Polyglutamine-expanded ataxin-7 decreases nuclear translocation of NF-kappaB p65 and impairs NF-kappaB activity by inhibiting proteasome activity of cerebellar neurons.
Our recent study indicated that polyglutamine-expanded ataxin-7-Q75 induced apoptotic death of cultured cerebellar neurons by downregulating Bcl-x(L) expression and activating mitochondrial apoptotic cascade. Mutant polyglutamine-expanded proteins are believed to impair the proteolytic function of ubiquitin-proteasome system by sequestering components of proteasomes. Proteasome degradation of IkappaBalpha permits nuclear translocation of NF-kappaB and is required for continuous NF-kappaB activity, which supports the survival of cultured cerebellar neurons by inducing Bcl-x(L) expression. Thus, we tested the hypothesis that mutant ataxin-7-Q75 causes proteasome dysfunction and impairs NF-kappaB activity, leading to reduced Bcl-x(L) expression, caspase activation and cerebellar neuronal death. EMSA assays indicate that DNA-binding activity of NF-kappaB was significantly decreased in cerebellar neurons expressing ataxin-7-Q75. Similar to mutant ataxin-7-Q75, NF-kappaB inhibitor APEQ induced cerebellar neuronal death by decreasing Bcl-x(L) expression and activating caspase-9. Mutant ataxin-7-Q75 inhibited the proteolytic activity of proteasomes in cerebellar neurons. Proteasome inhibitor MG132 also caused cerebellar neuronal death by decreasing Bcl-x(L) expression and activating caspase-9. Both ataxin-7-Q75 and MG132 caused the cytosolic accumulation of IkappaBalpha in cerebellar neurons. Mutant ataxin-7-Q75 or MG132 increased the cytosolic level of NF-kappaB p65 and decreased the nuclear NF-kappaB p65 level. Our study provides the evidence that polyglutamine-expanded ataxin-7-Q75 decreases nuclear translocation of NF-kappaB p65 and impairs NF-kappaB activity by inhibiting proteasome activity of cerebellar neurons.
Wang
Hung-Li
HL
Department of Physiology, Chang Gung University School of Medicine, Taiwan, ROC. hlwns@mail.cgu.edu.tw
He
Cai-Ying
CY
Chou
An-Hsun
AH
Yeh
Tu-Hsueh
TH
Chen
Ying-Ling
YL
Li
Allen H
AH
D021581:Active Transport, Cell Nucleus; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000067719:Ataxin-7; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D004926:Escherichia coli / Q000235:genetics; D005822:Genetic Vectors; D016328:NF-kappa B / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology*; D010957:Plasmids; D061988:Proteasome Inhibitors; D051381:Rats; D051996:Transcription Factor RelA / Q000378:metabolism*; D014170:Transformation, Genetic
D000067719:Ataxin-7; C000593832:Atxn7 protein, rat; D016328:NF-kappa B; D009419:Nerve Tissue Proteins; D010455:Peptides; D061988:Proteasome Inhibitors; D051996:Transcription Factor RelA; C097188:polyglutamine