Poly-ADP ribose polymerase activates nuclear proteasome to degrade oxidatively damaged histones

摘要

The 20S proteasome has heen shown to be largely responsible for the degradation of oxidatively modified proteins in the cytoplasm. Nuclear proteins are also subject to axidation, and the nucleus of mammalian cells contains proteasome. In human beings, tumor cells frequently are subjected to oxidation as a consequence of antitumor chemo- therapy, and K562 human myelogenous leukemia cells have a higher nuclear proteasome activity than do nonmalignant cells. Adaptation to oxidative stress appears to be one element in the development of long-term resistance to many chemo- therapeutic drugs and the mechanisms of inducible tumor resistance to oxidation are of obvious importance. After hydrogen peroxide treatment of K562 cells, degradation of the model proteasome peptide substrate suc-LLVY-MCA and degradation of oxidized histones in nuclei increases signifi- cantly within minutes. Both increased proteolytic susceptibil- ity of the histone substrates (caused by modification by oxidation) and activation of the proteasome enzyme complex occur independently during oxidative stress. This rapid up- regulation of 205 proteasome activity is accompanied by, and depends on, poly-ADP ribosylation of the proteasome, as shown by inhibitor experiments, ~(14)C-ADP ribose incorpora- tion assays, immunoblotting, in vitro reconstitution experi- ments, and immunoprecipitation of (activated) proteasome with anti-poly-ADP ribose polymerase antihodies. The poly- ADP ribosylation-mediated activated nuclear 20S proteasome is able to remove oxidatively damaged histones more effi- ciently and therefore is