RESPONSE OF PHAGOCYTIC LEUKOCYTES TO TUMOR PROMOTERS

理解多阶段癌变的一个基本问题是 剖析肿瘤促进剂最终可能通过的机制 抑制恶性表型相关基因的表达 通过接触小剂量致癌物而“启动”的细胞中。我们的 以前的工作表明，有一个参数可能在 确定基因活性的稳定变化是DNA的模式 甲基化和肿瘤促进剂12-0-十四烷酰 佛波酯(TPA)影响DNA甲基化的变化。我们有 还发现抗白血病药物5-氮胞苷会导致人类白血病 细胞(HL-60)在条件下成熟到相对正常的表型 在其中它抑制DNA甲基化，并已经能够证明 一旦被整合到DNA中，它就会特别地抑制DNA 与5-氮胞嘧啶紧密结合的甲基转移酶 富含DNA的区域。 在此基础上，我们打算：(1)使用5-氮胞嘧啶取代的DNA作为 研究HL-60细胞DNA甲基转移酶特异性的工具， HL-60细胞在染毒后失去分化能力 TPA(HL-60T)及正常和恶性白细胞； 限制性内切酶图谱：5-氮胞苷如何处理HL-60细胞 影响基因的甲基化，这些基因的活性可能是维持 并将甲基化模式与 HL-60T细胞以及正常和恶性白细胞中相同的基因；以及 (3)确定肿瘤促进剂是否对DNA有直接作用 HL-60细胞中的甲基化及其是否能够改变 5-氮胞苷治疗对DNA甲基化和DNA合成的影响 差异化。

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.