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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #186810
Title: PROTEIN QUALITY CONTROL BY THE UBIQUITIN PROTEOLYTIC PATHWAY: ROLES IN RESISTANCE TO OXIDATIVE STRESS AND DISEASE

Author
item Shang, Fu
item DUDEK, EDWARD - TUFTS/HNRCA
item LIU, QING - TUFTS/HNRCA
item BOULTON, MICHAEL - AMD CENTER, UNIV OF TX
item Taylor, Allen

Submitted to: Israel Journal of Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2005
Publication Date: 9/26/2006
Citation: Shang, F., Dudek, E., Liu, Q., Boulton, M.E., Taylor, A. 2006. Protein quality control by the ubiquitin proteolytic pathway: roles in resistance to oxidative stress and disease. Israel Journal of Chemistry. 46(2): 145-158.

Interpretive Summary: There is now agreement that cells are destroyed by the accumulation of proteins damaged by oxidative processes. Proteins are organic compounds found in cells. This type of cell destruction causes several age-related diseases including Alzheimer's Disease, Parkinson's Disease, cataract, and age-related macular degeneration. Scientists also agree that there is a quality control mechanism inside cells that limits the accumulation of damaged proteins. This mechanism is called the Ubiquitin Proteolytic Pathway (UPP). In this study, we asked if and how oxidative processes and the UPP interact with each other with an objective of obtaining information that can lead to development of strategies to delay age-related diseases. Mild oxidative stress was induced in several ways and cells and tissues from human and animal lenses, retinas, and liver were exposed to these stressors. We observed an increase in the presence of damaged proteins. The data suggest that if UPP system fails to keep up with production of damaged proteins, the resulting presence of high levels of damaged proteins that destroys cells may contribute to many age-related diseases.

Technical Abstract: There is now consensus that the accumulation of oxidatively modified proteins is cytotoxic and causally related to several age-related diseases including the amyloid diseases and age-related cataracts. There is also general agreement that proteolytic pathway (UPP) provides a quality control mechanism to limit accumulation of modified proteins. We asked if and how oxidative stress is related to function of the ubiquitin proteolytic pathway, and vice versa, with an objective of obtaining information that can lead to development of strategies to delay age-related "amyloid" or "protein precipitation" diseases such as cataract and age-related macular degeneration. Elevated levels of ubiquitin conjugates were observed when human, rabbit, bovine, and rat lens, retina, liver cells or tissues were exposed to mild oxidative stress which was created by exposure to paraquat, diamide, peroxide, light together with lipofuscin, and radiomimetic drugs. The increase in ubiquitin conjugates derived from an increase in substrates as well as by hyper activation of E1, rather than inactivation of the proteasome. Using a novel glutathiolated substrate, gammaC-crystallin, we demonstrated that the UPP shows a previously unrecognized selectivity for such specifically oxidatively modified proteins. Selectivity of the pathway for other oxidatively modified proteins, specifically for protein carbonyls, was indicated in assays which employed the ubiquitin conjugation competent, but degradation resistant ubiquitin variant K6W-ubiquitin. These experiments showed that failure to execute ubiquitin-dependent proteolysis renders cells more susceptible to oxidative-stress-related cytotoxicity. Activity of the pathway is regulated in part by cellular redox status, specifically as affected by GSSG. Ubiquitination is enhanced when GSSG/GSH ratios are 0.02-0.15. Since there is potentiation of ubiquitination even when GSSG/GSH ratios are indistinguishable from basal levels, it appears that ubiquitination provides one of the most sensitive indicators of oxidative stress. Ubiquitination is attenuated when GSSG/GSH rises >0.2 and does not occur when GSSG/GSH >/=2.9. The data indicate that inhibition of the pathway, which occurs upon aging, is associated with accumulation rather than the timely degradation of ubiquitin conjugates. They further suggest that if the system fails to keep up with production of substrates, high mass ubiquitin conjugates may accumulate and precipitate in cytotoxic aggregates such as are seen in many age-related syndromes, including lens cataracts or in lipofuscin and drusen in the aging retina.