A loss-of-function mutation of c-kit results in depletion of mast cells and interstitial cells of Cajal, while its gain-of-function mutation results in their oncogenesis

miR-222 regulates cell growth, apoptosis, and autophagy of interstitial cells of Cajal isolated from slow transit constipation rats by targeting c-kit

BACKGROUND

Excessive autophagy and apoptosis of the interstitial cells of Cajal (ICC) have been identified in gastrointestinal (GI) motility disorders including slow transit constipation (STC). MicroRNA 222 (miR-222) has been shown to affect GI motility. This study aimed to explore whether miR-222 influences apoptosis and excessive autophagy of isolated ICC.

METHODS

miR-222, c-kit, and stem cell factor (SCF) were evaluated in colon tissues in STC rats compared with normal control by qRT-PCR and western blot analysis. The condition of autophagy of colon tissue was observed by transmission electron microscope. ICC were isolated from the colon of STC rats. Cell Counting Kit-8 (CCK-8) assay and wound healing assay were carried out to examine the cell viability and migration rate. Cell apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) and Annexin V-Flourescein Isothiocyanate/Propidine Iodide (FITC/PI) apoptosis detection kit. Western blot analysis was performed to detect the c-kit and SCF expression; apoptosis-related proteins Bcl-2, Bax, caspase-3, and pro-caspase-3; and autophagy-related proteins LC3B and Beclin-1. The connection between miR-222 and c-kit was detected by bioinformatics and luciferase activity analysis.

RESULTS

miR-222 expression was significantly higher, whereas c-kit and SCF expressions were markedly lower in STC rats' colon tissue compared with normal control. Meanwhile, STC rats exhibited excessive autophagy in colon tissue than normal control. Inhibition of miR-222 expression promoted cell proliferation as well as migration and inhibited autophagy, whereas upregulation of miR-222 had the opposite effect. In addition, miR-222 upregulation induced apoptosis and excessive autophagy compared with normal controls (NC). Western blot analysis showed that miR-222 overexpression caused decreased c-kit and SCF protein levels compared with NC. Bioinformatics and luciferase activity analysis revealed that miR-222 could be a predictive regulator of c-kit.

CONCLUSION

miR-222 induces apoptosis and excessive autophagy of ICC and may serve as potential biomarker for ICC loss in STC.

Stabilization of c-KIT G-Quadruplex DNA Structures by the RNA Polymerase I Inhibitors BMH-21 and BA-41

The stabilization of G-quadruplex DNA structures by small molecules with affinity to oncogene promoters has emerged as a promising anticancer strategy, due to a potential role in gene expression regulation. We explored the ability of BMH-21 (1) and its analogue BA-41 (2) to bind the G-quadruplex structure present in the c-KIT promoter by biophysical methods and molecular modeling. We provide evidence that both compounds interact with the c-KIT 21-mer sequence. The stable monomeric intramolecular parallel G-quadruplex obtained by the mutation of positions 12 and 21 allowed the precise determination of the binding mode by NMR and molecular dynamics studies. Both compounds form a complex characterized by one ligand molecule positioned over the tetrad at the 3′-end, stabilized by an extensive network of π–π interactions. The binding constants (Kb) obtained with fluorescence are similar for both complexes (around 10⁶ M⁻¹). Compound BA-41 (2) showed significant antiproliferative activity against a human lymphoma cell line, SU-DHL4, known to express substantial levels of c-KIT. However, the partial inhibition of c-KIT expression by Western blot analysis suggested that the interaction of compound 2 with the c-KIT promoter is not the primary event and that multiple effects provide a contribution as determinants of biological activity.

Computational algorithms for in silico profiling of activating mutations in cancer

Methods to catalog and computationally assess the mutational landscape of proteins in human cancers are desirable. One approach is to adapt evolutionary or data-driven methods developed for predicting whether a single-nucleotide polymorphism (SNP) is deleterious to protein structure and function. In cases where understanding the mechanism of protein activation and regulation is desired, an alternative approach is to employ structure-based computational approaches to predict the effects of point mutations. Through a case study of mutations in kinase domains of three proteins, namely, the anaplastic lymphoma kinase (ALK) in pediatric neuroblastoma patients, serine/threonine-protein kinase B-Raf (BRAF) in melanoma patients, and erythroblastic oncogene B 2 (ErbB2 or HER2) in breast cancer patients, we compare the two approaches above. We find that the structure-based method is most appropriate for developing a binary classification of several different mutations, especially infrequently occurring ones, concerning the activation status of the given target protein. This approach is especially useful if the effects of mutations on the interactions of inhibitors with the target proteins are being sought. However, many patients will present with mutations spread across different target proteins, making structure-based models computationally demanding to implement and execute. In this situation, data-driven methods-including those based on machine learning techniques and evolutionary methods-are most appropriate for recognizing and illuminate mutational patterns. We show, however, that, in the present status of the field, the two methods have very different accuracies and confidence values, and hence, the optimal choice of their deployment is context-dependent.

Synthesis and evaluation of 7-substituted-5,6-dihydrobenzo[c]acridine derivatives as new c-KIT promoter G-quadruplex binding ligands

It has been shown that treatment of cancer cells with c-KIT G-quadruplex binding ligands can reduce their c-KIT expression levels thus inhibiting cell proliferation and inducing cell apoptosis. Herein, a series of new 7-substituted-5,6-dihydrobenzo[c]acridine derivatives were designed and synthesized. Subsequent biophysical evaluation demonstrated that the derivatives could effectively bind to and stabilize c-KIT G-quadruplex with good selectivity against duplex DNA. It was found that 12-N-methylated derivatives with a positive charge introduced at 12-position of 5,6-dihydrobenzo[c]acridine ring had similar binding affinity but lower stabilizing ability to c-KIT G-quadruplex DNA, compared with those of nonmethylated derivatives. Further molecular modeling studies showed possible binding modes of G-quadruplex with the ligands. RT-PCR assay and Western blot showed that compound 2b suppressed transcription and translation of c-KIT gene in K562 cells, which was consistent with the property of an effective G-quadruplex binding ligand targeting c-KIT oncogene promoter. Further biological evaluation showed that compound 2b could induce apoptosis through activation of the caspase-3 cascade pathway.

Existence of c-Kit negative cells with ultrastructural features of interstitial cells of Cajal in the subserosal layer of the W/W(v) mutant mouse colon

Interstitial cells of Cajal (ICC) are mesenchymal cells that are distributed along the gastrointestinal tract and function as pacemaker cells or intermediary cells between nerves and smooth muscle cells. ICC express a receptor tyrosine kinase c-Kit, which is an established marker for ICC. The c-kit gene is allelic with the murine white-spotting locus (W), and some ICC subsets were reported to be missing in heterozygous mutant W/W(v) mice carrying W and W(v) mutated alleles. In this study, the characterization of interstitial cells in the subserosal layer of W/W(v) mice was analyzed by immunohistochemistry and electron microscopy. In the proximal and distal colon of W/W(v) mutant mice, no c-Kit-positive cells were detected in the subserosal layer by immunohistochemistry. By electron microscopy, the interstitial cells, which were characterized by the existence of caveolae, abundant mitochondria and gap junctions, were observed in the W/W(v) mutant colon. The morphological characteristics were comparable to those of the multipolar c-Kit positive ICC seen in the subserosa of proximal and distal colon of wild-type mice. Fibroblasts were also located in the same layers, but the morphology of the fibroblasts was distinguishable from that of ICC in wild type mice or of ICC-like cells in W/W(v) mutant mice. Collectively, it is concluded that c-Kit-negative interstitial cells showing a typical ICC ultrastructure exist in the proximal and distal colon of W/W(v) mutant mice.

