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

Mast cell deficiency attenuates acupuncture analgesia for mechanical pain using c-kit gene mutant rats

Background

Acupuncture therapy plays a pivotal role in pain relief, and increasing evidence demonstrates that mast cells (MCs) may mediate acupuncture analgesia. The present study aims to investigate the role of MCs in acupuncture analgesia using c-kit gene mutant-induced MC-deficient rats.

Materials and methods

WsRC-Ws/Ws rats and their wild-type (WT) littermates (WsRC-+/+) were used. The number of MCs in skin of ST36 area was compared in two rats after immunofluorescence labeling. Mechanical withdrawal latency (MWL), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) were measured on bilateral plantar for pain threshold evaluation before and after each stimulus. Acupuncture- and moxibustion-like stimuli (43°C, 46°C heat, 1 mA electroacupuncture [EA], 3 mA EA, and manual acupuncture [MA]) were applied randomly on different days.

Results

Fewer MCs were observed in the skin of ST36 in mutant rats compared to WT rats (P<0.001). For pain thresholds, MWL and MWT were higher in WsRC-Ws/Ws compared to WsRC-+/+ on bilateral paws (P<0.05), but TWL was not different between the two rats (P>0.05). Bilateral MWL and MWT in WsRC-+/+ rats increased significantly after each stimulus compared to baseline (P<0.01, P<0.001). In WsRC-Ws/Ws rats, only noxious stimuli could produce anti-nociceptive effects for mechanical pain (46°C, 3 mA EA, MA) (P<0.01, P<0.001). Additionally, the net increases in MWL and MWT induced by most stimuli were greater in WT than in mutant rats (P<0.05). For thermal nociception, either high- or low-intensity stimuli could significantly augment TWL in two rats (P<0.001), and the net increases of TWL evoked by most stimuli were to the same extent in two genetic variants.

Conclusion

MCs influence the basic mechanical but not thermal pain threshold. MCs participate in acupuncture analgesia in mechanical but not in thermal nociception, in that MC deficiency may attenuate the mechanical analgesia evoked by high-intensity stimuli and eliminate analgesia provoked by low-intensity stimuli.

Surveillance strategies for gastrointestinal stromal tumors

Although only 10-30% of gastrointestinal stromal tumors (GISTs) are clinically malignant, all have some degree of malignant potential. The management of high risk patients should be evidence based. However, prospective data and a consensus for guidelines concerning the screening of asymptomatic high risk patients and surveillance following multidisciplinary treatment do not exist. This review provides an overview of GIST, with an emphasis on the available data regarding screening and surveillance of certain populations with GISTs.

MEK/Erk-based negative feedback mechanism involved in control of Steel Factor-triggered production of Krüppel-like factor 2 in mast cells

The receptor tyrosine kinase, c-kit (Steel Factor (SF) receptor) controls survival, proliferation, chemotaxis, and secretion of proinflammatory cytokines in mast cells (MCs). Activation of c-kit results, amongst others, in induction of the PI3K and MEK/Erk pathways. Comparison of two MEK inhibitors, the specific, widely used U0126 and the more selective PD0325901, in different MC models revealed severe differences on SF-induced expression of proinflammatory cytokines IL-6 and TNF-α as well as the transcription factor Krüppel-like factor 2 (KLF2). Expression of the latter in MCs was not investigated so far. Whereas SF-induced expression of IL-6, TNF-α, and KLF2 was unaltered by U0126, it was significantly augmented by PD0325901. The effect of PD0325901 was corroborated by a second selective MEK inhibitor, PD184352 (Cl-1040), indicating the presence of MEK/Erk-based negative feedback mechanism(s) downstream of c-kit activation. Further analysis of KLF2 production revealed a positive function of PI3K. Depending on additional stimuli (e.g. antigen, IGF-1, LPS, thapsigargin), SF-triggered KLF2 expression was differentially modified, most likely controlled by the respective ratio between MEK/Erk and PI3K pathway activation. Moreover, the statin, simvastatin, was demonstrated to upregulate expression of KLF2 in MCs. In conclusion, data obtained by solely using the MEK inhibitor U0126 have to be carefully corroborated by using more selective inhibitors, such as PD0325901 or PD184352. SF-induced expression of the transcription factor KLF2 and its regulation by the MEK/Erk and PI3K pathways could impact on physiological as well as pathophysiological MC functions.

