Enhanced proteolysis of IkappaBalpha and IkappaBbeta proteins in astrocytes by Moloney murine leukemia virus (MoMuLV)-ts1 infection: a potential mechanism of NF-kappaB activation.
Moloney murine leukemia virus (MoMuLV)-ts1-mediated neuronal degeneration in mice is likely due to loss of glial support and release of inflammatory cytokines and neurotoxins from surrounding ts1-infected glial cells including astrocytes. NF-kappaB is a transcription factor that participates in the transcriptional activation of a variety of immune and inflammatory genes. We investigated whether ts1 activates NF-kappaB in astrocytes and examined the mechanism(s) responsible for the activation of NF-kappaB by ts1 infection in vitro. Here we present evidence that ts1 infection of astrocytes in vitro activates NF-kappaB by enhanced proteolysis of the NF-kappaB inhibitors, IkappaBalpha and IkappaBbeta. In in vitro studies using protease inhibitors, IkappaBalpha proteolysis in ts1-infected astrocytes was significantly blocked by a specific calpain inhibitor calpeptin but not by MG-132, a specific proteasome inhibitor, whereas rapid IkappaBbeta proteolysis was blocked by MG-132. Furthermore, treatment with MG-132 increased levels of multiubiquitinated IkappaBbeta protein in ts1-infected astrocytes. These results indicate that the calpain proteolysis is a major mechanism of IkappaBalpha proteolysis in ts1-infected astrocytes. Additionally, ts1 infection of astrocytes in vitro increased expression of inducible nitric oxide synthase (iNOS), a NF-kappaB-dependent gene product. Our results suggest that NF-kappaB activation in ts1-infected astrocytes is mediated by enhanced proteolysis of IkappaBalpha and IkappaBbeta through two different proteolytic pathways, the calpain and ubiquitin-proteasome pathways, resulting in increased expression of iNOS, a NF-kappaB-dependent gene.
Kim
H T
HT
Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas 77843, USA.
Qiang
W
W
Wong
P K
PK
Stoica
G
G
D021581:Active Transport, Cell Nucleus; D000818:Animals; D001253:Astrocytes / Q000378:metabolism / Q000821:virology*; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004151:Dipeptides / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004790:Enzyme Induction; D015967:Gene Expression Regulation, Viral; D020672:I-kappa B Proteins; D007976:Leupeptins / Q000494:pharmacology; D008025:Ligases / Q000378:metabolism; D051379:Mice; D008979:Moloney murine leukemia virus / Q000502:physiology*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000235:genetics; D052247:Nitric Oxide Synthase Type II; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D025801:Ubiquitin / Q000378:metabolism
D004268:DNA-Binding Proteins; D004151:Dipeptides; C083487:I kappa B beta protein; D020672:I-kappa B Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D016328:NF-kappa B; D009419:Nerve Tissue Proteins; C000606205:Nfkbia protein, mouse; D011480:Protease Inhibitors; D025801:Ubiquitin; D000072000:NF-KappaB Inhibitor alpha; C071482:calpeptin; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D002154:Calpain; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases; C028812:guanosine 3',5'-polyphosphate synthetases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde