stress,Stress, Genotoxic,Injury, DNA,DNA Injuries
D004250 DNA Topoisomerases, Type II DNA TOPOISOMERASES that catalyze ATP-dependent breakage of both strands of DNA, passage of the unbroken strands through the breaks, and rejoining of the broken strands. These enzymes bring about relaxation of the supercoiled DNA and resolution of a knotted circular DNA duplex. DNA Topoisomerase (ATP-Hydrolysing),DNA Topoisomerase II,DNA Topoisomerase II alpha,DNA Topoisomerase II beta,DNA Type 2 Topoisomerase,TOP2A Protein,TOP2B Protein,Topoisomerase II,Topoisomerase II alpha,Topoisomerase II beta,Type II DNA Topoisomerase,alpha, Topoisomerase II,beta, Topoisomerase II
D004351 Drug Resistance Diminished or failed response of an organism, disease or tissue to the intended effectiveness of a chemical or drug. It should be differentiated from DRUG TOLERANCE which is the progressive diminution of the susceptibility of a human or animal to the effects of a drug, as a result of continued administration. Resistance, Drug
D005047 Etoposide A semisynthetic derivative of PODOPHYLLOTOXIN that exhibits antitumor activity. Etoposide inhibits DNA synthesis by forming a complex with topoisomerase II and DNA. This complex induces breaks in double stranded DNA and prevents repair by topoisomerase II binding. Accumulated breaks in DNA prevent entry into the mitotic phase of cell division, and lead to cell death. Etoposide acts primarily in the G2 and S phases of the cell cycle. Demethyl Epipodophyllotoxin Ethylidine Glucoside,Celltop,Eposide,Eposin,Eto-GRY,Etomedac,Etopos,Etoposide Pierre Fabre,Etoposide Teva,Etoposide, (5S)-Isomer,Etoposide, (5a alpha)-Isomer,Etoposide, (5a alpha,9 alpha)-Isomer,Etoposide, alpha-D-Glucopyranosyl Isomer,Etoposido Ferrer Farma,Exitop,Lastet,NSC-141540,Onkoposid,Riboposid,Toposar,VP 16-213,VP-16,Vepesid,Vépéside-Sandoz,Eto GRY,Etoposide, alpha D Glucopyranosyl Isomer,NSC 141540,NSC141540,Teva, Etoposide,VP 16,VP 16 213,VP 16213,VP16,Vépéside Sandoz,alpha-D-Glucopyranosyl Isomer Etoposide
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000972 Antineoplastic Agents, Phytogenic Agents obtained from higher plants that have demonstrable cytostatic or antineoplastic activity. Antineoplastics, Botanical,Antineoplastics, Phytogenic,Agents, Phytogenic Antineoplastic,Botanical Antineoplastics,Phytogenic Antineoplastic Agents,Phytogenic Antineoplastics

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