Protein kinases expressed by interstitial cells of Cajal

Mechanisms underlying initiation of propulsion in guinea pig distal colon

Colonic motor complexes (CMCs) are a major neurogenic activity in guineapig distal colon. The identity of the enteric neurons that initiate this activity is not established. Specialized intrinsic primary afferent neurons (IPANs) are a major candidate. We aimed to test this hypothesis. To do this, segments of guineapig distal colon were suspended vertically in heated organ baths and propulsive forces acting on a pellet inside the lumen were recorded by isometric force transducer while pharmacological agents were applied to affect IPAN function. In the absence of drugs, CMCs acted periodically on the pellet, generating peak propulsive forces of 12.7 ± 5 g at 0.56 ± 0.22 cpm, lasting 49 ± 17 s (215 preparations; n = 60). Most but not all CMCs were abolished by nicotinic receptor blockade to inhibit fast excitatory synaptic transmission (50/62 preparations; n = 25). Remarkably, CMCs inhibited by hexamethonium were restored by a pharmacological strategy that aimed to enhance IPAN excitability. Thus, CMCs were restored by increased smooth muscle tension (using BAY K8644, bethanechol or carbachol) and by IPAN excitation using phorbol dibutyrate; NK3 receptor agonist, senktide; and partially by αCGRP. The IPAN inhibitor, 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazole-2-one (DCEBIO), decreased CMC frequency. CGRP, but not NK3-receptor antagonists, decreased CMC frequency in naive preparations. Finally, CMCs were blocked by tetrodotoxin, and this was not reversed by any drugs listed above. These results support a major role for IPANs that does not require fast synaptic transmission, in the periodic initiation of neurogenic propulsive contractions. Endogenous CGRP plays a role in determining CMC frequency, whereas further unidentified signaling pathways may determine their amplitude and duration.NEW & NOTEWORTHY The colonic motor complex (CMC) initiates propulsion in guinea pig colon. Here, CMCs evoked by an intraluminal pellet were restored during nicotinic receptor blockade by pharmacological agents that directly or indirectly enhance intrinsic primary afferent neuron (IPAN) excitability. IPANs are the only enteric neuron in colon that contain CGRP. Blocking CGRP receptors decreased CMC frequency, implicating their role in CMC initiation. The results support a role for IPANs in the initiation of CMCs.

Clinical Diagnosis of Gastrointestinal Stromal Tumor (GIST): From the Molecular Genetic Point of View

Gastrointestinal stromal tumors (GISTs) originating from the interstitial cells of Cajal are mesenchymal tumors of the gastrointestinal tract and have been found to harbor c-KIT mutations and KIT (CD117) expression since 1998. Later, PDGFRA mutations, SDH alterations, and other drive mutations were identified in GISTs. In addition, more and more protein markers such as DOG1, PKCθ were found to be expressed in GISTs which might help clinicians diagnose CD117-negative GISTs. Therefore, we plan to comprehensively review the molecular markers and genetics of GISTs and provide clinicians useful information in diagnostic and therapeutic strategies of GISTs. Twenty years after the discovery of KIT in GISTs, the diagnosis of GISTs became much more accurate by using immunohistochemical (IHC) panel (CD117/DOG1) and molecular analysis (KIT/PDGFRA), both of which constitute the gold standard of diagnosis in GISTs. The accurately molecular diagnosis of GISTs guides clinicians to precision medicine and provides optimal treatment for the patients with GISTs. Successful treatment in GISTs prolongs the survival of GIST patients and causes GISTs to become a chronic disease. In the future, the development of effective treatment for GISTs resistant to imatinib/sunitinib/regorafenib and KIT/PDGFRA-WT GISTs will be the challenge for GISTs.

Protein Kinase 2β Is Expressed in Neural Crest-Derived Urinary Pacemaker Cells and Required for Pyeloureteric Contraction

Nonobstructive hydronephrosis, defined as dilatation of the renal pelvis with or without dilatation of the ureter, is the most common antenatal abnormality detected by fetal ultrasound. Yet, the etiology of nonobstructive hydronephrosis is poorly defined. We previously demonstrated that defective development of urinary tract pacemaker cells (utPMCs) expressing hyperpolarization-activated cyclic nucleotide-gated channel 3 (HCN3) and the stem cell marker cKIT causes abnormal ureteric peristalsis and nonobstructive hydronephrosis. However, further investigation of utPMC development and function is limited by lack of knowledge regarding the embryonic derivation, development, and molecular apparatus of these cells. Here, we used lineage tracing in mice to identify cells that give rise to utPMCs. Neural crest cells (NCCs) indelibly labeled with tdTomato expressed HCN3 and cKIT. Furthermore, purified HCN3+ and cKIT+ utPMCs were enriched in Sox10 and Tfap-2α, markers of NCCs. Sequencing of purified RNA from HCN3+ cells revealed enrichment of a small subset of RNAs, including RNA encoding protein kinase 2β (PTK2β), a Ca²⁺-dependent tyrosine kinase that regulates ion channel activity in neurons. Immunofluorescence analysis in situ revealed PTK2β expression in NCCs as early as embryonic day 12.5 and in HCN3+ and cKIT+ utPMCs as early as embryonic day 15.5, with sustained expression in HCN3+ utPMCs until postnatal week 8. Pharmacologic inhibition of PTK2β in murine pyeloureteral tissue explants inhibited contraction frequency. Together, these results demonstrate that utPMCs are derived from NCCs, identify new markers of utPMCs, and demonstrate a functional contribution of PTK2β to utPMC function.

