Many environmental toxins are oxidants. Proteins, which are major targets of oxidative modification, loose function/activity and must be proteolyticaly degraded or they will aggregate, and form cross-linked cellular inclusion bodies. In previous cycles of this grant, we have shown a major role for the proteasome in detoxifying oxidized proteins. Now we find proteasome is under dynamic control, exchanging regulators, and catalytic subunits in mild, acute stress. Understanding dynamic and inducible mechanisms of detoxification by proteasome is our immediate priority. Our broad, long-term objective is to define the mechanism(s) by which oxidized proteins undergo selective proteasomal proteolysis, the contributions of this detoxification system to health, and the impairment of proteasome under chronic or repeated stress.
Our specific aims are to test the following hypotheses: 1) During acute oxidative stress, 20S proteasome undergoes activation by 11 S(PA28) or PA200 regulators, or by PARP or HSP90;whereas 26S proteasome undergoes disassembly and reassembly facilitated by HSP70;2) Expression of proteasome, immunoproteasome, and proteasome regulators, is transiently induced by acute oxidative stress, allowing more efficient degradation of oxidized proteins;and 3) While acute (mild) oxidative stress transiently improves the ability of the proteasomal system to protect against oxidatively modified proteins, chronic or repeated stress actually impairs such adaptation and increases long-term susceptibility to environmental toxins. Hydrogen peroxide will be the major oxidant studied. Limited comparative studies will be conducted with peroxynitrite, hypochlorous acid/hypochlorite, hydroxyl radical, redox cycling quinones, and a hyperoxic cultivation environment. The importance of proteasome regulators and subunit exchanges will be tested with a combination of knockout mutants, siRNA (or antisense), antibody precipitation, and biochemical techniques. Direct activation versus increased subunit/regulator expression will be tested with transcriptional and translational inhibitors. Direct regulation by phosphorylation or glutathionylation will also be tested. Constitutively overexpressing cells and tet-off conditional transgenic cells, for proteasome subunits and regulators, will be used to model mechanisms of stress-adaptation, and to test our conclusions. Our studies will contribute to public health through improved understanding of mechanisms of toxicity, especially acute exposure versus chronic or repeated insults.
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