Intermediate filament transcription in astrocytes is repressed by proteasome inhibition.
Increased expression of the astrocytic intermediate filament protein glial fibrillary acidic protein (GFAP) is a characteristic of astrogliosis. This process occurs in the brain during aging and neurodegeneration and coincides with impairment of the ubiquitin proteasome system. Inhibition of the proteasome impairs protein degradation; therefore, we hypothesized that the increase in GFAP may be the result of impaired proteasomal activity in astrocytes. We investigated the effect of proteasome inhibitors on GFAP expression and other intermediate filament proteins in human astrocytoma cells and in a rat brain model for astrogliosis. Extensive quantitative RT-PCR, immunocytochemistry, and Western blot analysis resulted unexpectedly in a strong decrease of GFAP mRNA to <4% of control levels [Control (DMSO) 100+/-19.2%; proteasome inhibitor (epoxomicin) 3.5+/-1.3%, n=8; P < or = 0.001] and a loss of GFAP protein in astrocytes in vitro. We show that the proteasome alters GFAP promoter activity, possibly mediated by transcription factors as demonstrated by a GFAP promoter-luciferase assay and RT(2) Profiler PCR array for human transcription factors. Most important, we demonstrate that proteasome inhibitors also reduce GFAP and vimentin expression in a rat model for induced astrogliosis in vivo. Therefore, proteasome inhibitors could serve as a potential therapy to modulate astrogliosis associated with CNS injuries and disease.
Middeldorp
Jinte
J
Department of Astrocyte Biology and Neurodegeneration, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Amsterdam, The Netherlands.
Kamphuis
Willem
W
Sluijs
Jacqueline A
JA
Achoui
Dalila
D
Leenaars
Cathalijn H C
CH
Feenstra
Matthijs G P
MG
van Tijn
Paula
P
Fischer
David F
DF
Berkers
Celia
C
Ovaa
Huib
H
Quinlan
Roy A
RA
Hol
Elly M
EM