The Potential for Gut Organoid Derived Interstitial Cells of Cajal in Replacement Therapy

Effective digestion requires propagation of food along the entire length of the gastrointestinal tract. This process involves coordinated waves of peristalsis produced by enteric neural cell types, including different categories of interstitial cells of Cajal (ICC). Impaired food transport along the gastrointestinal tract, either too fast or too slow, causes a range of gut motility disorders that affect millions of people worldwide. Notably, loss of ICC has been shown to affect gut motility. Patients that suffer from gut motility disorders regularly experience diarrhoea and/or constipation, insomnia, anxiety, attention lapses, irritability, dizziness, and headaches that greatly affect both physical and mental health. Limited treatment options are available for these patients, due to the scarcity of human gut tissue for research and transplantation. Recent advances in stem cell technology suggest that large amounts of rudimentary, yet functional, human gut tissue can be generated in vitro for research applications. Intriguingly, these stem cell-derived gut organoids appear to contain functional ICC, although their frequency and functional properties are yet to be fully characterised. By reviewing methods of gut organoid generation, together with what is known of the molecular and functional characteristics of ICC, this article highlights short- and long-term goals that need to be overcome in order to develop ICC-based therapies for gut motility disorders.

Retinal Pigment Epithelium Atrophy 1 (rpea1): A New Mouse Model With Retinal Detachment Caused by a Disruption of Protein Kinase C, θ

Purpose

Retinal detachments (RDs), a separation of the light-sensitive tissue of the retina from its supporting layers in the posterior eye, isolate retinal cells from their normal supply of nourishment and can lead to their deterioration and death. We identified a new, spontaneous murine model of exudative retinal detachment, nm3342 (new mutant 3342, also referred to as rpea1: retinal pigment epithelium atrophy 1), which we characterize herein.

Methods

The chromosomal position for the recessive nm3342 mutation was determined by DNA pooling, and the causative mutation was discovered by comparison of whole exome sequences of mutant and wild-type controls. The effects of the mutation were examined in longitudinal studies by clinical evaluation, electroretinography (ERG), light microscopy, and marker and Western blot analyses.

Results

New mutant 3342, nm3342, also referred to as rpea1, causes an early-onset, complete RD on the ABJ/LeJ strain background, and central exudative RD and late-onset RPE atrophy on the C57BL/6J background. The ERG responses were normal at 2 months of age but deteriorate as mice age, concomitant with progressive pan-retinal photoreceptor loss. Genetic analysis localized rpea1 to mouse chromosome 2. By high-throughput sequencing of a whole exome capture library of an rpea1/rpea1 mutant and subsequent sequence analysis, a splice donor site mutation in the Prkcq (protein kinase C, θ) gene, was identified, leading to a skipping of exon 6, frame shift and premature termination. Homozygotes with a Prkcq-targeted null allele (Prkcq^tm1Litt) have similar retinal phenotypes as homozygous rpea1 mice. We determined that the PKCθ protein is abundant in the lateral surfaces of RPE cells and colocalizes with both tight and adherens junction proteins. Phalloidin-stained RPE whole mounts showed abnormal RPE cell morphology with aberrant actin ring formation.

Conclusions

The homozygous Prkcq^rpea1 and the null Prkcq^tm1Litt mutants are reliable novel mouse models of RD and can also be used to study the effects of the disruption of PRKCQ (PKCθ) signaling in RPE cells.

Dendritic cell c-kit signaling and adaptive immunity: implications for the upper airways

PURPOSE OF REVIEW

Binding of the receptor tyrosine kinase, c-kit, to its ligand, stem cell factor (SCF), mediates numerous biological functions. Important roles for c-kit in hematopoiesis, melanogenesis, erythropoiesis, spermatogenesis, and carcinogenesis are well documented. Similarly, activation of mast cells and eosinophils by c-kit ligation has long been known to result in degranulation with concomitant release of pro-inflammatory mediators including cytokines. This review will highlight a recently discovered function of c-kit in regulating the adaptive immune responses with relevance to allergic diseases.

RECENT FINDINGS

Recent studies in a number of laboratories including our own highlight the previously unappreciated functions for c-kit in immunological processes. Increased expression of c-kit and its ligand, SCF, on dendritic cells by Th2/Th17-inducing stimuli leads to c-kit activation and immune skewing toward these subsets and away from Th1 responses. Treatment of dendritic cells with inhibitors of c-kit activation such as imatinib mesylate (Gleevec) induces breach of T-cell tolerance, skewing of responses toward Th1, and activation of natural killer cells.

