Proteasomal degradation of oxidatively damaged endogenous histones in K562human leukemic cells

A number of antitumor drugs act via the oxidation of nuclear material in th e tumor cell. It is therefore important to know if tumor cells can effectiv ely and precisely cope not only with oxidatively induced DNA damage, but al so with nuclear protein oxidation. In this study, we investigated the endog enous degradation of oxidatively damaged histones in K562 human leukemic ce lls after oxidative challenge and demonstrated a link to the overall cellul ar stress response pathways by poly-ADP-ribose-polymerase (PARP). After an oxidative challenge, endogenous nuclear protein degradation, as well as his tone degradation, was enhanced. Among the histone fractions, histone H1 rev ealed the highest degradation rate, and more than 85% of the total degraded H1 disappeared in the first 30 min after oxidative challenge. Short-term d egradation of histones up to 30 min, as well as long-term degradation up to 48 h after oxidative challenge, was significantly reduced in the presence of the PARP inhibitor 3-aminobenzamide, and nearly completely abrogated by the selective proteasome inhibitor lactacystin. Immunoprecipitation experim ents indicated that the proteasome specifically degraded oxidized histones. Thus, we show that the nuclear proteosome system in tumor cells is capable of preventing the accumulation of oxidized proteins in this compartment an d may suggest further treatment strategies to effectively interfere with th e protein "repair" and replacement strategies of tumor cells. (C) 2001 Else vier Science Inc.