CONTROL OF ACTIVATOR PROTEIN-1 AND NUCLEAR FACTOR-KAPPA-B ACTIVITY BYINTERLEUKIN-1, INTERLEUKIN-6 AND METALS IN HEPG2 CELLS

The intracellular signals induced by IL-1 and IL-6 have been described but there are few details of the signals they induce in liver-derived cells during initiation of acute phase protein synthesis. We therefor e used an in vitro system to investigate signalling by IL-1 and IL-6 i n the human liver cell line, HepG2. Chloramphenicol acetyl transferase (CAT) expression vectors, under the control of activator protein-1 (p TRE-CAT), nuclear factor kappa B (pNF-CAT) or no enhancer region (pBLC AT2), were transfected into HepG2 cells and the effects of the cytokin es on their activity was studied. Profound changes in liver processing of heavy metals and the induction of metal-dependent acute proteins a re also seen during the acute phase response. To determine if the supp ly of metal ions could itself influence signalling we also investigate d the effects of cadmium and zinc on the activity of the transfected v ectors. Both alpha and beta forms of interleukin-1 increased the expre ssion of pTRE-CAT and pNF-CAT, but not pBLCAT2, while interleukin-6 ha d no effect, suggesting that activator protein-1 and nuclear factor ka ppa B activity was induced by interleukin-1, but not interleukin-6. Sp ecificity of the effect of interleukin-1 alpha was confirmed using an anti-interleukin-1 alpha monoclonal antibody. Zinc and cadmium also in creased pTRE-CAT expression, but not pNF-CAT or pBLCAT2. Removal of he avy metal ions from the culture medium resulted in decreased pTRE-CAT expression, while pNF-CAT and pBLCAT2 were relatively unaffected, conf irming the stimulatory effect of metals on activator protein-1, but no t nuclear protein kappa B activity. Therefore, metal and interleukin-1 -mediated signal transduction may involve overlapping pathways, wherea s interleukin-l and interleukin-6 act via different pathways in liver cells.