Abstract
One of the main characteristics of nonthyroidal illness (NTI) is a decrease in serum tri-iodothyronine, partly caused by a decrease in liver deiodinase type 1 (D1) mRNA and activity. Proinflammatory cytokines have been associated with NTI in view of their capability to decrease]:)I and thyroid hormone receptor (TR)beta 1 mRNA expression in hepatoma cells. Proinflammatory cytokine induction leads to activation of the inflammatory pathways nuclear factor (NF)kappa B and activator protein (AP)-1. The proinflammatory cytokine interleukin decreases thyroid hormone receptor (TR)beta 1 mRNA in an NF kappa B-dependent way. The aim of this Study was to unravel the effects of IL-1 beta on endogenous TR alpha gene expression in an animal model and in a liver cell line. The TR alpha gene product is alternatively spliced in TR alpha 1 and TR alpha 2, TR alpha 2 is capable of inhibiting TR alpha 1-induced gene transcription. We showed that both TR alpha 1 and TR alpha 2 mRNA decreased not only after lipopolysaccharide administration in liver of mice, but also after IL-1 beta stimulation of hepatoma cells (HepG2). Using the NF kappa B inhibitor sulfasalazine and the AP-1 inhibitor SP600125, it became clear that the IL-1 beta-induced decrease in TR alpha mRNA expression in HepG2 cells can only be abolished by simultaneous inhibition of NF kappa B and AP-1. The IL-1 beta-induced TR alpha 1 and TR alpha 2 mRNA decrease in HepG2 cells is the result of decreased TR alpha gene promoter activity, as evident from actinomycin D experiments. Cycloheximide experiments showed that the decreased promoter activity is independent of dc novo protein synthesis and therefore most likely due to posttranslational modifications such as phosphorylation or subcellular relocalization
Original language | English |
---|---|
Pages (from-to) | 257-265 |
Journal | Journal of endocrinology |
Volume | 194 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2007 |