Hypomethylation of DNA in Raji cells after treatment with N-methyl-N-nitrosourea

Abstract

Human Raji lymphoblast-like (Burkitt''s lymphoma] cells were propagated in the presence of various concentrations of [the carcinogen] N-methyl-N-nitrosourea (MNU) and the degree of enzymatic methylation of newly synthesized DNA was analyzed by 2 methods. The overall extent of enzymatic DNA methylation was measured on the basis of [14C]deoxycytidine derived radioactivity incorporated into DNA 5-methylcytosine and cytosine residues. Enzymatic methylation of internal cytosines at 5'' .cntdot. CCGG-3'' sequences of Raji DNA was analyzed by use of the bacterial restriction enzyme HpaII and its isoschizomer MspI. The treatment with MNU causes a lower level of enzymatic methylation of newly synthesized DNA. This lower extent of DNA methylation persists in the absence of the carcinogen in the cell cycles following treatment.