One enhancer mediates mafK transcriptional activation in both hematopoietic and cardiac muscle cells.
ABSTRACT: Members of the small Maf family of transcription factors play important roles in hematopoiesis. Using transgenic assays, we discovered a tissue-specific enhancer 3' to the mafK gene. This enhancer directs mafK transcription in hematopoietic as well as in developing cardiac muscle cells, and was thus designated the hematopoietic and cardiac enhancer of mafK (HCEK). Only two of four GATA consensus motifs identified within HCEK contributed to enhancer activity, and both of these sites were required for both cardiac and hematopoietic transcriptional activation. The expression profile of MafK significantly overlapped that of GATA-1 in hematopoietic cells and of GATA-4/-6 in cardiac tissues. Each of these GATA factors bound with high specificity to both of the critical GATA sites in HCEK. Hence, the mafK gene is regulated by different GATA proteins in the hematopoietic and cardiac compartments through the same two GATA-binding sites in HCEK. These data provide the first in vivo demonstration that distinct members of a related transcription factor family activate the tissue-specific expression of a single target gene using the same cis-regulatory element.
Project description:Members of the small Maf family (MafK, MafF, and MafG) are basic region leucine zipper (bZip) proteins that can function as transcriptional activators or repressors. The dimer compositions of their DNA binding forms determine whether the small Maf family proteins activate or repress transcription. Using a yeast two-hybrid screen with a GAL4-MafK fusion protein, we have identified two novel bZip transcription factors, Bach1 and Bach2, as heterodimerization partners of MafK. In addition to a Cap'n'collar-type bZip domain, these Bach proteins possess a BTB domain which is a protein interaction motif; Bach1 and Bach2 show significant similarity to each other in these regions but are otherwise divergent. Whereas expression of Bach1 appears ubiquitous, that of Bach2 is restricted to monocytes and neuronal cells. Bach proteins bind in vitro to NF-E2 binding sites, recognition elements for the hematopoietic transcription factor NF-E2, by forming heterodimers with MafK. Furthermore, a DNA binding complex that contained MafK as well as Bach2 or a protein related closely to Bach2 was found to be present in mouse brain cells. Bach1 and Bach2 function as transcription repressors in transfection assays using fibroblast cells, but they function as a transcriptional activator and repressor, respectively, in cultured erythroid cells. The results suggest that members of the Bach family play important roles in coordinating transcription activation and repression by MafK.
Project description:The MAF family transcription factors are homologs of v-Maf, the oncogenic component of the avian retrovirus AS42. They are subdivided into 2 groups, small and large MAF proteins, according to their structure, function, and molecular size. MAFK is a member of the small MAF family and acts as a dominant negative form of large MAFs. In previous research we generated transgenic mice that overexpress MAFK in order to suppress the function of large MAF proteins in pancreatic ?-cells. These mice developed hyperglycemia in adulthood due to impairment of glucose-stimulated insulin secretion. The aim of the current study is to examine the effects of ?-cell-specific Mafk overexpression in endocrine cell development. The developing islets of Mafk-transgenic embryos appeared to be disorganized with an inversion of total numbers of insulin+ and glucagon+ cells due to reduced ?-cell proliferation. Gene expression analysis by quantitative RT-PCR revealed decreased levels of ?-cell-related genes whose expressions are known to be controlled by large MAF proteins. Additionally, these changes were accompanied with a significant increase in key ?-cell transcription factors likely due to compensatory mechanisms that might have been activated in response to the ?-cell loss. Finally, microarray comparison of gene expression profiles between wild-type and transgenic pancreata revealed alteration of some uncharacterized genes including Pcbd1, Fam132a, Cryba2, and Npy, which might play important roles during pancreatic endocrine development. Taken together, these results suggest that Mafk overexpression impairs endocrine development through a regulation of numerous ?-cell-related genes. The microarray analysis provided a unique data set of differentially expressed genes that might contribute to a better understanding of the molecular basis that governs the development and function of endocrine pancreas.
