Isolation and molecular cloning of mast cell carboxypeptidase A

Choroid plexus mast cells drive tumor-associated hydrocephalus

Tumor-associated hydrocephalus (TAH) is a common and lethal complication of brain metastases. Although other factors beyond mechanical obstructions have been suggested, the exact mechanisms are unknown. Using single-nucleus RNA sequencing and spatial transcriptomics, we find that a distinct population of mast cells locate in the choroid plexus and dramatically increase during TAH. Genetic fate tracing and intracranial mast-cell-specific tryptase knockout showed that choroid plexus mast cells (CPMCs) disrupt cilia of choroid plexus epithelia via the tryptase-PAR2-FoxJ1 pathway and consequently increase cerebrospinal fluid production. Mast cells are also found in the human choroid plexus. Levels of tryptase in cerebrospinal fluid are closely associated with clinical severity of TAH. BMS-262084, an inhibitor of tryptase, can cross the blood-brain barrier, inhibit TAH in vivo, and alleviate mast-cell-induced damage of epithelial cilia in a human pluripotent stem-cell-derived choroid plexus organoid model. Collectively, we uncover the function of CPMCs and provide an attractive therapy for TAH.

Expression of Carboxypeptidase A3 and Tryptase as Markers for Lymph Node Metastasis of Canine Cutaneous Mast Cell Tumors

Detection of metastatic mast cell tumors (MCTs) in lymph nodes is a critical factor for treatment, prognosis, and clinical management. Presence/absence of mast cells in the lymph nodes cannot be used as a sole parameter to determine metastasis due to the inability to differentiate neoplastic from non-neoplastic/inflammatory mast cells. While cytologic and histopathologic classifications for assessment of metastatic MCTs based on the numbers and distribution of mast cells have been developed, inconsistency between the clinical interpretation of these grading schemes and actual metastatic status occurs. The aim of this study is to identify a novel diagnostic tool to accurately predict overt metastatic mast cell tumors in lymph nodes. We investigated the possibility of using RT-qPCR to detect mRNA expression of mast cell-specific genes in lymph nodes with different stages of MCT metastatic classification. We are able to establish a highly sensitive and discriminating RT-qPCR measuring Carboxy peptidase A3 (CPA3) and tryptase mRNA expression and identify the cut-off values with high sensitivity and specificity for overt metastatic MCTs in lymph nodes. An area of future interest would be to expand our analysis of the extent to which cut-off values for these markers in correctly identifying disease status, as well as predicting clinical outcomes and survival times. This would offer valuable information regarding the practical applicability of this technique and may enable us to improve our standards of detection metastasis, including possibility of molecular analysis of cytologic specimens obtained from suspicious nodes subjected to surgical excision.

Carboxypeptidase A3—A Key Component of the Protease Phenotype of Mast Cells

Carboxypeptidase A3 (CPA3) is a specific mast cell (MC) protease with variable expression. This protease is one of the preformed components of the secretome. During maturation of granules, CPA3 becomes an active enzyme with a characteristic localization determining the features of the cytological and ultrastructural phenotype of MC. CPA3 takes part in the regulation of a specific tissue microenvironment, affecting the implementation of innate immunity, the mechanisms of angiogenesis, the processes of remodeling of the extracellular matrix, etc. Characterization of CPA3 expression in MC can be used to refine the MC classification, help in a prognosis, and increase the effectiveness of targeted therapy.

Peptidase inhibitors in tick physiology

Peptidase inhibitors regulate a wide range of physiological processes involved in the interaction between hematophagous parasites and their hosts, including tissue remodeling, the immune response and blood coagulation. In tick physiology, peptidase inhibitors have a crucial role in adaptation to improve parasitism mechanisms, facilitating blood feeding by interfering with defense-related host peptidases. Recently, a larger number of studies on this topic led to the description of several new tick inhibitors displaying interesting novel features, for example a role in pathogen transmission to the host. A comprehensive review discussing these emerging concepts can therefore shed light on peptidase inhibitor functions, their relevance to tick physiology and their potential applications. Here, we summarize and examine the general characteristics, functional diversity and action of tick peptidase inhibitors with known physiological roles in the tick-host-pathogen interaction.

CD117+ Dendritic and Mast Cells Are Dependent on RasGRP4 to Function as Accessory Cells for Optimal Natural Killer Cell-Mediated Responses to Lipopolysaccharide

Ras guanine nucleotide-releasing protein-4 (RasGRP4) is an evolutionarily conserved calcium-regulated, guanine nucleotide exchange factor and diacylglycerol/phorbol ester receptor. While an important intracellular signaling protein for CD117⁺ mast cells (MCs), its roles in other immune cells is less clear. In this study, we identified a subset of in vivo-differentiated splenic CD117⁺ dendritic cells (DCs) in wild-type (WT) C57BL/6 mice that unexpectedly contained RasGRP4 mRNA and protein. In regard to the biologic significance of these data to innate immunity, LPS-treated splenic CD117⁺ DCs from WT mice induced natural killer (NK) cells to produce much more interferon-γ (IFN-γ) than comparable DCs from RasGRP4-null mice. The ability of LPS-responsive MCs to cause NK cells to increase their expression of IFN-γ was also dependent on this intracellular signaling protein. The discovery that RasGRP4 is required for CD117⁺ MCs and DCs to optimally induce acute NK cell-dependent immune responses to LPS helps explain why this signaling protein has been conserved in evolution.

Development of mast cells and importance of their tryptase and chymase serine proteases in inflammation and wound healing

Mast cells (MCs) are active participants in blood coagulation and innate and acquired immunity. This review focuses on the development of mouse and human MCs, as well as the involvement of their granule serine proteases in inflammation and the connective tissue remodeling that occurs during the different phases of the healing process of wounded skin and other organs. The accumulated data suggest that MCs, their tryptases, and their chymases play important roles in tissue repair. While MCs initially promote healing, they can be detrimental if they are chronically stimulated or if too many MCs become activated at the same time. The possibility that MCs and their granule serine proteases contribute to the formation of keloid and hypertrophic scars makes them potential targets for therapeutic intervention in the repair of damaged skin.

Protective and pathological roles of mast cells and basophils

Mast cells and basophils are potent effector cells of the innate immune system, and they have both beneficial and detrimental functions for the host. They are mainly implicated in pro-inflammatory responses to allergens but can also contribute to protection against pathogens. Although both cell types were identified more than 130 years ago by Paul Ehrlich, their in vivo functions remain poorly understood. The precursor cell populations that give rise to mast cells and basophils have recently been characterized and isolated. Furthermore, new genetically modified mouse strains have been developed, which enable more specific targeting of mast cells and basophils. Such advances offer new opportunities to uncover the true in vivo activities of these cells and to revisit their previously proposed effector functions.

