LPS-induced down-regulation of NO-sensitive guanylyl cyclase in astrocytes occurs by proteasomal degradation in clastosomes

We previously showed that treatment with bacterial lipopolysaccharide (LPS) or pro-inflammatory cytokines decreases NO-sensitive guanylyl cyclase (GC(NO)) activity in astrocytes by decreasing the half-life of the obligate GC(NO) beta 1 subunit in a NO-independent but transcription- and translation-dependent process. Here we show that LPS-induced beta 1 degradation requires proteasome activity and is independent of NF kappa B activation or PI interaction with HSP90. Immunocytochemistry and confocal microscopy analysis revealed that LPS promotes colocalization of the predominantly soluble beta 1 protein with ubiquitin and the 20S proteasome in nuclear aggregates that present characteristics of clastosomes, nuclear bodies involved in proteolysis via the ubiquitin-proteasome system. Proteasome and protein synthesis inhibitors prevented LPS-induced clastosome assembly and nuclear colocalization of beta 1 with ubiquitin and 20S proteasome, strongly supporting a role for these transient nuclear structures in GC(NO) down-regulation during neuroinflammation. (c) 2007 Elsevier Inc. All rights reserved.