Differential involvement of nuclear factor-kappaB and activator protein-1 pathways in the interleukin-1beta-mediated decrease of deiodinase type 1 and thyroid hormone receptor beta1 mRNA

One of the hallmarks of the sick euthyroid syndrome or non-thyroidal illness is a decrease of serum triiodothyronine, caused mainly by a decrease in liver deiodinase type 1 (D1) mRNA and activity. Proinflammatory cytokines like interleukin (IL)-1beta are likely involved in this disease, but are also known to inhibit thyroid hormone receptor (TR)-beta1 gene expression, which is of interest as the D1 promoter contains TREs. The aim of the present study was to evaluate whether the IL-1beta-induced decrease of D1 and TRbeta1 mRNA is mediated by the same cytokine signalling pathways in a human hepatoma cell line (HepG2). We observed a downregulation of both D1 and TRbeta1 mRNA after 4 h of incubating the cells with IL-1beta. Sulfasalazine was used to inhibit the nuclear factor-kappaB (NFkappaB) pathway and SP600125, a chemical inhibitor of the c-Jun N-terminal kinase, was used as an inhibitor of the activator protein-1 (AP-1) pathway. AP-1 inhibition did not affect the decrease of D1 and TRbeta1 mRNA, but the TRbeta1 mRNA decrease was completely abolished after inhibiting NFkappaB, while D1 mRNA was unaffected. Only simultaneous inhibition of both the NFkappaB and AP-1 pathways abolished the D1 mRNA decrease. We concluded that IL-1beta stimulation of HepG2 cells results in a marked decrease of D1 and TRbeta1 mRNA. The decrease of TRbeta1 mRNA is exclusively mediated by the NFkappaB pathway, while the decrease of D1 mRNA requires inhibition of both the AP-1 and the NFkappaB pathways.