Molecular characterization and localization of the human MAFG gene

Mendelian randomization analysis of plasma proteins reveals potential novel tumor markers for gastric cancer

This study aimed to elucidate the potential causal relationship between 4,907 plasma proteins and the risk of gastric cancer using a two-sample Mendelian randomization approach. We utilized genome-wide association study (GWAS) data to perform two-sample Mendelian randomization analyses, treating the 4,907 plasma proteins as exposure factors and gastric cancer as the outcome. Instrumental variables for plasma proteins were selected based on strongly correlated SNPs identified through data processing and screening of the GWAS data provided by the deCode database. We employed a set of statistical methods centered on inverse variance weighting (IVW) for Mendelian randomization analysis to estimate the odds ratios (ORs) for the effects of these plasma proteins on gastric cancer susceptibility. According to the IVW method, 14 plasma proteins were associated with gastric cancer (p < 0.005). Specifically, CHST15 (OR = 0.7553, 95% CI = 0.6346 - 0.8988), L1CAM (OR = 0.7230, 95% CI = 0.5876 - 0.8896), FTMT (OR = 0.8246, 95% CI = 0.7241 - 0.9391), and PMM2 (OR = 0.5767, 95% CI = 0.3943 - 0.8433) were negatively correlated with GASTRIC CANCER, whereas ABO (OR = 1.1868, 95% CI = 1.0638 - 1.3240), FAM3D (OR = 1.2109, 95% CI = 1.0850 - 1.3515), FAM3B (OR = 1.2988, 95% CI = 1.0953 - 1.5402), ADH7 (OR = 1.3568, 95% CI = 1.1044 - 1.6670), MAP1LC3A (OR = 1.3704, 95% CI = 1.1194 - 1.6778), PGLYRP1 (OR = 1.4071, 95% CI = 1.1235 - 1.7623), PDE5A (OR = 1.7446, 95% CI = 1.2693 - 2.3978), GLUL (OR = 3.1203, 95% CI = 1.5017 - 6.4839), NFE2L1 (OR = 3.1759, 95% CI = 1.6163 - 6.2402), and MAFG (OR = 3.1945, 95% CI = 1.5329 - 6.6575) were positively correlated. Convergent results from Weighted Median and MR-Egger analyses confirmed these associations. Reverse Mendelian randomization analysis indicated that gastric cancer does not significantly alter the levels of these 14 plasma proteins (p > 0.05). Sensitivity analyses, including assessments of heterogeneity and horizontal pleiotropy, confirmed the robustness and reliability of our findings without significant bias. Pathway enrichment analysis of gene expression associated with these 14 plasma proteins, using GO and KEGG pathways, revealed that CHST15, L1CAM, FTMT, and PMM2 may serve as protective factors against gastric cancer, while ABO, FAM3D, FAM3B, ADH7, MAP1LC3A, PGLYRP1, PDE5A, GLUL, NFE2L1, and MAFG may contribute to gastric cancer pathogenesis. These results highlight the complex biological interactions between plasma proteins and tumorigenesis, providing valuable insights for preventive and therapeutic strategies in gastric malignancy management.

The small MAF transcription factors MAFF, MAFG and MAFK: current knowledge and perspectives

The small MAFs, MAFF, MAFG and MAFK have emerged as crucial regulators of mammalian gene expression. Previous studies have linked small MAF function, by virtue of their heterodimerization with the Cap 'n' Collar (CNC) family of transcription factors, to the stress response and detoxification pathways. Recent analyses have revealed a complex regulatory network involving small MAF transcription factors and other cellular proteins. The expression and activity of small MAFs are tightly regulated at multiple levels. With regard to their clinical importance, small MAFs have been linked to various diseases, such as diabetes, neuronal disorders, thrombocytopenia and carcinogenesis. A better understanding of the molecular mechanisms governing the activity of small MAFs will provide novel insights into the control of mammalian transcription and may lead to the development of novel therapeutic strategies to treat common human disorders.

