Isolation, characterization, and transcription of the gene encoding mouse mast cell protease 7

A gene that encodes mouse mast cell protease (mMCP) 7 (also known as mouse mast cell tryptase 2) was isolated by genomic cloning with a cDNA that encodes mMCP-6, a tryptase in serosal mast cells. cDNAs encoding mMCP-7 were isolated from a bone-marrow-derived mast cell cDNA library. The mMCP-7 gene spans 2.3 kilobases and contains five exons rather than six, as found in the mMCP-6 and human mast cell tryptase I genes. Comparison of the 5' end of the transcript with the genomic sequence indicated that the region corresponding to the first intron in the mMCP-6 and human tryptase I genes is not spliced during transcription of mMCP-7 mRNA because of a point mutation at the intron 1 acceptor splice site; this results in a 5' untranslated region of 195 nucleotides, which is longer than that of any other known mast cell-specific transcript. mMCP-7 is 71-76% homologous with mMCP-6 and with dog and human mast cell tryptases, and it is the most acidic mast cell protease, with an overall net charge of -10. RNA blot analyses revealed that the mMCP-7 gene is transcribed in bone-marrow-derived mast cells but is not transcribed in mature serosal mast cells or in mucosal mast cell-enriched intestinal tissue of Trichinella spiralis-infected mice. Transcription of the mMCP-7 gene by differentiating bone-marrow-derived mast cells occurred within 1 week of bone-marrow culture but decreased dramatically after 3 weeks. Thus, the mMCP-7 gene displays a number of unusual structural characteristics and is distinctive in its transient and selective expression in immature mast cells maintained in interleukin 3-enriched medium.

Cloning and characterization of the novel gene for mast cell carboxypeptidase A

No gene for a hematopoietic cell carboxypeptidase has previously been characterized. Mast cell carboxypeptidase A (MC-CPA) is a prominent secretory granule marker of mast cell differentiation and phenotype. The 32-kb human MC-CPA gene was isolated, localized to chromosome 3, and found to contain 11 exons. No significant homology was found between the 5' flanking region of the MC-CPA gene and those of three rat pancreatic carboxypeptidase genes (carboxypeptidase A1 and A2, and carboxypeptidase B [CPB]). In contrast, the intron/exon organization of the MC-CPA gene was conserved, most closely resembling the CPB gene. MC-CPA is unique among carboxypeptidases in having a CPA-like substrate-binding pocket and enzymatic activity despite overall protein and gene structures more similar to CPB. Evolutionary tree analysis of the carboxypeptidase gene family showed that, before the mammalian species radiation, a common MC-CPA/CPB ancestor diverged by gene duplication from the lineage leading to CPA, and then underwent another gene duplication to form separate but similar gene structures for MC-CPA and CPB. MC-CPA mRNA was prominent in dispersed lung cells enriched for mast cells but was undetectable in other nontransformed populations of several lineages, demonstrating that transcription of MC-CPA, a novel carboxypeptidase gene, provides a specific molecular marker for mast cells among normal hematopoietic cell populations.

GATA-binding transcription factors in mast cells regulate the promoter of the mast cell carboxypeptidase A gene

The transcription factors GATA-1, GATA-2, and GATA-3 were found to be expressed in several mouse and rat mast cell lines that contain mast cell carboxypeptidase A (MC-CPA) and other proteases in their cytoplasmic granules. GATA-1 mRNA was not detected in P815 cells, an immature mouse mastocytoma-derived cell line that lacks electron-dense granules and has low levels of secretory granule proteases. Because the 5'-flanking regions of the mouse and human MC-CPA genes contained a conserved GATA-binding motif 51 base pairs upstream of their translation initiation sites, the ability of GATA-binding proteins to regulate the promoter activity of the MC-CPA gene was examined in rat basophilic leukemia cells, mouse P815 cells, and transfected mouse P815 cells that expressed GATA-1. In all three mast cell lines, the promoter activity of the MC-CPA gene depended on the GATA binding site. GATA-1, GATA-2, and GATA-3 are thus the first DNA-binding proteins identified in mast cells which regulate the promoter activity of a gene that encodes a secretory granule protease.