Gene of the month: KIT

Deranged pathway activation and KIT mutations occur in numerous solid and haematological malignancies, with gain-of-function mutations being the most common demonstrable abnormality. Through a complex series of interactions, activation of the KIT receptor tyrosine kinase leads to cell survival, evasion of apoptosis, angiogenesis, dysregulated cell cycle control and promotion of tumourigenesis. The KIT receptor tyrosine kinase is a well-studied therapeutic target in human malignancies. The KIT mutational status of a neoplasm plays an important role in predicting the response to targeted therapies. In this article we outline the structure, function and mutations of the KIT gene, its role in various neoplasms, therapeutic impacts and the role that these play in clinical patient outcome.

Hotspot mutations in KIT receptor differentially modulate its allosterically coupled conformational dynamics: impact on activation and drug sensitivity

Receptor tyrosine kinase KIT controls many signal transduction pathways and represents a typical allosterically regulated protein. The mutation-induced deregulation of KIT activity impairs cellular physiological functions and causes serious human diseases. The impact of hotspots mutations (D816H/Y/N/V and V560G/D) localized in crucial regulatory segments, the juxtamembrane region (JMR) and the activation (A-) loop, on KIT internal dynamics was systematically studied by molecular dynamics simulations. The mutational outcomes predicted in silico were correlated with in vitro and in vivo activation rates and drug sensitivities of KIT mutants. The allosteric regulation of KIT in the native and mutated forms is described in terms of communication between the two remote segments, JMR and A-loop. A strong correlation between the communication profile and the structural and dynamical features of KIT in the native and mutated forms was established. Our results provide new insight on the determinants of receptor KIT constitutive activation by mutations and resistance of KIT mutants to inhibitors. Depiction of an intra-molecular component of the communication network constitutes a first step towards an integrated description of vast communication pathways established by KIT in physiopathological contexts.

Receptor tyrosine kinase KIT plays a crucial role in the regulation of cell signaling. This allosterically controlled activity may be affected by gain-of-function mutations that promote the development of several cancers. Identification of the molecular basis of KIT constitutive activation and allosteric regulation has inspired computational study of KIT hotspot mutations. In the present contribution, we investigated the mutation-induced effects on KIT conformational dynamics and intra-protein communication conditionally on the mutation location and the nature of the substituting amino acid. Our data elucidate that all studied mutations stabilize an inactive non-autoinhibited state of KIT over the inactive auto-inhibited state prevalent for the native protein. This shift in the protein conformational landscape promotes KIT constitutive activation. Our in silico analysis established correlations between the structural and dynamical effects induced by oncogenic mutations and the mutants auto-activation rates and drug sensitivities measured in vitro and in vivo. Particularly, the A-loop mutations stabilize the drug-resistant forms, while the JMR mutations may facilitate inhibitors binding to the active site. Cross-correlations established between local and long-range structural and dynamical effects demonstrate the allosteric character of the gain-of-function mutations mode of action.

IL-33/ST2 axis promotes mast cell survival via BCLXL

Mast cells (MC) are potent innate immune cells that accumulate in chronically inflamed tissues. MC express the IL-33 receptor IL-1 receptor-related protein ST2 at high level, and this IL-1 family cytokine both activates MC directly and primes them to respond to other proinflammatory signals. Whether IL-33 and ST2 play a role in MC survival remains to be defined. In skin-derived human MC, we found that IL-33 attenuated MC apoptosis without altering proliferation, an effect mediated principally through the antiapoptotic molecule B-cell lymphoma-X large (BCLXL). Murine MC demonstrated a similar mechanism, dependent entirely on ST2. In line with these observations, St2(-/-) mice exhibited reduced numbers of tissue MC in inflamed arthritic joints, in helminth-infected intestine, and in normal peritoneum. To confirm an MC-intrinsic role for ST2 in vivo, we performed peritoneal transfer of WT and St2(-/-) MC. In St2(-/-) hosts treated with IL-33 and in WT hosts subjected to thioglycollate peritonitis, WT MC displayed a clear survival advantage over coengrafted St2(-/-) MC. IL-33 blockade specifically attenuated this survival advantage, confirming IL-33 as the relevant ST2 ligand mediating MC survival in vivo. Together, these data reveal a cell-intrinsic role for the IL-33/ST2 axis in the regulation of apoptosis in MC, identifying thereby a previously unappreciated pathway supporting expansion of the MC population with inflammation.

Complex chemoattractive and chemorepellent Kit signals revealed by direct imaging of murine mast cells in microfluidic gradient chambers

Besides its cooperating effects on stem cell proliferation and survival, Kit ligand (KL) is a potent chemotactic protein. While transwell assays permit studies of the frequency of migrating cells, the lack of direct visualization precludes dynamic chemotaxis studies. In response, we utilize microfluidic chambers that enable direct observation of murine bone marrow-derived mast cells (BMMC) within stable KL gradients. Using this system, individual Kit+ BMMC were quantitatively analyzed for migration speed and directionality during KL-induced chemotaxis. Our results indicated a minimum activating threshold of ~3 ng ml(-1) for chemoattraction. Analysis of cells at KL concentrations below 3 ng ml(-1) revealed a paradoxical chemorepulsion, which has not been described previously. Unlike chemoattraction, which occurred continuously after an initial time lag, chemorepulsion occurred only during the first 90 minutes of observation. Both chemoattraction and chemorepulsion required the action of G-protein coupled receptors (GPCR), as treatment with pertussis toxin abrogated directed migration. These results differ from previous studies of GPCR-mediated chemotaxis, where chemorepulsion occurred at high ligand concentrations. These data indicate that Kit-mediated chemotaxis is more complex than previously understood, with the involvement of GPCRs in addition to the Kit receptor tyrosine kinase and the presence of both chemoattractive and chemorepellent phases.

Phosphorylation of the activation loop tyrosine 823 in c-Kit is crucial for cell survival and proliferation

The receptor tyrosine kinase c-Kit, also known as the stem cell factor receptor, plays a key role in several developmental processes. Activating mutations in c-Kit lead to alteration of these cellular processes and have been implicated in many human cancers such as gastrointestinal stromal tumors, acute myeloid leukemia, testicular seminomas and mastocytosis. Regulation of the catalytic activity of several kinases is known to be governed by phosphorylation of tyrosine residues in the activation loop of the kinase domain. However, in the case of c-Kit phosphorylation of Tyr-823 has been demonstrated to be a late event that is not required for kinase activation. However, because phosphorylation of Tyr-823 is a ligand-activated event, we sought to investigate the functional consequences of Tyr-823 phosphorylation. By using a tyrosine-to-phenylalanine mutant of tyrosine 823, we investigated the impact of Tyr-823 on c-Kit signaling. We demonstrate here that Tyr-823 is crucial for cell survival and proliferation and that mutation of Tyr-823 to phenylalanine leads to decreased sustained phosphorylation and ubiquitination of c-Kit as compared with the wild-type receptor. Furthermore, the mutated receptor was, upon ligand-stimulation, quickly internalized and degraded. Phosphorylation of the E3 ubiquitin ligase Cbl was transient, followed by a substantial reduction in phosphorylation of downstream signaling molecules such as Akt, Erk, p38, Shc, and Gab2. Thus, we propose that activation loop tyrosine 823 is crucial for activation of both the MAPK and PI3K pathways and that its disruption leads to a destabilization of the c-Kit receptor and decreased survival of cells.