SUMMARY

Taken together, these observations suggest that the c-kit/SCF axis may be a useful target for redirecting deleterious immune responses in various disease settings, including allergic diseases that are often associated with Th2 and Th17 responses.

The role of cAMP dependent protein kinase in modulating spontaneous intracellular Ca²⁺ waves in interstitial cells of Cajal from the rabbit urethra

Interstitial cells of Cajal (ICC) serve as electrical pacemakers in the rabbit urethra. Pacemaking activity in ICC results from spontaneous intracellular Ca(2+) waves that rely on Ca(2+) release from endoplasmic reticulum (ER) stores. The purpose of this study was to investigate if the action of protein kinase A (PKA) affected the generation of Ca(2+) waves in ICC. Intracellular [Ca(2+)] was measured in fluo-4 loaded ICC, freshly isolated from the rabbit urethra using a Nipkow spinning disc confocal microscope. Application of the PKA inhibitor H-89 (10 μM) significantly inhibited the generation of spontaneous Ca(2+) waves in ICC and this was associated with a significant decrease in the ER Ca(2+) load, measured with 10mM caffeine responses. Ca(2+) waves could be rescued in the presence of H-89 by stimulating ryanodine receptors (RyRs) with 1mM caffeine but not by activation of inositol 1,4,5 tri-phosphate receptors (IP3Rs) with 10 μM phenylephrine. Increasing intracellular PKA with the cAMP agonists forskolin and 8-bromo-cAMP failed to yield an increase in Ca(2+) wave activity. We conclude that PKA may be maximally active under basal conditions in ICC and that inhibition of PKA with H-89 leads to a decreased ER Ca(2+) load sufficient to inactivate IP3Rs but not RyRs.

Esophageal telocytes and hybrid morphologies

TCs (telocytes) are actually defined as stromal cells with specific long and thin prolongations, called Tp (telopodes). They have been positively identified in various tissues and we now report their presence in the esophagus. These cells were identified by TEM (transmission electron microscopy) in esophageal samples of Wistar rats (n = 5) occurring beneath the basal epithelial layer, in submucosa, closely related to smooth and striated muscular fibres, as also in the adventitia. They are closely related to mast cells, macrophages and microvessels. Hybrid morphologies of stromal cells processes were found: cytoplasmic processes continued distally in a telopodial fashion. Telopodes alone may not be sufficient, however, for a safe diagnosis of TCs in TEM. A larger set of specific standards (such as the telopodial emergence, and the size of the cell body and telopodes) should be considered to differentiate TCs from various species of fibroblasts. The morphological and ultrastructural features should distinguish between TCs and interstitial cells of Cajal in the digestive tract.

CaMKII is essential for the function of the enteric nervous system

Background

Ca²⁺/calmodulin-dependent protein kinases (CaMKs) are major downstream mediators of neuronal calcium signaling that regulate multiple neuronal functions. CaMKII, one of the key CaMKs, plays a significant role in mediating cellular responses to external signaling molecules. Although calcium signaling plays an essential role in the enteric nervous system (ENS), the role of CaMKII in neurogenic intestinal function has not been determined. In this study, we investigated the function and expression pattern of CaMKII in the ENS across several mammalian species.

Methodology/Principal Findings

CaMKII expression was characterized by immunofluorescence analyses and Western Blot. CaMKII function was examined by intracellular recordings and by assays of colonic contractile activity. Immunoreactivity for CaMKII was detected in the ENS of guinea pig, mouse, rat and human preparations. In guinea pig ENS, CaMKII immunoreactivity was enriched in both nitric oxide synthase (NOS)- and calretinin-containing myenteric plexus neurons and non-cholinergic secretomotor/vasodilator neurons in the submucosal plexus. CaMKII immunoreactivity was also expressed in both cholinergic and non-cholinergic neurons in the ENS of mouse, rat and human. The selective CaMKII inhibitor, KN-62, suppressed stimulus-evoked purinergic slow EPSPs and ATP-induced slow EPSP-like response in guinea pig submucosal plexus, suggesting that CaMKII activity is required for some metabotropic synaptic transmissions in the ENS. More importantly, KN-62 significantly suppressed tetrodotoxin-induced contractile response in mouse colon, which suggests that CaMKII activity is a major determinant of the tonic neurogenic inhibition of this tissue.

Conclusion

ENS neurons across multiple mammalian species express CaMKII. CaMKII signaling constitutes an important molecular mechanism for controlling intestinal motility and secretion by regulating the excitability of musculomotor and secretomotor neurons. These findings revealed a fundamental role of CaMKII in the ENS and provide clues for the treatment of intestinal dysfunctions.

