Engineering of the major house dust mite allergen Der f 2 for allergen-specific immunotherapy

A major problem with allergen-specific immunotherapy involving repeated injection of allergens is the risk of an anaphylactic reaction. We engineered the major house dust mite allergen, Der f 2, to reduce its capacity to induce skin test reactivity and histamine release from peripheral blood basophils in allergic patients. The engineered allergen, in which the disulfide bond that linked the N- and C-terminal sequences of Der f 2 was disrupted, retained T-cell epitopes essential for immunotherapy and ability to stimulate T-cell proliferation. Such engineered allergens are potentially useful for safer and more effective immunotherapy for allergies.

Taking control over control: use of product sensing in single cells to remove flux control at key enzymes in biosynthesis pathways

Enzymes initiating the biosynthesis of cellular building blocks are frequently inhibited by the end-product of the respective pathway. Here we present an approach to rapidly generate sets of enzymes overriding this control. It is based on the in vivo detection of the desired end-product in single cells using a genetically encoded sensor. The sensor transmits intracellular product concentrations into a graded optical output, thus enabling ultrahigh-throughput screens by FACS. We randomly mutagenized plasmid-encoded ArgB of Corynebacterium glutamicum and screened the library in a strain carrying the sensor pSenLys-Spc, which detects l-lysine, l-arginine and l-histidine. Six of the resulting N-acetyl-l-glutamate kinase proteins were further developed and characterized and found to be at least 20-fold less sensitive toward l-arginine inhibition than the wild-type enzyme. Overexpression of the mutein ArgB-K47H-V65A in C. glutamicumΔargR led to the accumulation of 34 mM l-arginine in the culture medium. We also screened mutant libraries of lysC-encoded aspartate kinase and hisG-encoded ATP phosphoribosyltransferase. We isolated 11 LysC muteins, enabling up to 45 mM l-lysine accumulation, and 13 HisG muteins, enabling up to 17 mM l-histidine accumulation. These results demonstrate that in vivo screening of enzyme libraries by using metabolite sensors is extremely well suited to identify high-performance muteins required for overproduction.

Solution structure of Der f 2, the major mite allergen for atopic diseases

House dust mites cause heavy atopic diseases such as asthma and dermatitis. Among allergens from Dermatophagoides farinae, Der f 2 shows the highest positive rate for atopic patients, but its biological function in mites has been perfectly unknown, as well as the functions of its homologs in human and other animals. We have determined the tertiary structure of Der f 2 by multidimensional nuclear magnetic resonance spectroscopy. Der f 2 was found to be a single-domain protein of immunoglobulin fold, and its structure was the most similar to those of the two regulatory domains of transglutaminase. This fact, binding to the bacterial surface, and other small pieces of information hinted that Der f 2 is related to the innate antibacterial defense system in mites. The immunoglobulin E epitopes are also discussed on the basis of the tertiary structure.

Interleukin-11-expressing fibroblasts have a unique gene signature correlated with poor prognosis of colorectal cancer

Interleukin (IL)-11 is a member of the IL-6 family of cytokines and is involved in multiple cellular responses, including tumor development. However, the origin and functions of IL-11-producing (IL-11⁺) cells are not fully understood. To characterize IL-11⁺ cells in vivo, we generate Il11 reporter mice. IL-11⁺ cells appear in the colon in murine tumor and acute colitis models. Il11ra1 or Il11 deletion attenuates the development of colitis-associated colorectal cancer. IL-11⁺ cells express fibroblast markers and genes associated with cell proliferation and tissue repair. IL-11 induces the activation of colonic fibroblasts and epithelial cells through phosphorylation of STAT3. Human cancer database analysis reveals that the expression of genes enriched in IL-11⁺ fibroblasts is elevated in human colorectal cancer and correlated with reduced recurrence-free survival. IL-11⁺ fibroblasts activate both tumor cells and fibroblasts via secretion of IL-11, thereby constituting a feed-forward loop between tumor cells and fibroblasts in the tumor microenvironment.