Involvement of interstitial cells of Cajal in experimental severe acute pancreatitis in rats

AIM: To observe the changes in interstitial cells of Cajal (ICC) in rats with experimental severe acute pancreatitis (SAP).

METHODS: A total of twenty-four SD rats were randomly divided into two groups (n = 12), namely the sham (S) group and the SAP group; the SAP rat model was established by retrograde injection of 5% sodium taurocholate (1.0 mL/kg) into the pancreatic duct. Twenty-four hours later intestinal motility was assessed by testing small intestinal propulsion rate, and then the rats were sacrificed. The pancreas and jejunum were resected and underwent routine pathologic examination. Immunohistochemical staining was used to detect c-kit-positive cells in the jejunum. Expression of c-kit mRNA was detected by real-time polymerase chain reaction, and the expression of c-kit protein was evaluated by Western blotting. Ultrastructure of ICC was evaluated by transmission electron microscopy.

RESULTS: There was bleeding, necrosis and a large amount of inflammatory cell infiltration in pancreatic tissue in the SAP group, while in jejunal tissue we observed a markedly denuded mucosal layer, loss of villous tissue and a slightly dilated muscular layer. The small intestinal propulsion rate was 68.66% ± 2.66% in the S group and 41.55% ± 3.85% in the SAP group. Compared with the S group, the rate of the SAP group decreased sharply. The density of c-kit-positive cells in the SAP group was significantly lower than in the S group; the respective mean densities were 88.47 ± 10.49 in the S group and 56.11 ± 7.09 in the SAP group. The levels of c-kit protein and mRNA were 0.36 ± 0.04 and 1.29 ± 0.91 in the SAP group, respectively, which were significantly lower than those in the S group (0.53 ± 0.06, 0.64 ± 0.33, respectively). In the SAP group, ICC profiles showed the same change tendency, such as vacuolation of mitochondria, irregular vacuoles and loosened desmosome-like junctions.

CONCLUSION: Decreased c-kit-positive cells and ultrastructural changes in ICC resulting from blockade of the c-kit signaling pathway are involved in the intestinal dysmotility associated with SAP.

The identification of c-Kit-positive cells in the intestine of chicken

The ultrastructure of the interstitial cells of Cajal (ICC) has been examined in birds, but the distribution of these cells remains obscure because a suitable marker is lacking. In the present study, the identification and expression of c-Kit-positive cells in the chicken intestine were demonstrated by means of in situ hybridization histochemistry and the expression of the c-Kit gene by real-time quantitative PCR. Two types of cells stained positive for c-Kit mRNA. The first group consisted of spindle-shaped or bipolar cells identified as ICC. The ICC were found at a variety of locations: at the level of the myenteric plexus between the circular and longitudinal muscle and intermingled with smooth muscle cells within muscle bundles in the circular and longitudinal muscle layers. The ICC were also identified along the submucosal layer. The second group was composed of round-shaped cells, which resembled mast cells. Mast cells were mainly found in the lamina propria region as well as in the submucosal layer. The expression of the c-Kit gene by real-time quantitative PCR revealed the expression of c-Kit mRNA throughout the lamina muscularis and mucosa of the intestine; however, the quantitation was variable in different regions. This study reveals conclusively for the first time the distribution of ICC, quantifies the expression of c-Kit mRNA in the intestine of adult chicken, and also compares the c-Kit-positive cell types morphologically.

Prevalence of c-KIT mutations in gonadoblastoma and dysgerminomas of patients with disorders of sex development (DSD) and ovarian dysgerminomas

Activating c-KIT mutations (exons 11 and 17) are found in 10–40% of testicular seminomas, the majority being missense point mutations (codon 816). Malignant ovarian dysgerminomas represent ∼3% of all ovarian cancers in Western countries, resembling testicular seminomas, regarding chromosomal aberrations and c-KIT mutations. DSD patients with specific Y-sequences have an increased risk for Type II Germ Cell Tumor/Cancer, with gonadoblastoma as precursor progressing to dysgerminoma. Here we present analysis of c-KIT exon 8, 9, 11, 13 and 17, and PDGFRA exon 12, 14 and 18 by conventional sequencing together with mutational analysis of c-KIT codon 816 by a sensitive and specific LightCycler melting curve analysis, confirmed by sequencing. The results are combined with data on TSPY and OCT3/4 expression in a series of 16 DSD patients presenting with gonadoblastoma and dysgerminoma and 15 patients presenting pure ovarian dysgerminomas without DSD. c-KIT codon 816 mutations were detected in five out of the total of 31 cases (all found in pure ovarian dysgerminomas). A synonymous SNP (rs 5578615) was detected in two patients, one DSD patient (with bilateral disease) and one patient with dysgerminoma. Next to these, three codon N822K mutations were detected in the group of 15 pure ovarian dysgerminomas. In total activating c-KIT mutations were found in 53% of ovarian dysgerminomas without DSD. In the group of 16 DSD cases a N505I and D820E mutation was found in a single tumor of a patient with gonadoblastoma and dysgerminoma. No PDGFRA mutations were found. Positive OCT3/4 staining was present in all gonadoblastomas and dysgerminomas investigated, TSPY expression was only seen in the gonadoblastoma/dysgerminoma lesions of the 16 DSD patients. This data supports the existence of two distinct but parallel pathways in the development of dysgerminoma, in which mutational status of c-KIT might parallel the presence of TSPY.

Protease phenotype of constitutive connective tissue and of induced mucosal mast cells in mice is regulated by the tissue

Mouse mast cells (MCs) express a large number of serine proteases including tryptases, mouse mast cell protease (mMCP)-6 and -7; chymases, mMCP-1, -2, and -4; and an elastase, mMCP-5; along with carboxypeptidase-A3 (CPA3). In helminth-infected mouse intestine, distinct protease phenotypes are observed for connective tissue MCs (CTMCs) (mMCP-4(+)-7(+), and CPA3(+)) and mucosal MCs (MMCs) (mMCP-1(+) and 2(+)). To determine whether the protease phenotype was regulated by the tissue, we compared the phenotype of constitutive CTMCs and induced MMCs in trachea and large airways in antigen-sensitized unchallenged and challenged mice to MCs in skin and helminthic-infected intestine. We found that in the trachea, unlike in skin and intestine, CTMCs and MMCs both express all six serine proteases and CPA3 (mMCP-1(+), -2(+), 4(+)-7(+), CPA3(+)). This phenotype also holds for the lung CTMCs in the proximal bronchi, whereas the induced MMCs express only four proteases, mMCP-1, -2, -6, and -7. Thus, the T-cell-dependent induction of MMCs in trachea, large bronchi, and small intestine provides numbers but does not determine the protease phenotype. Furthermore, the CTMCs, which are constitutive, also show striking differences at these tissue sites, supporting the view that the differences in expression are tissue directed and not dependent on inflammation.