Progress in research of interstitial cells of Cajal

Interstitial cells of Cajal (ICCs) are a kind of cells mainly found in the gastrointestinal tract as pacemaker and signal transduction cells. They have a close connection with muscular cells and terminal neurons and can stimulate and promote gastrointestinal motility. With the help of electron microscopes, we can clearly recognize their distribution and inner structure. C-kit protein is expressed by ICCs. Besides, many disorders of gastrointestinal motility are related to ICCs. In recent years, many scholars have found the trace of ICCs in different organs such as the gastrointestinal tract, biliary tract, bladder, and uterus, and they have tried to state the relationship between abnormal ICCs and some diseases. This article will review the progress in research of ICCs in terms of their origin, morphology, receptors, function, and related diseases.

Long-term culture and cryopreservation of interstitial cells of Cajal

OBJECTIVE

Interstitial cells of Cajal (ICCs) in the gastrointestinal tract generate and propagate slow waves and mediate neuromuscular neurotransmission. Damage to ICCs has been described in several gastrointestinal motor disorders, and although many studies have examined ICCs in culture, they have been largely limited to freshly dissociated cells or short-term cultures. An efficient and reliable method to establish a source of ICCs is much needed. The aim of this study was to investigate methods for culturing, subculturing, cryopreservation, and recovery of ICCs.

METHODS

ICCs were derived from intestinal segments of domestic rabbits, and immunohistochemistry for c-Kit was used to identify ICCs in culture and after recovery. Recovered ICCs were also examined for motilin receptor expression.

RESULTS

Optimal conditions for ICC culture and cryopreservation were based on cell growth curves and MTT assay. On the basis of these findings, recovered cells were cultured for 7 days and then sorted via flow cytometry based on c-Kit immunoreactivity. The percent of c-Kit positive cells was 64.3%, and the number of ICCs sorted was 6.7 × 10(5). Reverse-transcription polymerase chain reaction and western blotting verified motilin receptor expression in c-Kit-positive ICCs.

CONCLUSIONS

This is the first study to describe the culture, passage, and recovery of ICCs and to show motilin receptor expression. Our results suggest that ICCs play an important role, at least in some species, in initiating the migrating myoelectric complex induced by motilin.

Gastrointestinal stromal tumours: origin and molecular oncology

Gastrointestinal stromal tumours (GISTs) are a paradigm for the development of personalized treatment for cancer patients. The nearly simultaneous discovery of a biomarker that is reflective of their origin and the presence of gain-of-function kinase mutations in these tumours set the stage for more accurate diagnosis and the development of kinase inhibitor therapy. Subsequent studies of genotype and phenotype have led to a molecular classification of GIST and to treatment optimization on the basis of molecular subtype. The study of drug-resistant tumours has advanced our understanding of kinase biology, enabling the development of novel kinase inhibitors. Further improvements in GIST treatment may require targeting GIST stem cell populations and/or additional genomic events.

Diagnostic value of protein kinase C theta for gastrointestinal stromal tumors: a meta-analysis

AIM: To perform a meta-analysis to assess the value of protein kinase C theta in the diagnosis of gastrointestinal stromal tumors.

METHODS: English or Chinese papers published from 1998 to 2010, which evaluated the diagnostic value of protein kinase C theta for gastrointestinal stromal tumors using pathologic diagnosis as the gold standard, were identified by searching Pubmed, Embase, Wanfang data, VIP, CBM and CNKI. The quality of included studies was assessed using the QUADAS tool. Meta-disc 1.4 software was used to extract data and to calculate the overall sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio. The summary receiver operating characteristic (SROC) curve was plotted.

RESULTS: Nine studies involving 1 141 patients were included in the meta-analysis. The results for the nine studies were inconsistent (P = 0.0042, I² = 64.3%). The overall sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio were 93% (95%CI: 91%-95%), 93% (95%CI: 91%-95%), 12.47 (95%CI: 6.30-24.70), 0.10 (95%CI: 0.05-0.17) and 138.19 (95%CI: 52.75-362.04), respectively. The weighted area under the ROC curve (AUC) was 0.9713 (SE = 0.0116).

CONCLUSION: Protein kinase C theta has a high value in the diagnosis of gastrointestinal stromal tumors.

Signaling of c-kit in dendritic cells influences adaptive immunity

The binding of the receptor tyrosine kinase, c-kit, to its ligand, stem cell factor (SCF), mediates numerous biological functions. Important roles for c-kit in hematopoiesis, melanogenesis, erythropoiesis, spermatogenesis, and carcinogenesis are well documented. Similarly, activation of granulocytes, mast cells, and of eosinophils in particular, by c-kit ligation has long been known to result in degranulation with concomitant release of pro-inflammatory mediators, including cytokines. However, recent work from a number of laboratories, including our own, highlights previously unappreciated functions for c-kit in immunologic processes. These novel findings strongly suggest that signaling through the c-kit-SCF axis could have a significant impact on the pathogenesis of diseases associated with an immunologic component. In our own studies, c-kit upregulation on dendritic cells via T helper (Th)2- and Th17-inducing stimuli led to c-kit activation and immune skewing toward these T helper subsets and away from Th1 responses. Others have shown that dendritic cell treatment with inhibitors of c-kit activation, such as imatinib mesylate (Gleevec), favored breaking of T-cell tolerance, skewing of responses toward production of Th1 cytokines, and activation of natural killer cells. These data all indicate that deeper understanding of, and ability to control, the c-kit-SCF axis could lead to improved treatment modalities aimed at redirecting unwanted and/or deleterious immune responses in a wide variety of conditions.

