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

Cancer-associated mutations in protein kinase C theta are loss-of-function

The Ca2+-independent, but diacylglycerol-regulated, novel protein kinase C (PKC) theta (θ) is highly expressed in hematopoietic cells where it participates in immune signaling and platelet function. Mounting evidence suggests that PKCθ may be involved in cancer, particularly blood cancers, breast cancer, and gastrointestinal stromal tumors, yet how to target this kinase (as an oncogene or as a tumor suppressor) has not been established. Here, we examine the effect of four cancer-associated mutations, R145H/C in the autoinhibitory pseudosubstrate, E161K in the regulatory C1A domain, and R635W in the regulatory C-terminal tail, on the cellular activity and stability of PKCθ. Live-cell imaging studies using the genetically-encoded fluorescence resonance energy transfer-based reporter for PKC activity, C kinase activity reporter 2 (CKAR2), revealed that the pseudosubstrate and C1A domain mutations impaired autoinhibition to increase basal signaling. This impaired autoinhibition resulted in decreased stability of the protein, consistent with the well-characterized behavior of Ca2+-regulated PKC isozymes wherein mutations that impair autoinhibition are paradoxically loss-of-function because the mutant protein is degraded. In marked contrast, the C-terminal tail mutation resulted in enhanced autoinhibition and enhanced stability. Thus, the examined mutations were loss-of-function by different mechanisms: mutations that impaired autoinhibition promoted the degradation of PKC, and those that enhanced autoinhibition stabilized an inactive PKC. Supporting a general loss-of-function of PKCθ in cancer, bioinformatics analysis revealed that protein levels of PKCθ are reduced in diverse cancers, including lung, renal, head and neck, and pancreatic. Our results reveal that PKCθ function is lost in cancer.

PKCθ-mediated serine/threonine phosphorylations of FAK govern adhesion and protrusion dynamics within the lamellipodia of migrating breast cancer cells

The cytoskeleton and cell-matrix adhesions constitute a dynamic network that controls cellular behavior during development and cancer. The Focal Adhesion Kinase (FAK) is a central actor of these cell dynamics, promoting cell-matrix adhesion turnover and active membrane fluctuations. However, the initial steps leading to FAK activation and subsequent promotion of cell dynamics remain elusive. Here, we report that the serine/threonine kinase PKCθ participates in the initial steps of FAK activation. PKCθ, which is strongly expressed in aggressive human breast cancers, controls the dynamics of cell-matrix adhesions and active protrusions through direct FAK activation, thereby promoting cell invasion and lung metastases. Using various tools for in vitro and live cell studies, we precisely decipher the molecular mechanisms of FAK activation. PKCθ directly interacts with the FAK FERM domain to open FAK conformation through PKCθ's specific V3 domain, while phosphorylating FAK at newly identified serine/threonine residues within nascent adhesions, inducing cell dynamics and aggressive behavior. This study thus places PKCθ-directed FAK opening and phosphorylations as an original mechanism controlling dynamic, migratory, and invasive abilities of aggressive breast cancer cells, further strengthening the emerging oncogenic function of PKCθ.

The Emerging Function of PKCtheta in Cancer

Protein Kinase C theta (PKCθ) is a serine/threonine kinase that belongs to the novel PKC subfamily. In normal tissue, its expression is restricted to skeletal muscle cells, platelets and T lymphocytes in which PKCθ controls several essential cellular processes such as survival, proliferation and differentiation. Particularly, PKCθ has been extensively studied for its role in the immune system where its translocation to the immunological synapse plays a critical role in T cell activation. Beyond its physiological role in immune responses, increasing evidence implicates PKCθ in the pathology of various diseases, especially autoimmune disorders and cancers. In this review, we discuss the implication of PKCθ in various types of cancers and the PKCθ-mediated signaling events controlling cancer initiation and progression. In these types of cancers, the high PKCθ expression leads to aberrant cell proliferation, migration and invasion resulting in malignant phenotype. The recent development and application of PKCθ inhibitors in the context of autoimmune diseases could benefit the emergence of treatment for cancers in which PKCθ has been implicated.

