v-maf, a viral oncogene that encodes a "leucine zipper" motif

Comparative Transcriptome Analysis of Cold Tolerance Mechanism in Honeybees (Apis mellifera sinisxinyuan)

Honeybees are important pollinators worldwide that are closely related to agricultural production and ecological balance. The biological activities and geographical distribution of honeybees are strongly influenced by temperature. However, there is not much research on the cold tolerance of honeybees. The Apis mellifera sinisxinyuan, a kind of western honeybee, exhibits strong cold hardiness. Here, we determined that short-term temperature treatment could regulate the honeybee's cold tolerance ability by measuring the supercooling point of A. m. sinisxinyuan treated with different temperatures. Transcriptome data were analyzed between the treated and untreated honeybees. A total of 189 differentially expressed genes were identified. Among them, Abra, Pla1, rGC, Hr38, and Maf were differentially expressed in all comparisons. GO and KEGG analysis showed that the DEGs were enriched in molecular functions related to disease, signal transduction, metabolism, and the endocrine system's function. The main components involved were ribosomes, nucleosomes, proteases, and phosphokinases, among others. This study explored the formation and regulation mechanism of cold tolerance in honeybees, not only providing a theoretical basis for cultivating honeybees with excellent traits but also promoting research and practice on insect stress tolerance.

The Hippo kinases control inflammatory Hippo signaling and restrict bacterial infection in phagocytes

The Hippo kinases MST1 and MST2 initiate a highly conserved signaling cascade called the Hippo pathway that limits organ size and tumor formation in animals. Intriguingly, pathogens hijack this host pathway during infection, but the role of MST1/2 in innate immune cells against pathogens is unclear. In this report, we generated Mst1/2 knockout macrophages to investigate the regulatory activities of the Hippo kinases in immunity. Transcriptomic analyses identified differentially expressed genes (DEGs) regulated by MST1/2 that are enriched in biological pathways, such as systemic lupus erythematosus, tuberculosis, and apoptosis. Surprisingly, pharmacological inhibition of the downstream components LATS1/2 in the canonical Hippo pathway did not affect the expression of a set of immune DEGs, suggesting that MST1/2 control these genes via alternative inflammatory Hippo signaling. Moreover, MST1/2 may affect immune communication by influencing the release of cytokines, including TNFα, CXCL10, and IL-1ra. Comparative analyses of the single- and double-knockout macrophages revealed that MST1 and MST2 differentially regulate TNFα release and expression of the immune transcription factor MAF, indicating that the two homologous Hippo kinases individually play a unique role in innate immunity. Notably, both MST1 and MST2 can promote apoptotic cell death in macrophages upon stimulation. Lastly, we demonstrate that the Hippo kinases are critical factors in mammalian macrophages and single-cell amoebae to restrict infection by Legionella pneumophila, Escherichia coli, and Pseudomonas aeruginosa. Together, these results uncover non-canonical inflammatory Hippo signaling in macrophages and the evolutionarily conserved role of the Hippo kinases in the anti-microbial defense of eukaryotic hosts.

IMPORTANCE

Identifying host factors involved in susceptibility to infection is fundamental for understanding host-pathogen interactions. Clinically, individuals with mutations in the MST1 gene which encodes one of the Hippo kinases experience recurrent infection. However, the impact of the Hippo kinases on innate immunity remains largely undetermined. This study uses mammalian macrophages and free-living amoebae with single- and double-knockout in the Hippo kinase genes and reveals that the Hippo kinases are the evolutionarily conserved determinants of host defense against microbes. In macrophages, the Hippo kinases MST1 and MST2 control immune activities at multiple levels, including gene expression, immune cell communication, and programmed cell death. Importantly, these activities controlled by MST1 and MST2 in macrophages are independent of the canonical Hippo cascade that is known to limit tissue growth and tumor formation. Together, these findings unveil a unique inflammatory Hippo signaling pathway that plays an essential role in innate immunity.

Traditional and emerging strategies using hepatocytes for pancreatic regenerative medicine

Although pancreas and islet cell transplantation are the only ways to prevent the late complications of insulin-dependent diabetes, a shortage of donors is a major obstacle to tissue and organ transplantation. Stem cell therapy is an effective treatment for diabetes and other pancreatic-related diseases, which can be achieved by inducing their differentiation into insulin-secreting cells. The liver is considered an ideal source of pancreatic cells due to its similar developmental origin and strong regenerative ability as the pancreas. This article reviews the traditional and emerging strategies using hepatocytes for pancreatic regenerative medicine and evaluates their advantages and challenges. Gene reprogramming and chemical reprogramming technologies are traditional strategies with potential to improve the efficiency and specificity of cell reprogramming and promote the transformation of hepatocytes into islet cells. At the same time, organoid technology, as an emerging strategy, has received extensive attention. Biomaterials provide a three-dimensional culture microenvironment for cells, which helps improve cell survival and differentiation efficiency. In addition, clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing technology has brought new opportunities and challenges to the development of organoid technology.

Cellular senescence-driven transcriptional reprogramming of the MAFB/NOTCH3 axis activates the PI3K/AKT pathway and promotes osteosarcoma progression

Osteosarcoma is the most common primary malignancy of bones and primarily occurs in adolescents and young adults. However, a second smaller peak of osteosarcoma incidence was reported in the elderly aged more than 60. Elderly patients with osteosarcoma exhibit different characteristics compared to young patients, which usually results in a poor prognosis. The mechanism underlying osteosarcoma development in elderly patients is intriguing and of significant value in clinical applications. Senescent cells can accelerate tumor progression by metabolic reprogramming. Recent research has shown that methylmalonic acid (MMA) was significantly up-regulated in the serum of older individuals and played a central role in the development of aggressive characteristics. We found that the significant accumulation of MMA in elderly patients imparted proliferative potential to osteosarcoma cells. The expression of MAFB was excessively up-regulated in osteosarcoma specimens and was further enhanced in response to MMA accumulation as the patient aged. Specifically, we first confirmed a novel molecular mechanism between cellular senescence and cancer, in which the MMA-driven transcriptional reprogramming of the MAFB-NOTCH3 axis accelerated osteosarcoma progression via the activation of PI3K-AKT pathways. Moreover, the down-regulation of the MAFB-NOTCH3 axis increased the sensitivity and effect of AKT inhibitors in osteosarcoma through significant inhibition of AKT phosphorylation. In conclusion, we confirmed that MAFB is a novel age-dependent biomarker for osteosarcoma, and targeting the MAFB-NOTCH3 axis in combination with AKT inhibition can serve as a novel therapeutic strategy for elderly patients with osteosarcoma in experimental and clinical trials.

An Insight into Vital Genes Responsible for β-cell Formation

The regulation of glucose homeostasis and insulin secretion by pancreatic β-cells, when disturbed, will result in diabetes mellitus. Replacement of dysfunctional or lost β-cells with fully functional ones can tackle the problem of β-cell generation in diabetes mellitus. Various pancreatic-specific genes are expressed during different stages of development, which have essential roles in pancreatogenesis and β-cell formation. These factors play a critical role in cellular-based studies like transdifferentiation or de-differentiation of somatic cells to multipotent or pluripotent stem cells and their differentiation into functional β-cells. This work gives an overview of crucial transcription factors expressed during various stages of pancreas development and their role in β-cell specification. In addition, it also provides a perspective on the underlying molecular mechanisms.

