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A.F. Fernandes, W. Guo, X. Zhang, M. Gallagher, A. Taylor, P. Pereira, F. Shang; Differential Regulation of IL–8 and MCP–1 Expression by the Ubiquitin–Proteasome Pathway in Retinal Pigment Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4885.
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© ARVO (1962-2015); The Authors (2016-present)
Choroidal neovascularization (CNV) is a hallmark of advanced age–related macular degeneration (AMD). Pro–angiogenic factors produced by retinal pigment epithelial cells (RPE) are major triggers of CNV. The ubiquitin–proteasome pathway (UPP) plays critical roles in regulating levels of transcription factors. Both interleukin–8 (IL–8) and monocyte chemoattractant protein–1 (MCP–1) gene expression are controlled by the nuclear factor kappa B (NF–kB). The objective of this study is to assess novel functions for the UPP in controlling transcription factors, such as NF–kB, as well as the expression and secretion of factors that are involved in angiogenesis.
Cultured RPE (ARPE–19) were treated with or without proteasome inhibitors, 10 µM MG132 or 5 µM epoxomicin, for 2–8 hours. NF–kB and AP–1 activities were determined by electrophoretic mobility shift assays. Levels of mRNA for IL–8 and MCP–1 were assessed by real–time RT–PCR. Protein levels of IL–8 and MCP–1 in the medium were determined by ELISA.
Inhibition of proteasome activity reduced NF–kB activity and delayed activation of AP–1 in RPE cells. Consistent with these observations, the expression and secretion of MCP–1 by RPE were substantially attenuated when proteasome activity was inhibited. For IL–8, however, proteasome inhibition had a dual effect: it initially reduced IL–8 secretion and then significantly enhanced IL–8 secretion when proteasome activity was inhibited for longer than 4 hours.
These data demonstrate that the UPP plays an important role in controlling transcription factors in RPE, particularly in modulating the activity of NF–kB. Consequences of impairment of the UPP include diminished NF–kB activity, which leads to attenuated expression of MCP–1. Also, long–term inhibition of proteasome could trigger angiogenesis due to enhanced secretion of IL–8, one of the most potent angiogenesis factors. Taken together, these molecular changes associated with impairment of the UPP are likely to participate in the upstream events triggering development of AMD.
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