C/EBPβGene Inactivation Causes Both Impaired and Enhanced Gene Expression and Inverse Regulation of IL-12 p40 and p35 mRNAs in Macrophages

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Abstract
The transcription factor C/EBPβ is believed to play a fundamental role in regulating activated macrophage functions. However, the molecular mechanisms and the target genes involved have been, so far, poorly characterized, partly due to the difficulty of reproducibly obtaining homogeneous and abundant primary macrophage populations. In this study, we describe the generation and characterization of immortalized macrophage-like cell lines from C/EBPβ-deficient and wild-type mice. Using these cells, we were able to identify a number of genes involved in activated macrophage functions whose induction was affected in the C/EBPβ−/− cells. IFN-γ/LPS-dependent induction of IL-6, IL-1β, TNF-α, inducible NO synthase, and plasminogen activator inhibitor-1 mRNAs was variably impaired, while IL-12 p40, RANTES and macrophage inflammatory protein-1β mRNAs were up-regulated in the absence of C/EBPβ. The differential mRNA expression correlated with differential transcription levels of the corresponding genes, and was in most cases confirmed in primary macrophage populations. Moreover, in sharp contrast to the enhanced induction of IL-12 p40 mRNA, C/EBPβ−/− primary macrophages derived from both the bone marrow and the peritoneal cavity displayed totally defective expression of IL-12 p35 mRNA. Therefore, the IL-12 p35 gene represents a novel obligatory target for C/EBPβ in macrophages and this may explain the defective production of bioactive IL-12 and the impaired Th1 responses of C/EBPβ-deficient mice to Candida albicans infection observed in previous work.

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