The Protooncogene c-Maf Is an Essential Transcription Factor for IL-10 Gene Expression in Macrophages

Abstract

IL-10 is an important immunoregulatory factor. However, our understanding of IL-10 gene regulation remains very limited. In this study, following up on our previous novel finding that the protooncogene c-Maf of the basic leucine zipper family of transcription factors is expressed in monocytes and macrophages, we investigate the role of c-Maf in the transcriptional regulation of IL-10 and the underlying molecular mechanism in macrophages. c-Maf-null macrophages exhibit strongly impaired IL-10 protein production and mRNA expression upon LPS stimulation. Ectopic expression of c-Maf stimulates not only exogenously transfected IL-10 promoter-driven luciferase activity in a dose-dependent manner but also enhances endogenous IL-10 gene expression stimulated by LPS. Both in vitro and in vivo experiments identify a c-Maf response element localized to nucleotides −196/−184 relative to the transcription initiation site in the IL-10 promoter. This site represents an atypical 12-O-tetradecanoate-13-acetate-responsive element for musculoaponeurotic fibrosarcoma recognition and functions as an enhancer element in a heterologous and orientation-independent manner. Furthermore, c-Maf is expressed constitutively in resting monocytes/macrophages. IL-4 can up-regulate c-Maf expression, its binding to IL-10 promoter, and dose dependently enhance IL-10 production induced by LPS; moreover, IL-4 failed to enhance LPS-induced IL-10 production in c-Maf-null macrophages. Taken together, these data demonstrate that c-Maf is an indispensable yet constitutive transcription factor for IL-10 gene expression in LPS-activated macrophages, and IL-4 modulates IL-10 production in inflammatory macrophages likely via its ability to induce c-Maf expression. Thus, this study uncovers a novel and important function of c-Maf in macrophages and elucidates its transcriptional mechanism in the regulation of IL-10 gene expression.

Adenosine Augments IL-10 Production by Macrophages through an A2B Receptor-Mediated Posttranscriptional Mechanism

“…Although we wished to determine IL-10 promoter activity 5 h after LPS stimulation, as was the case for IL-10 protein and mRNA measurements, luciferase levels were measured 8 h after LPS treatment, because shorter incubation times produced insufficient signal levels (data not shown). Similar to results reported in previous studies (6,11), LPS was found to elicit an ϳ10-fold increase in IL-10 promoter activity (Fig. 2C).…”

“…Induction of IL-10 gene expression following LPS administration depends on a transcriptional process initiated by binding of the transcription factors Sp1 (6 -9), Sp3 (9), Stat3 (10), C/EBP␤ and ␥ (9), and c-Maf (11) to the IL-10 promoter. cAMP-elevating agents trigger IL-10 promoter activity and IL-10 secretion in human monocytic cells, secondary to an enhanced binding of CREB, as well as C/EBP␣ and ␤, to the IL-10 promoter (12).…”

IFN-γ Negatively Regulates CpG-Induced IL-10 in Bone Marrow-Derived Dendritic Cells

“…The transcription factor cMaf is induced by IL-10 and acts to up-regulate IL-10 production and to inhibit IL-12p40 and IL-12p35 expression (49). Most recently the presence of c-Maf was shown to be essential for optimal IL-10 production by macrophages (50). Interestingly the addition of IL-4 in this system resulted in enhanced c-Maf and IL-10 expression (50).…”

MicroRNA-155 Regulates Inflammatory Cytokine Production in Tumor-associated Macrophages via Targeting C/EBPβ

“…Rodriguez and colleagues have recently shown that c-Maf is also the putative target of miR-155 (33), and ectopically expressed c-Maf is sufficient to trigger IL-10 production by immune cells (39,40). In addition to miR-155, several other miRNAs, including miR-146 and miR-150 have been shown to play pivotal roles in the inflammatory responses and hematopoiesis of immune cells (21,41).…”