The stromal fibroblast population in the colon is composed of heterogeneous and distinct cell subtypes that play a crucial role in the development of colitis and colon cancer. Here the authors generate IL-11 reporter mice and characterize the origin and phenotype of inflammatory IL-11⁺ fibroblasts in colitis and colon cancer preclinical models.

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

Transcriptional regulation of the gene-encoding human Fc epsilon RI alpha-chain was analyzed in detail. EMSA revealed that either YY1 or PU.1 bound to the region close to that recognized by Elf-1. The alpha-chain promoter activity was up-regulated approximately 2-fold by exogenously expressed YY1 or PU.1 and approximately 7-fold by GATA-1, respectively, in KU812 cells. In contrast, coexpression of GATA-1 with either of PU.1 or YY1 dramatically activated the promoter approximately 41- or approximately 27-fold, respectively. Especially synergic activation by GATA-1 and PU.1 was surprising, because these transcription factors are known to inhibit the respective transactivating activities of each other. These up-regulating effects of PU.1 and YY1 with GATA-1 were inhibited by overexpression of Elf-1, indicating that Elf-1 serves as a repressor for the alpha-chain gene expression. Transcriptional regulation of the alpha-chain gene through four transcriptional factors is discussed.

Inhibitory Effect of Polyphenol-Enriched Apple Extracts on Mast Cell Degranulationin VitroTargeting the Binding between IgE and FcεRI

Extracts from immature fruit of the apple (Rosaceae, Malus sp.), which contain procyanidins (polymers of catechins) as the major ingredients, are known to inhibit histamine release from mast cells. We analyzed in this study the mechanism for the anti-allergic activity of two polyphenol-enriched apple extracts. These extracts, termed "crude apple polyphenol (CAP)" and "apple condensed tannin (ACT)", reduced the degranulation of mast cells caused by cross-linking of the high-affinity receptor for IgE (FcepsilonRI) with IgE and the antigen in a dose-dependent manner. Furthermore, western blotting revealed that phosphorylation of the intracellular signal-transduction molecules caused by cross-linking of FcepsilonRI was markedly decreased by the addition of CAP or ACT. We then analyzed the effects of CAP and ACT on the binding of the IgE antibody to FcepsilonRI on mast cells, which is the first key step in the allergic reaction mediated by mast cells, and found that this binding was markedly inhibited by both CAP and ACT. These results indicate that the inhibition of binding between FcepsilonRI and IgE by either CAP or ACT was the probable cause of the suppression of mast cell activation. This is the first report demonstrating the molecular mechanism for the anti-allergic effect of procyanidin-enriched extracts from apples.

Circadian regulation of allergic reactions by the mast cell clock in mice

BACKGROUND

It remains elusive how allergic symptoms exhibit prominent 24-hour variations. In mammals the circadian clocks present in nearly all cells, including mast cells, drive the daily rhythms of physiology. Recently, we have shown that the circadian clocks drive the daily rhythms in IgE/mast cell-mediated allergic reactions. However, the precise mechanisms, particularly the specific roles of the mast cell-intrinsic clockwork in temporal regulation, remain unclear.

OBJECTIVE

We determined whether the mast cell clockwork contributes to the temporal regulation of IgE/mast cell-mediated allergic reaction.

METHODS

The kinetics of a time of day-dependent variation in passive cutaneous anaphylactic reactions were compared between mast cell-deficient mice reconstituted with bone marrow-derived cultured mast cells generated from mice with a wild-type allele and a dominant negative type mutation of the key clock gene Clock. We also examined the temporal responses of wild-type and Clock-mutated bone marrow-derived cultured mast cells to IgE stimulation in vitro. Furthermore, factors influencing the mast cell clockwork were determined by using in vivo imaging.

RESULTS

The Clock mutation in mast cells resulted in the absence of temporal variations in IgE-mediated degranulation in mast cells both in vivo and in vitro associated with the loss of temporal regulation of FcεRI expression and signaling. Additionally, adrenalectomy abolished the mast cell clockwork in vivo.