Cyclin D1 is a mediator of gastrointestinal stromal tumor KIT-independence

Oncogenic KIT or PDGFRA tyrosine kinase mutations are compelling therapeutic targets in most gastrointestinal stromal tumors (GISTs), and the KIT inhibitor, imatinib, is therefore standard of care for patients with metastatic GIST. However, some GISTs lose expression of KIT oncoproteins, and therefore become KIT-independent and are consequently resistant to KIT-inhibitor drugs. We identified distinctive biologic features in KIT-independent, imatinib-resistant GISTs as a step towards identifying drug targets in these poorly understood tumors. We developed isogenic GIST lines in which the parental forms were KIT oncoprotein-dependent, whereas sublines had loss of KIT oncoprotein expression, accompanied by markedly downregulated expression of the GIST biomarker, protein kinase C-theta (PRKCQ). Biologic mechanisms unique to KIT-independent GISTs were identified by transcriptome sequencing, qRT-PCR, immunoblotting, protein interaction studies, knockdown and expression assays, and dual-luciferase assays. Transcriptome sequencing showed that cyclin D1 expression was extremely low in two of three parental KIT-dependent GIST lines, whereas cyclin D1 expression was high in each of the KIT-independent GIST sublines. Cyclin D1 inhibition in KIT-independent GISTs had anti-proliferative and pro-apoptotic effects, associated with Rb activation and p27 upregulation. PRKCQ, but not KIT, was a negative regulator of cyclin D1 expression, whereas JUN and Hippo pathway effectors YAP and TAZ were positive regulators of cyclin D1 expression. PRKCQ, JUN, and the Hippo pathway coordinately regulate GIST cyclin D1 expression. These findings highlight the roles of PRKCQ, JUN, Hippo, and cyclin D1 as oncogenic mediators in GISTs that have converted, during TKI-therapy, to a KIT-independent state. Inhibitors of these pathways could be effective therapeutically for these now untreatable tumors.

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.

Gigantic GIST: A Case of the Largest Gastrointestinal Stromal Tumor Found to Date

Gastrointestinal stromal tumors are uncommon when compared to all gastrointestinal neoplasms but are the most common mesenchymal tumors of the gastrointestinal tract. The largest gastrointestinal stromal tumor ever recorded in literature weighed approximately 6.1 kg and measured 39 cm × 27 cm × 14 cm. About two-thirds of GISTs are malignant. The tumor size, mitotic rate, cellularity, and nuclear pleomorphism are the most important parameters when considering prognosis and recurrence. The definitive treatment for these tumors is resection. In the year 2000, the first patient was treated with the tyrosine kinase inhibitor imatinib and since then, gastrointestinal stromal tumors with high-risk features have been treated successfully with tyrosine kinase inhibitors. We present the largest gastrointestinal stromal tumor recorded in medical literature measuring 42.0 cm × 31.0 cm × 23.0 cm in maximum dimensions and weighing in at approximately 18.5 kg in a 65-year-old African-American male who presented with increased abdominal distention. The mass was successfully excised, and the patient was treated with imatinib without local or distant recurrence 1.5 years postoperatively.

Structural determinants of phorbol ester binding activity of the C1a and C1b domains of protein kinase C theta

The PKC isozymes represent the most prominent family of signaling proteins mediating response to the ubiquitous second messenger diacylglycerol. Among them, PKCθ is critically involved in T-cell activation. Whereas all the other conventional and novel PKC isoforms have twin C1 domains with potent binding activity for phorbol esters, in PKCθ only the C1b domain possesses potent binding activity, with little or no activity reported for the C1a domain. In order to better understand the structural basis accounting for the very weak ligand binding of the PKCθ C1a domain, we assessed the effect on ligand binding of twelve amino acid residues which differed between the C1a and C1b domains of PKCθ. Mutation of Pro⁹ of the C1a domain of PKCθ to the corresponding Lys⁹ found in C1b restored in vitro binding activity for [³H]phorbol 12,13-dibutyrate to 3.6 nM, whereas none of the other residues had substantial effect. Interestingly, the converse mutation in the C1b domain of Lys⁹ to Pro⁹ only diminished binding affinity to 11.7 nM, compared to 254 nM in the unmutated C1a. In confocal experiments, deletion of the C1b domain from full length PKCθ diminished, whereas deletion of the C1a domain enhanced 5-fold (at 100 nM PMA) the translocation to the plasma membrane. We conclude that the Pro¹⁶⁸ residue in the C1a domain of full length PKCθ plays a critical role in the ligand and membrane binding, while exchanging the residue (Lys²⁴⁰) at the same position in C1b domain of full length PKCθ only modestly reduced the membrane interaction.