Protein kinase C{gamma} mediates regulation of proliferation by the serotonin 5-hydroxytryptamine receptor 2B

Activation of the 5-hydroxytryptamine receptor 2B (5-HT(2B)), a G(q/11) protein-coupled receptor, results in proliferation of various cell types. The 5-HT(2B) receptor is also expressed on the pacemaker cells of the gastrointestinal tract, the interstitial cells of Cajal (ICC), where activation triggers ICC proliferation. The goal of this study was to characterize the mitogenic signal transduction cascade activated by the 5-HT(2B) receptor. All of the experiments were performed on mouse small intestine primary cell cultures. Activation of the 5-HT(2B) receptor by its agonist BW723C86 induced proliferation of ICC. Inhibition of phosphatidylinositol 3-kinase by LY294002 decreased base-line proliferation but had no effect on 5-HT(2B) receptor-mediated proliferation. Proliferation of ICC through the 5-HT(2B) receptor was inhibited by the phospholipase C inhibitor U73122 and by the inositol 1,4,5-trisphosphate receptor inhibitor Xestospongin C. Calphostin C, the alpha, beta, gamma, and micro protein kinase C (PKC) inhibitor Gö6976, and the alpha, beta, gamma, delta, and zeta PKC inhibitor Gö6983 inhibited 5-HT(2B) receptor-mediated proliferation, indicating the involvement of PKC alpha, beta, or gamma. Of all the PKC isoforms blocked by Gö6976, PKCgamma and micro mRNAs were found by single-cell PCR to be expressed in ICC. 5-HT(2B) receptor activation in primary cell cultures obtained from PKCgamma(-/-) mice did not result in a proliferative response, further indicating the requirement for PKCgamma in the proliferative response to 5-HT(2B) receptor activation. The data demonstrate that the 5-HT(2B) receptor-induced proliferative response of ICC is through phospholipase C, [Ca(2+)](i), and PKCgamma, implicating this PKC isoform in the regulation of cellular proliferation.

Updating old ideas and recent advances regarding the Interstitial Cells of Cajal

Since their discovery by Cajal in 1889, the Interstitial Cells of Cajal (ICC) have generated much controversy in the scientific community. Indeed, the nervous, muscle or fibroblastic nature of the ICC has remained under debate for more than a century, as has their possible physiological function. Cajal and his colleagues considered them to be neurons, while contemporary histologists like Kölliker and Dogiel categorized these cells as fibroblasts. More recently, the role of ICC in the origin of slow-wave peristaltism has been elucidated, and several studies have shown that they participate in neurotransmission (intercalation theory). The fact that ICC assemble in the circular muscular layer and that they originate from cells which emerge from the ventral neural tube (VENT cells), a source of neurons, glia and ICC precursors other than the neural crest, suggests a neural origin for this particular subset of ICC. The discovery that ICC express the Kit protein, a type III tyrosine kinase receptor encoded by the proto-oncogene c-kit, has helped better understand their physiological role and implication in pathological conditions. Gleevec, a novel molecule designed to inhibit the mutant activated version of c-Kit receptors, is the drug of choice to treat the so-called gastrointestinal stromal tumours (GIST), the most common non-epithelial neoplasm of the gastrointestinal tract. Here we review Cajal's original contributions with the aid of unique images taken from Cajal's histological slides (preserved at the Cajal Museum, Cajal Institute, CSIC). In addition, we present a historical review of the concepts associated with this particular cell type, emphasizing current data that has advanced our understanding of the role these intriguing cells fulfil.

Emerging functions of c-kit and its ligand stem cell factor in dendritic cells: regulators of T cell differentiation

The receptor tyrosine kinase, c-kit, and its ligand, stem cell factor (SCF), function in a diverse range of biological functions. The role of c-kit in the maintenance and survival of hematopoietic stem cells and of mast cells is well recognized. c-kit also plays an important role in melanogenesis, erythropoiesis and spermatogenesis. Recent work from our laboratory highlights an important role of c-kit in the regulation of expression of two molecules in dendritic cells (DCs), interleukin-6 (IL-6) and Jagged-2 (a ligand of Notch), which are known to regulate T helper cell differentiation. Our study shows that induction of c-kit expression and its signaling in DCs promotes Th2 and Th17 responses but not Th1 response. c-kit inhibition by imatinib mesylate (Gleevec) in DCs was previously shown to promote natural killer cell activation which may be due to dampening of IL-6 production by the DCs. Since dysregulation of c-kit function has been associated with various disease states including cancer, in this perspective we have focused on known and novel functions of c-kit to include molecules such as IL-6 and Notch that were not previously recognized to be within the purview of c-kit biology. We have also reviewed the differential expression pattern of SCF and c-kit on various cell types and its variation during development or pathology. The recognition of previously unappreciated roles for c-kit will provide better insights into its function within and beyond the immune system and pave the way for developing better therapeutic strategies.