Identification of a novel nonsense mutation on the Pax3 gene in ENU-derived white belly spotting mice and its genetic interaction with c-Kit

In the course of a large-scale screening program of N-ethyl-N-nitrosourea mutagenesis, we isolated two semidominant mutation lines with white belly spotting, named as wps and wbs. Direct sequencing detected a nucleotide G-to-A transversion in exon 2 of the c-Kit gene in wps, which resulted in a missense D60N mutation. Another mutant, wbs, was mapped to chromosome 1 by genome-wide linkage analysis. In 93 meioses, the wbs locus was confined to a 5.2-Mb region between D1Mit380 and D1Mit215, including the Pax3 gene. A nonsense mutation K107X on the Pax3 coding region in wbs mice was identified, causing the loss of Pax3 protein in the homozygous mutant. We further demonstrated that Pax3 exhibited genetic interaction with c-Kit by intercrossing the wps and wbs mice. Further, Pax3 transactivated the c-Kit promoter in different cell lines. However, electrophoretic mobility shift assays showed that Pax3 did not bind to the c-Kit promoter, indicating that Pax3 may interact with c-Kit in an indirect way. This expands our understanding of the intricate regulatory network governing the melanocyte development.

Expression of C-kit messenger ribonucleic acid and C-kit protein in the gallbladders in guinea pigs of high cholesterol diet

The c-kit protooncogene receptor and its ligand-stem cell factor regulating the proliferation and survival of interstitial cells of Cajal (ICCs) have been described. The aim of this study was to determine the expression of c-kit mRNA and c-kit protein in the gallbladders in guinea pigs of high cholesterol diet (HCD). The gallbladder samples from 16 guinea pigs of HCD and from 16 guinea pigs of standard diet (StD) were used for this study. Expression of c-kit mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR), and expression of c-kit protein was detected by Western blot analysis. Serum total cholesterol (TC) (39 +/- 6 vs. 109 +/- 20 mg/dl), low density lipoprotein (LDL) cholesterol (24 +/- 4 vs. 71 +/- 10 mg/dl), high density lipoprotein (HDL) cholesterol (2.4 +/- 0.4 vs. 7.0 +/- 1.6 mg/dl), and triglyceride (TG) (58 +/- 8 vs. 118 +/- 23 mg/dl) concentrations were significantly higher in the HCD group than in the StD group of guinea pigs (P < 0.001, respectively). Decreased expression of c-kit mRNA was demonstrated in the HCD group compared with the StD group. The ratio of c-kit mRNA and GAPDH was 0.56 +/- 0.09 in controls and 0.50 +/- 0.07 in the HCD group (P = 0.033). C-kit protein expression significantly declined in the HCD group. The mean value of optical density was 129 +/- 25 in the StD group and 103 +/- 19 in the HCD group (P = 0.0009). The data indicate that the expression of c-kit mRNA and c-kit protein significantly decreased in the gallbladders in guinea pigs of HCD.

c-Kit-negative fibroblast-like cells express platelet-derived growth factor receptor alpha in the murine gastrointestinal musculature

Platelet-derived growth factor receptors (PDGFRs) belong to the same kinase group as c-Kit receptor tyrosine kinase that is specifically expressed in the interstitial cells of Cajal (ICC) in the gastrointestinal tract. In this study, we examined PDGFRalpha immunoreactivity in the murine gastrointestinal tract. PDGFRalpha-immunopositive (PDGFRalpha-ip) cells were observed in the musculature in all parts of the gastrointestinal tract. Although PDGFRalpha-ip cells were distinct from ICC and neurons, these cells were closely associated with intramuscular ICC and enteric nerve fibers. In the myenteric layer, PDGFRalpha-ip cells formed a cellular network with their ramified processes and encompassed myenteric ganglia. Numerous PDGFRalpha-ip cells were observed in the subserosal plane and showed a multipolar shape. The distribution pattern of the PDGFRalpha-ip cells in the ICC-deficient W(v)/W(v) mutant mice was the same as that in normal mice. PDGFRalpha-ip cells that showed intense immunoreactivity of SK3 potassium channel were considered to correspond to fibroblast-like cells or non-Cajal interstitial cells. Our observations suggest that PDGFRalpha-ip cells are basic cellular elements throughout the gastrointestinal musculature and are involved in the gastrointestinal functions.

TGF-beta1 attenuates mediator release and de novo Kit expression by human skin mast cells through a Smad-dependent pathway

TGF-beta has pleiotropic effects on many cell types at different stages of their development, including mast cells. The present study examines the effects of TGF-beta on human skin mast cells of the MC(TC) type. The expression of TGF-beta receptors (TGF-R) was verified at the mRNA and protein levels for TGF-RI and TGF-RII, and at the mRNA level for accessory molecules beta-glycan and endoglin. TGF-beta did not affect mast cell viability after 1 wk at concentrations < or = 10 ng/ml, but at 50 ng/ml caused significant cell death. TGF-beta inhibited surface and total expression of Kit in a dose-dependent manner, whereas the surface expression of Fc epsilonRI, Fc gammaRI, and Fc gammaRII was not affected. TGF-beta inhibited degranulation and cytokine production, but not PGD(2) production. TGF-beta diminished surface Kit expression through a TGF-RI kinase/Smad-dependent pathway by inhibiting new synthesis of Kit protein, which became evident following internalization and degradation of Kit after mast cells were exposed to the Kit ligand, stem cell factor. In contrast, addition of TGF-beta had no discernible effect on surface Kit expression when administered 3 days after stem cell factor, by which time surface Kit levels had returned to baseline. Although both transcription and translation are important for de novo expression of Kit, Kit mRNA levels were not affected by TGF-beta. Therefore, transcription of a gene other than Kit might be involved in Kit expression. Finally, activation of mast cells increased their susceptibility to TGF-beta-mediated apoptosis, a process that might regulate the survival of activated mast cells in vivo.

Gastrointestinal stromal tumors: past, present, and future

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. The name "GIST" was proposed in 1983, but the cell origin of GIST remained unclear until 1998, when my colleagues and I reported immunohistochemical evidence that GIST originated from interstitial cells of Cajal or their precursors. At the same time, we reported gain-of-function mutations of the Kit gene in GISTs. The Kit gene encodes KIT receptor tyrosine kinase, whose structure is similar to that of platelet-derived growth factor receptor (PDGFR). Imatinib mesylate was initially developed as an inhibitor of PDGFR. Then, it was found to be a potent inhibitor of BCR-ABL. Imatinib was successfully used for the treatment of chronic myeloid leukemia. When we reported gain-of-function mutations of the Kit gene in GISTs, the inhibitory effect of imatinib on KIT was already known. Imatinib was then successfully applied to the treatment of GISTs. The interrelationship between the type of Kit gain-of-function mutation and the therapeutic effect of imatinib has been well characterized in GISTs. Although various mutations of Kit and Pdgfr-alpha genes have been found in GISTs, most GISTs are luckily imatinibsensitive. After long-term administration of imatinib, however, new imatinib-resistant clones develop a secondary mutation of the Kit or Pdgfr-alpha gene. New drugs and adjuvant regimens against such secondary progression are now being intensively explored.

