Characterization of various types of mast cells derived from model mice of familial gastrointestinal stromal tumors with KIT-Asp818Tyr mutation

Sporadic mast cell neoplasms and gastrointestinal stromal tumors (GISTs) often have various types of somatic gain-of-function mutations of the c-kit gene which encodes a receptor tyrosine kinase, KIT. Several types of germline gain-of-function mutations of the c-kit gene have been detected in families with multiple GISTs. All three types of model mice for the familial GISTs with germline c-kit gene mutations at exon 11, 13 or 17 show development of GIST, while they are different from each other in skin mast cell number. Skin mast cell number in the model mice with exon 17 mutation was unchanged compared to the corresponding wild-type mice. In the present study, we characterized various types of mast cells derived from the model mice with exon 17 mutation (KIT-Asp818Tyr) corresponding to human familial GIST case with human KIT-Asp820Tyr to clarify the role of the c-kit gene mutation in mast cells. Bone marrow-derived cultured mast cells (BMMCs) derived from wild-type mice, heterozygotes and homozygotes were used for the experiments. Immortalized BMMCs, designated as IMC-G4 cells, derived from BMMCs of a homozygote during long-term culture were also used. Ultrastructure, histamine contents, proliferation profiles and phosphorylation of various signaling molecules in those cells were examined. In IMC-G4 cells, presence of additional mutation(s) of the c-kit gene and effect of KIT inhibitors on both KIT autophosphorylation and cell proliferation were also analyzed. We demonstrated that KIT-Asp818Tyr did not affect ultrastructure and proliferation profiles but did histamine contents in BMMCs. IMC-G4 cells had an additional novel c-kit gene mutation of KIT-Tyr421Cys which is considered to induce neoplastic transformation of mouse mast cells and the mutation appeared to be resistant to a KIT inhibitor of imatinib but sensitive to another KIT inhibitor of nilotinib. IMC-G4 cells might be a useful mast cell line to investigate mast cell biology.     

Preferential localization of c-kit product in tissue mast cells,basal cells of skin,epithelial cells of breast,small cell lung carcinoma and seminoma/dysgerminoma in human: immunohistochemical study on formalin-fixed,paraffin-embedded tissues

Eighteen hundred and eighty-four cases of human solid tumours and 833 samples of normal human tissues, formalin-fixed and paraffin-embedded, were examined immunohistochemically for expression of c-kit oncogene product using polyclonal antibody against synthesized c-kit peptide. Seminoma/dysgerminoma and small cell lung carcinoma (SCLC) show preferential c-kit expression at 92% and 36% frequency, respectively, whereas only sporadic cases of cervical carcinoma and non-SCLC lung carcinoma show c-kit positivity. A normal tissue counterpart positive for c-kit product is detected in the testis (spermatocyte) and ovary (oocyte) but not in the lung or the cervix. In contrast, normal epithelial cells of the breast, skin basal cells and tissue mast cells harbour c-kit product, but transformed cells of the former two are largely deficient in the c-kit protein. One hundred and thirty-nine neuroendocrine tumours and 39 non-pulmonary small cell carcinomas were all negative, except for two cases of neuroblastoma. This indicates a distinct character for SCLC in c-kit expression. The c-kit product may be a useful marker in diagnostic pathology of seminoma/dysgermona and SCLC among human solid tumours, and in distinction of SCLC from non-pulmonary small cell carcinoma.     

Differential expression of the c-kit proto-oncogene in germ cell tumours

The c-kit proto-oncogene product and its ligand stem cell factor play an important role in haematopoiesis, spermatogenesis, and melanogenesis. Using an anti-c-kit antiserum raised against a synthetic peptide, we studied the immunohistochemical expression of the c-kit gene product in 60 germ cell tumours (GCTs) (53 testicular, 7 extragonadal), derived from primary GCTs in 45 cases and metastatic tumours in 15 cases. Twenty-eight out of 28 seminomas showed c-kit membranous staining in the majority of cells. A similar pattern of expression was seen in intratubular germ cell neoplasia. Nine out of 29 (32 per cent) non-seminomas displayed cytoplasmic, but not membranous, c-kit immunoreactivity in occasional cells. In three mixed GCTs, c-kit expression was limited to the seminoma component. In normal testis, c-kit expression was observed in some basal tubular cells, corresponding to undifferentiated spermatogonia. These results suggest a role for c-kit in the oncogenesis of GCT, where down-regulation of c-kit might be a critical step during progression from seminomas to non-seminomas. Immunohistochemical analysis of c-kit should be considered as a diagnostic aid for GCT and in particular may be helpful in the identification of certain extragonadal seminomas.     

