Z Gastroenterol 2005; 43 - 1_30
DOI: 10.1055/s-2005-861609

Regulation of Rat Heme Oxygenase–1 Gene Expression by Interleukin–6 via Jak/STAT Pathway

K Tron 1, A Samoylenko 2, G Musikowski 2, F Kobe 2, S Immenschuh 3, F Schaper 4, G Ramadori 1, T Kietzmann 5
  • 1Abt. Gastroenterologie und Endokrinologie, Uniklinikum Göttingen, Göttingen
  • 2Institut für Biochemie und Molekulare Zellbiologie, Georg-August-Universität Göttingen, Göttingen
  • 3Institut für Klinische Chemie und Pathobiochemie, Giessen
  • 4Institut für Biochemie Universitätsklinikum Aachen, Aachen
  • 5Biochemie, Universität Kaiserslautern, Kaiserslautern

Background and Aims: Heme oxygenase–1 (HO–1) is the inducible enzyme that catalyzes oxidative degradation of heme. It has been recently shown that HO–1 expression is up-regulated in the liver by proinflammatory cytokines. However, the signal transduction pathways of the cytokine-dependent HO–1 regulation are not known in detail. Therefore, the aim of the present study was to investigate the mechanisms of the IL–6-mediated HO–1 induction.

Methods: Rat primary hepatocytes (rPH) and HepG2 hepatoma cells were used as model systems. The HO–1 expression at the mRNA and protein levels was studied by Northern and Western blot analyses, respectively. The functional analysis of the rat HO–1 promoter was performed by luciferase (Luc) reporter gene assay. The binding of activated transcription factors to their specific DNA sequences was proved by electrophoretic mobility shift assay (EMSA).

Results: In rPH, HO–1 mRNA and protein expression was induced by IL–6 in a time- and concentration-dependent manner. The Luc activity of the reporter gene construct containing 754 bp of the HO–1 promoter (pHO–754) was induced by IL–6 in rPH and in HepG2. When pHO–754 was co-transfected with an expression vector encoding a chimeric receptor comprising the external region of the erythropoietin (Epo) receptor and cytoplasmic region of the gp130 IL–6 receptor subunit, Luc activity was stimulated by Epo. No induction by Epo was observed when a chimeric receptor unable to bind STAT was used. Among three putative STAT binding elements (SBE) found in the HO–1 promoter by sequence analysis, only deletion or mutation of SBE3 (–386/–378) reduced Luc induction by Epo. As confirmed by EMSA, SBE3 was able to bind activated STAT3 after treatment of HepG2 cells with IL–6.

Conclusions: Our data demonstrate, that rat HO–1 is transcriptionally induced by IL–6 in hepatocytes via activation of the Jak/STAT pathway. Moreover, SBE3 in the rat HO–1 promoter binds activated STAT3 and mediates HO–1 gene induction by IL–6.

Key words

STAT - heme oxygenase-1 - interleukin-6