Pathogenesis, classification and treatment of mastocytosis: state of the art in 2010 and future perspectives

Mastocytosis is a myeloid neoplasm characterized by abnormal accumulation and frequent activation of mast cells (MCs) in various organs. Organ systems typically involved are the bone marrow, skin, liver and gastrointestinal tract. In most adult patients, the systemic form of mastocytosis (SM) is diagnosed, which includes an indolent subvariant, an aggressive subvariant and a leukemic subvariant, also termed MC leukemia. Whereas in pediatric mastocytosis, which is usually confined to the skin, a number of different KIT mutations and other defects may be detected, the KIT mutation D816V is detectable in most (adult) patients with SM. In a subset of these patients, additional oncogenic factors may lead to enhanced survival and growth of MCs and, thus, to advanced SM. Other factors may lead to MC activation, with consecutive anaphylactic reactions that can be severe or even fatal. Treatment of SM usually focuses on symptom relief by histamine receptor antagonists and other supportive therapy. However, in aggressive and leukemic variants, cytoreductive and targeted drugs must be applied. Unfortunately, the prognosis in these patients remains poor, even when treated with novel KIT-targeting agents, polychemotherapy or stem cell transplantation. This article provides a summary of our knowledge on the pathogenesis and on treatment options in SM.

Oncogenic osteomalacia caused by a phosphaturic mesenchymal tumor of the thoracic spine

Phosphaturic mesenchymal tumors that cause the paraneoplastic syndrome known as oncogenic osteomalacia are rare. The authors report on the case of a 57-year-old man with a history of osteomalacia and in whom was diagnosed a thoracic spine tumor at the T-4 level. Complete tumor resection was accomplished. The histological diagnosis was phosphaturic mesenchymal tumor (mixed connective tissue variant). After lesion removal, the paraneoplastic syndrome resolved. At the 24-month follow-up, no recurrence of the disease was observed. The clinical presentation, surgical technique, and follow-up in this case were reviewed in detail.

Expression of c-kit proto-oncogene in canine mastocytoma: a kinetic study using real-time polymerase chain reaction

KIT receptor, the c-kit gene product, is thought to play a major role in canine mastocytoma, one of the most common neoplastic diseases in dogs. In the present study, the expression of c-kit proto-oncogene in blood and in tumor biopsies from 41 dogs with histologically confirmed mastocytoma at different grades of cellular differentiation and 5 negative control dogs was investigated using real-time (quantitative) reverse transcription-polymerase chain reaction (RRT-PCR). The animals were followed up for over 1 year after surgery in order to characterize the kinetics of c-kit expression in blood. Transcript mRNAs extracted from blood at different time points after surgery and from tumor tissue surgically removed from each dog were used in a quantitative RRT-PCR assay targeting the extracellular coding region of the c-kit gene. Tissues constitutively expressing c-kit (brain and spleen) were used as positive controls. Levels of expression of c-kit were higher in tumor biopsies than in blood; the blood level decreased in the patients between 1 and 3 months after surgery. No KIT expression was detected in blood from the 5 dogs not affected by mastocytoma (negative controls). The RRT-PCR appears to be a suitable method for sensitive and quantitative detection of c-kit gene expression in canine blood and neoplastic tissues. Although c-kit expression levels measured by RRT-PCR do not correlate with prognosis, they confirm that surgery remains the main treatment to reduce circulating mastocytes and that circulating mast cells can be detected even in benign highly differentiated forms of mastocytoma such as grade I.

Point mutations in the juxtamembrane domain of FLT3 define a new class of activating mutations in AML

In acute myeloid leukemia (AML), two clusters of activating mutations are known in the FMS-like tyrosine kinase-3 (FLT3) gene: FLT3-internal tandem duplications (FLT3-ITDs) in the juxtamembrane (JM) domain in 20% to 25% of patients, and FLT3 point mutations in the tyrosine-kinase domain (FLT3-TKD) in 7% to 10% of patients, respectively. Here, we have characterized a new class of activating point mutations (PMs) that cluster in a 16-amino acid stretch of the juxtamembrane domain of FLT3 (FLT3-JM-PMs). Expression of 4 FLT3-JM-PMs in interleukin-3 (IL-3)-dependent Ba/F3 cells led to factor-independent growth, hyperresponsiveness to FLT3 ligand, and resistance to apoptotic cell death. FLT3-JM-PM receptors were autophosphorylated and showed a higher constitutive dimerization rate compared with the FLT3-wild-type (WT) receptor. As a molecular mechanism, we could show activation of STAT5 and up-regulation of Bcl-x(L) by all FLT3-JM-PMs. The FLT3 inhibitor PKC412 abrogated the factor-independent growth of FLT3-JM-PM-expressing cells. Compared with FLT3-ITD and FLT3-TKD mutants, the FLT3-JM-PMs showed a weaker transforming potential related to lower autophosphorylation of the receptor and its downstream target STAT5.