Nuclear factor E2-associated factor 2 and musculoaponeurotic fibrosarcoma K mediate regulation glutathione peroxidase of Cristaria plicata after microcystin-induced oxidative stress

Nuclear factor E2-associated factor 2 (Nrf2)/Antioxidant Response Element (ARE) signaling pathway is an endogenous antioxidant pathway that protects cells from oxidative damage. This pathway is triggered when aquatic organisms are exposed to environmental toxicants. In this study, CpMafK (musculoaponeurotic fibrosarcoma K of Cristaria plicata) mRNA expression in hepatopancreas and gills were up regulated after Cristaria plicata (C. plicata) was exposed to microcystin (MC), which showed that CpMafK protected C. plicata from MC. After MC treatment and CpNrf2 (Nrf2 of Cristaria plicata) knockdown, the mRNA expression of CpMafK was down regulated. After MC treatment and CpMafK knockdown, the mRNA expression of CpNrf2 was down regulated. Indicating that the expression of CpNrf2 was positively correlated with CpMafK. CpGPx (GPx of Cristaria plicata) mRNA was also down regulated with the down regulation of CpMafK and CpNrf2. CpGPx promoter contains a variety of transcription factor binding sites, including Nrf2, ARE elements, etc. Gel blocking experiments showed that CpNrf2/CpMafK heterodimers were bound to CpGPx promoters in vitro. Dual luciferase reporter assay showed that CpNrf2/CpMafK heterodimer negatively regulated CpGPx promoter in cells. In conclusion, Nrf2 and MafK mediate regulation of GPx play a crucial role in protecting bivalves from MC.

Exploring Large MAF Transcription Factors: Functions, Pathology, and Mouse Models with Point Mutations

Large musculoaponeurotic fibrosarcoma (MAF) transcription factors contain acidic, basic, and leucine zipper regions. Four types of MAF have been elucidated in mice and humans, namely c-MAF, MAFA, MAFB, and NRL. This review aimed to elaborate on the functions of MAF transcription factors that have been studied in vivo so far, as well as describe the pathology of human patients and corresponding mouse models with c-MAF, MAFA, and MAFB point mutations. To identify the functions of MAF transcription factors in vivo, we generated genetically modified mice lacking c-MAF, MAFA, and MAFB and analyzed their phenotypes. Further, in recent years, c-MAF, MAFA, and MAFB have been identified as causative genes underpinning many rare diseases. Careful observation of human patients and animal models is important to examine the pathophysiological mechanisms underlying these conditions for targeted therapies. Murine models exhibit phenotypes similar to those of human patients with c-MAF, MAFA, and MAFB mutations. Therefore, generating these animal models emphasizes their usefulness for research uncovering the pathophysiology of point mutations in MAF transcription factors and the development of etiology-based therapies.

The Role of Nrf2/sMAF Signalling in Retina Ageing and Retinal Diseases

Age-related diseases, such as Parkinson's disease, Alzheimer's disease, cardiovascular diseases, cancers, and age-related macular disease, have become increasingly prominent as the population ages. Oxygen is essential for living organisms, but it may also cause disease when it is transformed into reactive oxygen species via biological processes in cells. Most of the production of ROS occurs in mitochondrial complexes I and III. The accumulation of ROS in cells causes oxidative stress, which plays a crucial role in human ageing and many diseases. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a key antioxidant transcription factor that plays a central role in many diseases and ageing in general. It regulates many downstream antioxidative enzymes when cells are exposed to oxidative stress. A basic-region leucine zipper (bZIP) transcription factor, MAF, specifically the small MAF subfamily (sMAFs), forms heterodimers with Nrf2, which bind with Maf-recognition elements (MAREs) in response to oxidative stress. The role of this complex in the human retina remains unclear. This review summarises the current knowledge about Nrf2 and its downstream signalling, especially its cofactor-MAF, in ageing and diseases, with a focus on the retina. Since Nrf2 is the master regulator of redox homeostasis in cells, we hypothesise that targeting Nrf2 is a promising therapeutic approach for many age-related diseases.

Tumor-suppressive role of the musculoaponeurotic fibrosarcoma gene in colorectal cancer

Somatic cell reprogramming using the microRNAs miR-200c, miR-302s, and miR-369s leads to increased expression of cyclin-dependent kinase inhibitors in human colorectal cancer (CRC) cells and suppressed tumor growth. Here, we investigated whether these microRNAs inhibit colorectal tumorigenesis in CPC;Apc mice, which are prone to colon and rectal polyps. Repeated administration of microRNAs inhibited polyp formation. Microarray analysis indicated that c-MAF, which reportedly shows oncogene-like behavior in multiple myeloma and T cell lymphoma, decreased in tumor samples but increased in microRNA-treated normal mucosa. Immunohistochemistry identified downregulation of c-MAF as an early tumorigenesis event in CRC, with low c-MAF expression associated with poor prognosis. Of note, c-MAF expression and p53 protein levels were inversely correlated in CRC samples. c-MAF knockout led to enhanced tumor formation in azoxymethane/dextran sodium sulfate-treated mice, with activation of cancer-promoting genes. c-MAF may play a tumor-suppressive role in CRC development.

Crosstalk between phytochemicals and inflammatory signaling pathways

Novel bioactive constituents from natural sources are actively being investigated. The phytochemicals in these phenolic compounds are believed to have a variety of beneficial effects on human health. Several phenolic compounds have been found in plants. The antioxidant potential of phenols has been discussed in numerous studies along with their anti-inflammatory effects on pro-inflammatory cytokine, inducible cyclooxygenase-2, and nitric oxide synthase. Through current study, an attempt is made to outline and highlight a wide variety of inflammation-associated signaling pathways that have been modified by several natural compounds. These signaling pathways include nuclear factor-kappa B (NF-кB), activator protein (AP)-1, protein tyrosine kinases (PTKs), mitogen-activated protein kinases (MAPKs), nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factors, tyrosine phosphatidylinositol 3-kinase (PI3K)/AKT, and the ubiquitin-proteasome system. In light of the influence of natural substances on signaling pathways, their impact on the production of inflammatory mediator is highlighted in this review.

The role and regulation of Maf proteins in cancer

The Maf proteins (Mafs) belong to basic leucine zipper transcription factors and are members of the activator protein-1 (AP-1) superfamily. There are two subgroups of Mafs: large Mafs and small Mafs, which are involved in a wide range of biological processes, such as the cell cycle, proliferation, oxidative stress, and inflammation. Therefore, dysregulation of Mafs can affect cell fate and is closely associated with diverse diseases. Accumulating evidence has established both large and small Mafs as mediators of tumor development. In this review, we first briefly describe the structure and physiological functions of Mafs. Then we summarize the upstream regulatory mechanisms that control the expression and activity of Mafs. Furthermore, we discuss recent studies on the critical role of Mafs in cancer progression, including cancer proliferation, apoptosis, metastasis, tumor/stroma interaction and angiogenesis. We also review the clinical implications of Mafs, namely their potential possibilities and limitations as biomarkers and therapeutic targets in cancer.

Podocyte-specific Transcription Factors: Could MafB Become a Therapeutic Target for Kidney Disease?

