title: Oxidative inactivation of the proteasome in retinal pigment epithelial cells. A potential link between oxidative stress and up-regulation of interleukin-8.
abstract: Oxidative stress and inflammation are implicated in the pathogenesis of many age-related diseases. Stress-induced overproduction of inflammatory cytokines, such as interleukin-8 (IL-8), is one of the early events of inflammation. The objective of this study was to elucidate mechanistic links between oxidative stress and overproduction of IL-8 in retinal pigment epithelial (RPE) cells. We found that exposure of RPE cells to H(2)O(2), paraquat, or A2E-mediated photooxidation resulted in increased expression and secretion of IL-8. All of these oxidative stressors also inactivated the proteasome in RPE cells. In contrast, tert-butylhydroperoxide (TBH), a lipophilic oxidant that did not stimulate IL-8 production, also did not inactivate the proteasome. Moreover, prolonged treatment of RPE cells with proteasome-specific inhibitors recapitulated the stimulation of IL-8 production. These data suggest that oxidative inactivation of the proteasome is a potential mechanistic link between oxidative stress and up-regulation of the proinflammatory IL-8. The downstream signaling pathways that govern the production of IL-8 include NF-kappaB and p38 MAPK. Proteasome inhibition both attenuated the activation and delayed the turnoff of NF-kappaB, resulting in biphasic effects on the production of IL-8. Prolonged proteasome inhibition (>2 h) resulted in activation of p38 MAPK via activation of MKK3/6 and increased the production of IL-8. Chemically inhibiting the p38 MAPK blocked the proteasome inhibition-induced up-regulation of IL-8. Together, these data indicate that oxidative inactivation of the proteasome and the related activation of the p38 MAPK pathway provide a potential link between oxidative stress and overproduction of proinflammatory cytokines, such as IL-8.
authors.affiliation: Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA.
authors.forename: Alexandre F
authors.initials: AF
authors.lastname: Fernandes
authors.forename: Jilin
authors.initials: J
authors.lastname: Zhou
authors.forename: Xinyu
authors.initials: X
authors.lastname: Zhang
authors.forename: Qingning
authors.initials: Q
authors.lastname: Bian
authors.forename: Janet
authors.initials: J
authors.lastname: Sparrow
authors.forename: Allen
authors.initials: A
authors.lastname: Taylor
authors.forename: Paulo
authors.initials: P
authors.lastname: Pereira
authors.forename: Fu
authors.initials: F
authors.lastname: Shang
mesh_terms: D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology*; D005786:Gene Expression Regulation; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007249:Inflammation; D016209:Interleukin-8 / Q000378:metabolism*; D008027:Light; D008954:Models, Biological; D018384:Oxidative Stress; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000166:cytology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D013997:Time Factors
chemical_list: D016209:Interleukin-8; D006861:Hydrogen Peroxide; D046988:Proteasome Endopeptidase Complex; D010100:Oxygen