Pregnancy: The expression of c-kit protein in human adult and fetal tissues

The c-kit proto-oncogene encodes a tyrosine kinase receptorand is allelic with the dominant white-spotting (W) locus ofthe mouse. In this study we investigated the expression of humanc-kit protein in various adult and fetal human tissues immunohistochemicallyusing anti-human c-kit monoclonal antibody. To discriminatec-kit+ cells from mast cells expressing c-kit, mast cells wereidentified by staining with Toluidine blue. In oogonia, spermatogoniaand skin melanocytes of the fetus and in oocytes of adult ovary,c-kit expression was detected. In adult uterus, c-kit+ cellswere widely distributed in the basal layer of the endometrium,myometrium and cervix, the number and distribution being almostidentical to those of mast cells. In fetal uterus, c-kit+ non-mastcells clustered beneath the epithelium and a few mast cellswere observed in the myometrium and subserosal layer. In bothadult and fetus, c-kit+ non-mast cells were detected withinsmooth muscle layers of the intestine, colon and oesophagus,while mast cells were observed in the mucosal and submucosallayers of these organs. In contrast to mice, no expression ofc-kit protein was detected in the human placenta and decidua.Thus, the distribution of c-kit+ cells in various tissues issimilar but not identical between adult and fetus and betweenhuman and mouse.     

Differential staining of mast cells with toluidine blue

Abstract

Mast cells play a significant role in inflammatory diseases such as asthma, inflammatory bowel disease, and autoimmune diseases. Inhibition of c-kit receptor tyrosine kinase, a growth factor receptor, significantly reduces mast cell numbers. The purpose of this study was to determine the effect of Compound X (a c-kit inhibitor) on mast cell numbers in rats. Connective tissue mast cells (CTMCs) and mucosal mast cells (MMCs) have differing histochemical characteristics which presents a challenge when staining for quantification by semi-automated image analysis. CTMCs are present in tissues such as tongue and skin and will stain readily in tissues fixed routinely. In contrast, MMCs, such as those present in the intestinal mucosa, are sensitive to fixation. Brief fixation in Carnoy’s solution, although seldom used due to its composition (a mixture of ethanol, chloroform, and acetic acid), was employed to fix tissues for MMC staining, while tissues for CTMC demonstration were fixed in 10% neutral buffered formalin. An enzyme histochemistry method, napthol AS-D choloroacetate (specific esterase), was briefly considered for staining; however, granulocytes stained along with mast cells, requiring manual identification and exclusion, thereby rendering the method incompatible with automated means of quantification. Instead, staining was performed using two different toluidine blue methods which have proven conducive to semi-automated image analysis techniques. CTMCs were stained using Luna’s toluidine blue, while MMCs were stained with Matsson’s toluidine blue modification. In summary, the selected methods, based upon a conventional stain, were easy to do and successfully identified both populations of mast cells for quantification by image analysis.     

Committed mast cell progenitors in mouse blood differ in maturity between Th1 and Th2 strains

Mast cell progenitors (MCp) leave the bone marrow and migrate to peripheral tissues where they mature. Although the existence of committed MCp in adult mouse and human blood has been postulated, they have never been found. We have isolated a rare population of cells in adult mouse blood, committed to the mast cell lineage. These were identified as lineage⁻ c‐kit^hi ST2⁺ integrin β7^hi CD16/32^hi cells. Moreover, a major difference in maturity of these cells based on FcεRI expression was observed between the Th2‐prone BALB/c strain and the Th1‐prone C57BL/6 strain (66% vs 25% FcεRI⁺, respectively). Therefore, the choice of mouse strain is critical when studying disease models such as experimental asthma where mast cells and their progenitors are involved.     

