POLY(ADP-RIBOSYL)ATION OF HISTONE H1 CORRELATES WITH INTERNUCLEOSOMALDNA FRAGMENTATION DURING APOPTOSIS

The biochemical role of poly(ADP-ribosyl)ation on internucleosomal DNA fragmentation associated with apoptosis was investigated in HL 60 hum an premyelocytic leukemia cells. It was found that UV light and chemot herapeutic drugs including adriamycin, mitomycin C, and cisplatin incr eased poly(ADP-ribosyl)ation of nuclear proteins, particularly histone H1. A poly(ADP-ribose) polymerase inhibitor, 3-aminobenzamide, preven ted both internucleosomal DNA fragmentation and histone H1 poly(ADP-ri bosyl)ation in cells treated with the apoptosis inducers, When nuclear chromatin was made accessible to the exogenous nuclease in a permeabi lized cell system, chromatin of W-treated cells was more susceptible t o micrococcal nuclease than the chromatin of control cells. Suppressio n of histone H1 poly(ADP-ribosyl)ation by 3-aminobenzamide reduced the micrococcal nuclease digestibility of internucleosomal chromatin in U V-treated cells, These results suggest that the poly(ADP-ribosyl)ation of histone H1 correlates with the internucleosomal DNA fragmentation during apoptosis mediated by DNA damaging agents, This suggestion is s upported by the finding that xeroderma pigmentosum cells which are def ective in introducing incision at the site of DNA damage, failed to in duce DNA fragmentation as well as histone H1 poly(ADP-ribosyl)ation af ter UV irradiation, We propose that poly(ADP-ribosyl)ation of histone H1 protein in the early stage of apoptosis facilitates internucleosoma l DNA fragmentation by increasing the susceptibility of chromatin to c ellular endonuclease.