Molecular cloning of gp49, a cell-surface antigen that is preferentially expressed by mouse mast cell progenitors and is a new member of the immunoglobulin superfamily

gp49 is a Mr 49,000 glycoprotein expressed on the surface of mouse bone marrow-derived mast cells, which are progenitors for the major in vivo mast cell subclasses, typified by intestinal mucosal mast cells and serosal mast cells. The amino-terminal amino acid sequence of gp49 was determined after isolation of the solubilized membrane protein by affinity chromatography with the B23.1 anti-gp49 monoclonal antibody. Redundant oligonucleotides were used to isolate a full-length 1.3-kilobase cDNA from a mouse mast cell library. The predicted amino acid sequence contains a signal peptide of 23 residues, an extracellular domain of 215 residues with three potential sites of N-linked glycosylation, a transmembrane domain of 23 residues, and a cytoplasmic tail of 42 residues. Hybridization of the gp49 cDNA was limited to mRNA extracted from those cell types that also bound the B23.1 monoclonal antibody as assessed by cytofluorographic analyses. The predicted extracellular domain of gp49 contains two regions of 48 and 51 amino acids, each flanked by cysteine residues. Both regions meet criteria for being C2-type domains of the immunoglobulin superfamily based upon the alignment of consensus amino acids and their predicted secondary structure organization. Thus, gp49, a membrane glycoprotein preferentially expressed by the progenitor mast cell population, is a new member of the immunoglobulin superfamily.

Cloning of the cDNA and gene for mouse mast cell protease 4. Demonstration of its late transcription in mast cell subclasses and analysis of its homology to subclass-specific neutral proteases of the mouse and rat

Based on the amino-terminal amino acid sequence of the mature form of mouse mast cell protease 4 (MMCP-4), previously identified in peritoneal connective tissue mast cells (CTMC) and Kirsten sarcoma virus-immortalized mast cells (KiSV-MC), a 26-mer oligonucleotide probe was constructed and used to clone cDNAs for MMCP-4 from a KiSV-MC1 cDNA library. MMCP-4 is the first secretory granule serine protease of CTMC to be molecularly cloned. Using a cDNA probe derived from the 3'-untranslated portion of the MMCP-4 cDNA, the gene for MMCP-4 and a second highly related gene (mouse mast cell protease-like, MMCP-L) were cloned from a BALB/c mouse genomic DNA library and sequenced entirely, including approximately 2 kilobases of the 5'-flanking region. MMCP-4 and MMCP-L have five exons of identical length, four introns of nearly identical length, and approximately 900 base pairs of 5'-flanking DNA with sequence similarity by dot matrix analysis. By RNA blot analysis with gene-specific probes for MMCP-4 (bases 497-633 of the cDNA) and MMCP-L (bases 502-638 of the cDNA), mRNA for MMCP-4 was present in KiSV-MC5, CTMC, and the intestine of a mouse infected with the parasite Nippostrongylus brasiliensis markedly enriched for mucosal mast cells (MMC); MMCP-L mRNA was detected only in the intestine of the N. brasiliensis-infected mouse. MMCP-4 mRNA was not expressed in normal mouse intestine or in interleukin 3-dependent bone marrow-derived mast cells, which can serve as precursors to both MMC and CTMC. This finding suggests that MMCP-4 is transcribed relatively late in the development of both the CTMC and MMC subclasses and underscores the fact that mouse bone-marrow-derived mast cells are immature mast cells, rather than tissue culture equivalents of the MMC subclass.

Different mouse mast cell populations express various combinations of at least six distinct mast cell serine proteases

Mouse serosal mast cells (SMCs) and Kirsten sarcoma virus-immortalized mast cells store large amounts of mast cell carboxypeptidase A and serine proteases in their secretory granules. Secretory granule proteins from 2.6 x 10(6) purified SMCs were separated by NaDodSO4/PAGE, trans-blotted to poly(vinylidine difluoride) membranes, and subjected to amino-terminal amino acid sequencing. Four distinct mast cell serine proteases were identified. With mast cell carboxypeptidase A, these serine proteases comprise the major proteins of mouse SMC secretory granules. Each of the four SMC serine proteases was distinct from the two serine proteases present in mucosal mast cells in the intestines of helminth-infected mice. The secretory granules of a Kirsten sarcoma virus-immortalized mast cell line contained three of the SMC-derived serine proteases and one of the mucosal mast cell-derived serine proteases. Thus, the family of mouse mast cell secretory granule serine proteases has at least six distinct members that can be expressed in different combinations in different mast cell populations.