Mast cell infiltrates in vulvodynia represent secondary and idiopathic mast cell hyperplasias

Mast cell infiltrates in tissues of vulvodynia are common, but they have not been characterized for criteria of neoplastic mast cell disease or correlated with patient's concomitant diseases associated with increased mast cells. Formalin‐fixed specimens of 35 patients with vulvodynia were evaluated immunohistochemically with antibodies to CD 3,4,8,20,117c and human mast cell tryptase, and for WHO‐criteria of neoplastic mastocytosis (>25% spindled mast cell, CD25 expression, point mutations of the c‐kit gene (D816V), and chronically elevated serum tryptase levels). Only 20/35 specimens showed a T‐lymphocyte dominant inflammatory infiltrate on HE‐stained sections, but all showed mast cells. 4/35 biopsies showed <10 mast cells/mm², 15/35 specimens 40–60 mast cells/mm² and 16/35 specimens >60 mast cells/mm² (average 80/mm²). Control tissue contained typically <10 mast cells/mm². Spindling, CD25‐expression, c‐kit gene mutations, or increased serum tryptase levels were not detected. 26/35 (74%) patients had concomitant autoimmune diseases, psoriasis, atopy, various allergies, preceding infections. Independent of the subtype of vulvodynia, the majority of mast cell rich biopsies with >40 mast cells/mm² were classified as a secondary mast cell disorder reflecting an activated immune system in 75% of vulvodynia patients. Patients with increased mast cells may benefit from medical therapy targeting mast cells.     

Abnormal Granulopoiesis of Leukemic Cells with Basophil/Mast Cell Features Cytochemical and Ultrastructural Observations

We have carried out cytochemical and ultrastructural examination of human leukemic cells showing basophil/mast cell features derived from patients with acute myelogenous leukemia or basophilic crisis in chronic myelogenous leukemia. Leukemic cells in each case initially showed meta-chromasia with toluidine blue and various degrees of positivity for astra blue. Other cytochemical results showed considerable variety among cases. The number of granules increased in short-term culture in every case. Ultrastructurally, small membrane-bound granules with or without myelinoid bodies or glycogen particles were present in immature blasts, followed by production of other granule types. In some cases, leukemic cells before and after liquid culture contained the typical basophil granules with or without myelinoid bodies, but the matrix was more loose than normal. Granules showing whorl or scroll matrix profiles, which were typical for mast cells, were present in two cases. In one case, immatue leukemic cells contained theta granules, and some mature forms after short term culture contained typical basophil/mast cell granules as well as theta granules. Leukemic cells occasionally contained multivesicular granules predominantly. These results indicate that leukemic cells with basophil/ mast cell features show a heterogeneous configuration and contain abnormal granules differing from normal ones. This abnormal granulopoiesis may be attributable to the results of leukemic events and may be a hallmark for recognition of leukemic basophils/mast cells. Acta Pathol Jpn 41: 531–539, 1991.     

Human mast cells express stem cell factor

Stem cell factor (SCF) is a major cytokine regulator of mast cell growth and function. The present study demonstrates that human mast cells are able to produce SCF. Constitutive synthesis of SCF mRNA was seen in the mast cells isolated from human lung and skin by RT-PCR. This was confirmed by in situ hybridization in conjunctival mast cells of both tryptase-only (MC_T) and tryptase/chymase (MC_TC) subsets. SCF protein product was found in conjunctival MC_T and MC_TC mast cells by immunohistochemistry. Soluble SCF protein was detected in the culture supernatant of isolated lung mast cells by ELISA, and cross-linkage of IgE receptor (Fcε–RI) on the lung mast cells in culture did not alter SCF mRNA expression, or the secreted soluble SCF protein. This was consistent with the finding that levels of SCF mRNA expression in conjunctival mast cells were similar between normal subjects and patients with seasonal allergic conjunctivitis (SAC). This study shows that human mast cells themselves are a cellular source of SCF, as well as being target cells for this growth factor. SCF may regulate mast cell growth and function via both paracrine and autocrine mechanisms. The production of SCF by mast cells may be regulated via mechanisms other than IgE receptor-mediated pathways. © 1998 John Wiley & Sons, Ltd.     

Effects of fostriecin on β2-adrenoceptor-driven responses in human mast cells

As part of the intracellular processes leading to mast cell and basophil activation, phosphorylation of key substrates is likely to be important. These processes, mediated by phosphatases, are responsible for regulating phosphorylation. The aim of the present study was to determine effects fostriecin – a selective inhibitor of PP2A (protein phosphatase-2) – on β₂-adrenoceptor-driven responses in human mast cells. Here, the effects of fostriecin (PP inhibitors) on the inhibition of histamine release from HLMC, on β-adrenoceptor-driven responses in mast cells and on desensitization were investigated. Long-term incubation (24?h) of mast cells with fostriecin (10^?6 M) resulted in a significant (p 2-adrenoceptors.     