Cre-mediated cell ablation contests mast cell contribution in models of antibody- and T cell-mediated autoimmunity

Immunological functions of mast cells remain poorly understood. Studies in Kit mutant mice suggest key roles for mast cells in certain antibody- and T cell-mediated autoimmune diseases. However, Kit mutations affect multiple cell types of both immune and nonimmune origin. Here, we show that targeted insertion of Cre-recombinase into the mast cell carboxypeptidase A3 locus deleted mast cells in connective and mucosal tissues by a genotoxic Trp53-dependent mechanism. Cre-mediated mast cell eradication (Cre-Master) mice had, with the exception of a lack of mast cells and reduced basophils, a normal immune system. Cre-Master mice were refractory to IgE-mediated anaphylaxis, and this defect was rescued by mast cell reconstitution. This mast cell-deficient strain was fully susceptible to antibody-induced autoimmune arthritis and to experimental autoimmune encephalomyelitis. Differences comparing Kit mutant mast cell deficiency models to selectively mast cell-deficient mice call for a systematic re-evaluation of immunological functions of mast cells beyond allergy.

Reduced mast cell and basophil numbers and function in Cpa3-Cre; Mcl-1fl/fl mice

It has been reported that the intracellular antiapoptotic factor myeloid cell leukemia sequence 1 (Mcl-1) is required for mast cell survival in vitro, and that genetic manipulation of Mcl-1 can be used to delete individual hematopoietic cell populations in vivo. In the present study, we report the generation of C57BL/6 mice in which Cre recombinase is expressed under the control of a segment of the carboxypeptidase A3 (Cpa3) promoter. C57BL/6-Cpa3-Cre; Mcl-1(fl/fl) mice are severely deficient in mast cells (92%-100% reduced in various tissues analyzed) and also have a marked deficiency in basophils (58%-78% reduced in the compartments analyzed), whereas the numbers of other hematopoietic cell populations exhibit little or no changes. Moreover, Cpa3-Cre; Mcl-1(fl/fl) mice exhibited marked reductions in the tissue swelling and leukocyte infiltration that are associated with both mast cell- and IgE-dependent passive cutaneous anaphylaxis (except at sites engrafted with in vitro-derived mast cells) and a basophil- and IgE-dependent model of chronic allergic inflammation, and do not develop IgE-dependent passive systemic anaphylaxis. Our findings support the conclusion that Mcl-1 is required for normal mast cell and basophil development/survival in vivo in mice, and also suggest that Cpa3-Cre; Mcl-1(fl/fl) mice may be useful in analyzing the roles of mast cells and basophils in health and disease.

Monomeric IgE and mast cell development, survival and function

Mast cells play a major role in allergy and anaphylaxis, as well as a protective role in immunity against bacteria and venoms (innate immunity) and T-cell activation (acquired immunity).1,2 It was long thought that two steps are essential to mast cell activation. The first step (sensitization) occurs when antigen-specific IgE binds to its high-affinity IgE receptor (FcεRI) expressed on the surface of mast cells. The second step occurs when antigen (Ag) or anti-IgE binds antigen-specific IgE antibodies bound to FcεRI present on the mast cell surface (this mode of stimulation hereafter referred to as IgE+Ag or IgE+anti-IgE stimulation, respectively).Conventional wisdom has been that monomeric IgE plays only an initial, passive role in mast cell activation. However, recent findings have shown that IgE binding to its receptor FcεRI can mediate mast cell activation events even in the absence of antigen (this mode of stimulation hereafter referred to as IgE(-Ag) stimulation). Different subtypes of monomeric IgEs act via IgE(-Ag) stimulation to elicit varied effects on mast cells function, survival and differentiation. This chapter will describe the role of monomeric IgE molecules in allergic reaction, the various effects and mechanisms of action of IgE(-Ag) stimulation on mast cells and what possible developments may arise from this knowledge in the future. Since mast cells are involved in a variety of pathologic and protective responses, understanding the role that monomeric IgE plays in mast cell function, survival and differentiation will hopefully lead to better understanding and treatment of asthma and other allergic diseases, as well as improved understanding of host response to infections.

The inflammatory response after an epidermal burn depends on the activities of mouse mast cell proteases 4 and 5

A second-degree epidermal scald burn in mice elicits an inflammatory response mediated by natural IgM directed to nonmuscle myosin with complement activation that results in ulceration and scarring. We find that such burn injury is associated with early mast cell (MC) degranulation and is absent in WBB6F1-Kit(W)/Kit(Wv) mice, which lack MCs in a context of other defects due to a mutation of the Kit receptor. To address further an MC role, we used transgenic strains with normal lineage development and a deficiency in a specific secretory granule component. Mouse strains lacking the MC-restricted chymase, mouse MC protease (mMCP)-4, or elastase, mMCP-5, show decreased injury after a second-degree scald burn, whereas mice lacking the MC-restricted tryptases, mMCP-6 and mMCP-7, or MC-specific carboxypeptidase A3 activity are not protected. Histologic sections showed some disruption of the epidermis at the scald site in the protected strains suggesting the possibility of topical reconstitution of full injury. Topical application of recombinant mMCP-5 or human neutrophil elastase to the scalded area increases epidermal injury with subsequent ulceration and scarring, both clinically and morphologically, in mMCP-5-deficient mice. Restoration of injury requires that topical administration of recombinant mMCP-5 occurs within the first hour postburn. Importantly, topical application of human MC chymase restores burn injury to scalded mMCP-4-deficient mice but not to mMCP-5-deficient mice revealing nonredundant actions for these two MC proteases in a model of innate inflammatory injury with remodeling.

Distinguishing mast cell and granulocyte differentiation at the single-cell level

The lineage restriction of prospectively isolated hematopoietic progenitors has been traditionally assessed by bulk in vitro culture and transplantation of large number of cells in vivo. These methods, however, cannot distinguish between homogenous multipotent or heterogeneous lineage-restricted populations. Using clonal assays of 1 or 5 cells in vitro, single-cell quantitative gene expression analyses, and transplantation of mice with low numbers of cells, we show that a common myeloid progenitor (CMP) is Sca-1(lo)lin(-)c-Kit(+)CD27(+)Flk-2(-) (SL-CMP; Sca-1(lo) CMP) and a granulocyte/macrophage progenitor (GMP) is Sca-1(lo)lin(-)c-Kit(+)CD27(+)Flk-2(+)CD150(-/lo) (SL-GMP; Sca-1(lo) GMP). We found that mast cell progenitor potential is present in the SL-CMP fraction, but not in the more differentiated SL-GMP population, and is more closely related to megakaryocyte/erythrocyte specification. Our data provide criteria for the prospective isolation of SL-CMP and SL-GMP and support the conclusion that mast cells are specified during hematopoiesis earlier than and independently from granulocytes.

Notch 1 keeps pro-T cells on track

In this issue of Immunity, Feyerabend et al. (2009) report that Delta-like 4, acting on Notch 1, prevents pro-T cells from differentiating into dendritic cells and B cells. In addition, in the absence of Notch 1, B cells in the thymus arose from a cell-extrinsic pathway.