Project description:The three small Maf proteins, MafF, MafG and MafK, have been implicated in a number of physiological processes, including development, differentiation, haematopoiesis and stress response. Here we report the constitutive expression of mafF, mafG and mafK in six human cell lines derived from various tissues (HepG2, IMR-32, K-562, HEK-293, RD and A549). The expression patterns of mafF, mafG and mafK varied widely among cell lines. Because small Maf proteins have been implicated in electrophile response element (EpRE)-mediated stress response, the ability of three EpRE activators [pyrrolidinedithiocarbamate (PDTC), phenylethyl isothiocyanate (PEITC) and t-butylhydroquinone (tBHQ)] to induce small Maf expression was examined in detail in HepG2 cells. Both PDTC and PEITC induced mafF, mafG and mafK expression, whereas tBHQ failed to markedly induce any of the three small Mafs. Where a response was observed, mafF was induced to the greatest extent compared with mafG and mafK, and this response was transcriptionally mediated. PDTC also induced small Maf expression in the other cell lines examined, with patterns of induction varying among cell lines. The differences in expression among the cell lines examined, coupled with the induction patterns observed, indicate that the three small maf genes are stress-responsive, but may be regulated via differing mechanisms. Furthermore, the fact that tBHQ, PDTC and PEITC induce EpRE activity, but that tBHQ fails to markedly induce any of the small Mafs, suggests that up-regulation of small Mafs is not an absolute requirement for EpRE-mediated gene expression.
Project description:Using a zebrafish model of hepatoerythropoietic porphyria (HEP), we identify a previously unknown mechanism underlying heme-mediated regulation of exocrine zymogens. Zebrafish bach1b, nrf2a and mafK are all expressed in the zebrafish exocrine pancreas. Overexpression of bach1b or knockdown of nrf2a result in the downregulation of the expression of the exocrine zymogens, whereas overexpression of nrf2a or knockdown of bach1b cause their upregulation. In vitro luciferase assays demonstrate that heme activates the zymogens in a dosage-dependent manner and that the zymogen promoter activities require the integral Maf recognition element (MARE) motif. The Bach1b-MafK heterodimer represses the zymogen promoters, whereas the Nrf2a-MafK heterodimer activates them. Furthermore, chromatin immunoprecipitation (ChIP) assays show that MafK binds to the MARE sites in the 5' regulatory regions of the zymogens. Taken together, these data indicate that heme stimulates the exchange of Bach1b for Nrf2a at MafK-occupied MARE sites and that, particularly in heme-deficient porphyria, the repressive Bach1b-MafK heterodimer dominates, which can be exchanged for the activating Nrf2a-MafK heterodimer upon treatment with hemin. These results provide novel insights into the regulation of exocrine function, as well as the pathogenesis of porphyria, and should be useful for designing new therapies for both types of disease.
Project description:Although majority of the genes linked to early-onset cataract exhibit lens fiber cell-enriched expression, our understanding of gene regulation in these cells is limited to function of just eight transcription factors and largely in the context of crystallins. We report on small Maf transcription factors Mafg and Mafk as regulators of several non-crystallin human cataract-associated genes in fiber cells and establish their significance to this disease. We applied a bioinformatics tool for cataract gene discovery iSyTE to identify Mafg and its co-regulators in the lens, and generated various null-allelic combinations of Mafg:Mafk mouse mutants for phenotypic and molecular analysis. By age 4 months, Mafg-/-:Mafk+/- mutants exhibit lens defects that progressively develop into cataract. High-resolution phenotypic characterization of Mafg-/-:Mafk+/- mouse lens reveals severely disorganized fiber cells, while microarray-based expression profiling identifies 97 differentially regulated genes (DRGs). Integrative analysis of Mafg-/-:Mafk+/- lens-DRGs with (1) binding motifs and genomic targets of small Mafs and their regulatory partners, (2) iSyTE lens expression data, and (3) interactions between DRGs in the String database, unravel a detailed small Maf regulatory network in the lens, several nodes of which are linked to cataract. This approach identifies 36 high-priority candidates from the original 97 DRGs. Significantly, 8/36 (22%) DRGs are associated with cataracts in human (GSTO1, MGST1, SC4MOL, UCHL1) or mouse (Aldh3a1, Crygf, Hspb1, Pcbd1), suggesting a multifactorial etiology that includes oxidative stress and misregulation of sterol synthesis. These data identify Mafg and Mafk as new cataract-associated candidates and define their function in regulating largely non-crystallin genes linked to human cataract.