Insights into the Proteome of Gastrointestinal Stromal Tumors-Derived Exosomes Reveals New Potential Diagnostic Biomarkers

Developing tumors continuously release nano-sized vesicles that represent circulating "fingerprints" of the tumor's identity. In gastrointestinal stromal tumor (GIST), we have previously reported that these tumors release "oncosomes" carrying the constitutively activated tyrosine kinase (TK) receptor KIT. Despite the clinical utility of TK inhibitors, such as imatinib mesylate (IM), recurrence and metastasis are clinical problems that urge the need to identify new tumor-derived molecules. To this aim, we performed the first high quality proteomic study of GIST-derived exosomes (GDEs) and identified 1,060 proteins composing the core GDE proteome (cGDEp). The cGDEp was enriched in diagnostic markers (e.g. KIT, CD34, ANO1, PROM1, PRKCQ, and ENG), as well as proteins encoded by genes previously reported expressed in GIST (e.g. DPP4, FHL1, CDH11, and KCTD12). Many of these proteins were validated using cell lines, patient-derived KIT⁺ exosomes, and GIST tissues. We further show that in vitro and in vivo-derived GDE, carry proteins associated with IM response, such as Sprouty homolog 4 (SPRY4), surfeit 4 (SURF4), ALIX, and the cGMP-dependent 3',5'-cyclic phosphodiesterase 2A (PDE2A). Additionally, we report that the total exosome levels and exosome-associated KIT and SPRY4 protein levels have therapeutic values. In fact, molecular characterization of in vivo-derived KIT⁺ exosomes indicate significant sorting of p-KIT^Tyr719, total KIT, and SPRY4 after IM-treatment of metastatic patients as compared with the pre-IM levels. Our data suggest that analysis of circulating exosomes levels and molecular markers of IM response in GIST patients with primary and metastatic disease is suitable to develop liquid based biopsies for the diagnosis, prognosis, and monitoring of response to treatment of these tumors. In summary, these findings provide the first insight into the proteome of GIST-derived oncosomes and offers a unique opportunity to further understand their oncogenic elements which contribute to tumorigenesis and drug resistance. Data are available via ProteomeXchange with identifier PXD007997.

Surgical Pathology of Gastrointestinal Stromal Tumors: Practical Implications of Morphologic and Molecular Heterogeneity for Precision Medicine

Gastrointestinal stromal tumor (GIST), the most common mesenchymal neoplasm of the gastrointestinal tract, exhibits diverse histologic and clinical manifestations. With its putative origin in the gastrointestinal pacemaker cell of Cajal, GIST can arise in association with any portion of the tubular gastrointestinal tract. Morphologically, GISTs are classified as spindled or epithelioid, though each of these subtypes encompasses a broad spectrum of microscopic appearances, many of which mimic other histologic entities. Despite this morphologic ambiguity, the diagnosis of GIST is aided in many cases by immunohistochemical detection of KIT (CD117) or DOG1 expression. The natural history of GIST ranges from that of a tumor cured by surgical resection to that of a locally advanced or even widely metastatic, and ultimately fatal, disease. This clinicopathologic heterogeneity is paralleled by an underlying molecular diversity: the majority of GISTs are associated with spontaneous activating mutations in KIT, PDGFRA, or BRAF, while additional subsets are driven by genetic lesions-often inherited-of NF1 or components of the succinate dehydrogenase enzymatic complex. Specific gene mutations correlate with particular anatomic or morphologic characteristics and, in turn, with distinct clinical behaviors. Therefore, prognostication and treatment are increasingly dictated not only by morphologic clues, but also by accompanying molecular genetic features. In this review, we provide a comprehensive description of the heterogenous molecular underpinnings of GIST, including implications for the practicing pathologist with regard to morphologic identification, immunohistochemical diagnosis, and clinical management.

PKCθ utility in diagnosing c-KIT/DOG-1 double negative gastrointestinal stromal tumors

BACKGROUND

The aim of this study was to evaluate the diagnosis value of an immunohistochemical (IHC) panel of three antibodies for the diagnosis of gastrointestinal stromal tumors (GISTs).

MATERIAL AND METHODS

In 80 consecutive GISTs without lymph node metastases, the IHC examinations were performed using the antibodies CD117 (c-KIT), DOG-1 and c-theta (PKCθ) protein. The diagnostic value of PKCθ in c-KIT/DOG-1 negative GISTs has been explored in fewer than 10 Medline-indexed papers.

RESULTS

The c-KIT, PKCθ and DOG-1 positivity was noted in 92.50% (n = 74), 90% (n = 72) and 76.25% (n = 61) of the cases, respectively. All of the C-KIT negative cases (n = 6) were also DOG-1 negative but displayed PKCθ positivity. All of the DOG-1 positive cases (n = 61) also expressed c-KIT. No correlation between the examined markers and clinicopathological parameters was noted.

CONCLUSIONS

The PKCθ sensitivity is similar to c-KIT and superior to DOG-1 sensitivity. All of the c-KIT/DOG-1 negative GISTs seem to express PKCθ. For a proper diagnosis of GIST, the c-KIT/DOG-1/PKCθ panel should be used, with possible therapeutic but not prognostic value.