Lack of c-kit receptor promotes mammary tumors in N-nitrosomethylurea-treated Ws/Ws rats

BACKGROUND

c-kit is expressed in various cell types during development and it has been linked to the promotion of cellular migration, proliferation and/or survival of melanoblasts, hematopoietic progenitors and primordial germ cells. Several reports have proposed a role for the c-kit gene on carcinogenesis. Gain-of-function mutations are associated with diseases such as mastocytosis and gastrointestinal stromal tumors among others. However, very little is known about pathologies associated with loss-of-function mutations. Regarding breast cancer, c-kit protein and mRNA are highly expressed in normal breast but their expression decreases or is absent in the presence of breast cancer. We studied the role of c-kit in mammary carcinogenesis in the Ws/Ws rats carrying spontaneous lack-of-function mutation in the c-kit gene. Fifty day-old virgin female Ws/Ws rats and their wild type counterparts were injected with either 50 mg/kg body weight of the chemical carcinogen N-nitrosomethylurea or with vehicle. The animals were followed-up for 6 months. Fisher 344 rats were used as positive controls for tumor development.

RESULTS

Eleven weeks after treatment, palpable tumors were detected in the Ws/Ws rats. The tumor incidence was 80% in Ws/Ws rats, while no tumors were observed in the wild type rats (p = 0.006). Our data show that the lack of c-kit is permissive for the development of mammary tumor in Ws/Ws rats treated with carcinogen.

CONCLUSION

We conclude that the lack of c-kit may contribute to an imbalanced homeostatic state in the mammary gland either by affecting signaling between stroma and epithelium, or through the lack of mast cells.

Human telomere, oncogenic promoter and 5'-UTR G-quadruplexes: diverse higher order DNA and RNA targets for cancer therapeutics

Guanine-rich DNA sequences can form G-quadruplexes stabilized by stacked G–G–G–G tetrads in monovalent cation-containing solution. The length and number of individual G-tracts and the length and sequence context of linker residues define the diverse topologies adopted by G-quadruplexes. The review highlights recent solution NMR-based G-quadruplex structures formed by the four-repeat human telomere in K⁺ solution and the guanine-rich strands of c-myc, c-kit and variant bcl-2 oncogenic promoters, as well as a bimolecular G-quadruplex that targets HIV-1 integrase. Such structure determinations have helped to identify unanticipated scaffolds such as interlocked G-quadruplexes, as well as novel topologies represented by double-chain-reversal and V-shaped loops, triads, mixed tetrads, adenine-mediated pentads and hexads and snap-back G-tetrad alignments. The review also highlights the recent identification of guanine-rich sequences positioned adjacent to translation start sites in 5′-untranslated regions (5′-UTRs) of RNA oncogenic sequences. The activity of the enzyme telomerase, which maintains telomere length, can be negatively regulated through G-quadruplex formation at telomeric ends. The review evaluates progress related to ongoing efforts to identify small molecule drugs that bind and stabilize distinct G-quadruplex scaffolds associated with telomeric and oncogenic sequences, and outlines progress towards identifying recognition principles based on several X-ray-based structures of ligand–G-quadruplex complexes.

Application of HapMap data to the evaluation of 8 candidate genes for pediatric slow transit constipation

BACKGROUND

Slow transit constipation (STC) affects up to 3% of all children and is an increasingly recognized cause of chronic constipation in children. We conducted a pilot study to investigate whether genes encoding neurotransmitters (TAC1, TAC3, VIP, NOS1) and receptors (TACR1, TACR2, TACR3, KIT) could be responsible for STC.

METHODS

One hundred seventeen tag single nucleotide polymorphisms (SNPs), distributed among the candidate genes, were selected from HapMap data and genotyped using Sequenom (San Diego, CA) technology in 35 affected families. Evaluation of association was performed by transmission disequilibrium test and multilocus analysis.

RESULTS

Five SNPs (rs3771863, rs4580655, rs11722288, rs4563545, and rs3782221) in the TACR1, TACR3, KIT, and NOS1 genes were found to be potentially associated with STC, although the significance of these results does not withstand correction for multiple testing.

CONCLUSIONS

Our data indicate that 5 SNPs in the NOS1, TACR1, TACR3, and KIT genes could be involved in STC, especially rs3771863 in intron 1 of TACR1, which showed the highest association.

Structure of an unprecedented G-quadruplex scaffold in the human c-kit promoter

The c-kit oncogene is an important target in the treatment of gastrointestinal tumors. A potential approach to inhibition of the expression of this gene involves selective stabilization of G-quadruplex structures that may be induced to form in the c-kit promoter region. Here we report on the structure of an unprecedented intramolecular G-quadruplex formed by a G-rich sequence in the c-kit promoter in K+ solution. The structure represents a new folding topology with several unique features. Most strikingly, an isolated guanine is involved in G-tetrad core formation, despite the presence of four three-guanine tracts. There are four loops: two single-residue double-chain-reversal loops, a two-residue loop, and a five-residue stem-loop, which contain base-pairing alignments. This unique structural scaffold provides a highly specific platform for the future design of ligands specifically targeted to the promoter DNA of c-kit.

Interstitial cells of Cajal in health and disease. Part II: ICC and gastrointestinal stromal tumours

Mesenchymal tumours in the gastrointestinal tract have long been problematic in terms of diagnosis, prognosis and therapy, but recent advances in immunohistochemistry and related therapies have allowed more specific diagnosis. In particular, the recognition that both the interstitial cells of Cajal (ICC) and many gastrointestinal stromal tumours (GISTs) are positive for c-kit and CD34 and have other features similar to those of ICC has led to the use of imatinib, a novel small molecule therapy that blocks the CD117/c-kit tyrosine kinase receptor, which shows remarkable efficacy in treatment of malignant and metastatic GISTs as well as other malignancies.

Interstitial cells of cajal are involved in neurotransmission in the gastrointestinal tract

Interstitial cells of Cajal (ICC) are important cells which coordinate gastrointestinal motility. ICC express Kit receptor tyrosine kinase, and Kit immunohistochemistry reveals ICC morphology and distribution in the gastrointestinal musculature. ICC show a highly branched morphology and form unique networks. Myenteric ICC (ICC-MY) are located at the layer of the myenteric plexus and serve as electrical pacemakers. Intramuscular ICC (ICC-IM) and ICC in the deep muscular plexus (ICC-DMP) are distributed within the muscular layers, and are densely innervated by excitatory and inhibitory enteric motor neurons and in close contact with nerve terminals. Recent studies combined with morphological and functional techniques directly revealed that ICC-IM and ICC-DMP are mediators of enteric motor neuro-transmission. These types of ICC express several receptors for neurotransmitters such as acetylcholine and substance P and show responses to excitatory nerve stimulations. ICC also express receptive mechanisms for nitric oxide, which is an inhibitory neurotransmitter in the gastrointestinal tract. They can respond to nitrergic nerve stimulation by cyclic GMP production. Kit mutant mice lack ICC-IM and show attenuated postsynaptic responses after intrinsic nerve stimulation. These findings indicate the importance for ICC in neurotransmission in the gastrointestinal tract.