Abnormal differentiation of erythroid precursors in p45 NF-E2(-/-) mice

The transcription factor p45 nuclear factor-erythroid-derived 2 (NF-E2) plays major roles in erythroid and megakaryocytic lineages. Here, we investigated the role of p45 NF-E2 in erythroid differentiation in vivo. Absence of p45 NF-E2 in mice leads to a twofold increase in serum erythropoietin levels. In the bone marrow of these animals, we found a different distribution of precursor populations compared to wild-type mice, suggesting abnormal differentiation. Loss of p45 NF-E2 was also associated with an increase in splenic erythropoiesis, as evidenced by an accumulation of early precursors, namely, late basophilic and polychromatic erythroblasts. These observations are consistent with a stress erythropoiesis phenotype and indicate that the spleen is likely compensating for ineffective erythropoiesis in the bone marrow. Analysis of bone marrow samples revealed increased GATA1 levels, as well as an increased proportion of erythroid cells arrested at the G(1) stage of cell cycle in p45 NF-E2-deficient mice. These results suggest that p45 NF-E2 is required for the differentiation of erythroid precursors.

Small Maf proteins in mammalian gene control: mere dimerization partners or dynamic transcriptional regulators?

The small Maf basic leucine zipper (bZIP) proteins MafF, MafG and MafK, while modest in size, have emerged as crucial regulators of mammalian gene expression. Intriguingly, small Mafs do not contain an obvious transcriptional activation domain. However, previously perceived as "mere" partner molecules conferring DNA binding specificity to complexes with larger bZIP proteins, such as the CNC family member Nrf2, it has become clear that small Maf proteins are essential and dynamically regulated transcription factors. Current data suggest stringent control of small Maf protein function through transcriptional and post-translational mechanisms. Initial gene targeting experiments revealed considerable functional redundancy among small Maf proteins in vivo. This was not unexpected, due to the high level of homology among the three small Mafs. Nevertheless, further studies showed that these transcription factors have critical roles in various cellular processes, including stress signaling, hematopoiesis, CNS function and oncogenesis. Recent data provide a possible link between small Maf-mediated transcription and the inflammatory response.

Heme Positively Regulates the Expression of β-Globin at the Locus Control Region via the Transcriptional Factor Bach1 in Erythroid Cells

The transcription factor Bach1 heterodimerizes with small Maf proteins to repress Maf recognition element (MARE)-dependent gene expression. The repressor activity of Bach1 is inhibited by the direct binding of heme. To investigate the involvement of Bach1 in the heme-dependent regulation of the expression of the beta-globin gene, mouse erythroleukemia (MEL) cells were cultured with succinylacetone (SA), a specific inhibitor of heme biosynthesis, and the level of beta-globin mRNA was examined. A marked decrease of beta-globin mRNA in SA-treated cells was observed, and this decrease was reversed by the addition of hemin. An iron chelator, desferrioxamine, also lowered the level of beta-globin mRNA. The heme-dependent expression of beta-globin is a transcriptional event since the expression of the human beta-globin gene promoter-reporter gene containing the microlocus control region (microLCR) was inhibited when human erythroleukemia K562 cells and MEL cells were cultured with SA. Hemin treatment restored the decrease in promoter activity caused by SA. The control of the microLCR-beta-globin promoter reporter gene by heme was dependent on DNase I-hypersensitive site 2 (HS2), which contains MARE. The MARE binding activity of Bach1 in K562 and MEL cells increased upon SA treatment, and the increase was diminished by the treatment with hemin. Transient expression of Bach1 suppressed the microLCR activity, and this repressor activity was cancelled by treatment with hemin. The expression of a mutated Bach1 lacking heme-binding sites led to a loss in the heme responsiveness of the microLCR. Furthermore, chromatin immunoprecipitation experiments revealed that Bach1 bound to the MARE of HS2 increased by the treatment of MEL cells with SA, and this was cancelled by hemin. We propose that heme positively regulates the beta-globin gene expression by blocking the interaction of Bach1 with the MARE in the LCR.