Protein kinase C (PKC) isoforms in cancer, tumor promotion and tumor suppression

The AGC family of serine/threonine kinases (PKA, PKG, PKC) includes more than 60 members that are critical regulators of numerous cellular functions, including cell cycle and differentiation, morphogenesis, and cell survival and death. Mutation and/or dysregulation of AGC kinases can lead to malignant cell transformation and contribute to the pathogenesis of many human diseases. Members of one subgroup of AGC kinases, the protein kinase C (PKC), have been singled out as critical players in carcinogenesis, following their identification as the intracellular receptors of phorbol esters, which exhibit tumor-promoting activities. This observation attracted the attention of researchers worldwide and led to intense investigations on the role of PKC in cell transformation and the potential use of PKC as therapeutic drug targets in cancer diseases. Studies demonstrated that many cancers had altered expression and/or mutation of specific PKC genes. However, the causal relationships between the changes in PKC gene expression and/or mutation and the direct cause of cancer remain elusive. Independent studies in normal cells demonstrated that activation of PKC is essential for the induction of cell activation and proliferation, differentiation, motility, and survival. Based on these observations and the general assumption that PKC isoforms play a positive role in cell transformation and/or cancer progression, many PKC inhibitors have entered clinical trials but the numerous attempts to target PKC in cancer has so far yielded only very limited success. More recent studies demonstrated that PKC function as tumor suppressors, and suggested that future clinical efforts should focus on restoring, rather than inhibiting, PKC activity. The present manuscript provides some historical perspectives on the tumor promoting function of PKC, reviewing some of the observations linking PKC to cancer progression, and discusses the role of PKC in the pathogenesis of cancer diseases and its potential usage as a therapeutic target.

Enzastaurin: A lesson in drug development

Enzastaurin is an orally administered drug that was intended for the treatment of solid and haematological cancers. It was initially developed as an isozyme specific inhibitor of protein kinase Cβ (PKCβ), which is involved in both the AKT and MAPK signalling pathways that are active in many cancers. Enzastaurin had shown encouraging preclinical results for the prevention of angiogenesis, inhibition of proliferation and induction of apoptosis as well as showing limited cytotoxicity within phase I clinical trials. However, during its assessment in phase II and III clinical trials the efficacy of enzastaurin was poor both in combination with other drugs and as a single agent. In this review, we will discuss the development of enzastaurin from drug design to clinical testing, exploring target identification, validation and preclinical assessment. Finally, we will consider the clinical evaluation of enzastaurin as an example of the challenges associated with drug development. In particular, we discuss the poor translation of drug efficacy from preclinical animal models, inappropriate end point analysis, limited standards in phase I clinical trials, insufficient use of biomarker analysis and also patient stratification, all of which contributed to the failure to achieve approval of enzastaurin as an anticancer therapeutic.

PKCθ-induced phosphorylations control the ability of Fra-1 to stimulate gene expression and cancer cell migration

The AP-1 transcription factor Fra-1 is aberrantly expressed in a large number of cancers and plays crucial roles in cancer development and progression by stimulating the expression of genes involved in these processes. However, the control of Fra-1 transactivation ability is still unclear and here we hypothesized that PKCθ-induced phosphorylation could be necessary to obtain a fully active Fra-1 protein. Using MCF7 stable cells overexpressing equivalent levels of unphosphorylated Fra-1 or PKCθ-phosphorylated Fra-1, we showed that PKCθ-induced phosphorylation of Fra-1 was crucial for the stimulation of MMP1 and IL6 expression. Consistently, we found a significant positive correlation between PRKCQ (coding for PKCθ) and MMP1 mRNA expression levels in human breast cancer samples. PKCθ-induced phosphorylations, in part at T217 and T227 residues, strongly and specifically increased Fra-1 transcriptional activity through the stimulation of Fra-1 transactivation domain, without affecting JUN factors. More importantly, these phosphorylations were required for Fra-1-induced migration of breast cancer cells and phosphorylated Fra-1 expression was enriched at the invasion front of human breast tumors. Taken together, our findings indicate that PKCθ-induced phosphorylation could be important for the function of Fra-1 in cancer progression.

PRKCQ promotes oncogenic growth and anoikis resistance of a subset of triple-negative breast cancer cells

Background

The protein kinase C (PKC) family comprises distinct classes of proteins, many of which are implicated in diverse cellular functions. Protein tyrosine kinase C theta isoform (PRKCQ)/PKCθ, a member of the novel PKC family, may have a distinct isoform-specific role in breast cancer. PKCθ is preferentially expressed in triple-negative breast cancer (TNBC) compared to other breast tumor subtypes. We hypothesized that PRKCQ/PKCθ critically regulates growth and survival of a subset of TNBC cells.