Subtractive hybridization unravels a role for the ion cotransporter NKCC1 in the murine intestinal pacemaker

In the small intestine, interstitial cells of Cajal (ICC) surrounding the myenteric plexus generate the pacemaking slow waves that are essential for an efficient intestinal transit. The underlying molecular mechanisms of the slow wave are poorly known. Our aim was to identify ICC-specific genes and their function in the mouse jejunum. Suppression subtractive hybridization using two independent ICC-deficient mouse models identified 56 genes putatively downregulated in the muscularis propria compared with wild-type littermates. Differential expression was confirmed by real-time quantitative PCR for the tyrosine kinase receptor KIT, the established marker for ICC, and for the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1). Immunoreactivity for NKCC1 was detected in myenteric ICC but not in the ICC population located at the deep muscular plexus. NKCC1 was also expressed in enteric neurons and mucosal crypts. Bumetanide, an NKCC1 inhibitor, reversibly affected the shape, amplitude, and frequency of the slow waves. Similar alterations were observed in NKCC1 knockout mice. These data support the hypothesis that NKCC1 expressed in myenteric ICC is involved in the mechanism of slow waves in the murine jejunum.

Mast cell-deficient W-sash c-kit mutant Kit W-sh/W-sh mice as a model for investigating mast cell biology in vivo

Mice carrying certain mutations in the white spotting (W) locus (ie, c-kit) exhibit reduced c-kit tyrosine kinase-dependent signaling that results in mast cell deficiency and other phenotypic abnormalities. The c-kit mutations in Kit(W/W-v) mice impair melanogenesis and result in anemia, sterility, and markedly reduced levels of tissue mast cells. In contrast, Kit(W-sh/W-sh) mice, bearing the W-sash (W(sh)) inversion mutation, have mast cell deficiency but lack anemia and sterility. We report that adult Kit(W-sh/W-sh) mice had a profound deficiency in mast cells in all tissues examined but normal levels of major classes of other differentiated hematopoietic and lymphoid cells. Unlike Kit(W/W-v) mice, Kit(W-sh/W-sh) mice had normal numbers of TCR gammadelta intraepithelial lymphocytes in the intestines and did not exhibit a high incidence of idiopathic dermatitis, ulcers, or squamous papillomas of the stomach, but like Kit(W/W-v) mice, they lacked interstitial cells of Cajal in the gut and exhibited bile reflux into the stomach. Systemic or local reconstitution of mast cell populations was achieved in nonirradiated adult Kit(W-sh/W-sh) mice by intravenous, intraperitoneal, or intradermal injection of wild-type bone marrow-derived cultured mast cells but not by transplantation of wild-type bone marrow cells. Thus, Kit(W-sh/W-sh) mice represent a useful model for mast cell research, especially for analyzing mast cell function in vivo.

KIT (c-kit oncogene product) pathway is constitutively activated in human testicular germ cell tumors

We investigated the expression of KIT (product of c-kit oncogene), gain-of-function mutations, and activation of its downstream signal transduction in human testicular cancers. KIT was expressed in 88% (22/25) of seminomas and in 44.4% (4/9) of non-seminomas compared to adjacent normal testicular tissue. Nine of the KIT-expressing seminomas had mutations (40.9%; 9/22) in the c-kit gene; two cases in exon 11 and 7 cases in exon 17. Two of these mutations in exon 17 were novel, and the other seven mutations were identical to the already known gain-of-function mutations which cause activation of KIT without ligand stem cell factor. All of the mutant KIT and 53.8% (7/13) of wild-type KIT were phosphorylated (activated) and associated with phosphorylated phosphatidylinositol 3-kinase (PI3K). Akt was also phosphorylated in these seminomas, suggesting that the KIT-PI3K-Akt pathway is activated in seminoma. These findings suggest that the KIT-PI3K-Akt pathway is constitutively activated in testicular germ cell tumors, due to overexpression of KIT protein and/or gain-of-function mutations in the c-kit gene.

A knock-in mouse model of gastrointestinal stromal tumor harboring kit K641E

A mouse model of gastrointestinal stromal tumor (GIST) has been developed by a knock-in gene targeting strategy, which introduced a Kit gene K641E mutation, originally identified in sporadic human GISTs and in the germ line of familial GIST syndrome patients. Homozygous and heterozygous Kit K641E mice develop gastrointestinal pathology with complete penetrance and all Kit K641E homozygotes die by age 30 weeks due to gastrointestinal obstruction by hyperplastic interstitial cells of Cajal (ICC) or GISTs. Heterozygous mice have less extensive ICC hyperplasia and smaller GISTs, suggesting a dose-response relationship between oncogenically activated Kit and ICC proliferation. Immunoprecipitation and Western blotting reveal GISTs to contain abundant phosphorylated/activated Kit. In addition to ICC hyperplasia and GISTs, homozygous Kit K641E mice exhibit loss-of-function Kit phenotypes, including white coat color, decreased numbers of dermal mast cells, and sterility, indicating that despite its oncogenic activity the mutant form cannot accomplish many activities of the wild-type gene. Kit K641E reproduces the pathology associated with the familial GIST syndrome and thus is an excellent model to study Kit pathway activation, ICC biology, GIST pathogenesis, and preclinical validations of GIST therapies and mechanisms of drug resistance.

Expression of c-kit messenger ribonucleic acid and c-kit protein in sigmoid colon of patients with slow transit constipation

BACKGROUND AND AIMS

The c-kit protooncogene receptor and its ligand stem cell factor regulate the proliferation and survival of germ cells as well as interstitial cells of Cajal (ICCs). Decreased numbers of ICCs and defects in its networks have been reported in the colon of patients with slow transit constipation (STC). However, little information about the c-kit messenger ribonucleic acid (mRNA) and protein expression in the constipated colon is available. The aim of this study was to determine whether the expression of c-kit mRNA and c-kit protein declined in the colon in STC.

PATIENTS AND METHODS

The sigmoid colonic samples from 12 patients with STC and from eight age-matched patients with non-obstructed colorectal cancer were used for this study. Expression of c-kit mRNA was detected by reverse transcriptase-polymerase chain reaction (RT-PCR), and expression of c-kit protein was detected by Western blot analysis.

RESULTS

Decreased expression of c-kit mRNA was demonstrated in the STC group compared with the control group. The ratio of c-kit and beta-actin was 1.26+/-0.32 in controls and 1.17+/-0.41 in the STC group (U=0.500, P=0.029). c-kit protein expression significantly declined in the STC group. The mean value of optical density was 162.97+/-5.43 in the control group and 96.64+/-8.80 in the STC group (U=0.000, P=0.021).

CONCLUSIONS

The data indicate that the expression of c-kit mRNA and c-kit protein significantly decreased in the colon of STC, suggesting that the c-kit signal pathway may play an important role in ICC reduction in STC.