Mapping of the FLT3-JM-PMs on the crystal structure of FLT3 showed that these mutations reduce the stability of the autoinhibitory JM domain, and provides a structural basis for the transforming capacity of this new class of gain-of-function mutations of FLT3.

Identification of a novel point mutation of mouse proto-oncogene c-kit through N-ethyl-N-nitrosourea mutagenesis

Manipulation of the mouse genome has emerged as an important approach for studying gene function and establishing human disease models. In this study, the mouse mutants were generated through N-ethyl-N-nitrosourea (ENU)-induced mutagenesis in C57BL/6J mice. The screening for dominant mutations yielded several mice with fur color abnormalities. One of them causes a phenotype similar to that shown by dominant-white spotting (W) allele mutants. This strain was named Wads because the homozygous mutant mice are white color, anemic, deaf, and sterile. The new mutation was mapped to 42 cM on chromosome five, where proto-oncogene c-kit resides. Sequence analysis of c-kit cDNA from Wads(m/m) revealed a unique T-to-C transition mutation that resulted in Phe-to-Ser substitution at amino acid 856 within a highly conserved tyrosine kinase domain. Compared with other c-kit mutants, Wads may present a novel loss-of-function or hypomorphic mutation. In addition to the examination of adult phenotypes in hearing loss, anemia, and mast cell deficiency, we also detected some early developmental defects during germ cell differentiation in the testis and ovary of neonatal Wads(m/m) mice. Therefore, the Wads mutant may serve as a new disease model of human piebaldism, anemia, deafness, sterility, and mast cell diseases.

Anaphylatoxin C3a receptors in asthma

The complement system forms the central core of innate immunity but also mediates a variety of inflammatory responses. Anaphylatoxin C3a, which is generated as a byproduct of complement activation, has long been known to activate mast cells, basophils and eosinophils and to cause smooth muscle contraction. However, the role of C3a in the pathogenesis of allergic asthma remains unclear. In this review, we examine the role of C3a in promoting asthma. Following allergen challenge, C3a is generated in the lung of subjects with asthma but not healthy subjects. Furthermore, deficiency in C3a generation or in G protein coupled receptor for C3a abrogates allergen-induced responses in murine models of pulmonary inflammation and airway hyperresponsiveness. In addition, inhibition of complement activation or administration of small molecule inhibitors of C3a receptor after sensitization but before allergen challenge inhibits airway responses. At a cellular level, C3a stimulates robust mast cell degranulation that is greatly enhanced following cell-cell contact with airway smooth muscle (ASM) cells. Therefore, C3a likely plays an important role in asthma primarily by regulating mast cell-ASM cell interaction.

Expression of dentin matrix protein 1 in tumors causing oncogenic osteomalacia

Oncogenic osteomalacia, which is characterized by renal phosphate wasting, low serum 1, 25-dihydroxyvitamin D, and osteomalacia, is caused by mesenchymal neoplasms that are termed phosphaturic mesenchymal tumors (PMTs). As PMTs are usually small and lack specific histological features, the pathological identification of PMTs is difficult. Dentin matrix protein 1 (DMP1) is an acidic phosphoprotein expressed in mineralized tissues including bone, tooth, and hypertrophic cartilage. Increased expression of DMP1 gene in PMTs has been reported by using differential cDNA screening. In the present study, DMP1 expression in PMTs and other soft tissue tumors was analyzed immunohistochemically to verify its utility in the differential diagnosis of PMTs. Anti-DMP1 polyclonal antibody was raised against the C-terminal sequence of DMP1. Three cases with PMTs and 11 other soft tissue tumors (two malignant hemangiopericytomas, three solitary fibrous tumors, three synovial sarcomas, and three malignant peripheral nerve sheath tumors) were analyzed for DMP1 expression. DMP1 expression was observed in all of the three cases with PMTs, but never found in other soft tissue tumors examined. DMP1 was detected in the extracellular matrix with myxomatous features or around capillary vessels, and in dystrophic calcified sites. Paranuclear DMP1 staining in the tumor cells was also observed. These findings indicate that DMP1 immunohistochemistry is a useful tool for identifying PMTs.

