Involvement of Nuclear Factor-kappa B and Nurr-1 in Cytokine-Induced Transcription of Proopiomelanocortin Gene in AtT20 Corticotroph Cells

Objective: The precise mechanism whereby proinflammatory cytokines activate the hypothalamo-pituitary-adrenal axis is still unclear. We examined whether transcription factors nuclear factor (NF)-kappa B and Nurr-1 are involved in the cytokine-induced proopiomelanocortin (POMC) gene expression. Methods: The mouse corticotropinoma cell line AtT20 was treated with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1 beta (IL-1 beta). Real-time PCR, luciferase assay and Western blotting were conducted to assess the gene expression, promoter activity and protein expression in various conditions. Results: Intrinsic expression of NF-kappa B was confirmed by RTPCR. An active component of NF-kappa B (p65) was upregulated in the nuclear fraction by both TNF-alpha and IL-1 beta treatment in a dose- and time-related manner. These cytokines potently stimulated the promoter activity of NF-kappa B and Nurr-1. We also found rapid upregulation of the Nurr-1 gene and protein after treatment with these cytokines. Cotreatment of the cells with either of the cytokines and corticotropin-releasing hormone resulted in additive effects. Cytokine-induced Nurr-1 transcription and Nurr-1 transcription induced by overexpression of NF-kappa B were both blunted by mutagenesis within the NF-kappa B responsive element, which implies that Nurr-1 upregulation specifically requires NF-kappa B binding to its own DNA-binding site. Proinflammatory cytokines exert positive effects on POMC gene expression, which were inhibited by pretreatment with a specific NF-kappa B inhibitor. Conclusion: These results together imply that Nurr-1 expression is a connecting point between neuroendocrine and immune systems in mediating cytokine-induced POMC gene expression. Copyright (C) 2009 S. Karger AG, Basel