Ménétrier disease and gastrointestinal stromal tumors: hyperproliferative disorders of the stomach

Ménétrier disease and gastrointestinal stromal tumors (GISTs) are hyperproliferative disorders of the stomach caused by dysregulated receptor tyrosine kinases (RTKs). In Ménétrier disease, overexpression of TGF-alpha, a ligand for the RTK EGFR, results in selective expansion of surface mucous cells in the body and fundus of the stomach. In GISTs, somatic mutations of the genes encoding the RTK KIT (or PDGFRA in a minority of cases) result in constitutive kinase activity and neoplastic transformation of gut pacemaker cells (interstitial cells of Cajal). On the basis of the involvement of these RTKs in the pathogenesis of these disorders, Ménétrier disease patients have been effectively treated with a blocking monoclonal antibody specific for EGFR and GIST patients with KIT and PDGFRA tyrosine kinase inhibitors.

Do gap junctions play a role in nerve transmissions as well as pacing in mouse intestine?

Varicosities of nitrergic and other nerves end on deep muscular plexus interstitial cells of Cajal or on CD34-positive, c-kit-negative fibroblast-like cells. Both cell types connect to outer circular muscle by gap junctions, which may transmit nerve messages to muscle. We tested the hypotheses that gap junctions transmit pacing messages from interstitial cells of Cajal of the myenteric plexus. Effects of inhibitors of gap junction conductance were studied on paced contractions and nerve transmissions in small segments of circular muscle of mouse intestine. Using electrical field stimulation parameters (50 V/cm, 5 pps, and 0.5 ms) which evoke near maximal responses to nitrergic, cholinergic, and apamin-sensitive nerve stimulation, we isolated inhibitory responses to nitrergic nerves, inhibitory responses to apamin-sensitive nerves and excitatory responses to cholinergic nerves. 18beta-Glycyrrhetinic acid (10, 30, and 100 microM), octanol (0.1, 0.3, and 1 mM) and gap peptides (300 microM of (40)Gap27, (43)Gap26, (37,43)Gap27) all failed to abolish neurotransmission. 18beta-Glycyrrhetinic acid inhibited frequencies of paced contractions, likely owing to inhibition of l-type Ca(2+) channels in smooth muscle, but octanol or gap peptides did not. 18beta-Glycyrrhetinic acid and octanol, but not gap peptides, reduced the amplitudes of spontaneous and nerve-induced contractions. These reductions paralleled reductions in contractions to exogenous carbachol. Additional experiments with gap peptides in both longitudinal and circular muscle segments after N(G)-nitro-l-arginine and TTX revealed no effects on pacing frequencies. We conclude that gap junction coupling may not be necessary for pacing or nerve transmission to the circular muscle of the mouse intestine.

PKC delta-isoform translocation and enhancement of tonic contractions of gastrointestinal smooth muscle

PKC is involved in mediating the tonic component of gastrointestinal smooth muscle contraction in response to stimulation by agonists for G protein-coupled receptors. Here, we present pharmacological and immunohistochemical evidence indicating that a member of the novel PKC isoforms, PKC-delta, is involved in maintaining muscarinic receptor-coupled tonic contractions of the guinea pig ileum. The tonic component of carbachol-evoked contractions was enhanced by an activator of conventional and novel PKCs, phorbol 12,13-dibutyrate (PDBu; 200 nM or 1 microM), and by an activator of novel PKCs, ingenol 3,20-dibenzoate (IDB; 100 or 500 nM). Enhancement was unaffected by concentrations of bisindolylmaleimide I (BIM-I; 22 nM) that block conventional PKCs or by a PKC-epsilon-specific inhibitor peptide but was attenuated by higher doses of BIM-I (2.2 microM). Relevant proteins were localized at a cellular and subcellular level using confocal analysis. Immunohistochemical staining of the ileum showed that PKC-delta was exclusively expressed in smooth muscles distributed throughout the layers of the gut wall. PKC-epsilon immunoreactivity was prominent in enteric neurons but was largely absent from smooth muscle of the muscularis externa. Treatment with PDBu, IDB, or carbachol resulted in a time- and concentration-dependent translocation of PKC-delta from the cytoplasm to filamentous structures within smooth muscle cells. These were parallel to, but distinct from, actin filaments. The translocation of PKC-delta in response to carbachol was significantly reduced by scopolamine or calphostin C. The present study indicates that the tonic carbachol-induced contraction of the guinea pig ileum is mediated through a novel PKC, probably PKC-delta.

