Regulation of TNF-α expression in normal macrophages: The role of C/EBPβ

C/EBPβ is present in monocytes and macrophages, binds to the proximal region of the TNF-α promoter, and contributes to its regulation. This study was performed to characterize the ability of C/EBPβ to regulate the TNF-α gene in myelomonocytic cells and primary macrophages. In transient transfection assays, overexpression of wild type C/EBPβ resulted in a 3-4-fold activation of a 120 base pair TNF-α promoter-reporter construct, while overexpression of a dominant negative (DN) C/EBPβ inhibited LPS-induced activation. In vitro monocyte-differentiated macrophages, infected with an adenoviral vector expressing the DN C/EBPβ (AdDNC/EBPβ) or the control Adβgal, expressed their transgenes weakly, however expression was greatly enhanced in the presence of PMA. Infection with AdDNC/EBPβ resulted in 60% suppression of LPS induced TNFα secretion compared to Adβgal infection (P < 0.001) in PMA-treated macrophages. Northern blot analysis demonstrated approximately a 40% reduction of the TNF-α mRNA in the presence of the DN C/EBPβ, suggesting that the effect of the DN C/EBPβ was at the transcriptional level. In contrast, AdDNC/EBPβ infection did not result in inhibition of LPS-induced TNF-α secretion in the absence of PMA. Further, DN versions of both C/EBPβ and c-Jun, but not NF-κB p65, suppressed PMA-induced TNF-α secretion in macrophages. These observations demonstrate that, C/EBPβ and c-Jun contribute to the regulation of the TNF-α gene in normal macrophages following treatment with PMA. (C) 2000 Academic Press.