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J. Biol. Chem., Vol. 277, Issue 28, 25283-25289, July 12, 2002
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,
From the Department of Biological Sciences, Hunter College of City
University of New York, New York, New York 10021
In many neurodegenerative disorders,
aggregates of ubiquitinated proteins are detected in neuronal
inclusions, but their role in neurodegeneration remains to be defined.
To identify intracellular mechanisms associated with the appearance of
ubiquitin-protein aggregates, mouse neuronal HT4 cells were treated
with cadmium. This heavy metal is a potent cell poison that mediates
oxidative stress and disrupts the ubiquitin/proteasome pathway. In the
current studies, the following intracellular events were found to be
also induced by cadmium: (i) a specific rise in cyclooxygenase-2
(COX-2) gene expression but not COX-1; (ii) an increase in the
extracellular levels of the proinflammatory prostaglandin E2, a
product of COX-2; and (iii) production of 4-hydroxy-2-nonenal-protein
adducts, which result from lipid peroxidation. In addition, cadmium
treatment led to the accumulation of high molecular weight
ubiquitin-COX-2 conjugates and perturbed COX-2 glycosylation. The
thiol-reducing antioxidant N-acetylcysteine, and, to a
lesser extent, the COX-2 inhibitor celecoxib, attenuated the
loss of cell viability induced by cadmium demonstrating that oxidative
stress and COX-2 activation contribute to cadmium cytotoxicity. These
findings establish that disruption of the ubiquitin/proteasome pathway
is not the only event triggered by cadmium. This oxidative stressor
also activates COX-2 function. Both events could be triggered by
formation of 4-hydroxy-2-nonenal as a result of cadmium-induced lipid
peroxidation. Proinflammatory responses stimulated by oxidative
stressors that mimic the cadmium effects may, therefore, be important
initiators of the neurodegenerative process and exacerbate its progress.
We dedicate this article to the memory of Dr. Gerald Cohen, Dept. of Neurology, Mount Sinai School of Medicine, New York, NY.
To whom correspondence should be addressed: Dept. of Biological
Sciences, Hunter College of City University of New York, 695 Park Ave.,
New York, NY 10021. Tel.: 212-650-3565; Fax: 212-772-5227; E-mail: pereira@genectr.hunter.cuny.edu.
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