Evaluation of neoplastic human mast cells by tryptase-immunoelectron microscopy

AIMS: To analyse and characterize the ultrastructural morphology of normal tissue mast cells (MC) and neoplastic bone marrow MC. METHODS: We have examined the ultrastructure and cytomorphological features of MC derived from cord blood cells, neoplastic bone marrow MC in patients with systemic mastocytosis (SM, n = 4), myelomastocytic leukaemia (MML, n = 2), mast cell leukaemia (MCL, n = 2) and tryptase-positive acute myeloid leukaemia (AML, n = 4). RESULTS: Based on their ultrastructure and morphology, four distinct cell types could be delineated: (i) mature well-granulated tissue MC exhibiting a round central nucleus; (ii) atypical MC type I with oval nuclei, hypogranulated cytoplasm, and prominent surface projections; (iii) immature atypical MC with bi- or polylobed nuclei (atypical MC type II = promastocytes); and (iv) metachromatic blasts. Type I atypical MC were detected in a patient with indolent SM, whereas type II MC and metachromatic blasts were primarily found in MML, MCL and tryptase-positive AML. In all samples examined, the identity of MC could be reconfirmed by immunoelectron microscopy, irrespective of the stage of cell maturation or the disease variant, all types of MC contained tryptase in their cytoplasmic granules. CONCLUSION: Immunoelectron microscopy may be a helpful approach in confirming the identity of neoplastic MC in myeloid neoplasms.     

Tryptase-positive mast cells accompany lymphocytic as well as lymphoplasmacytic lymphoma infiltrates in bone marrow trephine biopsies

AIMS: To investigate the specificity of increased bone marrow mast cell numbers in lymphoplasmacytic lymphoma (LPL) and to evaluate the relationship between mast cell number and the immunoglobulin phenotype of neoplastic lymphoid cells. METHODS AND RESULTS: Retrospective study of bone marrow trephine biopsy specimens from patients with LPL, compared with selected cases representing chronic lymphocytic leukaemia (CLL) and multiple myeloma (MM) of known immunoglobulin light and heavy chain phenotype. Bone marrow mast cells were counted following immunohistochemical staining of sections for mast cell tryptase. We have confirmed previous observations that mast cell numbers are increased in bone marrow infiltrates of LPL. However, we found similarly high mast cell numbers in CLL. High mast cell numbers were associated with neoplastic lymphoid cells expressing an IgM kappa phenotype. Mast cell numbers were low in all cases of MM studied and in controls with no lymphoma present. We observed an apparent bias towards kappa light chain expression in our cases of LPL. CONCLUSIONS: Mast cell number should not be considered a reliable factor in the differential diagnosis of LPL and CLL when assessing bone marrow histology. Possible bias towards kappa light chain expression in LPL requires further study, as do the mechanism and functions of mast cell recruitment by neoplastic lymphoid cells.     

The mast cell: Distribution and maturation in the rat

This paper reports preliminary studies in the rat of the connective tissue mast cell — its origin, distribution in various tissues, regeneration and function, as well as its relationship with basophil leucocytes and mucosal mast cells. Connective tissue mast cells and basophil leucocytes exhibit a reciprocity of incidence in animals such as the rat and rabbit, and with mucosal mast cells comprise a family of cells that share the common feature of having a cytoplasm packed with granules that stain metachromatically. At least in connective tissue mast cells, these granules represent miniature pharmacological storehouses.The relative insolubility in aqueous solutions of the granules of connective tissue mast cells in the rat has made this species a popular one for laboratory investigations of the mast cell. Progressive sulphation of the granules of rat mast cells is demonstrable by staining with Alcian blue and safranin. Coupled with morphological features, such staining permits the identification of four stages in the maturation of mast cells. The maturation and distribution of these cells is illustrated for mesentery, omentum and peritoneal fluid. Although it has long been accepted that mast cells are particularly associated with the blood vessels of the vascular arcades of the mesentery, our own work inneonatal rats has indicated clearly that the association is with lymphatic rather than blood vessels. However, this association with lymphatic vessels seems restricted to the mesentery and omentum.In further work in the newborn rat, mast cells have been observed in substantial numbers inskin andthymus, the population of mast cells in these organs being maintained during the next 3 months. In theliver andspleen of the newborn rat, mast cells are reasonably numerous in the foci of haemopoiesis, but progressively decline in number during the initial 4 weeks, in step with the disappearance of extramedullary haemopoiesis. On the other hand, thebone marrow becomes populated by mast cells, particularly during the 2nd and 3rd weeks of life. In theconnective tissue ofheart, lung, stomach andportal tract of the rat, mast cells are practically absent at birth but progressively increase in number during the initial postnatal month. Thereafter, their number remains fairly steady.The presence at birth of mast cells in extramedullary and subsequently in medullary foci of haemopoiesis, suggests that the process of mastopoiesis may be analogous to that of granulopoiesis in haemopoietic tissues. This possibility is discussed in relation to other evidence concerning the origin of mast cells.     