Chromatin structure and control of beta-like globin gene switching

The human beta-globin locus is a complex genetic system widely used for analysis of eukaryotic gene expression. The locus consists of five functional beta-like globin genes, epsilon, (G)gamma, (A)gamma, delta, and beta, arrayed on the chromosome in the order that they are expressed during ontogeny. Globin gene expression is regulated, in part, by the locus control region, which physically consists of five DNaseI-hypersensitive sites located 6-22 Kb upstream of the epsilon -globin gene. During ontogeny two switches occur in beta-globin gene expression that reflect the changing oxygen requirements of the fetus. The first switch from embryonic epsilon - to fetal gamma-globin occurs at six weeks of gestation. The second switch from gamma- to adult delta- and beta-globin occurs shortly after birth. Throughout the locus, cis-acting elements exist that are dynamically bound by trans-acting proteins, including transcription factors, co-activators, repressors, and chromatin modifiers. Discovery of novel erythroid-specific transcription factors and a role for chromatin structure in gene expression have enhanced our understanding of the mechanism of globin gene switching. However, the hierarchy of events regulating gene expression during development, from extracellular signaling to transcriptional activation or repression, is complex. In this review we attempt to unify the current knowledge regarding the interplay of cis-acting elements, transcription factors, and chromatin modifiers into a comprehensive overview of globin gene switching.

Characterization of a 500 kb region on 17q25 and the exclusion of candidate genes as the familial Tylosis Oesophageal Cancer (TOC) locus

The locus for a syndrome of focal palmoplantar keratoderma (Tylosis) associated with squamous cell oesophageal cancer (TOC) has been mapped to chromosome 17q25, a region frequently deleted in sporadic squamous cell oesophageal tumours. Further haplotype analysis described here, based on revised maps of marker order, has reduced the TOC minimal region to a genetic interval of 2 cM limited by the microsatellite markers D17S785 and D17S751. Partial sequence data and complete physical maps estimate the actual size of this region to be only 0.5 Mb. This analysis allowed the exclusion of proposed candidate tumour suppressor genes including MLL septin-like fusion (MSF), survivin, and deleted in multiple human cancer (DMC1). Computer analysis of sequence data from the minimal region identified 13 candidate genes and the presence of 50-70 other 'gene fragments' as ESTs and/or predicted exons and genes. Ten of the characterized genes were assayed for mutations but no disease-specific alterations were identified in the coding and promoter sequences. This region of chromosome 17q25 is, therefore, relatively gene-rich, containing 13 known and possibly as many as 50 predicted genes. Further mutation analysis of these predicted genes, and others possibly residing in the region, is required in order to identify the elusive TOC locus.

Activation of beta-major globin gene transcription is associated with recruitment of NF-E2 to the beta-globin LCR and gene promoter

The mouse beta-globin gene locus control region (LCR), located upstream of the beta-globin gene cluster, is essential for the activated transcription of genes in the cluster. The LCR contains multiple binding sites for transactivators, including Maf-recognition elements (MAREs). However, little is known about the specific proteins that bind to these sites or the time at which they bind during erythroid differentiation. We have performed chromatin immunoprecipitation experiments to determine the recruitment of the erythroid-specific transactivator p45 NF-E2/MafK (p18 NF-E2) heterodimer and small Maf proteins to various regions in the globin gene locus before and after the induction of murine erythroleukemia (MEL) cell differentiation. We report that, before induction, the LCR is occupied by small Maf proteins, and, on erythroid maturation, the NF-E2 complex is recruited to the LCR and the active globin promoters, even though the promoters do not contain MAREs. This differentiation-coupled recruitment of NF-E2 complex correlates with a greater than 100-fold increase in beta-major globin transcription, but is not associated with a significant change in locus-wide histone H3 acetylation. These findings suggest that the beta-globin gene locus exists in a constitutively open chromatin conformation before terminal differentiation, and we speculate that recruitment of NF-E2 complex to the LCR and active promoters may be a rate-limiting step in the activation of beta-globin gene expression.

The Maf transcription factors: regulators of differentiation

Since the identification of the v-maf oncogene in an avian tumor virus, the Maf protein family has grown rapidly, forming a unique subclass of basic-leucine zipper transcription (bZIP) factors. Maf family members appear to play important roles in the regulation of differentiation.