Interstitial cells from rat middle cerebral artery belong to smooth muscle cell type

It is now established that non-contractile cells with thin filopodia, also called vascular interstitial cells (VICs), are constitutively present in the media of many, if not all, blood vessels. The aim of this study was to determine the type of cell lineage to which arterial VICs belong using immunocytochemical, and real-time and reverse transcription PCR (RT-PCR). Using RT-PCR, we compared gene expression profiles of single VICs and smooth muscle cells (SMCs) freshly dispersed from rat middle cerebral artery. Both VICs and SMCs expressed the SMC marker, smooth muscle myosin heavy chain (SM-MHC), but did not express fibroblast, pericyte, neuronal, mast cell, endothelial or stem cell markers. Freshly isolated VICs also did not express c-kit, which is the marker for interstitial cells of Cajal in the gastrointestinal tract. Immunocytochemical labelling of contractile proteins showed that VICs and SMCs expressed SM-MHC similarly to the same degree, but VICs in contrast to SMCs had decreased expression of alpha-SM-actin and very low or no expression of calponin. Real-time RT-PCR was consistent with immunocytochemical experiments and showed that VICs had four times lower gene expression of calponin comparing to SMCs, which may explain VICs' inability to contract. VICs had greater expression than SMCs of structural proteins such as non-muscular beta-actin and desmin. The results obtained suggest that VICs represent a subtype of SMCs and may originate from the same precursor as SMCs, but later develop filopodia and a non-contractile cell phenotype.

Pivotal advance: IgE accelerates in vitro development of mast cells and modifies their phenotype

Antigen-dependent activation of IgE-bound mast cells is critical for immediate hypersensitivity and other allergic disorders. Recent studies have revealed the effects of monomeric IgEs on mast cell survival and activation. Furthermore, IgE molecules exhibit a wide range of heterogeneity in the ability to induce mast cell activation in the absence of antigen. Highly cytokinergic (HC) IgEs can induce a variety of activation events including cell survival, degranulation, cytokine production, and migration, whereas poorly cytokinergic (PC) IgEs can do so inefficiently. Here, we show that culture of bone marrow cells in the presence of monomeric IgEs results in an increased number of mast cells compared with cultures grown without IgE. Furthermore, time in culture required to generate > or =80% pure mast cells is decreased. IgE molecules can directly influence mast cell progenitors to differentiate into mast cells. mRNA expression of several mast cell proteases and mast cell-related transcription factors is higher in mast cells cultured with an HC IgE than those cultured with a PC IgE or without IgE. Expression of early growth response factor-1, a transcription factor that is involved in the production of TNF-alpha in mast cells, is enhanced in cultures containing high and low concentrations of HC IgE and a high concentration of PC IgE. Consistent with this, expression of TNF-alpha is higher in mast cells cultured with HC IgE than PC IgE. Therefore, our results suggest that monomeric IgEs, especially HC IgEs, not only promote mast cell development but also modulate the mast cell phenotype.

Doing What I Like

I have spent my entire professional life at Harvard Medical School, beginning as a medical student. I have enjoyed each day of a diverse career in four medical subspecialties while following the same triad of preclinical areas of investigation—cysteinyl leukotrienes, mast cells, and complement—with occasional translational opportunities. I did not envision a career with a predominant preclinical component. Such a path simply evolved because I chose instinctively at multiple junctures to follow what proved to be propitious opportunities. My commentary notes some of the highlights for each area of interest and the mentors, collaborators, and trainees whose counsel has been immensely important at particular intervals or over an extended period.

Molecular mechanism of mast cell mediated innate defense against endothelin and snake venom sarafotoxin

Mast cells are protective against snake venom sarafotoxins that belong to the endothelin (ET) peptide family. The molecular mechanism underlying this recently recognized innate defense pathway is unknown, but secretory granule proteases have been invoked. To specifically disrupt a single protease function without affecting expression of other proteases, we have generated a mouse mutant selectively lacking mast cell carboxypeptidase A (Mc-cpa) activity. Using this mutant, we have now identified Mc-cpa as the essential protective mast cell enzyme. Mass spectrometry of peptide substrates after cleavage by normal or mutant mast cells showed that removal of a single amino acid, the C-terminal tryptophan, from ET and sarafotoxin by Mc-cpa is the principle molecular mechanism underlying this very rapid mast cell response. Mast cell proteases can also cleave ET and sarafotoxin internally, but such “nicking” is not protective because intramolecular disulfide bridges maintain peptide function. We conclude that mast cells attack ET and sarafotoxin exactly at the structure required for toxicity, and hence sarafotoxins could not “evade” Mc-cpa's substrate specificity without loss of toxicity.

Characterization of a carboxypeptidase inhibitor from the tick Haemaphysalis longicornis

A carboxypeptidase inhibitor called HlTCI was isolated from Haemaphysalis longicornis in this study. The full-length cDNA of HlTCI contains an open reading frame (ORF) of 291bp, encoding 96 amino acid residues consisting of a predicted 19-residue signal peptide and a putative mature 77-residue protein. The expected mature protein is cysteine-rich and has 12 cysteine residues assumed to construct six disulfide bridges. The deduced peptide sequence shows 63.9% homology to the carboxypeptidase inhibitor from another ixodid tick, Rhipicephalus bursa. Reverse-transcription PCR (RT-PCR) indicated that HlTCI was specifically expressed in the ovary from partially engorged adult ticks. The recombinant protein of HlTCI (rHlTCI) with glutathione S-transferase (GST) was expressed in Escherichia coli strain BL21 (DE3) and purified by glutathione-Sepharose 4B beads. rHlTCI showed inhibitory activity against digestive metallocarboxypeptidases A and B, but the activity was affected by the increase of the temperature treatment. High concentrations of rHlTCI were shown to significantly accelerate fibrinolysis in vitro. This effect of rHlTCI on clot lysis suggests its promising potential for use in some thrombotic disorders.

Different mast cell mediators produced by different mast cell phenotypes

The activation of mast cells results in the release of a large variety of inflammatory mediators, many of which are preformed and stored within the secretory granules. Exocytosis of the secretory granule contents releases a macromolecular complex composed of proteoglycan and the neutral proteases. The proteases include both endo- and exopeptidases, suggesting the possibility of a concerted action on unknown substrates. Different proteases are expressed by different mast cells originally defined by histochemical and ultrastructural criteria. From adoptive transfer experiments it appears that the mast cell phenotype is profoundly influenced by the microenvironment. Understanding the development and regulation of the mast cell phenotype is being approached by the development of: (1) An in vitro system of differentiation using in vitro-differentiated mast cells which upon co-culture with fibroblasts demonstrate a phenotypic shift; (2) Kirsten virus-transformed mast cells exhibiting a spectrum of phenotypes. These reagents have allowed the isolation and characterization of the cDNAs of the various preformed protein mediators including the secretory granule proteoglycan peptide core, serine proteases and carboxypeptidase. These cDNAs have provided the first probes for the molecular characterization of the mast cell-associated proteoglycan peptide core, a carboxypeptidase A and a 28,000 Mr serine protease.

