Regulation of human Fc epsilon RI alpha-chain gene expression by multiple transcription factors

GATA-1 is required for expression of Fc{epsilon}RI on mast cells: analysis of mast cells derived from GATA-1 knockdown mouse bone marrow

The high-affinity receptor for IgE (FcepsilonRI) that is expressed on the surface of mast cells plays an important role in antigen/IgE-mediated allergic reactions. We have previously found that critical elements in the promoter of the FcepsilonRI alpha- and beta-chain genes are recognized by the transcription factor GATA-1 in electrophoretic mobility shift assays coupled with a transient expression system for the alpha- and beta-chain promoters. To confirm that GATA-1 is involved in the expression of FcepsilonRI definitively, we generated bone marrow-derived mast cells from GATA-1 knockdown (KD) heterozygous mice. FACS analysis showed that the frequency of FcepsilonRI-positive cells was significantly decreased in mast cells derived from bone marrow of GATA-1 KD mice. Reverse transcription-PCR analysis showed that the level of transcripts not only for GATA-1 but also for both the alpha- and beta-chains was significantly lower in KD mast cells, whereas that of the FcepsilonRI gamma-chain was not affected. Degranulation caused by cross-linking of FcepsilonRI on mast cells prepared from KD mice was markedly repressed in comparison with that of wild-type mast cells. We concluded that the transcription factor GATA-1 positively regulates FcepsilonRI alpha- and beta-chain expression and therefore is involved in mast cell development.

Analysis of PU.1/ICSBP (IRF-8) complex formation with various PU.1 mutants: molecular cloning of rat Icsbp (Irf-8) cDNA

We isolated cDNA encoding a full-length Interferon (IFN) consensus sequence binding protein [Icsbp; also called IFN regulatory factor-8 (Irf-8)] from rat and analyzed interaction between ICSBP and PU.1, an Ets-family transcription factor regulating hematopoietic cell-specific promoters. Electrophoretic mobility shift assay indicated that PU.1 with deletion of the PEST domain could not bind to ICSBP, although loss of the PEST domain had no effect on DNA-binding ability of PU.1 itself. An amino-acid replacement of Ser147 by Ala of the PEST domain of PU.1 did not affect DNA-binding ability of PU.1 to form a binary complex, PU.1/DNA, but clearly decreased the ternary complex formation of PU.1/ICSBP/DNA. Phosphatase treatment of the ternary complex markedly decreased PU.1/ICSBP/DNA-complex formation. These results indicated that Ser147 of PU.1 is definitively required for forming a complex with ICSBP and phosphorylation of PU.1 and/or ICSBP is critical for formation of the ternary complex.

Mast cells acquire monocyte-specific gene expression and monocyte-like morphology by overproduction of PU.1

PU.1 is a myeloid- and lymphoid-specific transcription factor that belongs to the Ets family. Recently, we found that overproduction of PU.1 in mouse bone marrow-derived hemopoietic progenitor cells induced monocyte-specific gene expression and caused their monocyte-like morphological change. In the present study, PU.1 was overproduced by using retrovirus expression system in differentiated bone marrow-derived mast cells. By overexpression of PU.1, cell surface expression of MHC class II, CD11b, CD11c, and F4/80 was induced, accompanied by reduced expression of c-kit, a mast cell-specific marker. Morphology of PU.1-transfected cells was altered toward monocyte-like one. PU.1-overproducing cells acquired T cell stimulatory ability and showed an increase in response to LPS stimulation, while response through FcepsilonRI was markedly reduced by overproduction of PU.1. These results suggest that the differentiated mast cells still have potential to display monocytic features. When PU.1 was overproduced in a different type of mast cell, peritoneal mast cells, similar monocyte-like morphological change, and the expression of CD11b and F4/80 were induced. However, surface level of CD11c and MHC class II was not affected. These results indicate that the potential capacity to exhibit monocytic features is different between both the mast cells.

Polymorphisms in the FcεRIβ Promoter Region Affecting Transcription Activity: A Possible Promoter-Dependent Mechanism for Association between FcεRIβ and Atopy

The beta subunit of the high-affinity IgE receptor (FcepsilonRI) plays an important role in IgE-mediated allergic reactions as an amplifier for cell surface expression and signal transduction of FcepsilonRI. FcepsilonRIbeta is presumed to be one of the genes linked with atopic diseases. However, the validity of the associations previously found between single nucleotide polymorphisms (SNPs) in FcepsilonRIbeta and atopic diseases is questionable. In the present study, we found correlation between the SNP of FcepsilonRIbeta at +6960A/G, resulting in a Glu237Gly amino acid substitution, and the cell surface expression level of FcepsilonRI on blood basophils, although it has been shown that the Glu237Gly mutation itself does not affect the surface expression or function of FcepsilonRI. We additionally found four SNPs in the promoter region of FcepsilonRIbeta, among which -426T/C and -654C/T were tightly linked with +6960A/G. Reporter plasmids carrying the -426C and -654T promoter displayed higher transcriptional activity than those carrying the -426T and -654C promoter. We found that transcription factor YY1 preferentially bound and transactivated the -654T promoter. Furthermore, expression of FcepsilonRI beta-chain mRNA in basophils from individuals who have the minor heterozygous genotype was significantly higher than that of the major homozygous genotype. These results suggest that the SNPs in the FcepsilonRIbeta promoter are causally linked with atopy via regulation of FcepsilonRI expression.