WZsGreen/+: a new green fluorescent protein knock-in mouse model for the study of KIT-expressing cells in gut and cerebellum

In the small intestine, interstitial cells of Cajal (ICC) surrounding the myenteric plexus generate the pacemaking slow waves that are essential for an efficient intestinal transit. The underlying molecular mechanisms of the slow wave are poorly known. KIT is currently the sole practical marker for ICC. Attempts to purify living ICC have so far largely failed, due to the loss of the KIT epitope during enzymatic dissociation. Aiming to identify and isolate living ICC, we designed a knock-in strategy to express a fluorescent tag in KIT-expressing cells by inserting the sequence of the novel green fluorescent protein ZsGreen into the first exon of the c-Kit gene, creating a null allele called W(ZsGreen). In the gastrointestinal tract of heterozygous W(ZsGreen)/+ mice, tiny ZsGreen fluorescent dots were observed in all KIT-expressing ICC populations, with exception of ICC at the deep muscular plexus in small intestine. During development of the gastrointestinal tract, ZsGreen expression followed KIT expression in a spatiotemporal way. Stellate and basket KIT-expressing cells in the molecular layer of the cerebellum also exhibited ZsGreen dots, whereas no ZsGreen was detected in skin, testis, and bone marrow. ZsGreen dot-containing intestinal cells could be isolated from jejunum and maintained alive in culture for at least 3 days. ZsGreen is a suitable alternative to EGFP in transgenic animals. The novel W(ZsGreen)/+ model reported here appears to be a promising tool for live studies of KIT-expressing cells in the gastrointestinal tract and cerebellum and for the further analysis of pacemaker mechanisms.

Multiple gastrointestinal stromal tumors in type I neurofibromatosis: a pathologic and molecular study

Multiple gastrointestinal stromal tumors typically occur in familial form associated with KIT receptor tyrosine kinase or platelet-derived growth factor receptor-alpha (PDGFRA) germline mutations, but may also develop in the setting of type 1 neurofibromatosis. The molecular abnormalities of gastrointestinal stromal tumors arising in neurofibromatosis have not been extensively studied. We identified three patients with type 1 neuro-fibromatosis and multiple small intestinal stromal tumors. Immunostains for CD117, CD34, desmin, actins, S-100 protein, and keratins were performed on all of the tumors. DNA was extracted from representative paraffin blocks from separate tumor nodules in each case and subjected to a nested polymerase chain reaction, using primers for KIT exons 9, 11, 13, and 17 and PDGFRA exons 12 and 18, followed by direct sequencing. The mean patient age was 56 years (range: 37-86 years, male/female ratio: 2/1). One patient had three tumors, one had five, and one had greater than 10 tumor nodules, all of which demonstrated histologic features characteristic of gastrointestinal stromal tumors and stained strongly for CD117 and CD34. One patient died of disease at 35 months, one was disease free at 12 months and one was lost to follow-up. DNA extracts from 10 gastrointestinal stromal tumors (three from each of two patients and four from one patient) were subjected to polymerase chain reactions and assessed for mutations. All of the tumors were wild type for KIT exons 9, 13, and 17 and PDGFRA exons 12 and 18. Three tumors from one patient had identical point mutations in KIT exon 11, whereas the other tumors were wild type at this locus. We conclude that, although most patients with type 1 neurofibromatosis and gastrointestinal stromal tumors do not have KIT or PDGFRA mutations, KIT germline mutations might be implicated in the pathogenesis of gastrointestinal stromal tumors in some patients.

c-kit gene mutations in intracranial germinomas

Gain-of-function mutations of the c-kit gene and the expression of phosphorylated KIT are found in most gastrointestinal stromal tumors and mastocytosis. Further, almost all gonadal seminomas/dysgerminomas exhibit KIT membranous staining, and several reports have clarified that some (10-25%) have a c-kit gene mutation. But, whether intracranial germinomas also have a c-kit gene mutation remains unsolved. To elucidate the presence, frequency, and location of c-kit gene mutations in intracranial germinomas, we analyzed five mutational hot spots (exons 9, 10, 11, 13, and 17) in the c-kit genomic DNA of 16 germinomas using polymerase chain reaction and direct sequencing. We found c-kit gene mutations at exon 11 (W557C) or 17 (D816V, D820V, and N822Y) in four germinomas (25.0%), although no statistically significant difference in any clinicopathological factor was found between patients with or without mutations. These results are similar to those seen in gonadal seminoma/dysgerminoma patients, and confirm that intracranial germinomas are exact counterparts of gonadal seminomas/dysgerminomas, as would be expected on histological and immunohistochemical grounds. Moreover, molecular targeting drugs such as imatinib mesylate (STI571), which is a selective inhibitor of KIT, might be promising agents for the treatment of intracranial germinomas with c-kit gene mutations.

Structural basis for the autoinhibition and STI-571 inhibition of c-Kit tyrosine kinase

The activity of the c-Kit receptor protein-tyrosine kinase is tightly regulated in normal cells, whereas deregulated c-Kit kinase activity is implicated in the pathogenesis of human cancers. The c-Kit juxtamembrane region is known to have an autoinhibitory function; however the precise mechanism by which c-Kit is maintained in an autoinhibited state is not known. We report the 1.9-A resolution crystal structure of native c-Kit kinase in an autoinhibited conformation and compare it with active c-Kit kinase. Autoinhibited c-Kit is stabilized by the juxtamembrane domain, which inserts into the kinase-active site and disrupts formation of the activated structure. A 1.6-A crystal structure of c-Kit in complex with STI-571 (Imatinib or Gleevec) demonstrates that inhibitor binding disrupts this natural mechanism for maintaining c-Kit in an autoinhibited state. Together, these results provide a structural basis for understanding c-Kit kinase autoinhibition and will facilitate the structure-guided design of specific inhibitors that target the activated and autoinhibited conformations of c-Kit kinase.

Structure of a c-kit product complex reveals the basis for kinase transactivation

The c-Kit proto-oncogene is a receptor protein-tyrosine kinase associated with several highly malignant human cancers. Upon binding its ligand, stem cell factor (SCF), c-Kit forms an active dimer that autophosphorylates itself and activates a signaling cascade that induces cell growth. Disease-causing human mutations that activate SCF-independent constitutive expression of c-Kit are found in acute myelogenous leukemia, human mast cell disease, and gastrointestinal stromal tumors. We report on the phosphorylation state and crystal structure of a c-Kit product complex. The c-Kit structure is in a fully active form, with ordered kinase activation and phosphate-binding loops. These results provide key insights into the molecular basis for c-Kit kinase transactivation to assist in the design of new competitive inhibitors targeting activated mutant forms of c-Kit that are resistant to current chemotherapy regimes.

Alterations of the c-kit gene in testicular germ cell tumors

Expression and gain-of-function mutation of the c-kit gene, that encodes a receptor tyrosine kinase (KIT), have been reported in mast cell tumors and gastrointestinal stromal tumors (GISTs). Among human testicular germ cell tumors (GCTs), seminomas and seminoma components of mixed GCTs have also been shown to express KIT, but only one study has found the c-kit gene mutation at exon 17 in seminoma. To elucidate the frequency and location of the c-kit gene mutation of testicular GCTs, we analyzed the whole coding region of the c-kit complementary DNA along with 4 mutational hot spots (exons 9, 11, 13 and 17) of the c-kit genomic DNA by polymerase chain reaction and direct sequencing. Somatic mutations were found in 4 pure seminomas of 34 testicular GCTs (11.8%). One mutation was found in exon 11 (W557R) and the others were observed in exon 17 (D816H and D816V). These types of mutations were reported in GISTs (W557R), seminoma (D816H) and mastocytosis (D816V) and were considered to be gain-of-function mutations, although there were no differences of any clinicopathological factors or outcome between patients with and without mutations. Additionally, we also demonstrated coexpression of Gly-Asn-Asn-Lys510-513 (GNNK) + and GNNK - isoforms of the c-kit gene with dominance of the GNNK - transcript in all testicular GCTs. The mutations and/or preferential expression of GNNK - isoform of the c-kit gene might play an important role in the development of testicular GCTs, and these tumors may also be targets for STI571, which is a promising drug for advanced and metastatic GISTs.