CONCLUSION

The mast cell-intrinsic clockwork, entrained by humoral factors from the adrenal gland, primarily contributes to the temporal regulation of IgE/mast cell-mediated allergic reactions. Our results reveal a novel regulatory mechanism for IgE-mediated mast cell responses that might underlie the circadian pathophysiology in patients with allergic diseases.

Notch signaling confers antigen-presenting cell functions on mast cells

BACKGROUND

Notch signaling is involved in cell fate determination along with the development of the immune system. However, very little is known about the role for Notch signaling in mast cells.

OBJECTIVE

We investigated the role of Notch signaling in mast cell functions.

METHODS

After mouse bone marrow-derived mast cells (BMMCs) or peritoneal mast cells (PMCs) were cocultured with mouse Notch ligand-expressing chinese hamster ovary cells for 5 days, we examined the mast cell surface expressions of MHC-II molecules and OX40 ligand (OX40L), Fc epsilon RI-mediated cytokine production, and the effects of the mast cells on proliferation and differentiation of naive CD4(+) T cells in vitro.

RESULTS

We showed that BMMCs and PMCs constitutively expressed Notch1 and Notch2 proteins on the cell surface. We also found that Delta-like 1 (Dll1)/Notch signaling induced the expression of MHC-II and upregulated the expression level of OX40L on the surface of the mast cells. Dll1/Notch signaling augmented Fc epsilon RI-mediated IL-4, IL-6, IL-13, and TNF production by BMMCs. Dll1-stimulated MHC-II(+)OX40L(high) BMMCs promoted proliferation of naive CD4(+) T cells and their differentiation into T(H)2 cells producing IL-4, IL-5, IL-10, and IL-13.

CONCLUSION

Dll1/Notch signaling confers the functions as an antigen-presenting cell on mast cells, which preferentially induce the differentiation of T(H)2.

Involvement of mast cells in IL-12/23 p40 production is essential for survival from polymicrobial infections

Interleukin-12 (IL-12), a heterodimeric cytokine (p35/p40) produced mainly from macrophages and dendritic cells, is an important regulator of T-helper 1 cell responses and for host defense. We found that interferon (IFN) consensus sequence binding protein (ICSBP), which is a transcription factor essential for the expression of p40, was expressed in mouse bone marrow-derived mast cells (BMMCs). The transcription levels of p35 and p40 were increased by stimulation of BMMCs with IFN-gamma/lipopolysaccharide (LPS). IL-12 was secreted from BMMCs in response to LPS but not by FcepsilonRI cross-linking. The p40 levels in the peritoneal cavity of mast cell-deficient W/W(v) and W/W(v) reconstituted with p40(-/-) BMMCs were significantly lower than those of WBB6F(1)(+/+) and wild-type (WT) BMMC-reconstituted W/W(v) in the acute septic peritonitis model. The survival rate of W/W(v) reconstituted with p40(-/-) BMMCs was significantly decreased compared to those of WBB6F(1)(+/+) and WT-BMMC-reconstituted W/W(v), which was due to reduced production of IFN-gamma and subsequent impaired activation of neutrophils in the peritoneal cavity. Survival rate of p40(-/-) mice was also restored by adoptive transfer of WT-BMMCs. These results demonstrate that mast cells play a significant role in the production of IL-12 required for host defense. This is the first report to demonstrate that mast cells are a crucial source of functional IL-12.

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.

FOG-1 represses GATA-1-dependent FcepsilonRI beta-chain transcription: transcriptional mechanism of mast-cell-specific gene expression in mice