Most osteomalacia-associated mesenchymal tumors are a single histopathologic entity: an analysis of 32 cases and a comprehensive review of the literature

Oncogenic osteomalacia (OO) is a rare paraneoplastic syndrome of osteomalacia due to phosphate wasting. The phosphaturic mesenchymal tumor (mixed connective tissue variant) (PMTMCT) is an extremely rare, distinctive tumor that is frequently associated with OO. Despite its association with OO, many PMTMCTs go unrecognized because they are erroneously diagnosed as other mesenchymal tumors. Expression of fibroblast growth factor-23 (FGF-23), a recently described protein putatively implicated in renal tubular phosphate loss, has been shown in a small number of mesenchymal tumors with known OO. The clinicopathological features of 32 mesenchymal tumors either with known OO (29) or with features suggestive of PMTMCT (3) were studied. Immunohistochemistry for cytokeratin, S-100, actin, desmin, CD34, and FGF-23 was performed. The patients (13 male, 19 female) ranged from 9 to 80 years in age (median 53 years). A long history of OO was common. The cases had been originally diagnosed as PMTMCT (15), hemangiopericytoma (HPC) (3), osteosarcoma (3), giant cell tumor (2), and other (9). The tumors occurred in a variety of soft tissue (21) and bone sites (11) and ranged from 1.7 to 14 cm. Twenty-four cases were classic PMTMCT with low cellularity, myxoid change, bland spindled cells, distinctive "grungy" calcified matrix, fat, HPC-like vessels, microcysts, hemorrhage, osteoclasts, and an incomplete rim of membranous ossification. Four of these benign-appearing PMTMCTs contained osteoid-like matrix. Three other PMTMCTs were hypercellular and cytologically atypical and were considered malignant. The 3 cases without known OO were histologically identical to the typical PMTMCT. Four cases did not resemble PMTMCT: 2 sinonasal HPC, 1 conventional HPC, and 1 sclerosing osteosarcoma. Three cases expressed actin; all other markers were negative. Expression of FGF-23 was seen in 17 of 21 cases by immunohistochemistry and in 2 of 2 cases by RT-PCR. Follow-up (25 cases, 6-348 months) indicated the following: 21 alive with no evidence of disease and with normal serum chemistry, 4 alive with disease (1 malignant PMTMCT with lung metastases). We conclude that most cases of mesenchymal tumor-associated OO, both in the present series and in the reported literature, are due to PMTMCT. Improved recognition of their histologic spectrum, including the presence of bone or osteoid-like matrix in otherwise typical cases and the existence of malignant forms, should allow distinction from other mesenchymal tumors. Recognition of PMTMCT is critical, as complete resection cures intractable OO. Immunohistochemistry and RT-PCR for FGF-23 confirm the role of this protein in PMTMCT-associated OO.

Angiomyofibroblastoma of the vulva: report of a case with immunohistochemical and molecular analysis

A 43-year-old woman presented with a mass in the subcutaneous tissue of the right labium majus. A lipoma or Bartholin gland cyst was suspected and excision of the lesion was performed. The lesion was well circumscribed, and histological examination revealed a typical angiomyofibroblastoma. The lesion was composed of alternating hypocellular edematous and hypercellular areas with abundant vessels, and plump tumor cells were loosely dispersed or aggregated mainly around the vessels. Tumor cells were immunoreactive for vimentin and desmin but negative for muscle actins. Ultrastructurally, the tumor cells contained a moderate amount of rough endoplasmic reticulum and abundant intermediate filaments, and had primitive junctions. Pinocytotic vesicles or basal lamina were not evident. Immunohistochemical studies also revealed that the tumor cells expressed basic fibroblast-growth factor, vascular-endothelial-growth factor, and stem-cell factor, factors that may contribute to the rich vascularity and mast cells within the tumor. Reverse transcription-polymerase chain reaction detected high mobility group I-C (HMGI-C) transcripts in the tumor tissue. Because the expression of HMGI-C is regulated by developmental and differentiation processes and is not found in adult normal tissues, HMGI-C may be involved in the tumorigenesis of angiomyofibroblastoma.

Emerging cancer-targeted therapies

There is reason to believe that the unfolding revolution in molecular biology and translational research will allow selective targeting of tumor cells, and radically change the way general practitioners and pediatric oncologists treat and follow children with cancer. This article highlights some of the most promising approaches being tested in the field. By learning about the underlying biology, the remaining hurdles, the projected timeline, and the possible impact of new therapies on the practice of pediatric oncology, health care professionals and patients should be better prepared for the future of pediatric oncology.

Critical roles of c-Kit tyrosine residues 567 and 719 in stem cell factor-induced chemotaxis: contribution of src family kinase and PI3-kinase on calcium mobilization and cell migration