The increasing number of patients with chronic kidney disease (CKD) is being recognized as an emerging global health problem. Recently, it has become clear that injury and loss of glomerular visceral epithelial cells, known as podocytes, is a common early event in many forms of CKD. Podocytes are highly specialized epithelial cells that cover the outer layer of the glomerular basement membrane. They serve as the final barrier to urinary protein loss through the formation and maintenance of specialized foot-processes and an interposed slit-diaphragm. We previously reported that the transcription factor MafB regulates the podocyte slit diaphragm protein production and transcription factor Tcf21. We showed that the forced expression of MafB was able to prevent CKD. In this review, we discuss recent advances and offer an updated overview of the functions of podocyte-specific transcription factors in kidney biology, aiming to present new perspectives on the progression of CKD and respective therapeutic strategies.

MafG-like contribute to copper and cadmium induced antioxidant response by regulating antioxidant enzyme in Procambarus clarkii

Avian musculoaponeurotic fibrosarcoma (Maf) proteins play an important role in Nrf2/Keap1 signaling pathway, which mainly resist the oxidant stress. The members of sMaf have a high homology basic leucine zipper (bZIP) and lack trans activation domain, and could interact with other transcriptional regulatory factors as a molecular chaperone. In this study, a full-length MafG-like gene was cloned from Procambarus Clarkii, designated as PcMafG-like, which consisted of an ORF length of 246 bp encoding 82 amino acids, a 5' untranslated region (UTR) of 483 bp, and a 3' UTR of 111 bp. The domain of PcMafG-like had a bZIP-Maf domain that binds to DNA. The cDNA sequence of PcMafG-like was 99 % similar to that of Penaeus vannamei. The mRNA of PcMafG-like was expressed in all tested tissues, and the highest expression was in muscle tissue. Under stimulation of Cu²⁺ and Cd²⁺, PcMafG-like was significantly up-regulated in hepatopancreas and gill, and the same result was testified by situ hybridization. The representative antioxidant genes, CAT, GPx and CZ-SOD, were significantly induced by Cu²⁺; CAT and GPx was induced by Cd²⁺. PcMafG-dsRNA significantly inhibited the expression of these up-regulated genes, but also inhibited the expression of other detected genes CZ-SOD, GST-θ and GST-1like. The antioxidant effect of PcMafG-like was further verified by oxidative stress markers (T-SOD, CuZnSOD, GPx, CAT, GSH and MDA) kits. Cu²⁺ and Cd²⁺ could induce the contents of these oxidative stress markers (MDA, GSH, CZ-SOD, CAT in Cu²⁺/Cd²⁺ treated group, and GSH-Px in Cd²⁺ group), while interference of PcMafG-like significantly inhibited the up-regulation. Furthermore, hematoxylin-eosin staining experiments showed that the degree of pathological damage was dose-dependent and time-dependent, and the pathological damage was more serious after dsRNA interfered with PcMafG-like. In addition, subcellular localization showed that PcMafG-like gene existed in nucleus. The recombinant protein PcMafG-like was expressed and purified in prokaryotic expression. The affinity analysis of promoter by agarose gel electrophoresis suggested that PcMafG-like could bind with CAT promoter in vitro. This indicated that PcMafG-like could activate antioxidant genes.

Genetic variation in chicken interferon signalling pathway genes in research lines showing differential viral resistance

Avian viruses of economic interest are a significant burden on the poultry industry, affecting production traits and resulting in mortality. Furthermore, the zoonosis of avian viruses risks pandemics developing in humans. Vaccination is the most common method of controlling viruses; however current vaccines often lack cross-protection against multiple strains of each virus. The mutagenicity of these viruses has also led to virulent strains emerging that can overcome the protection offered by vaccines. Breeding chickens with a more robust innate immune response may help in tackling current and emerging viruses. Understanding the genetic evolution of different lines will thus provide a useful tool in helping the host in the fight against pathogens. This study focuses on the interferon genes and their receptors in different chicken lines that are known to be more resistant or susceptible to particular avian viruses. Comparing genotypic differences in these core immune genes between the chicken lines may explain the phenotypic differences observed and aid the identification of causative variations. The relative resistance/susceptibility of each line to viruses of interest (Marek's disease virus, infectious bursal disease, infectious bronchitis virus and avian influenza virus) has previously been determined. Here we identify single nucleotide polymorphisms in interferons and downstream genes. Functional prediction tools were used to identify variants that may be affecting protein structure, mRNA secondary structure or transcription factor and micro-RNA binding sites. These variants were then considered in the context of the research lines and their distribution between phenotypes. We highlight 60 variants of interest in the interferon pathway genes that may account for susceptibility/resistance to viral pathogens.

Amino acid sensor GCN2 promotes SARS-CoV-2 receptor ACE2 expression in response to amino acid deprivation

Angiotensin-converting enzyme 2 (ACE2) has been identified as a primary receptor for severe acute respiratory syndrome coronaviruses 2 (SARS-CoV-2). Here, we investigated the expression regulation of ACE2 in enterocytes under amino acid deprivation conditions. In this study, we found that ACE2 expression was upregulated upon all or single essential amino acid deprivation in human colonic epithelial CCD841 cells. Furthermore, we found that knockdown of general control nonderepressible 2 (GCN2) reduced intestinal ACE2 mRNA and protein levels in vitro and in vivo. Consistently, we revealed two GCN2 inhibitors, GCN2iB and GCN2-IN-1, downregulated ACE2 protein expression in CCD841 cells. Moreover, we found that increased ACE2 expression in response to leucine deprivation was GCN2 dependent. Through RNA-sequencing analysis, we identified two transcription factors, MAFB and MAFF, positively regulated ACE2 expression under leucine deprivation in CCD841 cells. These findings demonstrate that amino acid deficiency increases ACE2 expression and thereby likely aggravates intestinal SARS-CoV-2 infection.

Amino acid deprivation increases ACE2 expression in the gut, potentially aggravating SARS-CoV-2 infection.

Targeting the oncogenic transcription factor c-Maf for the treatment of multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy derived from clonal expansion of plasma cells within the bone marrow and it may progress to the extramedullary region in late stage of the disease course. c-Maf, an oncogenic zipper leucine transcription factor, is overexpressed in more than 50% MM cell lines and primary species in association with chromosomal translocation, aberrant signaling transduction and modulation of stability. By triggering the transcription of critical genes including CCND2, ITGB7, CCR1, ARK5, c-Maf promotes MM progress, proliferation, survival and chemoresistance. Notably, c-Maf is usually expressed at the embryonic stage to promote cell differentiation but less expressed in healthy adult cells. c-Maf has long been proposed as a promising therapeutic target of MM and a panel of small molecule compounds have been identified to downregulate c-Maf and display potent anti-myeloma activities. In the current article, we take a concise summary on the advances in c-Maf biology, pathophysiology, and targeted drug discovery in the potential treatment of MM.

Mafa-dependent GABAergic activity promotes mouse neonatal apneas

While apneas are associated with multiple pathological and fatal conditions, the underlying molecular mechanisms remain elusive. We report that a mutated form of the transcription factor Mafa (Mafa^4A) that prevents phosphorylation of the Mafa protein leads to an abnormally high incidence of breath holding apneas and death in newborn Mafa^4A/4A mutant mice. This apneic breathing is phenocopied by restricting the mutation to central GABAergic inhibitory neurons and by activation of inhibitory Mafa neurons while reversed by inhibiting GABAergic transmission centrally. We find that Mafa activates the Gad2 promoter in vitro and that this activation is enhanced by the mutation that likely results in increased inhibitory drives onto target neurons. We also find that Mafa inhibitory neurons are absent from respiratory, sensory (primary and secondary) and pontine structures but are present in the vicinity of the hypoglossal motor nucleus including premotor neurons that innervate the geniohyoid muscle, to control upper airway patency. Altogether, our data reveal a role for Mafa phosphorylation in regulation of GABAergic drives and suggest a mechanism whereby reduced premotor drives to upper airway muscles may cause apneic breathing at birth.