Identification and molecular cloning of a novel mouse mucosal mast cell serine protease

A novel 28,000 Mr serine protease, designated mouse mast cell protease-2 (MMCP-2), that is stored in the secretory granules of Kirsten sarcoma virus-immortalized mouse mast cells (KiSV-MC) has been identified and its NH2-terminal amino acid sequence has been determined. Analysis of a 953-base pair cDNA that encodes MMCP-2 revealed that this serine protease is a basically charged protein, possessing the histidine-aspartic acid-serine charge relay system that is characteristic of other serine proteases. DNA blot analysis using the full-length MMCP-2 cDNA indicated the existence of a family of highly related serine protease genes in the mouse genome. When the same DNA blot was probed with the 149-base pair KpnI----3' fragment of the cDNA, the probe hybridized to a single DNA fragment, thereby demonstrating that this 3' fragment could be used as a gene-specific probe. The presence of high levels of the MMCP-2 mRNA transcript in the intestines of nematode-infected mice, and its absence in mouse bone marrow-derived mast cells and peritoneal cavity-derived connective tissue mast cells, suggest that this member of the mouse mast cell protease family is preferentially expressed late in the differentiation of mucosal mast cells.

Cloning of cDNAs that encode human mast cell carboxypeptidase A, and comparison of the protein with mouse mast cell carboxypeptidase A and rat pancreatic carboxypeptidases

Human skin and lung mast cells and rodent peritoneal mast cells contain a carboxypeptidase in their secretory granules. We have screened human lung cDNA libraries with a mouse mast cell carboxypeptidase A (MC-CPA) cDNA probe to isolate a near-full-length cDNA that encodes human MC-CPA. The 5' end of the human MC-CPA transcript was defined by direct mRNA sequencing and by isolation and partial sequencing of the human MC-CPA gene. Human MC-CPA is predicted to be translated as a 417 amino acid preproenzyme which includes a 15 amino acid signal peptide and a 94 amino acid activation peptide. The mature human MC-CPA enzyme has a predicted size of 36.1 kDa, a net positive charge of 16 at neutral pH, and 86% amino acid sequence identity with mouse MC-CPA. DNA blot analyses showed that human MC-CPA mRNA is transcribed from a single locus in the human genome. Comparison of the human MC-CPA with mouse MC-CPA and with three rat pancreatic carboxypeptidases shows that these enzymes are encoded by distinct but homologous genes.

Isolation and molecular cloning of mast cell carboxypeptidase A. A novel member of the carboxypeptidase gene family

Mast cell carboxypeptidase A has been isolated from the secretory granules of mouse peritoneal connective tissue mast cells (CTMC) and from a mouse Kirsten sarcoma virus-immortalized mast cell line (KiSV-MC), and a cDNA that encodes this exopeptidase has been cloned from a KiSV-MC-derived cDNA library. KiSV-MC-derived mast cell carboxypeptidase A was purified with a potato-derived carboxypeptidase-inhibitor affinity column and was found by analytical sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be a Mr 36,000 protein. Secretory granule proteins from KiSV-MC and from mouse peritoneal CTMC were then resolved by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transblotted to polyvinylidine difluoride membranes. Identical aminoterminal amino acid sequences were obtained for the prominent Mr 36,000 protein present in the granules of both cell types. Based on the amino-terminal sequence, an oligonucleotide probe was synthesized and used to isolate a 1,470-base pair cDNA that encodes this mouse exopeptidase. The deduced amino acid sequence revealed that, after cleavage of a 15-amino acid hydrophobic signal peptide and a 94-amino acid activation peptide from a 417-amino acid preproenzyme, the mature mast cell carboxypeptidase A protein core has a predicted Mr of 35,780 and a high positive charge [Lys + Arg) - (Asp + Glu) = 17) at neutral pH. Although critical zinc-binding amino acids (His67, Glu70, His195), substrate-binding amino acids (Arg69, Asn142, Arg143, Tyr197, Asp255, Phe278), and cysteine residues that participate in intrachain disulfide bonds (Cys64-Cys77, Cys136-Cys159) of pancreatic carboxypeptidases were also present in mast cell carboxypeptidase A, the overall amino acid sequence identities for mouse mast cell carboxypeptidase A relative to rat pancreatic carboxypeptidases A1, A2, and B were only 43, 41, and 53%, respectively. RNA and DNA blot analyses revealed that mouse peritoneal CTMC, KiSV-MC, and bone marrow-derived mast cells all express a prominent 1.5-kilobase mast cell carboxypeptidase A mRNA which is transcribed from a single gene. We conclude that mouse mast cell carboxypeptidase A is a prominent secretory granule enzyme of mast cells of the CTMC subclass and represents a novel addition to the carboxypeptidase gene family.

