Sudhakar S, Tew K D, Schein P S, Woolley P V, Smulson M E
Cancer Res. 1979 Apr;39(4):1411-7.
Poly(adenosine diphosphate ribose) polymerase, a chromatin-bound enzyme, was stimulated 150 to 200% after treatment of HeLa cells with methylnitrosourea (MNU). In contrast, a slight inhibitory effect on enzyme activity was observed after treatment of cells with various concentrations of chloroethylnitrosoureas. To define precisely the differential effects of nitrosoureas on the enzyme activity, their interactions with chromatin substructure were studied. A nonrandom, in vivo alkylation of chromatin DNA by equimolar concentrations of MNU and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) was revealed by digestion of nuclei from drug-treated cells with micrococcal nuclease and DNase I. [methyl-14C]MNU interacted preferentially with the more accessible regions of chromatin, the internucleosome linkers, whereas, the [chloroethyl-14C]CCNU alkylated the nucleosomal core DNA to a greater extent. These two drugs also differed in their extent of covalent modification of histone and nonhistone chromosomal protein. The binding of MNU to histones was greater than of CCNU. CCNU mainly affected nonhistone proteins. This difference in the reactivity of methyl and chloroethyl nitrosoureas with chromatin may relate to their differential effect on poly(adenosine diphosphate ribose) polymerase activity, as well as to their carcinogenic and antitumor properties.
聚（腺苷二磷酸核糖）聚合酶是一种与染色质结合的酶，在用甲基亚硝基脲（MNU）处理HeLa细胞后，其活性被刺激了150%至200%。相比之下，在用不同浓度的氯乙基亚硝基脲处理细胞后，观察到对该酶活性有轻微的抑制作用。为了精确界定亚硝基脲对该酶活性的不同影响，研究了它们与染色质亚结构的相互作用。用微球菌核酸酶和DNase I消化经药物处理细胞的细胞核，揭示了等摩尔浓度的MNU和1-（2-氯乙基）-3-环己基-1-亚硝基脲（CCNU）对染色质DNA进行的非随机体内烷基化。[甲基-14C]MNU优先与染色质中更容易接近的区域，即核小体间连接区相互作用，而[氯乙基-14C]CCNU则更大程度地烷基化核小体核心DNA。这两种药物在对组蛋白和非组蛋白染色体蛋白的共价修饰程度上也有所不同。MNU与组蛋白的结合大于CCNU。CCNU主要影响非组蛋白。甲基和氯乙基亚硝基脲与染色质反应性的这种差异可能与其对聚（腺苷二磷酸核糖）聚合酶活性的不同影响以及它们的致癌和抗肿瘤特性有关。