Apneas are associated with many pathological conditions. Here, the authors show in a mouse model that stabilization of the transcription factor Mafa in brainstem GABAergic neurons may contribute to apnea, by decreasing motor drive to muscles controlling the airways.

MafA Regulation in β-Cells: From Transcriptional to Post-Translational Mechanisms

β-cells are insulin-producing cells in the pancreas that maintain euglycemic conditions. Pancreatic β-cell maturity and function are regulated by a variety of transcription factors that enable the adequate expression of the cellular machinery involved in nutrient sensing and commensurate insulin secretion. One of the key factors in this regulation is MAF bZIP transcription factor A (MafA). MafA expression is decreased in type 2 diabetes, contributing to β-cell dysfunction and disease progression. The molecular biology underlying MafA is complex, with numerous transcriptional and post-translational regulatory nodes. Understanding these complexities may uncover potential therapeutic targets to ameliorate β-cell dysfunction. This article will summarize the role of MafA in normal β-cell function and disease, with a special focus on known transcriptional and post-translational regulators of MafA expression.

c-MAF-dependent perivascular macrophages regulate diet-induced metabolic syndrome

[Figure: see text].

Deletion of Cdk5 in Macrophages Ameliorates Anti-Inflammatory Response during Endotoxemia through Induction of C-Maf and Il-10

Immune response control is critical as excessive cytokine production can be detrimental and damage the host. Interleukin-10 (Il-10), an anti-inflammatory cytokine produced primarily by macrophages, is a key regulator that counteracts and controls excessive inflammatory response. Il-10 expression is regulated through the transcription factor c-Maf. Another regulator of Il-10 production is p35, an activator of the cyclin-dependent kinase 5 (Cdk5), which decreases Il-10 production in macrophages, thus increasing inflammation. However, Cdk5 regulation of c-Maf and the involvement of Il-10 production in macrophages has not yet been investigated. We used in vitro primary bone marrow-derived macrophages (BMDMs) lacking Cdk5, stimulated them with lipopolysaccharid (LPS) and observed increased levels of c-Maf and Il-10. In an in vivo mouse model of LPS-induced endotoxemia, mice lacking Cdk5 in macrophages showed increased levels of c-Maf and elevated levels of Il-10 in lungs as well as in plasma, resulting in ameliorated survival. Taken together, we identified Cdk5 as a potential novel regulator of Il-10 production through c-Maf in macrophages under inflammatory conditions. Our results suggest that inhibition of Cdk5 enhances the c-Maf-Il-10 axis and thus potentiates improvement of anti-inflammatory therapy.

Loss of the MAF Transcription Factor in Laryngeal Squamous Cell Carcinoma

MAF is a transcription factor that may act either as a tumor suppressor or as an oncogene, depending on cell type. We have shown previously that the overexpressed miR-1290 influences MAF protein levels in LSCC (laryngeal squamous cell carcinoma) cell lines. In this study, we shed further light on the interaction between miR-1290 and MAF, as well as on cellular MAF protein localization in LSCC. We confirmed the direct interaction between miR-1290 and MAF 3′UTR by a dual-luciferase reporter assay. In addition, we used immunohistochemistry staining to analyze MAF protein distribution and observed loss of MAF nuclear expression in 58% LSCC samples, of which 10% showed complete absence of MAF, compared to nuclear and cytoplasmatic expression in 100% normal mucosa. Using TCGA data, bisulfite pyrosequencing and CNV analysis, we excluded the possibility that loss-of-function mutations, promoter region DNA methylation or CNV are responsible for MAF loss in LSCC. Finally, we identified genes involved in the regulation of apoptosis harboring the MAF binding motif in their promoter region by applied FIMO and DAVID GO analysis. Our results highlight the role of miR-1290 in suppressing MAF expression in LSCC. Furthermore, MAF loss or mislocalization in FFPE LSCC tumor samples might suggest that MAF acts as a LSCC tumor suppressor by regulating apoptosis.

The HIF target MAFF promotes tumor invasion and metastasis through IL11 and STAT3 signaling

Hypoxia plays a critical role in tumor progression including invasion and metastasis. To determine critical genes regulated by hypoxia that promote invasion and metastasis, we screen fifty hypoxia inducible genes for their effects on invasion. In this study, we identify v-maf musculoaponeurotic fibrosarcoma oncogene homolog F (MAFF) as a potent regulator of tumor invasion without affecting cell viability. MAFF expression is elevated in metastatic breast cancer patients and is specifically correlated with hypoxic tumors. Combined ChIP- and RNA-sequencing identifies IL11 as a direct transcriptional target of the heterodimer between MAFF and BACH1, which leads to activation of STAT3 signaling. Inhibition of IL11 results in similar levels of metastatic suppression as inhibition of MAFF. This study demonstrates the oncogenic role of MAFF as an activator of the IL11/STAT3 pathways in breast cancer.

Hypoxia plays a critical role in tumor progression including invasion and metastasis. Here, the authors screened several hypoxia inducible genes and identified the oncogenic role of MAFF in breast cancer metastasis and that it activates IL11/STAT3 pathway.

Radiation inducible MafB gene is required for thymic regeneration

The thymus facilitates mature T cell production by providing a suitable stromal microenvironment. This microenvironment is impaired by radiation and aging which lead to immune system disturbances known as thymic involution. Young adult thymus shows thymic recovery after such involution. Although various genes have been reported for thymocytes and thymic epithelial cells in such processes, the roles of stromal transcription factors in these remain incompletely understood. MafB (v-maf musculoaponeurotic fibrosarcoma oncogene homolog B) is a transcription factor expressed in thymic stroma and its expression was induced a day after radiation exposure. Hence, the roles of mesenchymal MafB in the process of thymic regeneration offers an intriguing research topic also for radiation biology. The current study investigated whether MafB plays roles in the adult thymus. MafB/green fluorescent protein knock-in mutant (MafB^+/GFP) mice showed impaired thymic regeneration after the sublethal irradiation, judged by reduced thymus size, total thymocyte number and medullary complexity. Furthermore, IL4 was induced after irradiation and such induction was reduced in mutant mice. The mutants also displayed signs of accelerated age-related thymic involution. Altogether, these results suggest possible functions of MafB in the processes of thymic recovery after irradiation, and maintenance during aging.

Functional analysis of large MAF transcription factors and elucidation of their relationships with human diseases

The large MAF transcription factor group is a group of transcription factors with an acidic region, a basic region, and a leucine zipper region. Four types of MAF, MAFA, MAFB, c-MAF, and NRL, have been identified in humans and mice. In order to elucidate the functions of the large MAF transcription factor group in vivo, our research group created genetically modified MAFA-, MAFB-, and c-MAF-deficient mice and analyzed their phenotypes. MAFA is expressed in pancreatic β cells and is essential for insulin transcription and secretion. MAFB is essential for the development of pancreatic endocrine cells, formation of inner ears, podocyte function in the kidneys, and functional differentiation of macrophages. c-MAF is essential for lens formation and osteoblast differentiation. Furthermore, a single-base mutation in genes encoding the large MAF transcription factor group causes congenital renal disease, eye disease, bone disease, diabetes, and tumors in humans. This review describes the functions of large MAF transcription factors in vivo and their relationships with human diseases.