Immortalization of murine connective tissue-type mast cells at multiple stages of their differentiation by coculture of splenocytes with fibroblasts that produce Kirsten sarcoma virus

Mature connective tissue mast cells (CTMC) have not been previously available as a cell line from any species. Here we describe 15 novel mast cell lines (KiSV-MC) that were derived by coculturing murine splenocytes with fibroblasts that produce a Ki-ras-containing murine sarcoma virus. Some of the KiSV-MC lines are similar to CTMC in that they synthesize predominantly heparin proteoglycans, and contain up to 35 micrograms of histamine and 2.2 units of carboxypeptidase A/10(6) cells in secretory granules which stain red with Safranin. Other cell lines display phenotypic characteristics intermediate to CTMC and mucosal-like mast cells in being predominantly Safranin-, having lower amounts of histamine and carboxypeptidase A, and in synthesizing chondroitin sulfate E proteoglycans in preference to heparin proteoglycans. When the individual KiSV-MC lines were compared, a linear relationship was found between the number of Safranin+ granules, the cellular contents of histamine and carboxypeptidase A, and the biosynthesis of heparin relative to chondroitin sulfate E proteoglycans. Upon sensitization with monoclonal IgE and exposure to hapten-specific antigen, the cells exocytose the contents of their secretory granules. Thus, these immortalized cells provide the first source of CTMC-like lines for chemical and functional analysis and illustrate that murine mast cells can express a continuum of phenotypes.

Immunodeficiency in graft-versus-host disease. I. Mechanism of immune suppression

Irradiated CBA/J mice transplanted with H-2 compatible, minor histocompatibility disparate B10.BR bone marrow develop graft-versus-host disease (GVHD) if mature T lymphocytes are added to the marrow inoculum. In the setting of mild GVHD (receiving 10(4) or 10(5) T cells), by phenotypic analysis, lymphoid reconstitution occurs normally within 4 to 6 wk but there is a profound deficiency in the ability of splenic lymphocytes to respond to polyclonal activators such as LPS and Con A. This unresponsiveness is attributable to active suppression mediated by cells that express Thy-1 and can be removed with leucine methyl ester treatment. Thus, splenocytes from mice with GVHD suppress responses of normal T and B lymphocytes. Moreover, depletion of these suppressor cells restores normal function to splenocytes from mice with GVHD, and B cells isolated from these mice respond normally to T-dependent and -independent stimulation. Finally, IFN-gamma plays an important role in this suppression, because a neutralizing anti-IFN-gamma mAb significantly removes suppression of normal cells and restores functional responses of lymphocytes from mice with GVHD. These results provide insights into the mechanisms of immunodeficiency associated with GVHD, and suggest novel strategies for possible therapies for this disorder.

Immunodeficiency in graft-versus-host disease. I. Mechanism of immune suppression

Irradiated CBA/J mice transplanted with H-2 compatible, minor histocompatibility disparate B10.BR bone marrow develop graft-versus-host disease (GVHD) if mature T lymphocytes are added to the marrow inoculum. In the setting of mild GVHD (receiving 10(4) or 10(5) T cells), by phenotypic analysis, lymphoid reconstitution occurs normally within 4 to 6 wk but there is a profound deficiency in the ability of splenic lymphocytes to respond to polyclonal activators such as LPS and Con A. This unresponsiveness is attributable to active suppression mediated by cells that express Thy-1 and can be removed with leucine methyl ester treatment. Thus, splenocytes from mice with GVHD suppress responses of normal T and B lymphocytes. Moreover, depletion of these suppressor cells restores normal function to splenocytes from mice with GVHD, and B cells isolated from these mice respond normally to T-dependent and -independent stimulation. Finally, IFN-gamma plays an important role in this suppression, because a neutralizing anti-IFN-gamma mAb significantly removes suppression of normal cells and restores functional responses of lymphocytes from mice with GVHD. These results provide insights into the mechanisms of immunodeficiency associated with GVHD, and suggest novel strategies for possible therapies for this disorder.