Mast cell mediators in allergic inflammation and mastocytosis

Mast cells possess an array of potent inflammatory mediators capable of inducing acute symptoms after cell activation, including urticaria, angioedema, bronchoconstriction, diarrhea, vomiting, hypotension, cardiovascular collapse, and death in few minutes. In contrast, mast cells can provide an array of beneficial mediators in the setting of acute infections, cardiovascular diseases, and cancer. The balance between the detrimental and beneficial roles of mast cells is not completely understood. Although the symptoms of acute mast cell mediator release can be reversed with epinephrine, adrenergic agonists, and mediator blockers, the continued release of histamine, proteases, prostaglandins, leukotrienes, cytokines, and chemokines leads to chronic and debilitating disease, such as mastocytosis. Identification of the molecular factors and mechanisms that control the synthesis and release of mast cell mediators should benefit all patients with mast cell activation syndromes and mastocytosis.

Mast Cell Proteases

Mast cells (MCs) are traditionally thought of as a nuisance for its host, for example, by causing many of the symptoms associated with allergic reactions. In addition, recent research has put focus on MCs for displaying harmful effects during various autoimmune disorders. On the other hand, MCs can also be beneficial for its host, for example, by contributing to the defense against insults such as bacteria, parasites, and snake venom toxins. When the MC is challenged by an external stimulus, it may respond by degranulation. In this process, a number of powerful preformed inflammatory "mediators" are released, including cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases: chymases, tryptases, and carboxypeptidase A. Although the exact effector mechanism(s) by which MCs carry out their either beneficial or harmful effects in vivo are in large parts unknown, it is reasonable to assume that these mediators may contribute in profound ways. Among the various MC mediators, the exact biological function of the MC proteases has for a long time been relatively obscure. However, recent progress involving successful genetic targeting of several MC protease genes has generated powerful tools, which will enable us to unravel the role of the MC proteases both in normal physiology as well as in pathological settings. This chapter summarizes the current knowledge of the biology of the MC proteases.

The hypomorphic Gata1low mutation alters the proliferation/differentiation potential of the common megakaryocytic-erythroid progenitor

Recent evidence suggests that mutations in the Gata1 gene may alter the proliferation/differentiation potential of hemopoietic progenitors. By single-cell cloning and sequential replating experiments of prospectively isolated progenitor cells, we demonstrate here that the hypomorphic Gata1low mutation increases the proliferation potential of a unique class of progenitor cells, similar in phenotype to adult common erythroid/megakaryocytic progenitors (MEPs), but with the "unique" capacity to generate erythroblasts, megakaryocytes, and mast cells in vitro. Conversely, progenitor cells phenotypically similar to mast cell progenitors (MCPs) are not detectable in the marrow from these mutants. At the single-cell level, about 11% of Gata1low progenitor cells, including MEPs, generate cells that will continue to proliferate in cultures for up to 4 months. In agreement with these results, trilineage (erythroid, megakaryocytic, and mastocytic) cell lines are consistently isolated from bone marrow and spleen cells of Gata1low mice. These results confirm the crucial role played by Gata1 in hematopoietic commitment and identify, as a new target for the Gata1 action, the restriction point at which common myeloid progenitors become either MEPs or MCPs.

Loss of histochemical identity in mast cells lacking carboxypeptidase A

Mast cell carboxypeptidase A (Mc-cpa) is a highly conserved secretory granule protease. The onset of expression in mast cell progenitors and lineage specificity suggest an important role for Mc-cpa in mast cells. To address the function of Mc-cpa, we generated Mc-cpa-null mice. Mc-cpa-/- mast cells lacked carboxypeptidase activity, revealing that Mc-cpa is a nonredundant enzyme. While Mc-cpa-/- peritoneal mast cells were ultrastructurally normal and synthesized normal amounts of heparin, they displayed striking histochemical and biochemical hallmarks of immature mast cells. Wild-type peritoneal mast cells had a mature phenotype characterized by differential histochemical staining with proteoglycan-reactive dyes (cells do not stain with alcian blue but stain with safranin and with berberine) and a high side scatter to forward scatter ratio by flow cytometry and were detergent resistant. In contrast, Mc-cpa-/- peritoneal mast cells, like immature bone marrow-derived cultured mast cells, stained with alcian blue normally or weakly and either did not stain with safranin and berberine or stained weakly, had a low side scatter to forward scatter ratio, and were detergent sensitive. This phenotype was partially ameliorated with age. Thus, histochemistry and flow cytometry, commonly used to measure mast cell maturation, deviated from morphology in Mc-cpa-/- mice. The Mc-cpa-/- mast cell phenotype was not associated with defects in degranulation in vitro or passive cutaneous anaphylaxis in vivo. Collectively, Mc-cpa plays a crucial role for the generation of phenotypically mature mast cells.

Carboxypeptidase N: a pleiotropic regulator of inflammation

Carboxypeptidase N (CPN) is a plasma zinc metalloprotease, which consists of two enzymatically active small subunits (CPN1) and two large subunits (CPN2) that protect the protein from degradation. CPN cleaves carboxy-terminal arginines and lysines from peptides found in the bloodstream such as complement anaphylatoxins, kinins, and creatine kinase MM (CK-MM). By removing only one amino acid, CPN has the ability to change peptide activity and receptor binding. CPN is a member of a larger family of carboxypeptidases, many of which also cleave arginine and lysine. Because of the highly conserved active sites and the possible redundant functions of carboxypeptidases, it has been difficult to elucidate the role of CPN in disease processes. The future use of gene ablation technology may be the most appropriate way to understand the function of CPN in vivo.

Mast cells in the rat brain synthesize gonadotropin-releasing hormone

Mast cells occur in the brain and their number changes with reproductive status. While it has been suggested that brain mast cells contain the mammalian hypothalamic form of gonadotropin-releasing hormone (GnRH-I), it is not known whether mast cells synthesize GnRH-I de novo. In the present study, mast cells in the rat thalamus were immunoreactive to antisera generated against GnRH-I and the GnRH-I associated peptide (GAP); mast cell identity was confirmed by the presence of heparin, a molecule specific to mast cells, or serotonin. To test whether mast cells synthesize GnRH-I mRNA, in situ hybridization was performed using a GnRH-I cRNA probe, and the signal was identified as being within mast cells by the binding of avidin to heparin. GnRH-I mRNA was also found, using RT-PCR, in mast cells isolated from the peritoneal cavity. Given the function of GnRH-I in the regulation of reproduction, changes in the population of brain GnRH-I mast cells were investigated. While housing males with sexually receptive females for 2 h or 5 days resulted in a significant increase in the number of brain mast cells, the proportion of mast cells positive for GnRH-I was similar to that in males housed with a familiar male. These findings represent the first report showing that mast cells synthesize GnRH-I and that the mast cell increase seen in a reproductive context is the result of a parallel increase in GnRH-I positive and non-GnRH-I positive mast cells.

