Maf and Mafb control mouse pallial interneuron fate and maturation through neuropsychiatric disease gene regulation

​Maf (c-Maf) and Mafb transcription factors (TFs) have compensatory roles in repressing somatostatin (SST+) interneuron (IN) production in medial ganglionic eminence (MGE) secondary progenitors in mice. Maf and Mafb conditional deletion (cDKO) decreases the survival of MGE-derived cortical interneurons (CINs) and changes their physiological properties. Herein, we show that (1) Mef2c and Snap25 are positively regulated by Maf and Mafb to drive IN morphological maturation; (2) Maf and Mafb promote Mef2c expression which specifies parvalbumin (PV+) INs; (3) Elmo1, Igfbp4 and Mef2c are candidate markers of immature PV+ hippocampal INs (HIN). Furthermore, Maf/Mafb neonatal cDKOs have decreased CINs and increased HINs, that express Pnoc, an HIN specific marker. Our findings not only elucidate key gene targets of Maf and Mafb that control IN development, but also identify for the first time TFs that differentially regulate CIN vs. HIN production.

RBPJ Controls Development of Pathogenic Th17 Cells by Regulating IL-23 Receptor Expression

Interleukin-17 (IL-17)-producing helper T cells (Th17 cells) play an important role in autoimmune diseases. However, not all Th17 cells induce tissue inflammation or autoimmunity. Th17 cells require IL-23 receptor (IL-23R) signaling to become pathogenic. The transcriptional mechanisms controlling the pathogenicity of Th17 cells and IL-23R expression are unknown. Here, we demonstrate that the canonical Notch signaling mediator RBPJ is a key driver of IL-23R expression. In the absence of RBPJ, Th17 cells fail to upregulate IL-23R, lack stability, and do not induce autoimmune tissue inflammation in vivo, whereas overexpression of IL-23R rescues this defect and promotes pathogenicity of RBPJ-deficient Th17 cells. RBPJ binds and trans-activates the Il23r promoter and induces IL-23R expression and represses anti-inflammatory IL-10 production in Th17 cells. We thus find that Notch signaling influences the development of pathogenic and non-pathogenic Th17 cells by reciprocally regulating IL-23R and IL-10 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.

Pax-6 and c-Maf functionally interact with the alpha-cell-specific DNA element G1 in vivo to promote glucagon gene expression

Specific expression of the glucagon gene in the rat pancreas requires the presence of the G1 element localized at -100/-49 base pairs on the promoter. Although it is known that multiple transcription factors such as Pax-6, Cdx-2/3, c-Maf, Maf-B, and Brain-4 can activate the glucagon gene promoter through G1, their relative importance in vivo is unknown. We first studied the expression of Maf-B, c-Maf, and Cdx-2/3 in the developing and adult mouse pancreas. Although Maf-B was detectable in a progressively increasing number of alpha-cells throughout development and in adulthood, c-Maf and Cdx-2/3 were expressed at low and very low levels, respectively. However, c-Maf but not Cdx-2/3 was detectable in adult islets by Western blot analyses. We then demonstrated the in vivo interactions of Pax-6, Cdx-2/3, Maf-B, and c-Maf but not Brain-4 with the glucagon gene promoter in glucagon-producing cells. Although Pax-6, Cdx-2/3, Maf-B, and c-Maf were all able to bind G1 by themselves, we showed that Pax-6 could interact with Maf-B, c-Maf, and Cdx-2/3 and activate transcription of the glucagon gene promoter. Overexpression of dominant negative forms of Cdx-2/3 and Mafs in alpha-cell lines indicated that Cdx-2/3 and the Maf proteins interact on an overlapping site within G1 and that this binding site is critical in the activation of the glucagon gene promoter. Finally, we show that specific inhibition of Pax-6 and c-Maf but not Cdx-2/3 or Maf-B led to decreases in endogenous glucagon gene expression and that c-Maf binds the glucagon gene promoter in mouse islets. We conclude that Pax-6 and c-Maf interact with G1 to activate basal expression of the glucagon gene.

Regulation of GM-CSF expression by the transcription factor c-Maf

BACKGROUND

Inflammation is a key feature of asthma and allergic disease. The proinflammatory cytokines IL-4, IL-5, and IL-13 are clustered on chromosome 5q with GM-CSF in close proximity, and each of these cytokines has been implicated in the pathogenesis of inflammatory disease. Although the expression of IL-4, IL-5, and IL-13 is coordinately regulated, the T(H)2-associated transcription factor c-Maf is thought to be involved only in the regulation of IL-4, the cytokine thought to be the main driver of T(H)2 differentiation.

OBJECTIVE

We sought to determine whether c-Maf influenced the expression of proinflammatory cytokines other than IL-4 in the Jurkat human T-cell line.

METHODS

RT-PCR, ELISA, and promoter-driven CAT assays were used to determine the effect of c-Maf overexpression on cytokine genes. A biotinylated oligo pulldown assay was used to demonstrate recruitment of c-Maf to the GM-CSF promoter.

RESULTS

We found that in addition to induction of IL-4, c-Maf could upregulate GM-CSF expression at both mRNA and protein levels, and that c-Maf could strongly activate the promoters of GM-CSF and IL-4 but not IL-5. Recruitment of c-Maf to the -33 to -97 bp region of the GM-CSF promoter was demonstrated.