Project description:MafF-/-: MafG+/+: MafK-/- mice are viable, while MafF-/-: MafG-/-: MafK-/- mice are embryonic lethal. To get an insight into the cause of the lethality of small Maf triple knockout mice, transcriptome analysis was performed using whole embyos of MafF-/-: MafG-/-: MafK-/- at E10.5 and those of MafF-/-: MafG+/+: MafK-/- at E9.5 or E10.5. Because MafF-/-: MafG-/-: MafK-/- embryos exhibit growth retardation, the gene expression profile of MafF-/-: MafG-/-: MafK-/- embryos at E10.5 was compared with that of MafF-/-: MafG+/+: MafK-/- embyos at E9.5. The gene expression profile of MafF-/-: MafG+/+: MafK-/- embryos at E10.5 was also examined as an alternative control. Total RNA was prepared from pooled three embryos for each sample.
Project description:Oxidative stress and reactive oxygen species (ROS) are associated with diseases such as cancer, cardiovascular complications, inflammation and neurodegeneration. Cellular defense systems must work constantly to control ROS levels and to prevent their accumulation. We report here that the Jun dimerization protein 2 (JDP2) has a critical role as a cofactor for transcription factors nuclear factor-erythroid 2-related factor 2 (Nrf2) and small Maf protein family K (MafK) in the regulation of the antioxidant-responsive element (ARE) and production of ROS. Chromatin immunoprecipitation-quantitative PCR (qPCR), electrophoresis mobility shift and ARE-driven reporter assays were carried out to examine the role of JDP2 in ROS production. JDP2 bound directly to the ARE core sequence, associated with Nrf2 and MafK (Nrf2-MafK) via basic leucine zipper domains, and increased DNA-binding activity of the Nrf2-MafK complex to the ARE and the transcription of ARE-dependent genes. In mouse embryonic fibroblasts from Jdp2-knockout (Jdp2 KO) mice, the coordinate transcriptional activation of several ARE-containing genes and the ability of Nrf2 to activate expression of target genes were impaired. Moreover, intracellular accumulation of ROS and increased thickness of the epidermis were detected in Jdp2 KO mice in response to oxidative stress-inducing reagents. These data suggest that JDP2 is required to protect against intracellular oxidation, ROS activation and DNA oxidation. qPCR demonstrated that several Nrf2 target genes such as heme oxygenase-1, glutamate-cysteine ligase catalytic and modifier subunits, the notch receptor ligand jagged 1 and NAD(P)H dehydrogenase quinone 1 are also dependent on JDP2 for full expression. Taken together, these results suggest that JDP2 is an integral component of the Nrf2-MafK complex and that it modulates antioxidant and detoxification programs by acting via the ARE.