Responsive Expression of MafF to β-Amyloid-Induced Oxidative Stress

The small musculoaponeurotic fibrosarcoma (sMaf) proteins MafF, MafG, and MafK are basic region leucine zipper- (bZIP-) type transcription factors and display tissue- or stimulus-specific expression patterns. As the oxidative stress reactive proteins, sMafs are implicated in various neurological disorders. In the present study, the expressions of sMafs were investigated across five databases gathering transcriptomic data from 74 Alzheimer's disease (AD) patients and 66 controls in the Gene Expression Omnibus (GEO) database. The expression of MafF was increased in the hippocampus of AD patients, which was negatively correlated with the expression of the glutamate cysteine ligase catalytic subunit (GCLC). Furthermore, MafF was significantly increased in patients with Braak stage V-VI, compared to those with Braak stage III-IV. β-Amyloid (Aβ), a strong inducer of oxidative stress, plays a crucial role in the pathogenesis of AD. The responsive expressions of sMafs to Aβ-induced oxidative stress were studied in the APP/PS1 mouse model of AD, Aβ intrahippocampal injection rats, and several human cell lines from different tissue origins. This study revealed that only the induction of MafF was accompanied with reduction of GCLC and glutathione (GSH). MafF knockdown suppressed the increase of GSH induced by Aβ. Among sMafs, MafF is the most responsive to Aβ-induced oxidative stress and might potentiate the inhibition of antioxidation. These results provide a better understanding of sMaf modulation in AD and highlight MafF as a potential therapeutic target in AD.

Transcription factor c-Maf is a checkpoint that programs macrophages in lung cancer

Macrophages have been linked to tumor initiation, progression, metastasis, and treatment resistance. However, the transcriptional regulation of macrophages driving the protumor function remains elusive. Here, we demonstrate that the transcription factor c-Maf is a critical controller for immunosuppressive macrophage polarization and function in cancer. c-Maf controls many M2-related genes and has direct binding sites within a conserved noncoding sequence of the Csf-1r gene and promotes M2-like macrophage-mediated T cell suppression and tumor progression. c-Maf also serves as a metabolic checkpoint regulating the TCA cycle and UDP-GlcNAc biosynthesis, thus promoting M2-like macrophage polarization and activation. Additionally, c-Maf is highly expressed in tumor-associated macrophages (TAMs) and regulates TAM immunosuppressive function. Deletion of c-Maf specifically in myeloid cells results in reduced tumor burden with enhanced antitumor T cell immunity. Inhibition of c-Maf partly overcomes resistance to anti-PD-1 therapy in a subcutaneous LLC tumor model. Similarly, c-Maf is expressed in human M2 and tumor-infiltrating macrophages/monocytes as well as circulating monocytes of human non-small cell lung carcinoma (NSCLC) patients and critically regulates their immunosuppressive activity. The natural compound β-glucan downregulates c-Maf expression on macrophages, leading to enhanced antitumor immunity in mice. These findings establish a paradigm for immunosuppressive macrophage polarization and transcriptional regulation by c-Maf and suggest that c-Maf is a potential target for effective tumor immunotherapy.

Inherited cataracts: molecular genetics, clinical features, disease mechanisms and novel therapeutic approaches

Cataract is the most common cause of blindness in the world; during infancy and early childhood, it frequently results in visual impairment. Congenital cataracts are phenotypically and genotypically heterogeneous and can occur in isolation or in association with other systemic disorders. Significant progress has been made in identifying the molecular genetic basis of cataract; 115 genes to date have been found to be associated with syndromic and non-syndromic cataract and 38 disease-causing genes have been identified to date to be associated with isolated cataract. In this review, we briefly discuss lens development and cataractogenesis, detail the variable cataract phenotypes and molecular mechanisms, including genotype-phenotype correlations, and explore future novel therapeutic avenues including cellular therapies and pharmacological treatments.

c-MAF, a Swiss Army Knife for Tolerance in Lymphocytes

Beyond its well-admitted role in development and organogenesis, it is now clear that the transcription factor c-Maf has owned its place in the realm of immune-related transcription factors. Formerly introduced solely as a Th2 transcription factor, the role attributed to c-Maf has gradually broadened over the years and has extended to most, if not all, known immune cell types. The influence of c-Maf is particularly prominent among T cell subsets, where c-Maf regulates the differentiation as well as the function of multiple subsets of CD4 and CD8 T cells, lending it a crucial position in adaptive immunity and anti-tumoral responsiveness. Recent research has also revealed the role of c-Maf in controlling Th17 responses in the intestine, positioning it as an essential factor in intestinal homeostasis. This review aims to present and discuss the recent advances highlighting the particular role played by c-Maf in T lymphocyte differentiation, function, and homeostasis.

Binding partners of NRF2: Functions and regulatory mechanisms

NRF2 is a redox-sensitive transcription factor that plays an important role in protecting organisms against diverse types of electrophiles or oxidants. The level of NRF2 is maintained low in normal cells, but highly elevated in cancer provoking chemoresistance or radioresistance. It is now recognized that NRF2 does not merely maintain the redox balance, but also plays significant roles in autophagy, apoptosis, cell cycle progression, and stem cell differentiation, all of which could be possibly attributable to the existence of multiple binding proteins. In the present manuscript, we summarize direct binding partners of NRF2 and illustrate how they bind to NRF2 and regulate its stability or activity.

Role of MafB in macrophages

The transcription factor MafB regulates macrophage differentiation. However, studies on the phenotype of Mafb-deficient macrophages are still limited. Recently, it was shown that the specific expression of MafB permits macrophages to be distinguished from dendritic cells. In addition, MafB has been reported to be involved in various diseases related to macrophages. Studies using macrophage-specific Mafb-deficient mice show that MafB is linked to atherosclerosis, autoimmunity, obesity, and ischemic stroke, all of which exhibit macrophage abnormality. Therefore, MafB is hypothesized to be indispensable for the regulation of macrophages to maintain systemic homeostasis and may serve as an innovative target for treating macrophage-related diseases.

Direct and Specific Functional Evaluation of the Nrf2 and MafG Heterodimer by Introducing a Tethered Dimer into Small Maf-Deficient Cells

A group of cytoprotective genes is regulated by heterodimers composed of the cap'n'collar (CNC) family member Nrf2 and one of the small Maf (sMaf) proteins (MafF, MafG, or MafK) through the antioxidant response element (ARE, also referred to as the CNC-sMaf binding element [CsMBE]). Many lines of evidence support this model; however, a direct and specific evaluation of the Nrf2-sMaf heterodimer remains to be executed. To address this issue, we constructed a tethered Nrf2-MafG (T-N2G) heterodimer using a flexible linker peptide. We then introduced the T-N2G construct into cells lacking all three sMaf proteins to specifically evaluate the function of the tethered heterodimer without interference from other endogenous CNC-sMaf heterodimers or sMaf homodimers. In response to an Nrf2 activator, diethyl maleate, the T-N2G protein can widely activate the target genes of Nrf2 but not those of Nrf1, such as proteasome subunit genes. Genome-wide binding analysis showed that the T-N2G protein preferentially bound to the CsMBE motifs in the regulatory regions of the Nrf2 target genes. These results provide direct evidence that the Nrf2-MafG heterodimer acts as a transcriptional activator of Nrf2-dependent genes and show that this assay system will be a powerful tool to specifically examine the function of other CNC-sMaf heterodimers.