Structural examination of tryptase- and chymase-positive mast cells in livers, containing metastases from gastrointestinal cancers

Human mast cells are categorized into mast cells positive only for tryptase (MC_T) and mast cells positive for both tryptase and chymase (MC_TC). The structural appearance of tryptase-, and chymase-positive mast cells in metastatic liver disease and the variations in MC_T and MC_TC numbers in accordance with the origin of the primary tumors have been described in the present study. Liver mast cells are analyzed immunocytochemically using tryptase and chymase and by quantitative morphometry in 30 patients with colorectal (n=15), gastric (n=8), and pancreatic (n=7) cancers and in 5 control livers. The numbers of MC_T and MC_TC are increased in the extratumoral liver tissue (mainly portal tracts) as compared to controls. The numbers of MC_T and MC_TC in and around metastases with moderate or high grade of differentiation are statistically significantly higher, as compared to those with low grades of differentiation. The numbers of MC_TC are greater than that of MC_T in the extratumoral liver tissue and in metastases themselves. Ultrastructurally, mast cells immunostained with tryptase and chymase have three types of granules: electron dense granules with darkly precipitated reaction product, electron lucent granules without reaction product and electron lucent granules with sparse reaction product (altered granules). Both types of mast cells have small and large in size granules, resembling the MC_TC phenotype described earlier. Tryptase-positive mast cells have granules with discrete scrolls and particulate and beaded pattern. Chymase-positive mast cells have granules with finely granular or particulate material. Substance P (SP)- and vasointestinal polypeptide (VIP)-positive mast cells are not observed in livers with metastases. The present study suggests that liver mast cells are mainly from the MC_TC type, and are accumulated in peritumoral and metastatic areas. They may play a role in the formation of tumor stroma, or in tumor immunology in liver metastases from various primary gastrointestinal cancers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Histamine releasability of basophils and skin mast cells in chronic urticaria

In order to clarify the pathogenetic role of basophils and mast cells in chronic urticaria, histamine and leukotrienes (LT) C₄ release was examined in washed mixed leukocytes (n=8) and skin mast cells (n=5) from patients with chronic urticaria and compared with the same cells from normal controls (n=9). Anti-IgE-stimulated basophil histamine release was significantly reduced in urticaria patients (median 2.9% vs 15.1% in normal controls), whereas histamine release to A23187, FMLP, and PAF, as well as anti-IgE-induced LTC₄ release, showed no differences in both groups. In contrast, anti-IgE-stimulated skin mast cells from urticaria patients reacted similarly to those of controls (median histamine release 11.4% vs 14.2% in normal controls). Pretreatment of the cells with interleukin (IL)-3 upregulated responsiveness of basophil histamine release to anti-IgE in urticaria patients (median histamine release 14.3%), but pretreatment with the H₂-antagonist cimetidine showed no effect. These data show that reduced basophil histamine releasability in chronic urticaria is not H₂ mediated. It is a stimulus-, mediator-, and cell type-restricted phenomenon that can, at least partially, be reversed in the presence of the cytokine IL-3.     

Abnormal granulopoiesis of leukemic cells with basophil/mast cell features. Cytochemical and ultrastructural observations.