Cooperative and antagonistic interplay between PU.1 and GATA-2 in the specification of myeloid cell fates

PU.1 and GATA transcription factors appear to antagonize each other's function in the development of distinct lineages of the hematopoietic system. In contrast, we demonstrate that PU.1, like GATA-2, is essential for the generation of mast cells. PU.1-/- hematopoietic progenitors can be propagated in IL-3 and differentiate into mast cells or macrophages upon restoration of PU.1 activity. Using these progenitors and a conditionally activatable PU.1 protein, we show that PU.1 can negatively regulate expression of the GATA-2 gene. In the absence of GATA-2, PU.1 promotes macrophage but not mast cell differentiation. Reexpression of GATA-2 in such progenitors enables the generation of mast cells. We propose a developmental model in which cooperative function or antagonistic crossregulation by PU.1 of GATA-2 promotes distinct myeloid cell fates.

Regulation of extravascular coagulation and fibrinolysis by heparin-dependent mast cell chymase

We recently characterized a heparin-deficient mouse strain generated by targeting the gene for N-deacetylase/N-sulfotransferase-2 (NDST-2). The NDST-2-/- mice show severe defects in their organization of mast cell (MC) secretory granules, with an almost total absence of the various heparin-binding MC proteases. In the present report we have studied the consequences of heparin/MC protease deficiency for extravascular coagulation and fibrinolysis. Addition of prothrombin to peritoneal cells-a mixture of macrophages, lymphocytes, and MCs-resulted in formation of thrombin but the accumulation of thrombin occurred faster in the NDST-2-/-cells than in normal controls. Further, the generated thrombin was subsequently inactivated in the NDST-2+/+ cell cultures but not in the NDST-2-/- cells. Plasminogen was activated to plasmin at an apparently higher rate in peritoneal cells from NDST-2 null mice than in the normal controls. Similar to thrombin, the generated plasmin was inactivated by NDST-2+/+ but not by the NDST-2-/- cells. Subsequent experiments with normal cells showed that cell surface-associated MC chymase, in a strongly heparin-dependent manner, was responsible for both the thrombin-inactivating- and plasmin-inactivating activities. These results show that MC chymase-heparin complexes have the potential to regulate extravascular coagulation processes, as well as the plasminogen activator/plasmin system.

Promoted expression of mast cell-specific proteases in IgE-dependent passive cutaneous anaphylaxis responses

BACKGROUND

Various factors can influence the protease expression phenotype of mast cells.

METHODS

In an effort to understand the potential role of the mast cell proteases in the IgE-dependent passive cutaneous anaphylaxis (PCA) responses of murine tissues, we studied the changes of proteases expression. The expressions of proteases were examined by Northern blotting and immunohistochemistry.

RESULTS

Promoted expression phenotypes of mouse mast cell protease (mMCP)-4, and rat mast cell protease I were accompanied by initiation of anti-dinitrophenyl (DNP) IgE-induced PCA responses, suggesting that the induction of these proteases expression are associated with IgE-mediated anaphylaxis responses. Elevated level of the L-histidine decarboxylase (HDC) mRNA expression was also observed in the PCA tissues and the activated mast cells, compared with that of the corresponding control tissue and cells, due to the activation of mast cells.

CONCLUSIONS

Promoted protease expression phenotype appears to be linked with the induction of HDC expression.

Mast cell lineage development and phenotypic regulation

Three cornerstones of mast cell development are an absolute dependence on the presence of stem cell factor, T-cell-independent and T-cell-dependent tissue mast cell populations derived from a single lineage, and a diversity of phenotypes for mature tissue mast cells as defined by immunohistochemical and biochemical properties. The in vivo biology of the mast cell in the mouse has been deduced through the availability of mice with genetic and induced gene disruptions, whereas limited but compatible findings for the human have been acquired through the study of patients with systemic mastocytosis and T-cell deficiency. The characteristics of mast cells recognized from these in situ circumstances can be used to establish culture systems for obtaining mouse and human mast cells from progenitor cell sources. These cells allow studies of receptor-mediated gene regulation by cytokines derived from both stromal cells and T cells.

Tissue-dependent alteration of protease expression phenotype in murine peritoneal mast cells that were genetically labeled with green fluorescent protein

The changing process of protease expression phenotype was studied after transplantation of peritoneal mast cells (PMCs). To pursue the fate of the transplanted PMCs, we obtained PMCs from WBB6F(1)-c-kit(+)/c-kit(+) mice with a transgene encoding green fluorescent protein (GFP). A large (n = 10(4)) or small (n = 500) number of PMCs was injected into the stomach wall of genetically mast cell-deficient WBB6F(1)-c-kit(W)/c-kit(Wv) mice without the GFP transgene. The original PMCs expressed messenger (m) RNAs of both mast cell carboxypeptidase A (MC-CPA) and mouse mast cell protease (mMCP)-2. The MC-CPA(+)/mMCP-2(+) phenotype did not change in both the muscularis propria and mucosa when 10(4) PMCs were injected. In contrast, when 500 PMCs were injected, the mast cells that developed in the muscularis propria showed MC-CPA(+)/mMCP-2(-) phenotype and those that appeared in the mucosa showed MC-CPA(-)/mMCP-2(+) phenotype. On day 1 after the injection of 500 PMCs, only approximately 20 GFP(+) cells were detected in the muscularis propria and no GFP(+) cells in the mucosa. The proportion of Alcian blue(+) cells decreased until day 7 and increased thereafter. The GFP(+) but Alcian blue(-) cells were considered as degranulated PMCS: The remarkable decrease or degranulation seemed to be necessary for the alteration of protease expression phenotype.

Importance of leucine zipper domain of mi transcription factor (MITF) for differentiation of mast cells demonstrated using mi(ce)/mi(ce) mutant mice of which MITF lacks the zipper domain

The mi transcription factor (MITF) is a basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factor that is important for the development of mast cells. Mast cells of mi/mi genotype express normal amount of abnormal MITF (mi-MITF), whereas mast cells of tg/tg genotype do not express any MITFs. Mast cells of mi/mi mice show more severe abnormalities than those of tg/tg mice, indicating that the mi-MITF possesses the inhibitory function. The MITF encoded by the mi(ce) mutant allele (ce-MITF) lacks the Zip domain. We examined the importance of the Zip domain using mi(ce)/mi(ce) mice. The amounts of c-kit, granzyme B (Gr B), and tryptophan hydroxylase (TPH) messenger RNAs decreased in mast cells of mi(ce)/mi(ce) mice to levels comparable to those of tg/tg mice, and the amounts were intermediate between those of +/+ mice and those of mi/mi mice. Gr B mediates the cytotoxic activity of mast cells, and TPH is a rate-limiting enzyme for the synthesis of serotonin. The cytotoxic activity and serotonin content of mi(ce)/mi(ce) mast cells were comparable to those of tg/tg mast cells and were significantly higher than those of mi/mi mast cells. The phenotype of mi(ce)/mi(ce) mast cells was similar to that of tg/tg mast cells rather than to that of mi/mi mast cells, suggesting that the ce-MITF had no functions. The Zip domain of MITF appeared to be important for the development of mast cells. (Blood. 2001;97:2038-2044)

Inhibitory effect of the transcription factor encoded by the mutant mi microphthalmia allele on transactivation of mouse mast cell protease 7 gene