Secondary amyloidosis and gastrointestinal stromal tumors. A case report and discussion of pathogenesis

A 69-year-old man presented with a malignant gastrointestinal stromal tumor associated with secondary amyloidosis. The tumor had classic features of a malignant gastrointestinal stromal tumor with interlacing fascicles and whorls of spindled cells, numerous and conspicuous mitotic figures, and extensive coagulative necrosis. The cells stained diffusely for CD117 (c-Kit), confirming the diagnosis of gastrointestinal stromal tumor. The spleen, 1 adrenal gland, and part of the pancreas were removed en block with the stomach. By microscopy, the spleen and adrenal gland were partially replaced with amyloid deposits confirmed by Congo red staining, electron microscopy, and immunohistochemistry. In contrast, neither the tumor nor the surrounding vasculature showed amyloid deposition. To our knowledge, this represents only the second case of systemic amyloidosis associated with a gastrointestinal stromal tumor. This case is unique in that extensive, diffuse amyloid deposits were observed in the spleen, adrenal gland, and liver.

Interstitial Cells in the Musculature of the Gastrointestinal Tract: Cajal and Beyond

Expression of the receptor tyrosine kinase KIT on cells referred to as interstitial cells of Cajal (ICC) has been instrumental during the past decade in the tremendous interest in cells in the interstitium of the smooth muscle layers of the digestive tract. ICC generate the pacemaker component (electrical slow waves of depolarization) of the smooth musculature and are involved in neurotransmission. By integration of ICC functions, substantial progress has been made in our understanding of the neuromuscular control of gastrointestinal motility, opening novel therapeutic perspectives. In this article, the ultrastructure and light microscopic morphology, as well as the functions and the development of ICC and of neighboring fibroblast-like cells (FLC), are critically reviewed. Directions for future research are considered and a unifying concept of mesenchymal cells, either KIT positive (the "ICC") or KIT negative "non-Cajal" (including the FLC and possibly also other cell types) cell types in the interstitium of the smooth musculature of the gastrointestinal tract, is proposed. Furthermore, evidence is accumulating to suggest that, as postulated by Santiago Ramon y Cajal, the concept of interstitial cells is not likely to be restricted to the gastrointestinal musculature.

Insights from gene arrays on the development and growth regulation of uterine leiomyomata

OBJECTIVE

To use microarray analysis as an unbiased approach to identify genes involved in the induction and growth of uterine leiomyomata.

DESIGN

Screen by arrays for up to 12,000 genes in leiomyoma (L) and control myometrium (M) from nine patients.

SETTING

University research laboratories.

PATIENT(S)

Nine patients in the follicular and luteal phases of the menstrual cycle.

INTERVENTION(S)

mRNA from L and M was converted to biotin-labeled cRNA and hybridized to cDNA oligonucleotide sequences on the arrays.

MAIN OUTCOME MEASURE(S)

Greater than two-fold change in gene expression between leiomyoma and matched myometrium.

RESULT(S)

Prominent among the 67 genes overexpressed in L relative to M were dlk or Pref-1, doublecortin, JM27, ionotropic glutamate receptor subunit 2, apolipoprotein E3, IGF2, semaphorin F, myelin proteolipid protein, MEST, frizzled, CRABP II, stromelysin-3, and TGFbeta3. The genes dlk, IGF2, and MEST are paternally expressed imprinted genes, and the others are involved in tissue differentiation and growth. Prominent among the 78 genes down-regulated in L relative to M were alcohol dehydrogenases 1alpha-gamma, tryptase, dermatopontin, thrombospondin, coxsackievirus receptor, nur77, and c-kit.

CONCLUSION(S)

Arrays offer large-scale screening of mRNA expression, which will help us differentiate between the genes and metabolic pathways necessary for leiomyoma growth and those regulating myometrial contractions.

Epithelioid gastrointestinal stromal tumor of the stomach with liver metastases in a 12-year-old girl: aspiration cytology and molecular study

Gastrointestinal stromal tumor (GIST), a stromal tumor of the gastrointestinal tract defined as CD117 (c-kit)-positive neoplasm, occurs primarily in adults. GIST with CD117 (c-kit) mutation and certain cytogenetic abnormalities is associated with malignancy, though a definite relationship between prognosis and molecular alterations remains to be elucidated. We report the cytologic features of an epithelioid GIST arising in the stomach of a child and metastatic to the liver, and the molecular mutational analysis of both the primary gastric tumor and the liver metastasis. Literature of pediatric GISTs was also reviewed. Fine needle aspiration of the liver metastasis, processed by Ultrafast Papanicolaou stain, showed fragments of cohesive small epithelioid cells with bland oval nuclei and unipolar cytoplasm transected by capillaries. Immunohistochemically, all nodules in the stomach and liver expressed CD117 (c-kit). Interestingly, some of the gastric tumor clusters were uniformly CD34 positive, whereas others were uniformly CD34 negative, suggesting heterogeneity of tumor clones. The presence of neurosecretory granules further subtyped the tumor into gastric autonomic nerve tumor (GANT). Molecular mutational analysis, performed in both the gastric tumor and the liver metastasis, showed no sequence abnormality in exons 9, 11, and 13 of CD117 (c-kit). Cytogenetic study revealed normal karyotype. These features might suggest a different molecular mechanism leading to malignancy in certain GISTs arising in children.

C-kit expression in pediatric solid tumors: a comparative immunohistochemical study

The stem cell factor/c-kit tyrosine kinase receptor pathway has been shown to be important for tumor growth and progression in several cancers, including mast cell diseases, gastrointestinal stromal tumor, acute myeloid leukemia, small cell lung carcinoma, and Ewing sarcoma. Studies using the oral agent STI-571 (Gleevec, Novartis), an inhibitor of the tyrosine kinases bcr-abl, c-kit, and PDGFR, have shown significant responses in patients with chronic myelogenous leukemia and gastrointestinal stromal tumor. With the aim of identifying additional groups of tumors that may use the stem cell factor/c-kit pathway and secondarily may be responsive to STI-571 treatment, this study surveyed 151 primary tumors from patients treated at St. Jude Children's Research Hospital for immunohistochemical expression of c-kit. Formalin-fixed, paraffin-embedded sections were stained with rabbit polyclonal anti-human c-kit (CD117, Dako) using standard avidin-biotin-peroxidase complex technique, antigen retrieval, and an automated stainer. Strong, diffuse staining for c-kit was seen in a proportion of synovial sarcomas, osteosarcomas, and Ewing sarcomas. Strong, diffuse staining was less common in neuroblastomas, Wilms' tumors, and rhabdomyosarcomas and was negative in alveolar soft part sarcomas and desmoplastic small round cell tumors. Tumors with strong, diffuse staining for c-kit in a pattern similar to gastrointestinal stromal tumor may represent suitable targets for new therapeutic agents.