Evidence against requirement of Ser41 and Ser45 for function of PU.1 -- molecular cloning of rat PU.1

The transcription factor PU.1 plays an important role in the development of the myeloid and lymphoid lineages and regulates the transcription of several genes expressed in these cells. Ser41 is conserved in the acidic region (33-47) of PU.1 from a variety of eukaryocytes and has been reported to be one of the two important Ser residues (S41 and S45) for the function of PU.1. In the present study, however, we found that rat PU.1 has Gly at position 41. To elucidate the role of amino acid residues at 41 and 45 in functions of PU.1, we generated mutants of rat PU.1, G41S, G41A, and S45A, and analyzed their transcription-enhancing activities by using two different systems, transient reporter assay system and retroviral transfection system. The amino acid substitution at 41 of PU.1 causes no effect on both transcription-enhancing activity for M-CSF receptor promoter and the cooperative transcription-enhancing activity with GATA-1 for FcRI alpha-chain promoter. Furthermore, the substitution at 41 also had no effect on the activity to induce monocyte-specific gene expression in the bone marrow-derived hematopoietic cells. From these results, we conclude that Ser41 as well as Ser45 are not essential for the promoter-upregulating function of PU.1.

A Promoter Haplotype of the Immunoreceptor Tyrosine-Based Inhibitory Motif-Bearing FcγRIIb Alters Receptor Expression and Associates with Autoimmunity. II. Differential Binding of GATA4 and Yin-Yang1 Transcription Factors and Correlated Receptor Expression and Function

The immunoreceptor tyrosine-based inhibitory motif-containing FcgammaRIIb modulates immune function on multiple cell types including B cells, monocytes/macrophages, and dendritic cells. The promoter for the human FCGR2B is polymorphic, and the less frequent 2B.4 promoter haplotype is associated with the autoimmune phenotype of systemic lupus erythematosus. In the present study, we demonstrate that the 2B.4 promoter haplotype of FCGR2B has increased binding capacity for GATA4 and Yin-Yang1 (YY1) transcription factors in both B lymphocytes and monocytes, and that overexpression of GATA4 or YY1 enhances the FCGR2B promoter activity. The 2B.4 haplotype leads to elevated expression of the endogenous receptor in heterozygous donors by approximately 1.5-fold as assessed on EBV-transformed cells, primary B lymphocytes, and CD14(+) monocytes. This increased expression accentuates the inhibitory effect of FcgammaRIIb on B cell Ag receptor signaling, measured by Ca(2+) influx and cell viability in B cells. Our results indicate that transcription factors GATA4 and YY1 are involved in the regulation of FcgammaRIIb expression, and that the expression variants of FcgammaRIIb lead to altered cell signaling, which may contribute to autoimmune pathogenesis in humans.

Functional analysis of PU.1 domains in monocyte-specific gene regulation

The Ets family transcription factor PU.1 is required for the development of various lymphoid and myeloid cell lineages, and regulates the expression of several genes in a cell type-specific manner. Recently we found that overproduction of PU.1 in mouse bone marrow-derived mast cell progenitors induced the expression of monocyte-specific genes. This prompted us to analyze the functions of each domain of PU.1 in monocyte-specific gene expression, using transfection of mast cell progenitors with a series of retrovirus vectors for overexpression of various truncation mutants. Both the acidic region and the Ets domain of PU.1 were required for expression of monocyte-specific genes, and for enhanced interleukin-6 production in response to lipopolysaccharide. The Gln-rich region was suggested to be involved in expression of both MHC class II and F4/80. On the other hand, when PU.1 protein lacking the PEST domain was produced in the progenitor cells, expression of monocyte-specific genes was substantially enhanced, suggesting that the PEST domain plays a negative role in monocyte-specific gene expression.

Overproduction of PU.1 in mast cell progenitors: its effect on monocyte- and mast cell-specific gene expression

The Ets family transcription factor PU.1 is required for development of various lymphoid and myeloid cell lineages, and regulates the expression of several genes in a cell type-specific manner. Mouse bone marrow-derived hematopoietic progenitor cells are programmed to differentiate into mast cells, when the cells are maintained in the presence of pokeweed mitogen-stimulated spleen-conditioned medium. However, by retroviral introduction of PU.1 cDNA, the progenitor cells expressed MHC class II, CD11b, CD11c, and F4/80, and acquired the ability to stimulate T cells. Furthermore, PU.1-overproducing cells exhibited the morphology, in part, similar to that of monocyte. These results indicate that the mast cell progenitors still have the ability to express monocyte-specific genes by increased expression of PU.1.