The transcription factor encoded by the mi locus (MITF) is a transcription factor of the basic-helix-loop-helix zipper protein family. Mice of mi/mi genotype express a normal amount of abnormal MITF, whereas mice of tg/tg genotype do not express any MITFs due to the transgene insertional mutation. The effect of normal (+) and mutant (mi) MITFs on the expression of mouse mast cell protease (MMCP) 6 and 7 was examined. Both MMCP-6 and MMCP-7 are tryptases, and their coding regions with high homology are closely located on chromosome 17. Both MMCP-6 and MMCP-7 genes are expressed in normal cultured mast cells (+/+ CMCs). Although the transcription of MMCP-6 gene was severely suppressed in both mi/mi and tg/tg CMCs, that of MMCP-7 gene was severely suppressed only in mi/mi CMCs. The study identified the most significant segment for the transcription in the 5' flanking region of MMCP-7 gene. Unexpectedly, no CANNTG motifs were found that are recognized and bound by +-MITF in this segment. Instead, there was an AP-1 binding motif, and binding of c-Jun to the AP-1 motif significantly enhanced the transcription of MMCP-7 gene. The complex formation of c-Jun with either +-MITF or mi-MITF was demonstrated. The binding of +-MITF to c-Jun enhanced the transactivation of MMCP-7 gene, and that of mi-MITF suppressed the transactivation. Although the former complex was located only in the nucleus, the latter complex was predominantly found in the cytoplasm. The negative effect of mi-MITF on the transcription of MMCP-7 gene appeared to be executed through the interaction with c-Jun.

Independent influence of strain difference and mi transcription factor on the expression of mouse mast cell chymases

Expression of mouse mast cell protease (mMCP) genes was examined with particular attention to the transactivation effect of mi transcription factor (MITF) and the expression differences between C57BL/6 (B6) and WB strains. We had reported the enhancing effect of MITF on the expression of mMCP-4, -5, and -6 genes in cultured mast cells (CMCs) of B6 strain, and in the present study we demonstrated the enhancing effect on the expression of mMCP-2 and -9 genes as well. The enhancing effect of MITF on the expression of mMCP-2, -4, -5, -6, and -9 genes was also detected in CMCs of the WB strain. The regulation of mMCP-2, -4, and -9 genes was localized to a specific promoter element (CANNTG) which was recognized and bound by MITF and which was conserved between the B6 and WB strains. On the other hand, the expression of mMCP-2, -4, and -9 genes was smaller in CMCs of the B6 strain when compared to their expression in CMCs of the WB strain. Although mMCP-5 is a chymase as mMCP-2, -4, and -9, and genes encoding all of the chymases are located on chromosome 14, the mMCP-5 gene was regulated in a manner distinct from mMCP-2, -4, and -9 genes.

Metallocarboxypeptidases and their protein inhibitors. Structure, function and biomedical properties

Among the different aspects of recent progress in the field of metallocarboxypeptidases has been the elucidation of the three dimensional structures of the pro-segments (in monomeric or oligomeric species) and their role in the expression, folding and inhibition/activation of the pancreatic and pancreatic-like forms. Also of great significance has been the cloning and characterization of several new regulatory carboxypeptidases, enzymes that are related with important functions in protein and peptide processing and that show significant structural differences among them and also with the digestive ones. Many regulatory carboxypeptidases lack a pro-region, unlike the digestive forms or others in between from the evolutionary point of view. Finally, important advances have been made on the finding and characterization of new protein inhibitors of metallocarboxypeptidases, some of them with interesting potential applications in the biotechnological/biomedical fields. These advances are analyzed here and compared with the earlier observations in this field, which was first explored by Hans Neurath and collaborators.

Synergy of PEBP2/CBF with mi transcription factor (MITF) for transactivation of mouse mast cell protease 6 gene

The mi locus encodes a member of the basic - helix - loop - helix - leucine zipper (bHLH-Zip) protein family of transcription factors (hereafter called MITF). Although the bHLH-Zip family transcription factors generally recognize and bind CANNTG motifs, the expression of mouse mast cell protease 6 (MMCP-6) gene is regulated by MITF through the GACCTG motif in the promoter region. The GACCTG motif was partly overlapped the TGTGGTC sequence, which was bound by polyomavirus enhancer binding protein 2 (PEBP2). In the present study, the effect of PEBP2 on the expression of MMCP-6 gene was examined. PEBP2 that is composed of alpha and beta subunits was expressed by mast cell lines and cultured mast cells derived from spleen. The overexpression of dominant negative PEBP2 cDNA reduced the expression of MMCP-6. Moreover, the simultaneous transfection of the plasmid containing MITF cDNA and the plasmid containing PEBP2 cDNA increased the MMCP-6 promoter activity. For the synergistic action of PEBP2 and MITF, the intact GACCTG and TGTGGTC motifs were prerequisite. The PEBP2alphaB1 mutant which lacked the region downstream from the Runt domain did not bind MITF and lost the synergistic function. These results indicated that PEBP2 and MITF synergistically transactivated the MMCP-6 gene and that the region downstream from the Runt domain of PEBP2alphaB1 was essential for the physical and functional interactions with MITF.

Characterization of a functional relationship between hepatocyte growth factor and mouse bone marrow-derived mast cells

During the early stage (at 4 weeks) of interleukin-3 (IL-3)-induced development, mouse bone marrow-derived mast cells (BMMC) express alpha 4, alpha 5 and alpha 6 integrins, whereas with further maturation beyond 10 weeks, only alpha 5 integrin remains stably expressed. Hepatocyte growth factor (HGF) modulates the growth and movement of diverse cell types upon binding to its receptor, encoded by the proto-oncogene c-met. We report here the expression of c-met by BMMC throughout the course of their development. In addition, HGF stimulated migration of early week-4 BMMC, but not of the later stage week-10 BMMC, on fibronectin and laminin substrates. The developmental stage-dependent effect of HGF on BMMC was due to specific stimulation of the migratory function of alpha 4 and alpha 6, but not alpha 5 integrins. In addition, HGF had no effect on BMMC growth, either alone or in combination with IL-3. While HGF is stimulatory of the migratory function of BMMC, our results show that BMMC in turn can modulate HGF function. Thus, upon activation via the IgE receptors, BMMC released proteases that abolished HGF activities. Analyses of the degradation products by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot using antisera prepared against recombinant HGF and the kringle 3 domain of HGF revealed specific degradation of HGF alpha but not beta/beta' subunits. Therefore, our results suggest that: 1) the motogenic effect of HGF on BMMC varies according to the stage of their development, 2) HGF stimulation of BMMC migration is due to selective activation of alpha 4 and alpha 6, but not alpha 5 integrin function, and 3) there exists a two-way relationship between BMMC and HGF such that HGF stimulates the beta 1 integrin-mediated migratory function of BMMC, which can, in turn, modulate HGF function by release of serine proteases.

