Inhibition of NFκB in activated rat hepatic stellate cells by proteasome inhibitors and an IκB super-repressor



The hepatic stellate cell (HSC), following a fibrogenic stimulus, is transformed from a quiescent to an activated cell. Cytokines induce NFκB activity in activated but not in quiescent HSCs with subsequent expression of NFκB-responsive genes, such as intercellular adhesion molecule (ICAM)-1 and interleukin (IL)-6. We investigated the effect of proteasome inhibitors and an IκB super-repressor on the cytokine mediated activation of NFκB, ICAM-1, and IL-6 in activated HSCs. Culture-activated HSCs were stimulated with IL-1β or tumor necrosis factor α (TNFα) in the presence or absence of proteasome inhibitors, ALLN or MG-132, or after infection with an adenovirus expressing the IκB super-repressor (Ad5IκB) or β-galactosidase (Ad5LacZ) as a control. NFκB activity was evaluated by immunofluorescence and by electrophoretic mobility shift assay. The steady state level of cytoplasmic IκB protein was measured by Western Blot. ICAM-1 and IL-6 expression was measured by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbant assay. Proteasome inhibitors, which block the degradation of IκB, and the Ad5IκB, which provides an exogenous nondegradable IκB, block the stimulation of NFκB activity by TNFα and IL-1β in activated HSCs. These reagents block the subsequent nuclear translocation of p65 NFκB and induction of ICAM-1 and IL-6 by cytokines. The specificities of the proteasome inhibitors and the IκB super-repressor are demonstrated by their failure to block c-Jun N-terminal kinase induction by cytokines. Cytokine-induced stimulation of NFκB, ICAM-1, and IL-6 is blocked by proteasome inhibitors and Ad5IκB in activated HSCs. Inhibition of IκBα degradation is a potential target for anti-inflammatory therapy in the liver and might influence the activation process of HSCs following fibrotic stimuli.