Cell-type-specific transcription of mouse high-affinity IgE receptor (FcepsilonRI) beta-chain is positively regulated by the transcription factor GATA-1. Although GATA-1 is expressed in erythroid cells, megakaryocytes, and mast cells, the expression of mouse FcepsilonRI beta-chain is restricted to mast cells. In the present study, we characterized the role of GATA-associated cofactor FOG-1 in the regulation of the FcepsilonRI beta-chain promoter. The expression levels of FOG-1, GATA-1, and beta-chain in each hematopoietic cell line were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. FOG-1 expression was higher in the beta-chain-negative hematopoietic progenitor cell line Ba/F3 than in the beta-chain-positive mast cell line PT18. By contrast, GATA-1 expression was similar when comparing the 2 cell lines. A transient reporter assay demonstrated that the beta-chain promoter functioned in PT18 but not in Ba/F3 and that the transcription activity of the beta-chain promoter in PT18 was markedly suppressed by overexpression of FOG-1. Although the activity of the beta-chain promoter, which was upregulated by coexpression of GATA-1, was significantly suppressed by coexpression of FOG-1 in the simian kidney CV-1 cells (beta-chain(-), GATA-1(-), and FOG-1(-)), the transactivation of the beta-chain promoter by the GATA-1 mutant V205G, which cannot bind FOG-1, was not affected by coexpression of FOG-1. Further, overexpression of FOG-1 in PT18 resulted in decreases in cell surface expression of FcepsilonRI and beta-chain transcription. Finally, suppression of FOG-1 expression using an siRNA approach resulted in increased beta-chain promoter activity in Ba/F3. These results suggest that FOG-1 expression level regulates the GATA-1-dependent FcepsilonRI beta-chain promoter.

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.

Two different transcription factors discriminate the -315C>T polymorphism of the Fc epsilon RI alpha gene: binding of Sp1 to -315C and of a high mobility group-related molecule to -315T

The alpha-chain is a specific component of FcepsilonRI, which is essential for the cell surface expression of FcepsilonRI and the binding of IgE. Recently, two single nucleotide polymorphisms (SNPs) in the alpha-chain promoter, -315C>T and -66T>C, have been shown by statistic studies to associate with allergic diseases. The effect of -66 SNP on GATA-1-mediated promoter activity has been already indicated. In the present study, to investigate roles of the -315 SNP on the alpha-chain promoter functions, the transcription activity was evaluated by reporter assay. The alpha-chain promoter carrying -315T (minor allele) possessed significantly higher transcriptional activity than that of -315C (major allele). EMSA indicated that the transcription factor Sp1, but not Myc-associated zinc finger protein (MAZ), was bound to the -315C allele probe and that a transcription factor belonging to a high mobility group-family bound to the -315T allele probe. The chromatin immunoprecipitation assay suggested that high mobility group 1, 2, and Sp1 bound around -315 of FcepsilonRIalpha genomic DNA in vivo in the human basophil cell line KU812 with -315C/T and in human peripheral blood basophils with -315C/C, respectively. When cell surface expression level of FcepsilonRI on basophils was analyzed by flow cytometry, basophils from individuals carrying -315T allele expressed significantly higher amount of FcepsilonRI compared with those of -315C/C. The findings demonstrate that a -315 SNP significantly affects human FcepsilonRI alpha-chain promoter activity and expression level of FcepsilonRI on basophils by binding different transcription factors to the SNP site.

Analysis of the IgE-epitope of Der f 2, a major mite allergen, by in vitro mutagenesis

Der f 2 is a major mite allergen composed of 129 amino acid residues. To determine the major epitopes on Der f 2 recognized by human IgE antibodies, artificial mutations were introduced to Der f 2 protein. The IgE-binding activity of Der f 2 was significantly decreased by deletion of 10 amino acids at the N-terminus or nine amino acids at the C-terminus. Site-directed mutagenesis with a single amino acid replacement by Ala or Leu in both N- and C-terminal regions as well as a central portion was performed to generate 42 single-site mutations. Amino acid replacement around a disulfide bond of Cys8-Cys119 caused a marked decrease in IgE-binding activity. Furthermore, a distinct decrease in IgE-binding was also caused by Ala-substitution close to a disulfide bond of Cys73-Cys78 and by mutations of a few charged residues. From these results, it was concluded that the two disulfide-forming regions of Der f 2 and several charged residues are important for forming major epitope structures recognized by human IgE antibodies.

