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-κB is a transcription factor that participates in the transcriptional activation of a variety of immune and inflammatory genes. We investigated whether ts1 activates NF-κB in astrocytes and examined the mechanism(s) responsible for the activation of NF-κB by ts1 infection in vitro. Here we present evidence that ts1 infection of astrocytes in vitro activates NF-κB by enhanced proteolysis of the NF-κB inhibitors, IκBα and IκBβ. In in vitro studies using protease inhibitors, IκBα 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 IκBβ proteolysis was blocked by MG-132. Furthermore, treatment with MG-132 increased levels of multi-ubiquitinated IκBβ protein in ts 1-infected astrocytes. These results indicate that the calpain proteolysis is a major mechanism of IκBα proteolysis in ts1-infected astrocytes. Additionally, ts1 infection of astrocytes in vitro increased expression of inducible nitric oxide synthase (iNOS), a NF-κB-dependent gene product. Our results suggest that NF-κB activation in ts1-infected astrocytes is mediated by enhanced proteolysis of IκBα and IκBβ through two different proteolytic pathways, the calpain and ubiquitin-proteasome pathways, resulting in increased expression of iNOS, a NF-κB-dependent gene.
ASJC Scopus subject areas
- Clinical Neurology
- Cellular and Molecular Neuroscience