Stem cell factor (SCF) has crucial roles in proliferation, survival, and differentiation of hematopoietic stem cells and mast cells through binding to c-Kit receptor (KIT). Chemotaxis is another unique function of SCF. However, little is known about the intracellular signaling pathway of SCF/KIT-mediated cell migration. To investigate the signaling cascade, we made a series of 22 KIT mutants, in which tyrosine (Y) residue was substituted for phenylalanine (F) in the cytoplasmic domain, and introduced into BAF3 cells or 293T cells. On stimulation with SCF, BAF3 expressing KIT(WT)(WT) showed cell migration and Ca(2+) mobilization. Among 22 YF mutants, Y567F, Y569F, and Y719F showed significantly reduced cell migration and Ca(2+) mobilization compared to WT. In Y567F, Lyn activation on SCF stimulation decreased and C-terminal Src kinase (Csk) suppressed KIT-mediated Ca(2+) influx and cell migration, suggesting that Y567-mediated Src family kinase (SFK) activation leads to Ca(2+) influx and migration. Furthermore, we found that p38 mitogen-activated protein kinase (p38 MAPK) and Erk1/2 were also regulated by Y567/SFK and involved in cell migration, and that p38 MAPK induced Ca(2+) influx, thereby leading to Erk1/2 activation. In Y719F, the binding of phosphatidylinositol 3'-kinase (PI3K) to KIT was lost and KIT-mediated cell migration and Ca(2+) mobilization were suppressed by PI3K chemical inhibitors or dominant-negative PI3K, suggesting the involvement of Y719-mediated PI3K pathway in cell migration. Combination of Csk and the PI3K inhibitor synergistically reduced cell migration, suggesting the cooperation of SFK and PI3K. Taken together, these results indicate that 2 major KIT signaling pathways lead to cell migration, one is Y567-SFK-p38 MAPK-Ca(2+) influx-Erk and the other is Y719-PI3K-Ca(2+) influx.

Placental transmogrification of the lung is a histologic pattern frequently associated with pulmonary fibrochondromatous hamartoma

CONTEXT

Placental transmogrification of the lung is a term introduced to describe a peculiar histologic pattern characterized by formation of placental villuslike structures in the lung parenchyma. It has been reported to occur in association with bullous emphysema and lipomatosis.

OBJECTIVES

To study the relationship between placental transmogrification and pulmonary hamartomas.

DESIGN AND METHODS

Reports of 38 cases of pulmonary hamartomas during 18 years (1982-1999) were reviewed. All histologic slides of these cases were examined for the presence of villuslike papillary projections and placenta-like structures. Hamartomas with prominent papillary projections or placenta-like structures were further investigated to assess the histogenesis and proliferation of epithelial and stromal cells. Immunohistochemical analysis was performed on paraffin-embedded tissue using monoclonal antibodies against Ki-67 and thyroid transcription factor 1 (TTF-1) and polyclonal antibodies against c-Kit antigen (a stem cell factor receptor/mast cell growth factor receptor) in conjunction with Leder stain for naphthol-ASD-chloroacetate esterase.

RESULTS

Placental transmogrification was identified in 6 of 38 cases of pulmonary fibrochondromatous hamartomas. The histologic change consisted of an abundant myxoid or edematous fibroadipose stroma with a respiratory epithelial lining, resulting in papillary projections that resembled immature placental villi. Epithelium lining the papillary projections was positive for TTF-1 (70%-90%) and Ki-67 (3%-5%). In contrast, stromal cells were negative for TTF-1 with only rare cells immunoreactive for Ki-67. A number of stromal spindle cells and occasional cells in epithelium were c-Kit immunoreactive; however, concurrent Leder stain demonstrated that these c-Kit-positive cells were mast cells and not stem cells.

CONCLUSIONS

Placental transmogrification is frequently associated with pulmonary fibrochondromatous hamartomas and may be induced by or associated with a proliferation of lining epithelial components in the hamartomas. The significance of numerous mast cells within stroma of placental transmogrification is unclear and their possible role in inducing stromal proliferation needs to be further evaluated.

Mechanism of constitutive activation of FLT3 with internal tandem duplication in the juxtamembrane domain

Internal tandem duplication (ITD) of the juxtamembrane (JM) domain of FLT3 is the most frequent mutation in human acute myeloid leukemia, and is significantly associated with leukocytosis and a poor prognosis. Previously we reported that FLT3 with ITD (FLT3/ITD) formed a homodimer and was autophosphorylated on tyrosine residues, while the mechanism remains unclear. In this study, we elucidated the role of the JM domain in FLT3 activation. Mutant FLT3 with not only ITD but also an elongating or shortening JM domain transformed murine IL3-dependent myeloid progenitor cell line 32D regardless of the tyrosine residues in the JM domain. These mutant FLT3s were constitutively tyrosine phosphorylated and activated signal-transduction molecules such as SHC, MAP kinase and STAT5a. Notably, co-transfection of the truncated FLT3/ITD lacking kinase and C-terminal domains with the wild type (Wt)-FLT3 into 32D cells resulted in the autonomous proliferation. In these cells, truncated FLT3/ITD generated a hetero-complex with Wt-FLT3 and Wt-FLT3 was constitutively tyrosine phosphorylated. These findings indicate that the FLT3 JM domain plays an important role in receptor activation, and that the length-mutated JM domain induces ligand-independent receptor activation but also activates Wt-FLT3 in a trans-manner.