Effects of amino acid variations in recombinant Der fII on its human IgE and mouse IgG recognition

Amino acid sequencing of the major mite allergen Der fII purified from mite body extract revealed that it is a mixture of at least two variants. Substitutions were found only at positions in which amino acid variations were predicted from the nucleotide sequences of three cloned cDNAs. When cDNAs corresponding to the three variants were expressed in Escherichia coli, Der fII proteins were produced as inclusion bodies. Denaturation and renaturation with urea converted recombinant Der fII into a protein with three intramolecular disulfide bonds (Cys8-Cys119, Cys21-Cys27, and Cys73-Cys78), which were identical to those previously identified in native Der fII. All the variants, including native Der fII, were equally recognized by human IgE antibodies from 14 different sera of mite-allergic patients. These results suggested that recombinant Der fII proteins assumed a conformation identical to that of the native Der fII and that all the Der fII variants acted as allergens. This result also suggested that IgE antibody binds to the region where there were no amino acid variations. The binding ability of the monoclonal antibody (mAb) 18G8 for the variant clones 1, 2, and 11 Der fII was almost the same. However, mAb 15E11 bound to clone 1 Der fII more efficiently than to clones 2 and 11, whereas mAb 13A4 recognized clone 2 Der fII as the most preferable antigen. This suggested that these antibodies recognized the region of amino acid variations. The stability of Der fII variants was analyzed by measuring their IgE antibody binding activity after heating, freezing, or acid treatment, and was analyzed by resistance to trypsin digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

GATA2 is a critical transactivator for the human IL1RL1/ST2 promoter in mast cells/basophils: opposing roles for GATA2 and GATA1 in human IL1RL1/ST2 gene expression

The IL1RL1/ST2 gene encodes a receptor for IL-33. Signaling from IL1RL1/ST2 induced by IL-33 binding was recently identified as a modulator of the Th2 response. The target cells for IL-33 are restricted in some hematopoietic lineages, including mast cells, basophils, eosinophils, Th2 cells, natural killer cells, and dendritic cells. To clarify the molecular mechanisms of cell type-specific IL1RL1/ST2 expression in mast cells and basophils, transcriptional regulation of the human IL1RL1/ST2 promoter was investigated using the mast cell line LAD2 and the basophilic cell line KU812. Reporter assays suggested that two GATA motifs just upstream of the transcription start site in the ST2 promoter are critical for transcriptional activity. These two GATA motifs possess the capacity to bind GATA1 and GATA2 in EMSA. ChIP assay showed that GATA2, but not GATA1, bound to the ST2 promoter in LAD2 cells and that histone H3 at the ST2 promoter was acetylated in LAD2 cells, whereas binding of GATA1 and GATA2 to the ST2 promoter was detected in KU812 cells. Knockdown of GATA2 mRNA by siRNA reduced ST2 mRNA levels in KU812 and LAD2 cells and ST2 protein levels in LAD2 cells; in contrast, GATA1 siRNA transfection up-regulated ST2 mRNA levels in KU812 cells. The ST2 promoter was transactivated by GATA2 and repressed by GATA1 in coexpression analysis. When these siRNAs were introduced into human peripheral blood basophils, GATA2 siRNA reduced ST2 mRNA, whereas GATA1 siRNA up-regulated ST2 mRNA. These results indicate that GATA2 and GATA1 positively and negatively control human ST2 gene transcription, respectively.

An association of TLR2–16934A >T polymorphism and severity/phenotype of atopic dermatitis

BACKGROUND

Toll-like receptor 2 gene (TLR2) –16934A>T polymorphism has been shown to be associated with severity of atopic dermatitis (AD) as measured using severity scoring of atopic dermatitis (SCORAD) index. Moreover, TLR2–16934A>T polymorphism has been associated with atopy and allergic disorders in farmers’ children.

OBJECTIVE

The aim of this study was to evaluate an association between TLR2–16934A>T polymorphism and AD phenotype, including disease severity and concomitant atopic diseases, or potential serum markers of AD severity and also to find a molecular background of the clinical associations.

