HISTONE NUCLEAR PROTEINS ARE IRREVERSIBLY MODIFIED BY REACTIVE METABOLITES OF DIETHYLSTILBESTROL

We demonstrate for the first time that diethylstilbestrol (DES), a syn thetic estrogen, is converted by nuclei to histone-binding metabolite( s). Reaction of [H-3]DES with nuclei in the presence of cumene hydrope roxide or NADPH revealed binding of [H-3]DES to histone nuclear protei ns. Cel electrophoresis experiments revealed that all five histones, 1 , 2A, 2B, 3, and 4, were irreversibly bound to [H-3]DES. Histones 1 an d 3 were more susceptible to the attack by [H-3]DES quinone, a metabol ite of DES, than histones 2A, 2B, or 4. The kinetic constants, K-m and V-max of this binding reaction in the presence of cumene hydroperoxid e were 10 mu M and 750 pmol/mg protein/30 min, respectively. This bind ing was significantly inhibited by cytochromes P-450 inhibitors. Low-m olecular-weight thiols, such as glutathione and cysteine, or thiol mod ifiers, such as n-ethylmaleimide, dithionitrobenzoic acid, and hydroxy mercuric benzoate, drastically inhibited binding of [H-3]DES quinone t o histone 3. The binding of [H-3]DES metabolites to both transcription ally active and inactive chromatin histone proteins was observed. We c onclude that DES is metabolized to histone-binding metabolites, presum ably by nuclear cytochromes P-450. DES quinone may be one of the histo ne-binding DES metabolites. These data suggest that an analogous in vi vo modification in the transcriptionally active chromatin histones by DES metabolites may influence gene function.