title: Induction of deoxycytidine kinase by 5-azacytidine in an HL-60 cell line resistant to arabinosylcytosine.
abstract: Induction of 2'-deoxycytidine kinase (dCK) by 5-azacytidine (5-Aza-C) in a dCK-deficient HL-60 cell line resistant to 1-beta-D-arabinofuranosylcytosine (Ara-C) (HL-60/Ara-C) was examined by measurement of the incorporation of [3H]deoxycytidine ([3H] dCyd) into cellular DNA, the kinetic properties of purified dCK, the cytotoxic potency (IC50 values), and the DNA methylation patterns of 5-Aza-C-treated and untreated cells. Following a 72-hr exposure to 1 microM 5-Aza-C, the incorporation of [3H]dCyd into DNA was increased 6-fold and the total dCK activity was increased 12-fold, with a peak for both on day 6. The onset of dCK induction was dependent on the length of exposure time. The IC50 values for cell growth inhibition by Ara-C on day 3 were 0.08 microM for HL-60 cells, 12.5 microM for HL-60/Ara-C cells, and 0.55 microM for HL-60/Ara-C cells pretreated with 5-Aza-C for 40 hr. The Km and Vmax of dCyd for HL-60 dCK were similar to those for 5-Aza-C-induced HL-60/Ara-C dCK. The restriction enzymes Hpall, which cleaves CCGG sequences but cannot cleave at sites methylated at the internal cytosines (5'-CMeCGG), and Mspl, which cleaves sequences with internal methylated cytosine but cannot cleave at sites methylated at external cytosines (5'-MeCCGG), were used for DNA methylation pattern determination. The newly synthesized DNA of HL-60 wild-type cells was cleaved by Mspl to a greater extent than that of HL-60/Ara-C cells. After exposure to 1 microM 5-Aza-C for 40 hr, methylation patterns of newly synthesized DNA reverted in HL-60/Ara-C cells to a clevage pattern similar to that in HL-60 wild-type cells. When compared with untreated control, DNAs from 5-Aza-C-treated resistant cells were cleaved to a greater extent by Mspl than by Hpall, suggesting that internal cytosine-residue methylation was relatively uninhibited.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Laboratory of Biochemical Pharmacology, Memorial Sloan-Kettering Cancer Center, Cornell University Graduate School of Medical Sciences, New York, New York 10021.
authors.forename: X B
authors.initials: XB
authors.lastname: Kong
authors.forename: W P
authors.initials: WP
authors.lastname: Tong
authors.forename: T C
authors.initials: TC
authors.lastname: Chou
mesh_terms: D001374:Azacitidine / Q000494:pharmacology*; D001483:Base Sequence; D003561:Cytarabine / Q000493:pharmacokinetics / Q000494:pharmacology*; D004273:DNA, Neoplasm / Q000378:metabolism; D003841:Deoxycytidine / Q000378:metabolism; D003842:Deoxycytidine Kinase / Q000096:biosynthesis* / Q000378:metabolism; D004351:Drug Resistance; D004790:Enzyme Induction; D006801:Humans; D007700:Kinetics; D007942:Leukemia, Experimental / Q000201:enzymology* / Q000473:pathology; D007951:Leukemia, Myeloid / Q000201:enzymology* / Q000473:pathology; D008745:Methylation; D008969:Molecular Sequence Data; D013997:Time Factors; D014316:Tritium; D014407:Tumor Cells, Cultured
chemical_list: D004273:DNA, Neoplasm; D003561:Cytarabine; D003841:Deoxycytidine; D014316:Tritium; D003842:Deoxycytidine Kinase; D001374:Azacitidine