Oncogenic mutants of RON and MET receptor tyrosine kinases cause activation of the beta-catenin pathway

beta-Catenin is an oncogenic protein involved in regulation of cell-cell adhesion and gene expression. Accumulation of cellular beta-catenin occurs in many types of human cancers. Four mechanisms are known to cause increases in beta-catenin: mutations of beta-catenin, adenomatous polyposis coli, or axin genes and activation of Wnt signaling. We report a new cause of beta-catenin accumulation involving oncogenic mutants of RON and MET receptor tyrosine kinases (RTKs). Cells transfected with oncogenic RON or MET were characterized by beta-catenin tyrosine phosphorylation and accumulation; constitutive activation of a Tcf transcriptional factor; and increased levels of beta-catenin/Tcf target oncogene proteins c-myc and cyclin D1. Interference with the beta-catenin pathway reduced the transforming potential of mutated RON and MET. Activation of beta-catenin by oncogenic RON and MET constitutes a new pathway, which might lead to cell transformation by these and other mutant growth factor RTKs.

Germline mutation in the juxtamembrane domain of the kit gene in a family with gastrointestinal stromal tumors and urticaria pigmentosa

BACKGROUND

Gain-of-function mutations of the c-kit protooncogene, mainly clustered in the juxtamembrane domain, have been reported in a significant fraction of gastrointestinal (GI) stromal tumors (GISTs) that represent the most common mesenchymal tumor of the GI tract. Two families also have been described with a GIST predisposition syndrome with a germline c-kit mutation affecting either the juxtamembrane domain or the tyrosine kinase domain. Here, the authors report on a family in which the dominantly inherited trait of hyperpigmented spots was inherited from an individual who developed multiple GISTs with diffuse hyperplasia of the myenteric plexus by his son, who was affected with urticaria pigmentosa.

METHODS

Screening for the c-kit mutation was performed by means of polymerase chain reaction-based denaturing gradient gel electrophoresis/constant denaturing gel electrophoresis followed by direct sequencing of abnormal conformers. Expression of KIT and CD34 was determined by immunohistochemistry.

RESULTS

In peripheral blood DNA samples, both affected family members showed a previously undescribed c-kit mutation in the juxtamembrane domain, resulting in the substitution of alanine for valine(559). Mutation and polymorphic marker analyses on DNA samples from three GISTs and two skin biopsy specimens evidenced the same mutation in the heterozygous condition. Immunohistochemical examination showed coexpression of CD117 (c-kit) and CD34 in all independent GISTs and CD117 positivity in mast cells from the skin lesions.

CONCLUSIONS

Comparative analysis of clinical presentation and mutation mapping in the families described to date point to the peculiar association of mast cells, melanocytic dysfunction, and GIST predisposition in carriers of c-kit mutations within the juxtamembrane domain.

Gastrointestinal stromal tumors

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. A relationship to the interstitial cells of Cajal (ICCs) has been proposed, and expression of CD117, the c-kit receptor present in ICCs, has been suggested as a marker for GISTs.

METHODS

The English literature has been reviewed with an emphasis on histogenetic features, especially the potential relationship of GISTs to ICCs.

RESULTS

GISTs are most common in the stomach (70%), followed by small intestine (20%), colon and rectum (5%), and esophagus (<5%). GISTs commonly have activating mutations in exon 11 (or rarely exon 9 and exon 13) of the KIT gene that encodes a tyrosine kinase receptor for the stem cell factor or mast cell growth factor.

CONCLUSIONS

Malignant potential is best estimated by the simultaneous evaluation of several clinical parameters. The only absolute criterion for malignancy is tumor spread beyond the organ of origin at the time of diagnosis. The remarkable clinical response of tumors that express c-kit to treatment with the tyrosine kinase inhibitor STI571 is a triumph of molecular pharmacology.

The Raf signal transduction cascade as a target for chemotherapeutic intervention in growth factor-responsive tumors

This review focuses on the Ras-Raf-mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) signal transduction pathway and the consequences of its unregulation in the development of cancer. The roles of some of the cell membrane receptors involved in the activation of this pathway, the G-protein Ras, the Raf, MEK and ERK kinases, the phosphatases that regulate these kinases, as well as the downstream transcription factors that become activated, are discussed. The roles of the Ras-Raf-MEK-ERK pathway in the regulation of apoptosis and cell cycle progression are also analyzed. In addition, potential targets for pharmacological intervention in growth factor-responsive cells are evaluated.

