Abstract
We examined whether the proteasome could regulate endothelin (ET)-1 production in vascular endothelial cells (ECs). A proteasome inhibitor N-benzyloxycarbonyl-Ile-Glu (O-t-Bu)-Ala-leucinal (PSI) significantly decreased ET-1 release from ECs by about 25% of the basal release. PSI also suppressed tumor necrosis factor (TNF)-α-induced ET-1 release from ECs in a dose-dependent manner. Similar inhibitory effects were observed using another proteasome inhibitor lactacystin, whereas a calpain inhibitor calpeptin had no apparent effect on ET-1 release. Furthermore, PSI significantly attenuated prepro ET-1 mRNA expression under basal and TNF-α-stimulated conditions. Electrophoretic mobility shift assay showed that proteasome inhibitors diminished TNF-α-stimulated nuclear factor-kappa B (NF-κB) activation in ECs. Pretreatment with antioxidants, pyrrolidine dithiocarbamate and α-lipoic acid, both of which are known to be suppressors of NF-κB activation, effectively attenuated basal and TNF-α-induced ET-1 release. Thus, a proteasome-dependent proteolytic pathway is at least partly involved in ET-1 production under basal conditions, and this proteolytic pathway seems to have a crucial role in ET-1 production enhanced by TNF-α. The reduction of NF-κB activation may be involved in the mechanisms for suppressive effects of proteasome inhibitors on ET-1 gene transcription and the consequent decrease in ET-1 mRNA expression and ET-1 release.
