Cytokines induce NF-κB in activated but not in quiescent rat hepatic stellate cells

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Abstract
The hepatic stellate cell (HSC), after a fibrogenic stimulus, is transformed from a quiescent to an activated phenotype, including the induction of responsiveness to a variety of agonists. We investigated the activation of nuclear factor-κB (NF-κB) and the expression of the NF-κB-responsive genes intercellular adhesion molecule 1 (ICAM-1) and macrophage inflammatory protein-2 (MIP-2) in freshly isolated and culture-activated HSC by tumor necrosis factor-α (TNF-α) or interleukin-1β. Inhibitor-κB was rapidly (<15 min) degraded, and NF-κB activity was induced in culture-activated but not in freshly isolated HSC after cytokine stimulation. After 30 min of stimulation, immunofluorescence revealed that the NF-κB p65 subunit was predominantly found in the nuclei of activated HSC compared with the cytoplasmic localization in unstimulated cells. No nuclear translocation appeared in freshly isolated HSC after stimulation, despite the presence of functional TNF-α receptors. NF-κB nuclear translocation appeared first partially after 4–5 days and completely after 9 days in culture. Consistent with this time course TNF-α induced the mRNA of the NF-κB-dependent genes ICAM-1 and MIP-2 in activated but not in quiescent HSC. Therefore, cytokines induce NF-κB activity and ICAM-1 and MIP-2 mRNAs in activated but not in quiescent HSC, through a postreceptor mechanism of regulation.

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