Different Effect of Various Mutant MITF Encoded by mi,Mior, or Miwh Allele on Phenotype of Murine Mast Cells

The mi locus encodes a member of the basic-helix-loop-helix-leucine zipper protein family of transcription factors (hereafter called MITF). Mutant alleles of mi,Mior, and Miwh are deletion or point mutation of the basic domain by which MITF binds DNA. The basic domain also has nuclear localization potential. In the present study, we compared the mast cell abnormalities ofMior/Mior andMiwh/Miwh mice with those ofmi/mi mice, of which many have been described by us. The number of mast cells in the skin of Mior/Miorsuckling mice was remarkably decreased from that observed inmi/mi suckling mice, but the number was normal in the skin ofMiwh/Miwh suckling mice. The decrease in skin mast cells was more severe in the mi/mi embryos than inmi/mi suckling mice, but the magnitude of the decrease was comparable between Mior/Mior embryos and Mior/Mior suckling mice. The poor mRNA expression of granzyme B and tryptophan hydroxylase genes was observed in all cultured mast cells (CMCs) derived from the spleens ofMiwh/Miwh,Mior/Mior, and mi/mi mice. However, the poor expression of mouse mast cell protease-4 (MMCP-4), MMCP-5, and MMCP-6 was observed only inMior/Mior and mi/mi CMCs. MITF encoded by Miwh mutant allele (Miwh-MITF) showed deficient but demonstratable DNA binding, but mi-MITF and Mior-MITF did not show any DNA binding ability. Although Miwh-MITF and Mior-MITF showed normal nuclear localization potential, the potential was significantly impaired in mi-MITF. The rank order of mast cell abnormality (mi/mi >Mior/Mior >Miwh/Miwh) appears to be related to the functional abnormality of MITF encoded by each mutant gene.

Different Effect of Various Mutant MITF Encoded by mi,Mior, or Miwh Allele on Phenotype of Murine Mast Cells

The mi locus encodes a member of the basic-helix-loop-helix-leucine zipper protein family of transcription factors (hereafter called MITF). Mutant alleles of mi,Mior, and Miwh are deletion or point mutation of the basic domain by which MITF binds DNA. The basic domain also has nuclear localization potential. In the present study, we compared the mast cell abnormalities ofMior/Mior andMiwh/Miwh mice with those ofmi/mi mice, of which many have been described by us. The number of mast cells in the skin of Mior/Miorsuckling mice was remarkably decreased from that observed inmi/mi suckling mice, but the number was normal in the skin ofMiwh/Miwh suckling mice. The decrease in skin mast cells was more severe in the mi/mi embryos than inmi/mi suckling mice, but the magnitude of the decrease was comparable between Mior/Mior embryos and Mior/Mior suckling mice. The poor mRNA expression of granzyme B and tryptophan hydroxylase genes was observed in all cultured mast cells (CMCs) derived from the spleens ofMiwh/Miwh,Mior/Mior, and mi/mi mice. However, the poor expression of mouse mast cell protease-4 (MMCP-4), MMCP-5, and MMCP-6 was observed only inMior/Mior and mi/mi CMCs. MITF encoded by Miwh mutant allele (Miwh-MITF) showed deficient but demonstratable DNA binding, but mi-MITF and Mior-MITF did not show any DNA binding ability. Although Miwh-MITF and Mior-MITF showed normal nuclear localization potential, the potential was significantly impaired in mi-MITF. The rank order of mast cell abnormality (mi/mi >Mior/Mior >Miwh/Miwh) appears to be related to the functional abnormality of MITF encoded by each mutant gene.

Glu300 of rat carboxypeptidase E is essential for enzymatic activity but not substrate binding or routing to the regulated secretory pathway

Several recently discovered members of the carboxypeptidase E (CPE) gene family lack critical active site residues that are conserved in other family members. For example, three CPE-like proteins contain a Tyr in place of Glu300 (equivalent to Glu270 of carboxypeptidase A and B). To investigate the importance of this position, Glu300 of rat CPE was converted into Gln, Lys, or Tyr, and the proteins expressed in Sf9 cells using the baculovirus system. All three mutants were secreted from the cells, but the media showed no enzyme activity above background levels. Wild-type CPE and the Gln300 point mutant bound to a p-aminobenzoyl-Arg-Sepharose affinity resin, and this binding was competed by an active site-directed inhibitor, guanidinoethylmercaptosuccinic acid. The affinity purified mutant CPE protein showed no detectable enzyme activity (<0.004% of wild-type CPE) toward dansyl-Phe-Ala-Arg. Expression of the Gln300 and Lys300 mutant CPE proteins in the NIT3 mouse pancreatic beta-cell line showed that these mutants are routed into secretory vesicles and secreted via the regulated pathway. Taken together, these results indicate that Glu300 of CPE is essential for enzyme activity, but not required for substrate binding or for routing into the regulated secretory pathway.

Purification and characterization of human metallocarboxypeptidase Z

Carboxypeptidase Z (CPZ) is a recently discovered member of the metallocarboxypeptidase gene family that has an N-terminal domain related to the Wnt/wingless binding domain of frizzled receptors and other proteins. To further characterize the enzymatic properties of CPZ, the enzyme was purified using Arg- and heparin-affinity columns. CPZ has a neutral pH optimum, and is inhibited by chelating agents and several divalent cations (Zn2+, Mn2+, Cd2+, Cu2+, Hg2+). Active site-directed inhibitors of several other metallocarboxypeptidases also inhibit CPZ activity with moderate potency. CPZ cleaves substrates with C-terminal Arg residues, preferring peptides with an Ala in the penultimate position. No activity is detected toward substrates with an Ile-Arg or a Pro-Arg sequence. The Km for dansyl-Phe-Ala-Arg and dansyl-Pro-Ala-Arg are both approximately 2 mM. Taken together, these data suggests a selective role for CPZ in the processing of extracellular peptides or proteins.

Deficient Transcription of Mouse Mast Cell Protease 4 Gene in Mutant Mice of mi/mi Genotype

The mi locus encodes a member of the basic-helix-loop-helix-leucine zipper (bHLH-Zip) protein family of transcription factors (hereafter called MITF). We reported that expression of the mouse mast cell protease 5 (MMCP-5) and MMCP-6 genes were deficient in cultured mast cells (CMC) derived from mutant mice ofmi/mi genotype. Despite the reduced expression of both MMCP-5 and MMCP-6, their regulation mechanisms were different. Because MMCP-5 is a chymase and MMCP-6 a tryptase, there was a possibility that the difference in regulation mechanisms was associated with their different characteristics as proteases. We compared the regulation mechanisms of another chymase, MMCP-4, with those of MMCP-5 and MMCP-6. The expression of the MMCP-4 gene was also deficient in mi/mi CMC. The overexpression of the normal (+) MITF but not of mi-MITF normalized the poor expression of the MMCP-4 gene in mi/mi CMC, indicating the involvement of +-MITF in transactivation of the MMCP-4 gene. Although MMCP-4 is chymase as MMCP-5, the regulation of MMCP-4 expression was more similar to MMCP-6 than to MMCP-5. We also showed the deficient expression of granzyme B and cathepsin G genes inmi/mi CMC. Genes encoding granzyme B, cathepsin G, MMCP-4, and MMCP-5 are located on chromosome 14. Because all these genes showed deficient expression in mi/mi CMC, there is a possibility that MITF might regulate the expression of these genes through a locus control region.

