c-Maf Function Research Articles

Transcription factor c-Maf deletion improves streptozotocin-induced diabetic nephropathy by directly regulating Sglt2 and Glut2.

The transcription factor c-Maf has been widely studied and has been reported to play a critical role in embryonic kidney development; however, the postnatal functions of c-Maf in adult kidneys remain unknown as c-Maf-null C57BL/6J mice exhibit embryonic lethality. In this study, we investigated the role of c-Maf in adult mouse kidneys by comparing the phenotypes of tamoxifen-inducible (TAM-inducible) c-Maf-knockout mice (c-Maffl/fl; CAG-Cre-ERTM mice named "c-MafΔTAM") with those of c-Maffl/fl control mice, 10 days after TAM injection [TAM(10d)]. In addition, we examined the effects of c-Maf deletion on diabetic conditions by injecting the mice with streptozotocin, 4 weeks before TAM injection. c-MafΔTAM mice displayed primary glycosuria caused by sodium-glucose cotransporter 2 (Sglt2) and glucose transporter 2 (Glut2) downregulation in the kidneys without diabetes, as well as morphological changes and life-threatening injuries in the kidneys on TAM(10d). Under diabetic conditions, c-Maf deletion promoted recovery from hyperglycemia and suppressed albuminuria and diabetic nephropathy by causing similar effects as did Sglt2 knockout and SGLT2 inhibitors. In addition to demonstrating the potentially unique gene regulation of c-Maf, these findings highlight the renoprotective effects of c-Maf deficiency under diabetic conditions and suggest that c-Maf could be a novel therapeutic target gene for treating diabetic nephropathy.

Germinal Center T follicular helper (GC-Tfh) cell impairment in chronic HIV infection involves c-Maf signaling.

We have recently demonstrated that the function of T follicular helper (Tfh) cells from lymph nodes (LN) of HIV-infected individuals is impaired. We found that these cells were unable to provide proper help to germinal center (GC)-B cells, as observed by altered and inefficient anti-HIV antibody response and premature death of memory B cells. The underlying molecular mechanisms of this dysfunction remain poorly defined. Herein, we have used a unique transcriptional approach to identify these molecular defects. We consequently determined the transcriptional profiles of LN GC-Tfh cells following their interactions with LN GC-B cells from HIV-infected and HIV-uninfected individuals, rather than analyzing resting ex-vivo GC-Tfh cells. We observed that proliferating GC-Tfh cells from HIV-infected subjects were transcriptionally different than their HIV-uninfected counterparts, and displayed a significant downregulation of immune- and GC-Tfh-associated pathways and genes. Our results strongly demonstrated that MAF (coding for the transcription factor c-Maf) and its upstream signaling pathway mediators (IL6R and STAT3) were significantly downregulated in HIV-infected subjects, which could contribute to the impaired GC-Tfh and GC-B cell functions reported during infection. We further showed that c-Maf function was associated with the adenosine pathway and that the signaling upstream c-Maf could be partially restored by adenosine deaminase -1 (ADA-1) supplementation. Overall, we identified a novel mechanism that contributes to GC-Tfh cell impairment during HIV infection. Understanding how GC-Tfh cell function is altered in HIV is crucial and could provide critical information about the mechanisms leading to the development and maintenance of effective anti-HIV antibodies.

C-MAF deletion in adult C57BL/6J mice induces cataract formation and abnormal differentiation of lens fiber cells.

The transcription factor c-MAF is a member of the large MAF family, members of which possess transactivation and bZIP domains. c-MAF plays an important role in lens formation, T-lymphocyte differentiation, hypertrophic chondrocyte differentiation, and kidney development in mouse embryos. However, because homozygous deletion of c-Maf in C57BL/6J mice causes embryonic lethality, the functions of c-MAF in adult mice remain largely uninvestigated. To address this issue, we generated c-Maf floxed (c-Maffl/fl) C57BL/6J mice and established tamoxifen-inducible c-Maf knockout mice (c-Maffl/fl; CAG-Cre-ERTM mice, c-MafΔTAM). After tamoxifen injection, adult c-MafΔTAM mice showed successful deletion of c-Maf protein and developed severe cataracts; cataracts are also seen in human patients who have mutations in the c-MAF DNA binding domain. Furthermore, adult c-MafΔTAM mice exhibited abnormal lens structure and impaired differentiation of lens fiber cells. In summary, we established c-Maffl/fl and c-MafΔTAM C57BL/6J mice, which can be useful animal models for the investigation of c-MAF function in various developmental stages and can also be used as a disease model for cataracts.

The role of interleukin 22 in multiple sclerosis and its association with c-Maf and AHR.

The aim of this paper was to summarise knowledge of IL-22 involvement in multiple sclerosis (MS) and the possible link between IL-22 and two transcription factors - AHR and c-Maf. The conclusion is that despite numerous studies, the exact role of IL-22 in the pathogenesis of MS is still unknown. The expression and function of c-Maf in MS have not been studied. It seems that the functions of c-Maf and AHR are at least partly connected with IL-22, as both directly or indirectly influence the regulation of IL-22 expression. This possible connection has never been studied in MS.