METHODS

Genotyping for TLR2–16934A>T polymorphism was performed in 130 consecutive adult ambulatory patients with AD. Total serum (TS) IgE levels, serum tryptase, plasma interleukin-6 and C-reactive protein were measured. In addition, luciferase assay and electrophoretic-mobility shift assay were conducted to assess the effect of –16934A>T polymorphism on transcriptional activity.

RESULTS

There was an inverse association of TLR2–16934TT genotype and/or –16934T allele with SCORAD, but not with TS IgE, tryptase or inflammatory markers. Interestingly, –16934AA genotype and/or –16934A allele were overrepresented in AD patients with concomitant asthma or a family history of atopy. In a subgroup analysis, TLR2–16934A>T polymorphism was associated with SCORAD, asthma, allergic conjunctivitis or family history of atopy in AD patients with TS IgE ≥106 IU/mL but not in those having TS IgE <106 IU/mL. Functional analyses showed that TLR2–16934T allele is associated with higher luciferase activity in human monocytic THP-1 cells and preferential binding of the THP-1-derived nuclear protein.

CONCLUSION

TLR2–16934A>T polymorphism could be a genetic predictor of AD severity, the coexistence of asthma or atopic conjunctivitis as well as a family history of atopic diseases, especially in subjects having higher TS IgE. TLR2–16934A>T polymorphism affects transcriptional activity, which may at least in part account for the clinical associations observed for the –16934A>T polymorphism.

Determination of three disulfide bonds in a major house dust mite allergen, Der f II

Der f II is a major mite allergen consisting of 129 amino acid residues. Der f II contains six cysteine residues, suggesting the existence of three disulfide bonds which would stabilize this small protein. As the first step in revealing the relationship between the structure and the allergenic property of Der f II, the formation of disulfide bonds was examined. Der f II purified from Dermatophagoides farinae was treated with lysyl-endopeptidase or proline-specific endopeptidase, and the peptide fragments thus generated were separated by reverse phase high performance liquid chromatography. Determination of the amino acid sequence of each peptide collected in this way proved the existence of three disulfide bonds between Cys8 and Cys119, Cys21 and Cys27, and Cys73 and Cys78.

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.

Role of PU.1 in MHC class II expression through transcriptional regulation of class II transactivator pI in dendritic cells

BACKGROUND

PU.1 is a hematopoietic cell-specific transcription factor belonging to the Ets family. We hypothesized that PU.1 is involved in MHC class II expression in dendritic cells (DCs).

OBJECTIVE

The role of PU.1 in MHC class II expression in DCs was analyzed.

METHODS

Transcriptional regulation of the DC-specific pI promoter of the class II transactivator (CIITA) gene and subsequent MHC class II expression was investigated by using PU.1 small interfering RNA (siRNA) and reporter, chromatin immunoprecipitation, and electrophoretic mobility shift assays.

RESULTS

PU.1 siRNA introduction suppressed MHC class II expression, allogeneic and syngeneic T-cell activation activities of bone marrow-derived DCs (BMDCs) with reduction of CIITA mRNA driven by the DC-specific promoter pI, and MHC class II mRNA. The chromatin immunoprecipitation assay showed constitutive binding of PU.1 to the pI region in BMDCs, whereas acetylation of histone H3 on pI was suppressed by LPS stimulation in parallel with shutdown of CIITA transcription. PU.1 transactivated the pI promoter through cis-elements at -47/-44 and -30/-27 in a reporter assay and to which PU.1 directly bound in an electrophoretic mobility shift assay. Acetylation of histones H3 and H4 on pI was reduced in PU.1 siRNA-introduced BMDCs. Knockdown of interferon regulatory factor 4 or 8, which is a heterodimer partner of PU.1, by siRNA did not affect pI-driven CIITA transcription or MHC class II expression.

CONCLUSION

PU.1 basally transactivates the CIITA pI promoter in DCs by functioning as a monomeric transcription factor and by affecting histone modification, resulting in the subsequent expression and function of MHC class II.