Identification of mouse CPX-1, a novel member of the metallocarboxypeptidase gene family with highest similarity to CPX-2

The recent finding that Cpe(fat)/Cpe(fat) mice, which lack carboxypeptidase E (CPE) activity because of a point mutation, are still capable of a reduced amount of neuroendocrine peptide processing suggested that additional carboxypeptidases (CPs) participate in this processing reaction. Searches for novel members of the CPE gene family led to the discovery of CPD, CPZ, AEBP1, and CPX-2. In the present report, we describe mouse CPX-1, another novel member of this gene family. Like AEBP1 and CPX-2, CPX-1 contains an N-terminal region of 160 amino acids with sequence similarity to the discoidin domain of a variety of proteins. The 410-residue CP-like domain of CPX-1 has 54% to 62% amino acid sequence identity with AEBP1 and CPX-2 and 33% to 49% amino acid identity with other members of the CPE subfamily. However, several active-site residues that are important for catalytic activity of other CPs are not conserved in CPX-1. Furthermore, CPX-1 expressed in either the baculovirus system or the mouse AtT-20 cell line does not cleave standard CP substrates. Northern blot analysis showed the highest levels of CPX-1 mRNA in testis and spleen and lower levels in salivary gland, brain, heart, lung, and kidney. In situ hybridization of CPX-1 mRNA in embryonic and fetal mouse tissue showed expression throughout the head and thorax, with abundance in primordial cartilage and skeletal structures. In the head, high levels of CPX-1 mRNA were associated with the nasal mesenchyme, primordial cartilage structures in the ear, and the meninges. In the thorax, CPX-1 mRNA was expressed in multiple developing skeletal structures, including chondrocytes and perichondrial cells of the rib, vertebral, and long-bone primordia. Taken together, these findings suggest that it is unlikely that CPX-1 functions in the processing of neuroendocrine peptides. Instead, CPX-1 may have a role in development, possibly mediating cell interactions via its discoidin domain.

Identification of mouse CPX-2, a novel member of the metallocarboxypeptidase gene family: cDNA cloning, mRNA distribution, and protein expression and characterization

A novel member of the metallocarboxypeptidase gene family was identified from its homology with carboxypeptidase E and has been designated CPX-2. The cDNA of 2500 nucleotides encodes a protein of 764 amino acids that contains an N-terminal signal peptide-like sequence, a 158-residue discoidin domain, and a 400-residue carboxypeptidase domain. The 400-residue metallocarboxypeptidase domain has 59% amino acid identity with a protein designated AEBP-1; 44% to 46% identity with carboxypeptidases E, N, and Z; and lower homology with other members of the metallocarboxypeptidase gene family. The discoidin domain of CPX-2 has 22% amino acid identity with the carbohydrate-binding domain of discoideum-I, 29% to 34% identity with the phospholipid-binding domain of human factors V and VIII, and 59% identity with the discoidin-like domain on AEBP-1. CPX-2 is missing several of the predicted active-site residues that are conserved in most other members of the metallocarboxypeptidase gene family and which are thought to be required for enzyme activity. Expression of CPX-2 using the baculovirus system produced several forms of protein, from 80 to 105 kDa, but no detectable activity toward a variety of carboxypeptidase substrates. A shorter 50-kDa form of CPX-2, which contains the carboxypeptidase domain but not the discoidin domain, was also inactive when expressed in the baculovirus system. CPX-2 is able to bind to Sepharose-Arg; this binding is blocked by 10 mM Arg. Northern blot analysis showed CPX-2 mRNA in mouse brain, liver, kidney, and lung. In situ hybridization analysis of brain revealed a broad distribution. Areas that are enriched in CPX-2 include the hippocampus, cerebral cortex, median eminence, and choroid plexus. Taken together, these data suggest a widespread function for CPX-2, possibly as a binding protein rather than an active carboxypeptidase.

Alteration of protease expression phenotype of mouse peritoneal mast cells by changing the microenvironment as demonstrated by in situ hybridization histochemistry

Mouse mast cell protease (MMCP) mRNA expression was examined by in situ hybridization histochemistry. Peritoneal mast cells (PMCs) of WBB6F1-(+/+) mice expressed MMCP-2, MMCP-4, MMCP-5, and MMCP-6 mRNAs, but did not express MMCP-1 mRNA. When proliferation of PMCs was induced by culturing them in methylcellulose with T cell-derived cytokines, cells in mast cell colonies expressed MMCP-1 mRNA. These mast cells were transferred to a suspension culture to induce further proliferation. The phenotype of the resulting PMC-derived cultured mast cells was similar to that of bone marrow-derived cultured mast cells. When 10(5) PMC-derived cultured mast cells or 10(5) bone marrow-derived cultured mast cells were injected into the stomach wall of mast cell-deficient WBB6F1-W/Wv mice, mast cells that appeared in the mucosa and muscularis propria were similar to mast cells in the stomach of intact WBB6F1-(+/+) mice, indicating the injected cells adapted to a new tissue environment. In contrast, when 10(5) PMCs were injected into the stomach wall of WBB6F1-W/Wv mice, the injected PMCs did not adapt to the mucosa. When 20 PMCs were injected, they proliferated and adapted to the mucosal environment. The present results suggest that PMCs adapt to new environments when proliferation occurs before redifferentiation.

Reversible Expression of Tryptases and Chymases in the Jejunal Mast Cells of Mice Infected with Trichinella spiralis

It is has been established that mouse mast cells (MCs) can reversibly alter their expression of serglycin proteoglycans and the homologous granule chymases that have been designated mouse MC protease (mMCP)-1, mMCP-2, and mMCP-5 in vivo. Nevertheless, it remained to be determined whether these immune cells could modify their expression of other chymases and the granule tryptases mMCP-6 and mMCP-7. As assessed immunohistochemically, we now show that MCs reversibly change their expression of the recently described chymase mMCP-9 and both tryptases as these cells traverse the jejunum during the amplification and regression stages of the reactive MC hyperplasia. In noninfected mice, most jejunal MCs reside in the submucosa and express mMCP-6 and mMCP-7, but not mMCP-9 or the chymase mMCP-2. During the inductive phase of the helminth-induced inflammation, when the jejunal MCs move from the submucosa to the tips of the villus, the MCs briefly express mMCP-9, cease expressing mMCP-6 and mMCP-7, and then express mMCP-2. During the recovery phase of the inflammation, jejunal MCs cease expressing mMCP-2 and then express varied combinations of mMCP-6, mMCP-7, and mMCP-9 as they move from the tips of the villus back toward the submucosa. In other model systems, mMCP-6 elicits neutrophil extravasation, and mMCP-7 regulates fibrin deposition and fibrinogen-mediated signaling events. Thus, the ability of a jejunal MC to reversibly alter its tryptase expression during an inflammatory event has important functional implications.