Mastocytosis cells bearing a c-kit activating point mutation are characterized by hypersensitivity to stem cell factor and increased apoptosis

Mastocytosis is characterized by abnormal infiltration of mast cells into various organs. An activating mutation in c-kit, involving an A --> T substitution at nucleotide 2648 has recently been described in some patients with mastocytosis. We describe a 12-year-old girl with this mutation in her bone marrow cells at diagnosis with a myelodysplastic syndrome (MDS) without evidence of mastocytosis, and then in peripheral blood mononuclear cells 1 year later after the emergence of mastocytosis. The role of the c-Kit receptor and its ligand stem cell factor (SCF) in the pathogenesis of the disease was analysed in marrow cell clonogenic assays. We show that the genetic abnormalities in the patient resulted in factor-independent growth and hypersensitivity of primitive progenitors to SCF, with increased production of mast cells. Increased apoptosis and cluster formation, consistent with the myelodysplastic nature of the disorder, accompanied accumulation of abnormal cells with increasing concentrations of SCF.

Evaluation of role of mast cells in the development of liver fibrosis using mast cell-deficient rats and mice

BACKGROUND/AIMS

Several studies have suggested that mast cells participate in the development of liver fibrosis in rodent models. In this study mast cell-deficient mutant Ws/Ws rats and W/Wv mice were used to examine whether mast cells are involved in the development of liver fibrosis.

METHODS

Liver fibrosis was induced in rats by bile duct resection (BDR), and by intraperitoneal injections of carbon tetrachloride (CCl4) or porcine serum, and in mice by intragastric administrations of CCl4, and BDR. The degree of fibrosis was evaluated by measuring the hydroxyproline content (microg/mg tissue) of the liver as an index of the collagen content. The density of mast cells (number/cm2 liver section) was determined by counting mast cells in liver sections stained with alcian blue.

RESULTS

In the liver of control non-mutant (+/+) rats, mast cells were found principally in portal areas, and their average density was 200-300/cm2 liver section. BDR, and treatments with CCl4 and porcine serum increased the density of mast cells in the liver of +/+ rats several-fold, and induced liver fibrosis, increasing the liver hydroxyproline content markedly. BDR, and treatments with CCl4 and porcine serum also induced liver fibrosis in Ws/Ws rats, increasing the liver hydroxyproline content to a similar or higher level than that in +/+ rats. However, the average densities of mast cells in the liver of Ws/Ws rats after BDR and treatment with CCl4 and porcine serum were at most 10.2/cm2 liver section. The density of mast cells in the liver of control +/+ mice was extremely low (average, less than 2), and neither BDR nor treatment with CCl4 caused any significant increase in their density, whereas these treatments induced liver fibrosis and markedly increased the liver hydroxyproline content. Furthermore, treatment with CCl4 induced fibrosis in the liver of W/Wv mice similarly to that in +/+ mice, but the density of mast cells in the liver of W/Wv mice was very low (average, less than 1), and was not increased by treatment with CCl4.

CONCLUSIONS

The present results indicate that mast cells play no role in the development of liver fibrosis in rats and mice.

Frequent expression of the c-kit proto-oncogene in canine malignant mammary tumor

The mammary tumor is one of the popular neoplastic diseases in female dogs. In the present study, the expression of canine c-kit proto-oncogene in mammary tumor specimens was investigated to evaluate its potential usefulness as a tumor marker. By comparing the homology among the nucleotide sequences reported for human mouse, rat and feline c-kit c-DNA, a pair of primers was synthesized for the reverse transcriptase-polymerase chain reaction (RT-PCR) method. The RT-PCR product of canine spleen total RNA was shown to have 756 bp in size and to be highly homologous to the corresponding sequences reported for the mammalian species. The expression of c-kit transcript was detected in 11 mammary tumors of different histopathology including adenocarcinomas, benign and malignant mixed tumors. The level of the transcription in adenocarcinomas was significantly higher than those in malignant mixed tumors. Fifteen canine tumor specimens originated from various tissues were also tested for their c-kit transcript. In all of the mastocytoma samples examined, high expression of the mRNA was detected. Of other 12 tumors, only low level of RT-PCR products were detected in 5 samples, whereas no apparent amplification was observed in 7 tumors. These results indicate that the high expression of c-kit transcript is helpful for the diagnosis of canine mammary tumors.

