NITROSOUREA INTERACTION WITH CHROMATIN AND EFFECT ON POLY(ADENOSINE DIPHOSPHATE RIBOSE) POLYMERASE-ACTIVITY

  • 1 January 1979
    • journal article
    • research article
    • Vol. 39  (4) , 1411-1417
Abstract
Poly(ADP ribose) polymerase, a chromatin-bound enzyme, was stimulated 150-200% after treatment of HeLa cells with methylnitrosourea (MNU). A slight inhibitory effect on enzyme activity was observed after treatment of cells with various concentrations of cholorethylnitrosoureas. 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 l. [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 2 drugs also differed in their extent of covalent modification of histone and nonhistone chromosomal proteins. The binding of MNU to histones was greater than that 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(ADP ribose) polymerase activity, and to their carcinogenic and antitumor properties.