The transcription factor cMaf is targeted by mTOR, and regulates the inflammatory response via the TLR4 signaling pathway.

cMaf is a leucine-zipper transcription factor that is involved in cell differentiation, oncogenic transformation, and human diseases; however, the functions of cMaf in inflammatory responses in macrophages are still not fully understood. Western blot analysis showed that cMaf expression was induced by lipopolysaccharide (LPS) stimulation in mouse macrophages. An enzyme-linked immunosorbent assay was performed to detect the level of expression of inflammatory cytokines after knockdown of cMaf expression in macrophages using a small interfering RNA (siRNA). Signaling pathway inhibitor analyses indicated that extracellular signal-related kinase and phosphoinositide 3-kinase contribute to mammalian target of rapamycin phosphorylation(mTOR), which controls cMaf expression at the translational level by regulating the expression of eIF4E-binding protein1 and S6 ribosomal kinase1 in response to Toll-like receptor4 signaling. Histopathological findings of the lung and a survival analysis showed that mice transplanted with cMaf-knockdown macrophages were more susceptible to LPS challenge. Taken together, our study revealed that the control of cMaf expression at the translational level by mTOR regulated the expression of inflammatory genes in response to LPS challenge. Moreover, cMaf protected mice from septic shock indicating that cMaf may improve host fitness, thereby enabling the survival of certain infectious diseases.

Multiple functions of Maf in the regulation of cellular development and differentiation.

SummaryCellular muscular aponeurotic fibrosarcoma (c‐Maf) is a member of the large macrophage‐activating factor family. C‐Maf plays important roles in the morphogenetic processes and cellular differentiation of the lens, kidneys, liver, T cells and nervous system, and it is particularly important in pancreatic islet and erythroblastic island formation. However, the exact role of c‐Maf remains to be elucidated. In this review, we summarize the research to clarify the functions of c‐Maf in the cellular development and differentiation. The expression of c‐Maf is higher in pancreatic duct cells than in pancreatic islet cells. Therefore, we suggest that pancreatic duct cells may be converted to the functional insulin‐secreting cells by regulating c‐Maf. © 2015 National Natural Science Foundation of China. Diabetes/Metabolism Research and Reviews Published by John Wiley & Sons Ltd.

Molecular insights into dimerization inhibition of c-Maf transcription factor

The Maf protein family belongs to the activator protein 1 (AP-1) superfamily of transcription factors that bind specific DNA target sequences through a basic region and exploit a leucine zipper (LZ) motif for protein–protein interactions leading to homo- or hetero-dimerization. Mafs unique DNA-binding domain contains a highly conserved extended homology region (EHR) that allows to recognize longer DNA sequences than other basic leucine zipper (bZIP) transcription factors.Inspired by the fact that overexpression of Mafs is observed in about 50% of cases of multiple myeloma, a hematological malignant disorder, we undertook a peptide inhibitor approach. The LZ domain of c-Maf, one of large Mafs, was produced by solid phase peptide synthesis. We characterized its secondary structure and dimerization properties, and found that dimerization and folding events are strictly coupled. Moreover, potential peptidic c-Maf dimerization inhibitors were computationally designed and synthesized. These compounds were demonstrated by circular dichroism (CD) spectroscopy and MALDI-TOF mass spectrometry to bind to c-Maf LZ monomers, to drive folding of their partially disordered structure and to efficiently compete with dimerization, suggesting a way for interfering with the function of c-Maf and, more generally, of intrinsically disordered proteins, till now considered undruggable targets.

Role of Blimp-1 in programing Th effector cells into IL-10 producers.

Secretion of the immunosuppressive cytokine interleukin (IL) 10 by effector T cells is an essential mechanism of self-limitation during infection. However, the transcriptional regulation of IL-10 expression in proinflammatory T helper (Th) 1 cells is insufficiently understood. We report a crucial role for the transcriptional regulator Blimp-1, induced by IL-12 in a STAT4-dependent manner, in controlling IL-10 expression in Th1 cells. Blimp-1 deficiency led to excessive inflammation during Toxoplasma gondii infection with increased mortality. IL-10 production from Th1 cells was strictly dependent on Blimp-1 but was further enhanced by the synergistic function of c-Maf, a transcriptional regulator of IL-10 induced by multiple factors, such as the Notch pathway. We found Blimp-1 expression, which was also broadly induced by IL-27 in effector T cells, to be antagonized by transforming growth factor (TGF) β. While effectively blocking IL-10 production from Th1 cells, TGF-β shifted IL-10 regulation from a Blimp-1-dependent to a Blimp-1-independent pathway in IL-27-induced Tr1 (T regulatory 1) cells. Our findings further illustrate how IL-10 regulation in Th cells relies on several transcriptional programs that integrate various signals from the environment to fine-tune expression of this critical immunosuppressive cytokine.

Role of c-Maf in Chondrocyte Differentiation: A Review.