Disturbed pyloric motility in Ws/Ws mutant rats due to deficiency of c-kit-expressing interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are believed to initiate the basic contractile activity of the gastrointestinal tract. Interstitial cells of Cajal express c-kit receptor tyrosine kinase and are deficient in Ws/Ws mutant rats with a small deletion of the c-kit gene. As Ws/Ws rats show remarkable bile reflux to the stomach, the contraction pressure of the pylorus was compared between Ws/Ws and control +/+ rats. The contraction pressure of the pylorus was measured using a microtransducer, which was inserted through a pin-hole in the anterior wall of the stomach under anesthesia. The magnitude of bile reflux was estimated by measuring the content of bile acids in the stomach. The c-kit messenger RNA-expressing cells were detected by in situ hybridization. Frequency and the maximum pressure of the contraction were comparable between Ws/Ws and +/+ rats, but the duration of the contraction was significantly shorter in Ws/Ws rats than in +/+ rats. The number of c-kit messenger RNA-expressing ICC in the pylorus of Ws/Ws rats was 1.7% that of +/+ rats. The bile reflux observed in Ws/Ws rats was attributed to the decrease in the duration of the pyloric contraction, which appeared to result from the deficiency of c-kit messenger RNA-expressing ICC.

Brain mast cells lack the c-kit receptor: immunocytochemical evidence

Mast cells are reported to differ from other cells of the hematopoietic lineage in that as mature cells, they retain the c-kit receptor, and are thus capable of responding to the stem cell factor (SCF) ligand. SCF is important for development and survival of mast cells. In this study, c-kit expression was examined immunocytochemically in the brains of mice, rats and doves. The results indicate that brain mast cells lack the c-kit receptor; those of the leptomeninges and other connective tissues are a mixed population of c-kit positive and negative cells. The mechanisms whereby brain mast cells might survive in the absence of SCF-c-kit signaling are discussed.

Inherited carcinomas of the kidney

Studies of families with inherited carcinomas have provided powerful tools to identify the genes involved in the pathogenesis of human cancers. In this review, we summarize the clinical, pathological, and genetic characteristics of the inherited carcinomas of the kidney. We emphasize the observation that different genes predispose to histologically different types of renal carcinoma. Hereditary papillary renal carcinoma, a recently described inherited disorder, is discussed in detail along with the predisposing gene, the MET protooncogene. The data support a classification of renal carcinomas based on molecular genetics.

In vivo differentiation of mast cells from acute myeloid leukemia blasts carrying a novel activating ligand-independent C-kit mutation

The primary role of protooncogene c-kit in mast cell differentiation is supported by the development of mast cells from CD34+/CD117+(c-kit) myeloid precursors. Growth factor independence, neoplastic transformation and differentiation of mast cells were found in association with c-kit activating mutations in both murine and human mastocytoma and mast cell diseases. We have identified a novel c-kit mutation (D816Y) in peripheral blood mononuclear cells from a patient with AML (M2), massive presence of mast cells in bone marrow and rapid progression of the disease. The mutation, a G-->T transversion at nt 2467 of the c-kit gene resulting in Asp816-->Tyr substitution, corresponds to the D814Y and D817Y mutations identified and characterized in the murine P815 mastocytoma and the rat RBL-2H3 mast cell leukemia cell lines. The absence of SCF transcripts that we found by RTPCR in the patient's blasts indicates that, also in humans, this activating mutation leads to SCF independent growth. The expression of the mutant allele on Kit signaling may be further enhanced by trisomy of chromosome 4 (carrying the c-kit gene) in the patient's blasts. From these findings it is concluded that mast cells could be generated from a leukemic CD34/CD117-positive clone, that combines the antigenic expression of mast cell precursor to the growth and differentiation factor-independence which was derived by the c-kit D816Y mutation.

Systemic mast cell disease with splenic infarction: a case report

An autopsy case of systemic mast cell disease (SMCD) without primary skin lesions in a 57-year-old Japanese male is described. Initially the patient was suspected of having liver cirrhosis or malignant lymphoma because of hepatomegaly and lymph node enlargement on admission. However, a lymph node biopsy and bone marrow aspiration conducted on his third admission indicated a SMCD because of the existence of metachromatic cell aggregates stained with toluidine blue. At autopsy, the diagnosis was confirmed because the proliferating cells were histochemically proven to be mast cells by naphthol AS.D chloroacetate esterase, Giemsa and alcian blue, in addition to toluidine blue staining. The intra-abdominal and retroperitoneal lymph nodes were replaced by mast cell aggregates, which caused the splenic infarction and bilateral hydronephrosis, with infiltration of mast cells into the spleen and kidneys also being apparent. Mast cell infiltration was similarly found in the bone marrow, liver, ileum and ascending colon. Immunohistochemically, the mast cells were positive for antibodies of alpha 1-antichymotrypsin, CD45 (LCA), CD43 (MT-1), CD45R (MB-1) and the oncoprotein c-kit. Electron microscopic examination using formalin-fixed tissue gave supportive evidence of a mast cell origin for the lesions.