RESPONSE OF PHAGOCYTIC LEUKOCYTES TO TUMOR PROMOTERS

理解多阶段癌变的一个基本问题是 剖析肿瘤促进者最终 抑制恶性表型相关基因的表达 在暴露于小剂量致癌物的细胞中“启动”。 我们 以前的工作表明，一个参数可能发挥作用， 决定基因活性稳定变化的是DNA的模式 甲基化和肿瘤启动子12-0-十四烷酰基 佛波醇-13-乙酸酯（TPA）影响DNA甲基化的变化。 我们有 还发现抗白血病药物5-氮杂胞苷会导致人类白血病， 细胞（HL-60）在一定条件下成熟为相对正常的表型 它能抑制DNA甲基化， 一旦进入DNA，它会特异性地抑制DNA， 甲基转移酶通过酶与5-氮杂胞嘧啶的紧密结合 丰富的DNA区域。 在此基础上，我们打算：（1）使用5-氮杂胞嘧啶取代的DNA作为 研究HL-60细胞DNA甲基转移酶特异性的工具， HL-60细胞在暴露于 TPA（HL-60 T）和正常及恶性白细胞; 限制性内切酶图谱，5-氮杂胞苷如何处理HL-60细胞 甲基化影响基因的活性，这些基因的活性可能对维持 恶性肿瘤，并比较甲基化的模式与那些 HL-60 T细胞和正常及恶性白细胞中的相同基因;以及 (3)确定肿瘤促进剂是否对DNA有直接影响 HL-60细胞中的甲基化，以及它们是否能够修饰HL-60细胞中的甲基化。 5-氮杂胞苷处理对DNA甲基化和 分化

A basic problem in understanding multistage carcinogenesis is the dissection of the mechanisms by which tumor promoters can eventually derepress the expression of genes responsible for the malignant phenotype in cells "initiated" by exposure to small doses of carcinogens. Our previous work indicates that one parameter which may play a role in determining stable changes in gene activity is the pattern of DNA methylation and that the tumor promoter 12-0-tetradecanoyl phorbol-13-acetate (TPA) influences changes in DNA methylation. We have also found that the antileukemic drug 5-azacytidine causes human leukemic cells (HL-60) to mature to relatively normal phenotypes under conditions in which it inhibits DNA methylation and have been able to demonstrate that, once incorporated into DNA, it specifically inhibits DNA methyltransferase through tight binding of the enzyme to 5-azacytosine rich regions of DNA. On this basis, we intend to: (1)\use 5-azacytosine substituted DNA as a tool to study the specificity of DNA methyltransferases from HL-60 cells, HL-60 cells that have lost the ability to differentiate after exposure to TPA (HL-60T) and from normal and malignant leukocytes; (2)\determine, by restriction enzyme mapping, how 5-azacytidine treatment of HL-60 cells affects methylation of genes whose activity may be critical in maintaining malignancy and to compare the patterns of methylation with those of the same genes in HL-60T cells and normal and malignant leukocytes; and (3)\determine whether tumor promoters have a direct effect on DNA methylation in HL-60 cells and whether they are capable of modifying the influence of 5-azacytidine treatment on DNA methylation and differentiation.