Project description:The small Maf proteins (sMafs) are basic region leucine zipper (bZIP)-type transcription factors. The basic region of the Maf family is unique among the bZIP factors, and it contributes to the distinct DNA-binding mode of this class of proteins. MafF, MafG and MafK are the three vertebrate sMafs, and no functional differences have been observed among them in terms of their bZIP structures. sMafs form homodimers by themselves, and they form heterodimers with cap 'n' collar (CNC) proteins (p45 NF-E2, Nrf1, Nrf2, and Nrf3) and also with Bach proteins (Bach1 and Bach2). Because CNC and Bach proteins cannot bind to DNA as monomers, sMafs are indispensable partners that are required by CNC and Bach proteins to exert their functions. sMafs lack the transcriptional activation domain; hence, their homodimers act as transcriptional repressors. In contrast, sMafs participate in transcriptional activation or repression depending on their heterodimeric partner molecules and context. Mouse genetic analyses have revealed that various biological pathways are under the regulation of CNC-sMaf heterodimers. In this review, we summarize the history and current progress of sMaf studies in relation to their partners.
Project description:We used serial analysis of gene expression to identify new NGF-responsive immediate early genes (IEGs) with potential roles in neuronal differentiation. Among those identified was MafK, a small Maf family basic region and leucine zipper transcriptional repressor and coactivator expressed in immature neurons. NGF treatment elevates the levels of both MafK transcripts and protein. In contrast, there is no effect on expression of the closely related MafG. Unlike many other NGF-responsive IEGs, MafK regulation shows selectivity and is unresponsive to epidermal growth factor, depolarization, or cAMP derivatives. Inhibitor studies indicate that NGF-promoted MafK regulation is mediated by an atypical isoform of PKC but not by mitogen-activated kinase kinase, phospholipase Cgamma, or phosphoinositide 3'-kinase. Interference with MafK expression or activity by small interfering RNA and dominant negative strategies, respectively, suppresses NGF-promoted outgrowth and maintenance of neurites by PC12 cells and neurite outgrowth by immature telencephalic neurons. Our findings support a role for MafK as a novel regulator of neuronal differentiation.
Project description:The rat GST-P (placental glutathione S-transferase), a phase II detoxifying enzyme, is not expressed in normal liver cells, but is highly and specifically induced during early hepatocarcinogenesis as well as in hepatocellular carcinoma cells. Results of previous studies indicated that GST-P gene activation was mainly controlled by an enhancer element, GPE1 (GST-P enhancer 1), but the specific activation mechanism of the GST-P gene was not fully understood [Morimura, Suzuki, Hochi, Yuki, Nomura, Kitagawa, Nagatsu, Imagawa and Muramatsu (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2065-2068; Suzuki, Imagawa, Hirabayashi, Yuki, Hisatake, Nomura, Kitagawa and Muramatsu (1995) Cancer Res. 55, 2651-2655]. In the present study, we investigate the transcription factor Nrf2/MafK heterodimer (where Nrf2 stands for NF-E2 p45-related factor 2) as an activator of the GST-P gene through the action of GPE1 during hepatocarcinogenesis. Electrophoretic mobility-shift assay and footprinting analysis with wild-type GPE1 and GPE1 point mutants showed that the Nrf2/MafK heterodimer specifically bound GPE1. Reporter transfection assays indicated that Nrf2 strongly stimulated GST-P gene expression in mouse F9 embryonal carcinoma cells and H4IIE rat hepatoma cells. Northern-blot analysis indicated that GST-P and Nrf2 mRNA increased in parallel with development of precancerous lesions and hepatocellular carcinoma. Keap1 (Kelch-like ECH-associated protein 1), an inhibitory factor of Nrf2, decreased the activation of GPE1 by Nrf2 and this suppression was restored after treatment with electrophilic compounds. GST-P mRNA expression in H4IIE cells was induced by electrophilic compounds, as was the expression of mRNAs of other phase II detoxifying enzymes. Chromatin immunoprecipitation analyses showed that antibodies both against Nrf2 and against MafK precipitated GPE1 from the chromatin of the pre-neoplastic hepatocytes and rat hepatoma cells (H4IIE and dRLh84), but not from normal hepatocytes. These results indicate that the Nrf2/MafK heterodimer regulates GST-P gene expression during early hepatocarcinogenesis and in hepatoma cells.