Chondrocyte differentiation in the growth plate is an important process for the longitudinal growth of endochondral bones. Sox9 and Runx2 are the most often-studied transcriptional regulators of the chondrocyte differentiation process, but the importance of additional factors is also becoming apparent. Mafs are a subfamily of the basic ZIP (bZIP) transcription factor superfamily, which act as key regulators of tissue-specific gene expression and terminal differentiation in many tissues. There is increasing evidence that c-Maf and its splicing variant Lc-Maf play a role in chondrocyte differentiation in a temporal-spatial manner. This review summarizes the functions of c-Maf in chondrocyte differentiation and discusses the possible role of c-Maf in osteoarthritis progression.

Cover Picture: Eur. J. Immunol. 4/10

The cover image of this issue consists of confocal images of c-Maf localization in HEK293 T cells, taken from Lin et al. (pp. 1174–1184). In this article, the authors examine regulation of c-Maf function by SUMOylation. The authors show that c-Maf colocalizes with SUMO (small ubiquitin-like modifier) ligases; SUMOylation attenuates c-Maf transcriptional activity, and subsequently, IL-4 expression.

C‐Maf interacts with c‐Myb to down‐regulate Bcl‐2 expression and increase apoptosis in peripheral CD4 cells

The transcription factor c-Maf is critical for IL-4 production and the development of Th2 cells, which promote humoral immunity and protect against extracellular parasites. Yet, little else is known of c-Maf function in CD4 cells. Here, we identify a novel role for c-Maf in regulating susceptibility to apoptosis. Overexpression of c-Maf results in increased susceptibility of CD4 cells to apoptosis induced by multiple stimuli, including growth factor withdrawal, dexamethasone, irradiation, and TCR engagement. This effect is independent of Fas or p53; however, Bcl-2 expression is reduced in c-Maf Tg CD4 cells. Immunoprecipitation and Western blot analyses demonstrate that c-Maf-c-Myb complex formation is enhanced among T cells from c-Maf Tg mice compared to non-Tg littermates following TCR engagement. Unlike non-Tg T cells, c-Myb binding to the Bcl-2 promoter is not detectable in c-Maf Tg T cells by chromatin immunoprecipitation. In reporter assays, Bcl-2 promoter activity is reduced by c-Maf in a dose-dependent manner. Furthermore, transgene-mediated Bcl-2 expression corrects the apoptosis defect observed among c-Maf Tg CD4 cells. These data suggest that c-Maf can interact with c-Myb to reduce Bcl-2 expression, thereby limiting CD4 cell survival following TCR engagement.

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

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.

Regulation and differential expression of the c-maf gene in differentiating cultured cells

The Maf transcription factors are involved in a variety of developmental and cellular differentiation processes, but their role in the differentiation of mesenchymal cells has not been described. Here, we have analyzed c-maf expression during the differentiation of adipocytes and muscle cells in cultured systems. The expression of c-maf mRNA was down-regulated during adipogenesis and up-regulated during myogenesis. In adipogenesis, the c-maf mRNA was down-regulated 58 h after switching to the differentiation medium and just after PPARγ2 mRNA was induced. A transient transfection analysis of a reporter gene containing the 5 ′-flanking region of the c-maf gene showed that PPARγ2 represses c-maf gene expression. We previously found that c-Maf, c-Jun, and Pax6 bind to and stimulate the c-maf gene. The PPARγ2 repression of c-maf expression seems to be due, at least in part, to inhibition of the transactivation functions of c-Maf, c-Jun, and Pax6. The repression of c-maf was partly reversed by CBP, suggesting that these transcription factors compete for CBP or related transcription co-factors. In myogenesis, there was a differentiation-dependent stimulation of c-maf mRNA expression. The increased expression correlated with myoD expression. A transient transfection analysis showed that myoD stimulated a c-maf reporter gene through binding to two typical E-box elements located between 160 and 180 nucleotides upstream of the cap site. Binding of MyoD to the E-boxes was confirmed by a gel mobility shift assay and DNaseI footprinting analysis. Combined, these results suggest that the c-maf gene plays an important role during the differentiation of adipocyte and muscle cells from mesenchymal fibroblast cells.

An IL-4-independent and CD25-mediated function of c-maf in promoting the production of Th2 cytokines.

c-maf is a T helper (Th)2 cell-specific transcription factor, which promotes the differentiation of Th2 cells mainly by an IL-4-dependent mechanism. It remains unclear whether c-maf possesses any IL-4-independent function in regulating the production of Th2 cytokines. Here, we provide evidence demonstrating that c-maf, independent of IL-4, is essential for normal induction of CD25 in developing Th2 cells. The levels of CD25 are significantly higher in developing Th2 cells than in developing Th1 cells during in vitro differentiation. In addition, timely blockade of IL-2 receptor signaling selectively inhibits the production of Th2 cytokines, but not IFN-gamma or IL-2. Taken together, our results uncover an IL-4-independent and CD25-mediated function of c-maf in promoting the production of Th2 cytokines.