We have carried out cytochemical and ultrastructural examination of human leukemic cells showing basophil/mast cell features derived from patients with acute myelogenous leukemia or basophilic crisis in chronic myelogenous leukemia. Leukemic cells in each case initially showed metachromasia with toluidine blue and various degrees of positivity for astra blue. Other cytochemical results showed considerable variety among cases. The number of granules increased in short-term culture in every case. Ultrastructurally, small membrane-bound granules with or without myelinoid bodies or glycogen particles were present in immature blasts, followed by production of other granule types. In some cases, leukemic cells before and after liquid culture contained the typical basophil granules with or without myelinoid bodies, but the matrix was more loose than normal. Granules showing whorl or scroll matrix profiles, which were typical for mast cells, were present in two cases. In one case, immature leukemic cells contained theta granules, and some mature forms after short-term culture contained typical basophil/mast cell granules as well as theta granules. Leukemic cells occasionally contained multivesicular granules predominantly. These results indicate that leukemic cells with basophil/mast cell features show a heterogeneous configuration and contain abnormal granules differing from normal ones. This abnormal granulopoiesis may be attributable to the results of leukemic events and may be a hallmark for recognition of leukemic basophils/mast cells.     

Effects of PBMC-derived histamine-releasing factors on histamine release from human skin and lung mast cells

Background: A field of study which has attracted much recent interest is the ability of mononuclear cells and neutrophils to interact with hislamine releasing cells by production of specific histamine releasing factors (HRFs). However, almost all of these studies have been performed on basophils rather than human mast ceils. Objective: We have investigated the effects of lyophilized fractions of HRF preparations on histamine release from human skin and lung mast cells. Methods: Lyophilized fractions of HRF preparations include crude supernatant from mononuclear cell/platelet (crude), void peak from union exchange chromatography column (void), second peak from anion exchange chromatography (peak 2), neutrophil-activating peptide-2 (NAP-2), which was purified from void peak at molecular weight of 8-12 kDa, and monocyte chemotactic-activating factor (MCAF). Mast cells were enzymatically dispersal. Results: Crude (24.2μg/mL-2.42mg/mL), void (5.4μg/mL-0.54mg/mL). peak 2 (3.5μg/mL-0.35mg/tnL), and NAP-2 (1-20μg/mL) failed to release hislamine from lung mast cells. In skin mast cells, only higher concentrations of crude and void caused minimal release of histamine. MCAF up to micromolar concentrations failed to have an effect on mast cells from either source, However, these HRFs induced histamine release from human basophils. We also explored whether HRFs and stem cell factor could act as either priming agents for each other or for anti-IgE. The response of skin mast cells to all these preparations was not enhanced by preincubation in stem cell factor at 1 ng/mL. nor did the HRFs and MCAF enhance the response of skin mast cells to anti-IgE. Conclusion: These results suggest that these HRFs have no significant effect on dispersed human cutaneous and lung mast cells.     

Human bone marrow mast cells in systemic mast cell disease

In a case of systemic mast cell disease with moderate bone marrow involvement, we studied the sensitivity of mast cell cationic dye-binding to formaldehyde fixation, as well as the mast cell ultrastructure, so as to determine whether these cells possess characteristics of mucosal mast cells. This histochemical method has proved to be one of the few which reveal heterogeneity of the mast cells in human intestine. Even though rat bone marrow mast cells have been shown to belong to the mucosal mast cell compartment, we have found no difference in mast cell counts in samples fixed either in formaldehyde or Carnoy's fixative. The ultrastructure did not show major differences with cutaneous mast cells. A few cells presented two nuclei, suggesting mitotic division of mature mast cells in bone marrow.     

Role of c-kit receptor tyrosine kinase in the development, survival and neoplastic transformation of mast cells

The c-kit gene is allelic with the dominant spotting ( W ) locus on mouse chromosome 5 and encodes a receptor tyrosine kinase. The llgand for c-klt receptor is stem cell factor (SCF), which is the principal growth factor for mast cells. The loss-of-function mutations of c-kit receptor affect the development of mast cells, thereby resulting in a depletion of mast cells. The abundant expression of c-ktt receptor is indispensable for the survival of mast cells. In addition, the galn-of-function mutations of c-kit receptor were found in several tumor mast cell lines. When these galn-of-function mutations were introduced to cells of murine interleukin (IL)-3-dependent cell lines, the expression of c-kit receptor with constitutive tyrosine kinase activity not only abrogated the IL-3 requirement of the cells, but also caused them to become tumorlgenic in nude athymic mice. The gain-of-function mutations of c-kit receptor appear to result in the malignant transformation of mast cells. Taken together, the signals from the c-ktt receptor are essential for the development, survival, and malignant transformation of mast cells.