CONCLUSION

We propose a novel role for c-Maf in the transcriptional regulation of GM-CSF in human T cells.

CLINICAL IMPLICATIONS

These data suggest that c-Maf may be a therapeutic target affecting both IL-4 and GM-CSF.

Requirement of bic/microRNA-155 for normal immune function

MicroRNAs are a class of small RNAs that are increasingly being recognized as important regulators of gene expression. Although hundreds of microRNAs are present in the mammalian genome, genetic studies addressing their physiological roles are at an early stage. We have shown that mice deficient for bic/microRNA-155 are immunodeficient and display increased lung airway remodeling. We demonstrate a requirement of bic/microRNA-155 for the function of B and T lymphocytes and dendritic cells. Transcriptome analysis of bic/microRNA-155-deficient CD4+ T cells identified a wide spectrum of microRNA-155-regulated genes, including cytokines, chemokines, and transcription factors. Our work suggests that bic/microRNA-155 plays a key role in the homeostasis and function of the immune system.

A heterozygous c-Maf transactivation domain mutation causes congenital cataract and enhances target gene activation

MAF, one of a family of large Maf bZIP transcription factors, is mutated in human developmental ocular disorders that include congenital cataract, microcornea, coloboma and anterior segment dysgenesis. Expressed early in the developing lens vesicle, it is central to regulation of lens crystallin gene expression. We report a semi-dominant mouse c-Maf mutation recovered after ENU mutatgenesis which results in the substitution, D90V, at a highly conserved residue within the N-terminal 35 amino-acid minimal transactivation domain (MTD). Unlike null and loss-of-function c-Maf mutations, which cause severe runting and renal abnormalities, the phenotype caused by the D90V mutation is isolated cataract. In reporter assays, D90V results in increased promoter activation, a situation similar to MTD mutations of NRL that also cause human disease. In contrast to wild-type protein, the c-Maf D90V mutant protein is not inhibited by protein kinase A-dependent pathways. The MTD of large Maf proteins has been shown to interact with the transcriptional co-activator p300 and we demonstrate that c-Maf D90V enhances p300 recruitment in a cell-type dependent manner. We observed the same for the pathogenic human NRL MTD mutation S50T, which suggests a common mechanism of action.

Cell context reveals a dual role for Maf in oncogenesis

Maf b-Zip transcription factors are involved in both terminal differentiation and oncogenesis. To investigate this apparent contradiction, we used two different primary cell types and performed an extensive analysis of transformation parameters induced by Maf proteins. We show that MafA and c-Maf are potent oncogenes in chicken embryo fibroblasts, while MafB appears weaker. We also provide the first evidence that MafA can confer growth factor independence and promote cell division at low density. Moreover, using MafA as a model, we identified several parameters that are critical for Maf transforming activities. Indeed, MafA ability to induce anchorage-independent cell growth was sensitive to culture conditions. In addition, the transforming activity of MafA was dependent on its phosphorylation state, since mutation on Ser65 impaired its ability to induce growth at low density and anchorage-independent growth. We next examined transforming activity of large Maf proteins in embryonic neuroretina cells, where they are known to induce differentiation. Unlike v-Jun, MafA, MafB and c-Maf did not show oncogenic activity in these cells. Moreover, they counteracted transformation induced by constitutive activation of the Ras/Raf/MEK pathway. Taken together, our results show that Maf proteins could display antagonistic functions in oncogenesis depending on the cellular context, and support a dual role for Maf as both oncogenes and tumor suppressor-like proteins.

Overexpression of c-Maf Contributes to T-Cell Lymphoma in Both Mice and Human

c-Maf translocation or overexpression has been observed in human multiple myeloma. Although c-maf might function as an oncogene in multiple myeloma, a role for this gene in other cancers has not been shown. In this study, we have found that mice transgenic for c-Maf whose expression was direct to the T-cell compartment developed T-cell lymphoma. Moreover, we showed that cyclin D2, integrin beta(7), and ARK5 were up-regulated in c-Maf transgenic lymphoma cells. Furthermore, 60% of human T-cell lymphomas (11 of 18 cases), classified as angioimmunoblastic T-cell lymphoma, were found to express c-Maf. These results suggest that c-Maf might cause a type of T-cell lymphoma in both mice and humans and that ARK5, in addition to cyclin D2 and integrin beta(7), might be downstream target genes of c-Maf leading to malignant transformation.

Immunolocalization of cyclin D1 in the developing lens of c-maf -/- mice

The maf gene encodes a transcription factor protein containing a typical basic/leucine zipper domain structure, a motif for protein dimerization and DNA binding. It has been demonstrated that maf family genes have important roles in embryonic development and cellular differentiation. In this study, localization of cyclin D1, one of the cell cycle-related molecules, was examined immunohistochemically in developing lens cells of c-maf knockout (-/-) mice. At embryonic day 14 in wild-type mice, lens cells consisted of round epithelial cells in a single layer and regularly arranged elongated lens cells, indicating primary lens fiber cells. Cyclin D1-positive nuclei were observed in the lens epithelial cells, whereas cyclin D1 was not detected in the primary lens fiber cells. In c-maf -/- mice, a variety of round epithelial cells were located in the anterior and posterior lens. Many cyclin D1-positive nuclei were observed in lens epithelial cells as well as posterior lens cells. These results are consistent with c-maf playing a role in the regulation of cyclin D1 in developing lens cells.