Transcription factor MafB contributes to the activation of spinal microglia underlying neuropathic pain development

Microglia, which are pathological effectors and amplifiers in the central nervous system, undergo various forms of activation. A well-studied microglial-induced pathological paradigm, spinal microglial activation following peripheral nerve injury (PNI), is a key event for the development of neuropathic pain but the transcription factors contributing to microglial activation are less understood. Herein, we demonstrate that MafB, a dominant transcriptional regulator of mature microglia, is involved in the pathology of a mouse model of neuropathic pain. PNI caused a rapid and marked increase of MafB expression selectively in spinal microglia but not in neurons. We also found that the microRNA mir-152 in the spinal cord which targets MafB expression decreased after PNI, and intrathecal administration of mir-152 mimic suppressed the development of neuropathic pain. Reduced MafB expression using heterozygous Mafb deficient mice and by intrathecal administration of siRNA alleviated the development of PNI-induced mechanical hypersensitivity. Furthermore, we found that intrathecal transfer of Mafb deficient microglia did not induce mechanical hypersensitivity and that conditional Mafb knockout mice did not develop neuropathic pain after PNI. We propose that MafB is a key mediator of the PNI-induced phenotypic alteration of spinal microglia and neuropathic pain development.

The Basic Science of Dupuytren Disease

Dupuytren disease is a fibroproliferative condition affecting the hands of millions of patients worldwide. The hypothesis of pathogenesis involves genetic factors and internal factors. Recent genome-wide association studies have provided much needed evidence for the long-held belief of a strong genetic component to the pathogenesis of Dupuytren disease. Specifically, abnormal activation of the Wnt signaling pathway plays an important role. Regarding internal factors, microvascular angiopathy and ischemia have been shown to lead to activation of transforming growth factor-β1 and proliferation of myofibroblasts.

Antioxidant response elements: Discovery, classes, regulation and potential applications

Exposure to antioxidants and xenobiotics triggers the expression of a myriad of genes encoding antioxidant proteins, detoxifying enzymes, and xenobiotic transporters to offer protection against oxidative stress. This articulated universal mechanism is regulated through the cis-acting elements in an array of Nrf2 target genes called antioxidant response elements (AREs), which play a critical role in redox homeostasis. Though the Keap1/Nrf2/ARE system involves many players, AREs hold the key in transcriptional regulation of cytoprotective genes. ARE-mediated reporter constructs have been widely used, including xenobiotics profiling and Nrf2 activator screening. The complexity of AREs is brought by the presence of other regulatory elements within the AREs. The diversity in the ARE sequences not only bring regulatory selectivity of diverse transcription factors, but also confer functional complexity in the Keap1/Nrf2/ARE pathway. The different transcription factors either homodimerize or heterodimerize to bind the AREs. Depending on the nature of partners, they may activate or suppress the transcription. Attention is required for deeper mechanistic understanding of ARE-mediated gene regulation. The computational methods of identification and analysis of AREs are still in their infancy. Investigations are required to know whether epigenetics mechanism plays a role in the regulation of genes mediated through AREs. The polymorphisms in the AREs leading to oxidative stress related diseases are warranted. A thorough understanding of AREs will pave the way for the development of therapeutic agents against cancer, neurodegenerative, cardiovascular, metabolic and other diseases with oxidative stress.

The KEAP1-NRF2 System: a Thiol-Based Sensor-Effector Apparatus for Maintaining Redox Homeostasis

The Kelch-like ECH-associated protein 1-NF-E2-related factor 2 (KEAP1-NRF2) system forms the major node of cellular and organismal defense against oxidative and electrophilic stresses of both exogenous and endogenous origins. KEAP1 acts as a cysteine thiol-rich sensor of redox insults, whereas NRF2 is a transcription factor that robustly transduces chemical signals to regulate a battery of cytoprotective genes. KEAP1 represses NRF2 activity under quiescent conditions, whereas NRF2 is liberated from KEAP1-mediated repression on exposure to stresses. The rapid inducibility of a response based on a derepression mechanism is an important feature of the KEAP1-NRF2 system. Recent studies have unveiled the complexities of the functional contributions of the KEAP1-NRF2 system and defined its broader involvement in biological processes, including cell proliferation and differentiation, as well as cytoprotection. In this review, we describe historical milestones in the initial characterization of the KEAP1-NRF2 system and provide a comprehensive overview of the molecular mechanisms governing the functions of KEAP1 and NRF2, as well as their roles in physiology and pathology. We also refer to the clinical significance of the KEAP1-NRF2 system as an important prophylactic and therapeutic target for various diseases, particularly aging-related disorders. We believe that controlled harnessing of the KEAP1-NRF2 system is a key to healthy aging and well-being in humans.

MAFA missense mutation causes familial insulinomatosis and diabetes mellitus

We report a disease-causing mutation in the β-cell–enriched MAFA transcription factor. Strikingly, the missense p.Ser64Phe MAFA mutation was associated with either of two distinct phenotypes, multiple insulin-producing neuroendocrine tumors of the pancreas—a condition known as insulinomatosis—or diabetes mellitus, recapitulating the physiological properties of MAFA both as an oncogene and as a key islet β-cell transcription factor. The implication of MAFA in these human phenotypes will provide insights into how this transcription factor regulates human β-cell activity as well as into the mechanisms of Maf-induced tumorigenesis.

The β-cell–enriched MAFA transcription factor plays a central role in regulating glucose-stimulated insulin secretion while also demonstrating oncogenic transformation potential in vitro. No disease-causing MAFA variants have been previously described. We investigated a large pedigree with autosomal dominant inheritance of diabetes mellitus or insulinomatosis, an adult-onset condition of recurrent hyperinsulinemic hypoglycemia caused by multiple insulin-secreting neuroendocrine tumors of the pancreas. Using exome sequencing, we identified a missense MAFA mutation (p.Ser64Phe, c.191C>T) segregating with both phenotypes of insulinomatosis and diabetes. This mutation was also found in a second unrelated family with the same clinical phenotype, while no germline or somatic MAFA mutations were identified in nine patients with sporadic insulinomatosis. In the two families, insulinomatosis presented more frequently in females (eight females/two males) and diabetes more often in males (12 males/four females). Four patients from the index family, including two homozygotes, had a history of congenital cataract and/or glaucoma. The p.Ser64Phe mutation was found to impair phosphorylation within the transactivation domain of MAFA and profoundly increased MAFA protein stability under both high and low glucose concentrations in β-cell lines. In addition, the transactivation potential of p.Ser64Phe MAFA in β-cell lines was enhanced compared with wild-type MAFA. In summary, the p.Ser64Phe missense MAFA mutation leads to familial insulinomatosis or diabetes by impacting MAFA protein stability and transactivation ability. The human phenotypes associated with the p.Ser64Phe MAFA missense mutation reflect both the oncogenic capacity of MAFA and its key role in islet β-cell activity.

