Mononuclear phagocytes (monocytes, macrophages) play a pivotal role for theregulation of inflammation. An uncontrolled immunological response of activatedmononuclear cells may cause irreversible tissue damage and chronic inflammatorydisorders. Therefore, antioxidant and anti-inflammatory mechanisms of mononuclearcells are essential for the resolution of inflammation and restoration of immunehomeostasis. Up-regulation of peroxiredoxin I (Prx I) and heme oxygenase-1 (HO-1)has been shown to have potent antioxidant and immunomodulatory properties.
This thesis integrates three original articles that demonstrate the signalingpathways involved in the regulation of the antioxidant genes Prx I and HO-1 by theprototypical monocyte activators phorbol myristate acetate (PMA) andlipopolysaccharide (LPS), in monocytic cells.
Prx I gene expression was up-regulated by PMA and was inhibited bysimultaneous treatment with LPS in RAW264.7 monocytic cells. The repressive effectof LPS on Prx I gene activation by PMA was mediated via a newly identified kappaB siteof the Prx I gene promoter. A "non-classical" kappaB pathway, that includesphosphorylation of the NF-kappaB subunit p65 at serine 276 and a non-receptor tyrosinekinase Bruton s tyrosine kinase, was involved in the regulation of LPS-dependentinhibition of Prx I gene activation by PMA (Paper I).
HO-1 gene expression was transcriptionally induced by PMA with a regulatorypattern different from that by LPS in RAW264.7 monocytic cells. PMA-dependentHO-1 gene activation was mediated via a newly defined kappaB element of the rat HO-1promoter that serves as a nuclear target of p65. An IkappaB kinase-2-independent atypicalNF-kappaB pathway, which was mediated via activation of p38 MAPK and CK2, wasinvolved in HO-1 gene regulation by PMA (Paper II).
An unexpected up-regulation of HO-1 gene expression was observed bypharmacological inhibition of p38 in monocytes and by genetic deficiency of p38alpha inmouse embryonic fibroblasts (MEFs). The inhibitory effect of p38 on HO-1 geneexpression was mediated via a stress response element (StRE) of the mouse HO-1gene promoter that is a nuclear target of the transcription factor NF-E2-relatedfactor 2 (Nrf2). Activation of the ERK pathway and generation of reactive oxygenspecies (ROS) were involved in HO-1 gene activation by p38 inhibition (paper III).
Taken together, the thesis demonstrates the complex regulatory pathways thatcontrol the induction of Prx I and HO-1 gene expression in activated monocytic cells.Thus, further studies on the regulation of these two genes may help to develop noveltherapeutic strategies for the treatment of inflammatory diseases.
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