A novel -66T/C polymorphism in Fc epsilon RI alpha-chain promoter affecting the transcription activity: possible relationship to allergic diseases

We found a novel polymorphism, -66T/C, in the promoter region of human FcepsilonRIalpha, the specific component of the high affinity receptor for IgE (FcepsilonRI), which is essential for the cell surface expression of FcepsilonRI and the binding of IgE Ab. When the effect of the single nucleotide replacement on the promoter function was analyzed, the transcription activity of the T allele promoter was found to be higher than that of the C allele promoter, and was markedly up-regulated by the overexpression of GATA-1 when compared with the C allele promoter. This is probably because the promoter with T at -66 has an additional GATA-1-binding motif in the region, which may assure higher affinity of the transcription factor to the promoter. In accordance with this, EMSA actually indicated that GATA-1 bound to the T allele probe (-80/-59) with the affinity higher than that to the C allele probe. Statistical analysis suggested that a significant portion of nonallergic individuals has heterozygous -66T/C genotype, while most of allergic individuals have homozygous -66T/T genotype in Japanese population. Our findings for the first time demonstrate the presence of FcepsilonRIalpha polymorphism related to the allergic diseases.

Regulation of the human Fc epsilon RI alpha-chain distal promoter

The alpha-chain of the high affinity receptor for IgE (Fc epsilon RI) is essential for cell surface expression of Fc epsilon RI and binding of the IgE Ab. The human alpha-chain gene possesses two promoters: the proximal promoter, which is highly conserved with that of rodent; and the distal promoter, the structure and role of which are largely unknown. Transcriptional regulation of the alpha-chain distal promoter was investigated in this study. Transient reporter assay revealed critical region for transcription activity located within -27/-17. EMSA identified Elf-1, YY1, and PU.1 as transcription factors binding to this region. In contrast to the proximal promoter, which was trans-activated by YY1 and PU.1, these transcription factors exhibited repressive function on this promoter. Addition of IL-4 caused a marked increase in transcription from the distal promoter and subsequently increased the intracellular production of the alpha-chain. These results indicate that IL-4-dependent up-regulation of the human alpha-chain was due to enhancement of distal promoter activity and suggests that the two promoters have different regulatory mechanisms for alpha-chain expression.

Molecular cloning of rat transcription factor YY1

YY1 is a ubiquitously expressed multifunctional transcription factor that is involved in both positive and negative regulation of gene expression as well as initiation of transcription. Here, we isolated cDNA encoding a full-length open reading frame (ORF) of rat YY1. Rat YY1 is composed of 411 amino acid residues and its amino acid sequence is 97.6% identical to that of mouse YY1 and 97.8% identical to that of human YY1. The transactivating abilities of wild-type rat YY1 and four truncated mutant forms of YY1 were examined by transient reporter assays. When residues 114-193, which sequence includes a portion of the activation region and most of the Gly/Lys-rich region, were lacking, transactivation activity decreased somewhat, but the further deletion in the activation region (of residues 56-113) did not cause further decrease of the activity. On the other hand, N-terminus of the activation region (1-78/100-106) did not have transactivation activity by itself as well as synergistic activity with an erythroid specific transcription factor GATA-1.

Regulation of cell type-specific mouse Fc epsilon RI beta-chain gene expression by GATA-1 via four GATA motifs in the promoter

The FcR beta-chain, a subunit of two related multisubunit receptor complexes, the FcepsilonRI and FcgammaRIII, amplifies the mast cell response and is necessary for the cell surface expression of FcepsilonRI in mouse. The transient reporter assay indicated that -69/+4 region is required for cell type-specific transcriptional regulation of mouse beta-chain gene. EMSA using Abs against transcription factors or competitive oligonucleotides demonstrated that -58/-40 region (containing overlapping three GATA-1 sites, -53/-48, -46/-51, and -42/-47) and -31/-26 region (containing one GATA-1 site) are recognized by GATA-1. The promoter activity of beta-chain was decreased by nucleotide replacements of the GATA-1 sites in mouse mast cell line PT18. Furthermore, exogenously produced GATA-1 up-regulated the promoter activity in CV-1 cells, which are negative in the beta-chain production and the up-regulation was apparently suppressed by GATA-1 site mutations. These results indicate that cell type-specific transcription of mouse beta-chain gene is regulated by GATA-1.

Transcriptional regulation of the human high affinity IgE receptor alpha-chain gene

Transcriptional regulation of the gene encoding human high affinity IgE receptor (Fc epsilon RI) alpha-chain was analyzed. Previously, we reported that GATA-1 and Elf-1 recognition sites were necessary for cell type-specific activation of the alpha-chain gene promoter. More detailed analysis revealed that other transcription factors bound the regions close to the Elf-1 recognition site and there was a more complex mechanism for the regulation of the promoter activity. On the other hand, during a course of studies to find cis-elements over this gene, CAGCTG sequence in the first intron was revealed to serve as an enhancer. A complex composed of USF1 and USF2 activated the human alpha-chain gene expression via this intronic element. Furthermore, we found two novel exons at 18.4 and 12.6kb upstream from the reported first exon and discovered an additional distal promoter.