Inhibition of B lymphocyte activation by interferon-gamma

Helper/inducer T cell clones specific for protein antigens and class II MHC determinants consist of two nonoverlapping subsets. One (called Th1) secretes IL 2 and IFN-gamma and the other (Th2) produces BSF1 upon stimulation with antigen or polyclonal activators. By using hapten-binding normal B cells and the B lymphoma line WEHI-279 as assays for B cell helper (maturation) factors, we have shown that Th2 clone supernatants (SN) induce differentiation to antibody secretion, whereas Th1 SN do not. The failure of Th1 SN to activate B cells is due to inhibitory effects of IFN-gamma, because it can be reversed by a neutralizing monoclonal antibody specific for IFN-gamma. Thus, in the presence of this antibody, even Th1 SN stimulate B cell maturation maximally. Conversely, recombinant IFN-gamma inhibits proliferation and differentiation of B cells induced by active Th2 SN. These results demonstrate that IFN-gamma is a potent inhibitor of B lymphocyte activation and can be distinguished from growth and maturation-inducing helper factors that are produced by both subsets of helper T cells.

Inhibition of B lymphocyte activation by interferon-gamma

Helper/inducer T cell clones specific for protein antigens and class II MHC determinants consist of two nonoverlapping subsets. One (called Th1) secretes IL 2 and IFN-gamma and the other (Th2) produces BSF1 upon stimulation with antigen or polyclonal activators. By using hapten-binding normal B cells and the B lymphoma line WEHI-279 as assays for B cell helper (maturation) factors, we have shown that Th2 clone supernatants (SN) induce differentiation to antibody secretion, whereas Th1 SN do not. The failure of Th1 SN to activate B cells is due to inhibitory effects of IFN-gamma, because it can be reversed by a neutralizing monoclonal antibody specific for IFN-gamma. Thus, in the presence of this antibody, even Th1 SN stimulate B cell maturation maximally. Conversely, recombinant IFN-gamma inhibits proliferation and differentiation of B cells induced by active Th2 SN. These results demonstrate that IFN-gamma is a potent inhibitor of B lymphocyte activation and can be distinguished from growth and maturation-inducing helper factors that are produced by both subsets of helper T cells.

Mature murine B lymphocytes immortalized by Kirsten sarcoma virus

Clonal, antigen-specific, functionally responsive cell populations have proved critical for the analysis of the activation and regulation of lymphocytes. Such studies with B lymphocytes, the precursors of antibody-secreting cells, are hampered by the difficulty in generating phenotypically mature, antigen-reactive lines from defined cell populations. One method is to use acutely transforming retroviruses, which can transform B-lineage lymphocytes in vitro. However, Abelson murine leukaemia virus (A-MuLV) infection of murine bone marrow cells in vitro yields mostly immature B-cell lines, and infection of murine bone marrow cells with murine sarcoma viruses carrying ras related genes produces only immature lymphoid cell lines. Retroviruses which contain ras can immortalize nonlymphoid cells without causing loss of mature phenotypic characteristics. We used ras-containing Kirsten sarcoma virus (KiSV) pseudotyped with an amphotropic MuLV helper virus, to infect a purified population of mature, hapten-binding murine splenic B lymphocytes, aiming to generate mature B-cell lines to use as models for the study of B-cell growth and differentiation physiology. Immortalized B-cell lines which retain the same mature phenotype as the starting population, including hapten-specific binding, were produced. This is the first demonstration of a method for immortalizing selected antigen-binding B lymphocytes, and the first example of immortalization of mature B cells in vitro with an acutely transforming ras-containing retrovirus.

Direct inhibitory effect of GnRH on androgen secretion by ovarian interstitial cells

We report here 1) that GnRH and a potent GnRH agonist inhibit basal and LH stimulated ovarian androgen biosynthesis in vitro, 2) that the inhibitory effects of GnRH are dose-dependent and completely inhibited by concomitant treatment with a GnRH antagonist and 3) that the GnRH action is very rapid (t1/2 = 10 min) and persists after thorough washing of the cells. These data suggest that GnRH acts at a stereospecific binding site on ovarian theca and/or interstitial cells (probably the theca cells) to rapidly and perhaps irreversibly inhibit androgen biosynthesis.