A common variant of MAF/c-MAF, transcriptional factor gene in the kidney, is associated with gout susceptibility

Gout is a multifactorial disease characterized by acute inflammatory arthritis, and it is caused as a consequence of hyperuricemia. A recent meta-analysis of genome-wide association studies has newly identified the relationship between serum uric acid (SUA) levels and rs889472, a single nucleotide polymorphism of musculoaponeurotic fibrosarcoma oncogene (MAF/c-MAF). However, it remained unclear whether rs889472 is associated with gout susceptibility. In the present study, we investigate the association between c-MAF rs889472 and gout in Japanese male population. We genotyped 625 male patients who were clinically diagnosed as gout and 1221 male control subjects without hyperuricemia or a history of gout by TaqMan method. As a result, the major allele (C), which reportedly increases SUA levels, had a higher frequency in the gout cases (58.8%) than in the controls (55.0%). A logistic regression analysis showed a significant association between rs889472 and gout (p = 0.029, odds ratio = 1.17; 95% confidence interval 1.02-1.34). C-MAF is reported as a pivotal transcriptional factor in the development and differentiation of renal proximal tubular cells. Because urate is mainly regulated in renal proximal tubular cells, c-MAF may have an important role in urate regulation in the kidney and influence not only SUA but also gout susceptibility. Our finding shows that rs889472 of c-MAF is associated with gout susceptibility.

Ectopic expression of the transcription factor MafB in basal keratinocytes induces hyperproliferation and perturbs epidermal homeostasis

Mammalian epidermis is composed of four morphologically and functionally distinct layers of keratinocytes. The innermost basal layer consists of proliferating self-renewing keratinocytes, which also undergo asymmetric cell division to differentiate into postmitotic suprabasal cells throughout life. Control of the balance between growth and differentiation of basal cells is important for epidermal homeostasis to prevent skin disorders including malignancies; however, the underlying mechanism remains to be elucidated. Recently, MafB was identified as one of the transcription factors that regulate epidermal keratinocyte differentiation. MafB is expressed in postmitotic differentiating keratinocytes, and epidermal differentiation is partially impaired in MafB-deficient mice. To further establish the roles of MafB in the epidermis in vivo, we generated mice transgenic for MafB under the control of the basal cell-specific keratin (Krt) 14 promoter. In the epidermis of transgenic mice at embryonic day 18.5, the number of proliferating Krt14-positive basal-like cells was increased, and the granular and cornified layers were thickened. Furthermore, these MafB transgenic mice developed papillomas spontaneously with age. Therefore, MafB promotes differentiation in postmitotic keratinocytes and simultaneously has potential to promote growth when ectopically expressed in undifferentiated basal keratinocytes.

IL-27 triggers IL-10 production in Th17 cells via a c-Maf/RORγt/Blimp-1 signal to promote the progression of endometriosis

Endometriosis is an estrogen-dependent inflammatory disease. The anti-inflammatory cytokine IL-10 is also increased in endometriosis. IL-10 production by Th17 cells is critical for limiting autoimmunity and inflammatory responses. However, the mechanism of inducing IL-10-producing Th17 cells is still largely unknown. The present study investigated the differentiation mechanism and role of IL-10-producing Th17 cells in endometriosis. Here, we report that IL-10⁺Th17 cells are significantly increased in the peritoneal fluid of women with endometriosis, along with an elevation of IL-27, IL-6 and TGF-β. Compared with peripheral CD4⁺ T cells, endometrial CD4⁺ T cells highly expressed IL-27 receptors, especially the ectopic endometrium. Under external (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) and local (estrogen, IL-6 and TGF-β) environmental regulation, IL-27 from macrophages and endometrial stromal cells (ESCs) induces IL-10 production in Th17 cells in vitro and in vivo. This process may be mediated through the interaction between c-musculoaponeurotic fibrosarconna (c-Maf) and retinoic acid-related orphan receptor gamma t (RORγt), and associated with the upregulation of downstream B lymphocyte-induced maturation protein-1 (Blimp-1). IL-10⁺Th17 cells, in turn, stimulate the proliferation and implantation of ectopic lesions and accelerate the progression of endometriosis. These results suggest that IL-27 is a pivotal regulator in endometriotic immune tolerance by triggering Th17 cells to produce IL-10 and promoting the rapid growth and implantation of ectopic lesions. This finding provides a scientific basis for potential therapeutic strategies aimed at preventing the development of endometriosis, especially for patients with high levels of IL-10⁺Th17 cells.

MAF protein mediates innate resistance to proteasome inhibition therapy in multiple myeloma

Multiple myeloma (MM) patients with the t(14;16) translocation have a poor prognosis, and unlike other molecular subgroups, their outcome has not improved with the introduction of bortezomib (Bzb). The mechanism underlying innate resistance of MM to Bzb is unknown. In the present study, we have investigated how MAF overexpression impacts resistance to proteasome inhibitor (PI) therapy (Bzb and carfilzomib). High levels of MAF protein were found in t(14;16) cell lines; cell lines from the t(4;14) subgroup had intermediate levels, whereas cell lines from the other subgroups had low levels. High expression of MAF protein in t(14;16) was associated with significantly higher PI half-maximum inhibitory concentration values compared with other molecular subgroups. PI exposure abrogated glycogen synthase kinase 3β (GSK3β)-mediated degradation of MAF protein, resulting in increased MAF protein stability and PI resistance. Subsequent studies using loss-of-function and gain-of-function models showed that silencing MAF led to increased sensitivity to PIs, enhanced apoptosis, and activation of caspase-3, -7, -8, -9, poly (ADP-ribose) polymerase, and lamin A/C. In contrast, overexpression of MAF resulted in increased resistance to PIs and reduced apoptosis. These results define the role of MAF and GSK3 in the resistance of t(14;16) MM to PIs and identifies a novel mechanism by which MAF protein levels are regulated by PIs, which in turn confers resistance to PIs.

BACH1, the master regulator gene: A novel candidate target for cancer therapy

BACH1 (BTB and CNC homology 1, basic leucine zipper transcription factor 1) is a transcriptional factor and a member of cap 'n' collar (CNC) and basic region leucine zipper factor family. In contrast to other bZIP family members, BACH1 appeared as a comparatively specific transcription factor. It acts as transcription regulator and is recognized as a recently hypoxia regulator and functions as an inducible repressor for the HO-1 gene in many human cell types in response to stress oxidative. In regard to studies lately, although, BACH1 has been related to the regulation of oxidative stress and heme oxidation, it has never been linked to invasion and metastasis. Recent studies have showed that BACH1 is involved in bone metastasis of breast cancer by up-regulating vital metastatic genes like CXCR4 and MMP1. This newly discovered aspect of BACH1 gene provides new insight into cancer progression study and stands on its master regulator role in metastasis process, raising the possibility of considering it as a potential target for cancer therapy.

Small Maf proteins (MafF, MafG, MafK): History, structure and function

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.