Selective labeling and isolation of functional classes of interstitial cells of Cajal of human and murine small intestine

Specific functions of interstitial cells of Cajal (ICC) have been linked to distinct classes that differ by morphology and distribution. In the small intestine, slow wave-generating ICC are located in the myenteric region (ICC-MY), whereas ICC that mediate neuromuscular neurotransmission occur either throughout the circular muscle layer (intramuscular ICC, ICC-IM) or in association with the deep muscular plexus (ICC-DMP). Selective isolation of ICC to characterize specific properties has been difficult. Recently, neurokinin-1 receptors have been detected in murine ICC-DMP and neurons but not in ICC-MY. Here we identified and isolated ICC-DMP/IM by receptor-mediated internalization of fluorescent substance P and Kit immunofluorescence. Specificity of labeling was verified by confocal microscopy. Mouse and human ICC-DMP/IM were detected in suspension by fluorescent microscopy and harvested for RT-PCR with micropipettes. The isolated cells expressed Kit but not markers for neurons, smooth muscle, or antigen-presenting cells. ICC-DMP expressed neurokinin-1 receptor, M(2) and M(3) muscarinic receptors, P2Y(1) and P2Y(4) purinergic receptors, VIP receptor 2, soluble guanylate cyclase-1 subunits, and protein kinase G. L- or T-type Ca(2+) channels were not detected in these cells. ICC-MY and ICC-DMP were simultaneously detected and enumerated by flow cytometry and sorted to purity by fluorescence-activated cell sorting. In summary, functional classes of ICC have distinct molecular identities that can be used to selectively identify and harvest these cells with, for example, receptor-mediated uptake of substance P and Kit immunofluorescence. ICC-DMP express neurotransmitter receptors and signaling intermediate molecules that are consistent with their role in neuromuscular neurotransmission.

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.

Caveolae and calcium handling, a review and a hypothesis

Caveolae are associated with molecules crucial for calcium handling. This review considers the roles of caveolae in calcium handling for smooth muscle and interstitial cells of Cajal (ICC). Structural studies showed that the plasma membrane calcium pump (PMCA), a sodium-calcium exchanger (NCX1), and a myogenic nNOS appear to be colocalized with caveolin I, the main constituent of these caveolae. Voltage dependent calcium channels (VDCC) are associated but not co-localized with caveolin 1, as are proteins of the peripheral sarcoplasmic reticulum (SR) such as calreticulin. Only the nNOS is absent from caveolin 1 knockout animals. Functional studies in calcium free media sugest that a source of calcium in tonic smooth muscles exists, partly sequestered from extracellular EGTA. This source supported sustained contractions to carbachol using VDCC and dependent on activity of the SERCA pump. This source is postulated to be caveolae, near peripheral SR. New evidence, presented here, suggests that a similar source exists in phasic smooth muscle of the intestine and its ICC. These results suggest that caveolae and peripheral SR are a functional unit recycling calcium through VDCC and controlling its local concentration. Calcium handling molecules associated with caveolae in smooth muscle and ICC were identified and their possible functions also reviewed.

The distribution of PKC isoforms in enteric neurons, muscle and interstitial cells of the human intestine

In many organs, different protein kinase C (PKC) isoforms are expressed in specific cell types, suggesting that the different PKCs have cell-specific roles, and also that drugs acting on a particular PKC may have effects on the whole organ that are distinguishable from drugs that target other isoforms. Previous studies of the guinea-pig and mouse intestine indicate that there are cell-specific expressions of PKC isoforms in neurons, muscle and the interstitial cells of Cajal. In the present study we have investigated the expression of different PKCs in human intestine. Immunohistochemical studies showed that the forms that are prominent in human enteric neurons are PKCs gamma and epsilon and in muscle the dominant form is PKCdelta. Neurons were weakly stained for PKCbetaI. These observations parallel findings in guinea-pig and mouse, except that in human PKCgamma-IR was not present in the same types of neurons that express it in the guinea-pig. Enteric glial cells were strongly immunoreactive for PKCalpha, which is also the major isoform in enteric glial cells of guinea-pig. In human and guinea-pig, glial cells also express PKCbetaI. Spindle-shaped cells in the mucosa were immunoreactive for PKCalpha and PKCgamma and in the muscle layers similar cells had PKCgamma-IR and PKCtheta-IR. The spindle-shaped cells were similar in morphology to interstitial cells of Cajal. Western analysis and RT-PCR confirmed the presence of the PKC isoform proteins and mRNA in the tissue. We conclude that there is cell-type specific expression of different PKCs in enteric neurons and intestinal muscle in human tissue, and that there are strong similarities in patterns of expression between laboratory animals and human, but some clear differences are also observed.