MafB promotes atherosclerosis by inhibiting foam-cell apoptosis

MafB is a transcription factor that induces myelomonocytic differentiation. However, the precise role of MafB in the pathogenic function of macrophages has never been clarified. Here we demonstrate that MafB promotes hyperlipidemic atherosclerosis by suppressing foam-cell apoptosis. Our data show that MafB is predominantly expressed in foam cells found within atherosclerotic lesions, where MafB mediates the oxidized LDL-activated LXR/RXR-induced expression of apoptosis inhibitor of macrophages (AIM). In the absence of MafB, activated LXR/RXR fails to induce the expression of AIM, a protein that is normally responsible for protecting macrophages from apoptosis; thus, Mafb-deficient macrophages are prone to apoptosis. Haematopoietic reconstitution with Mafb-deficient fetal liver cells in recipient LDL receptor-deficient hyperlipidemic mice revealed accelerated foam-cell apoptosis, which subsequently led to the attenuation of the early atherogenic lesion. These findings represent the first evidence that the macrophage-affiliated MafB transcription factor participates in the acceleration of atherogenesis.

Large Maf Transcription Factors: Cousins of AP-1 Proteins and Important Regulators of Cellular Differentiation

A large number of mammalian transcription factors possess the evolutionary conserved basic and leucine zipper domain (bZIP). The basic domain interacts with DNA while the leucine zipper facilitates homo- and hetero-dimerization. These factors can be grouped into at least seven families: AP-1, ATF/CREB, CNC, C/EBP, Maf, PAR, and virus-encoded bZIPs. Here, we focus on a group of four large Maf proteins: MafA, MafB, c-Maf, and NRL. They act as key regulators of terminal differentiation in many tissues such as bone, brain, kidney, lens, pancreas, and retina, as well as in blood. The DNA-binding mechanism of large Mafs involves cooperation between the basic domain and an adjacent ancillary DNA-binding domain. Many genes regulated by Mafs during cellular differentiation use functional interactions between the Pax/Maf, Sox/Maf, and Ets/Maf promoter and enhancer modules. The prime examples are crystallin genes in lens and glucagon and insulin in pancreas. Novel roles for large Mafs emerged from studying generations of MafA and MafB knockouts and analysis of combined phenotypes in double or triple null mice. In addition, studies of this group of factors in invertebrates revealed the evolutionarily conserved function of these genes in the development of multicellular organisms.

β-Cell-Specific Mafk Overexpression Impairs Pancreatic Endocrine Cell Development

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 β-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 β-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 β-cell proliferation. Gene expression analysis by quantitative RT-PCR revealed decreased levels of β-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 β-cell transcription factors likely due to compensatory mechanisms that might have been activated in response to the β-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 β-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.

Application of Mass Spectrometry Profiling to Establish Brusatol as an Inhibitor of Global Protein Synthesis

The KEAP1/Nrf2 pathway senses and responds to changes in intracellular oxidative stress. Mutations that result in constitutive activation of Nrf2 are present in several human tumors, especially non-small cell lung cancer. Therefore, compounds that inhibit Nrf2 activity might be beneficial in treating patients whose tumors show activation of this pathway. Recent reports suggest that the natural product brusatol can potently and selectively inhibit Nrf2 activity, resulting in cell cytotoxicity, and can be effectively combined with chemotherapeutic agents. Here, we analyzed the effects of brusatol on the cellular proteome in the KEAP1 mutant non-small cell lung cancer cell line A549. Brusatol was found to rapidly and potently decrease the expression of the majority of detected proteins, including Nrf2. The most dramatically decreased proteins are those that display a short half-life, like Nrf2. This effect was confirmed by restricting the analysis to newly synthesized proteins using a labeled methionine analogue. Moreover, brusatol increased the expression of multiple components of the ribosome, suggesting that it regulates the function of this macromolecular complex. Finally, we show that brusatol induces its potent cellular cytotoxicity effects on multiple cancer cell lines in a manner independent of KEAP1/Nrf2 activity and with a profile similar to the protein translation inhibitor silvestrol. In conclusion, our data show that the activity of brusatol is not restricted to Nrf2 but, rather, functions as a global protein synthesis inhibitor.

Regulation and function of the NFE2 transcription factor in hematopoietic and non-hematopoietic cells

The NFE2 transcription factor was identified over 25 years ago. The NFE2 protein forms heterodimers with small MAF proteins, and the resulting complex binds to regulatory elements in a large number of target genes. In contrast to other CNC transcription family members including NFE2L1 (NRF1), NFE2L2 (NRF2) and NFE2L3 (NRF3), which are widely expressed, earlier studies had suggested that the major sites of NFE2 expression are hematopoietic cells. Based on cell culture studies it was proposed that this protein acts as a critical regulator of globin gene expression. However, the knockout mouse model displayed only mild erythroid abnormalities, while the major phenotype was a defect in megakaryocyte biogenesis. Indeed, absence of NFE2 led to severely impaired platelet production. A series of recent data, also summarized here, shed new light on the various functional roles of NFE2 and the regulation of its activity. NFE2 is part of a complex regulatory network, including transcription factors such as GATA1 and RUNX1, controlling megakaryocytic and/or erythroid cell function. Surprisingly, it was recently found that NFE2 also has a role in non-hematopoietic tissues, such as the trophoblast, in which it is also expressed, as well as the bone, opening the door to new research areas for this transcription factor. Additional data showed that NFE2 function is controlled by a series of posttranslational modifications. Important strides have been made with respect to the clinical significance of NFE2, linking this transcription factor to hematological disorders such as polycythemias.

Role of large MAF transcription factors in the mouse endocrine pancreas

The members of the MAF family of transcription factors are homologs of v-Maf –the oncogenic component of the avian retrovirus AS42. The MAF family is subdivided into 2 groups, small and large MAFs. To elucidate the role of the large MAF transcription factors in the endocrine pancreas, we analyzed large MAF gene knockout mice. It has been shown that Mafa^−/− mice develop phenotypes including abnormal islet structure soon after birth. This study revealed that Ins1 and Ins2 transcripts and the protein contents were significantly reduced in Mafa^−/− mice at embryonic day 18.5. In addition, Mafa^−/−;Mafb^−/− mice contained less than 10% of the insulin transcript and protein of those of wild-type mice, suggesting that Mafa and Mafb cooperate to maintain insulin levels at the embryonic stage. On the other hand, the number of insulin-positive cells in Mafa^−/− mice was comparable to that of wild-type mice, and even under a Mafb-deficient background the number of insulin-positive cells was not decreased, suggesting that Mafb plays a dominant role in embryonic β-cell development. We also found that at 20 weeks of age Mafa^−/−;Mafb^+/− mice showed a higher fasting blood glucose level than single Mafa^−/− mice. In summary, our results indicate that Mafa is necessary for the maintenance of normal insulin levels even in embryos and that Mafb is important for the maintenance of fasting blood glucose levels in the Mafa-deficient background in adults.

Transcriptional factors, Mafs and their biological roles

The Maf family of transcription factors is characterized by a typical bZip structure; these transcription factors act as important regulators of the development and differentiation of many organs and tissues, including the kidney. The Maf family consists of two subgroups that are characterized according to their structure: large Maf transcription factors and small Maf transcription factors. The large Maf subgroup consists of four proteins, designated as MAFA, MAFB, c-MAF and neural retina-specific leucine zipper. In particular, MAFA is a distinct molecule that has been attracting the attention of researchers because it acts as a strong transactivator of insulin, suggesting that Maf transcription factors are likely to be involved in systemic energy homeostasis. In this review, we focused on the regulation of glucose/energy balance by Maf transcription factors in various organs.