The role of protein kinase C isoforms in modulating injury and repair of the intestinal barrier

Gastrointestinal cells express a diverse group of protein kinase C (PKC) isoforms that play critical roles in a number of cell functions, including intracellular signaling and barrier integrity. PKC isoforms expressed by gastrointestinal epithelial cells consist of three major PKC subfamilies: conventional isoforms (alpha, beta1, beta2, and gamma), novel isoforms (delta, epsilon, theta, eta, and mu), and atypical isoforms (lambda, tau, and zeta). This review highlights recent discoveries, including our own, that some PKC isoforms in gastrointestinal epithelia monolayer cell culture are involved in injury to, whereas others are involved in protection of, intestinal barrier integrity. For example, certain PKC isoforms aggravate oxidative damage, whereas others protect against it. These findings suggest that the development of agents that selectively activate or inhibit specific PKC isoforms may lead to new therapeutic modalities for important gastrointestinal disorders such as cancer and inflammatory bowel disease.

PKC theta, a novel immunohistochemical marker for gastrointestinal stromal tumors (GIST), especially useful for identifying KIT-negative tumors

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor in the digestive tract and the majority of GIST has characteristic gain-of-function mutations of the c-kit gene, which encodes the KIT receptor for stem cell factor. The present study aimed to establish the usefulness of protein kinase C theta (PKC theta) as an immunohistochemical marker for GIST in comparison with KIT immunohistochemistry. PKC theta immunohistochemistry was carried out not only on 48 cases of GIST and another 40 cases of gastrointestinal mesenchymal tumors, but also on 24 cases of various tumors known to be immunohistochemically positive for KIT. Immunohistochemically, 41 out of 48 cases (85%) of GIST were positive for PKC theta, and its expression was confirmed by Western blot analysis using six cases of surgically resected GIST. In the present study there were six GIST immunohistochemically negative for KIT, which histologically revealed a myxoid epithelioid appearance characteristic to that of GIST with platelet-derived growth factor receptor alpha mutation. All six GIST were immunohistochemically positive for PKC theta. No PKC theta immunoreactivity was observed in other gastrointestinal mesenchymal tumors and various KIT-positive tumors except for three cases (14%) of gastrointestinal schwannomas. The present study revealed that PKC theta is an immunohistochemically novel and useful marker for GIST, especially for GIST negative for KIT.

News and views in Histochemistry and Cell Biology

Advances in histochemical methodology and ingenious applications of novel and improved methods continue to confirm the standing of morphological means and approaches in research efforts, and contribute significantly to increasing our knowledge about structures and functions in all areas of the life sciences from cell biology to pathology. Reports published during recent months documenting this progress are summarized in the present review.

Protein Kinase C theta (PKCtheta) expression and constitutive activation in gastrointestinal stromal tumors (GISTs)

KIT expression is a key diagnostic feature of gastrointestinal stromal tumors (GISTs), and virtually all of the GISTs express oncogenic forms of the KIT or PDGFRA receptor tyrosine kinase proteins, which serve as therapeutic targets of imatinib mesylate (Gleevec; Novartis, Basel, Switzerland). However, KIT expression can be low in PDGFRA-mutant GISTs, increasing the likelihood of misdiagnosis as other types of sarcoma. We report that the signaling intermediate protein kinase C theta (PKCtheta) is a diagnostic marker in GISTs, including those that lack KIT expression and/or contain PDGFRA mutations. PKCtheta is strongly activated in most GISTs and hence may serve, along with KIT/PDGFRA, as a novel therapeutic target.

Protein Kinase C θ Is Highly Expressed in Gastrointestinal Stromal Tumors But Not in Other Mesenchymal Neoplasias

Purpose: Gastrointestinal stromal tumors (GIST) are a distinctive group of mesenchymal neoplasms of the gastrointestinal tract. The oncogene KIT has a central role in the pathogenesis of GIST, with c-kit receptor tyrosine kinase (KIT) protein expression being the gold standard in its diagnosis. The identification of GIST patients has become crucial, because the tyrosine kinase inhibitor Imatinib is effective in the treatment of this malignancy. However, a small set of GISTs remain unrecognized, because KIT protein expression is not always evident. The aim of this study was the identification of new markers for the differential diagnosis of GIST.

Experimental Design: By analyzing publicly available data from transcriptional profiling of sarcomas, we found that protein kinase C θ (PKC-θ), a novel PKC isotype involved in T-cell activation, is highly and specifically expressed in GIST. PKC-θ expression in GIST was confirmed by reverse transcription-PCR and Western blot. PKC-θ was analyzed by immunohistochemistry in a panel of 26 GIST, 12 non-GIST soft-tissue sarcomas, and 35 tumors from other histologies.

Results: We found that all of the GISTs expressed PKC-θ, whereas this protein was undetectable in other mesenchymal or epithelial tumors, including non-GIST KIT-positive tumors. PKC-θ immunoreactivity was also observed in interstitial cells of Cajal.

Conclusions: Our results show that PKC-θ is easily detected by immunohistochemistry in GIST specimens and that it could be a sensitive and specific marker for the diagnosis of this malignancy.