Methods

To elucidate the role of PRKCQ/PKCθ in regulating growth and anoikis resistance, we used both gain and loss of function to modulate expression of PRKCQ. We enhanced expression of PKCθ (kinase-active or inactive) in non-transformed breast epithelial cells (MCF-10A) and assessed effects on epidermal growth factor (EGF)-independent growth, anoikis, and migration. We downregulated expression of PKCθ in TNBC cells, and determined effects on in vitro and in vivo growth and survival. TNBC cells were also treated with a small molecule inhibitor to assess requirement for PKCθ kinase activity in the growth of TNBC cells.

Results

PRKCQ/PKCθ can promote oncogenic phenotypes when expressed in non-transformed MCF-10A mammary epithelial cells; PRKCQ/PKCθ enhances anchorage-independent survival, growth-factor-independent proliferation, and migration. PKCθ expression promotes retinoblastoma (Rb) phosphorylation and cell-cycle progression under growth factor-deprived conditions that typically induce cell-cycle arrest of MCF-10A breast epithelial cells. Proliferation and Rb phosphorylation are dependent on PKCθ-stimulated extracellular signal-related kinase (Erk)/mitogen-activated protein kinase (MAPK) activity. Enhanced Erk/MAPK activity is dependent on the kinase activity of PKCθ, as overexpression of kinase-inactive PKCθ does not stimulate Erk/MAPK or Rb phosphorylation or promote growth-factor-independent proliferation. Downregulation of PRKCQ/PKCθ in TNBC cells enhances anoikis, inhibits growth in 3-D Matrigel^TM cultures, and impairs triple-negative tumor xenograft growth. AEB071, an inhibitor of PKCθ kinase activity, also inhibits growth and invasive branching of TNBC cells in 3-D cultures, further supporting a role for PKCθ kinase activity in triple-negative cancer cell growth.

Conclusions

Enhanced PRKCQ/PKCθ expression can promote growth-factor-independent growth, anoikis resistance, and migration. PRKCQ critically regulates growth and survival of a subset of TNBC. Inhibition of PKCθ kinase activity may be an attractive therapeutic approach for TNBC, a subtype in need of improved targeted therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0749-6) contains supplementary material, which is available to authorized users.

Sustained Mutant KIT Activation in the Golgi Complex Is Mediated by PKC-θ in Gastrointestinal Stromal Tumors

PURPOSE

Tumorigenesis of gastrointestinal stromal tumors (GIST) is driven by gain-of-function mutations in the KIT gene, which result in overexpression of activated mutant KIT proteins (MT-KIT). However, the mechanism of MT-KIT overexpression is poorly understood.

EXPERIMENTAL DESIGN

By protein expression analysis and immunofluorescent microscopic analysis, we determine the stability and localization of MT-KIT in four GIST cell lines with different mutations and HeLa cells transfected with mutant KIT model vectors. We also used 154 human GIST tissues to analyze the relationship between the expression of PKC-θ and MT-KITs, and correlations between PKC-θ overexpression and clinicopathological parameters.

RESULTS

We report that four different MT-KIT proteins are intrinsically less stable than wild-type KIT due to proteasome-mediated degradation and abnormally localized to the endoplasmic reticulum (ER) or the Golgi complex. By screening a MT-KIT-stabilizing factor, we find that PKC-θ is strongly and exclusively expressed in GISTs and interacts with intracellular MT-KIT to promote its stabilization by increased retention in the Golgi complex. In addition, Western blotting analysis using 50 GIST samples shows strong correlation between PKC-θ and MT-KIT expression (correlation coefficient = 0.682, P < 0.000001). Immunohistochemical analysis using 154 GISTs further demonstrates that PKC-θ overexpression significantly correlates with several clinicopathological parameters such as high tumor grade, frequent recurrence/metastasis, and poor patient survival.

CONCLUSIONS

Our findings suggest that sustained MT-KIT overexpression through PKC-θ-mediated stabilization in the Golgi contributes to GIST progression and provides a rationale for anti-PKC-θ therapy in GISTs. Clin Cancer Res; 23(3); 845-56. ©2016 AACR.

Inhibition of EP2/EP4 signaling abrogates IGF-1R-mediated cancer cell growth: involvement of protein kinase C-θ activation

Associations between growth factor receptor-mediated cell signaling and cancer cell growth have been previously characterized. Receptors for prostaglandin E₂, such as EP2, and EP4, play roles in cancer growth, progression and invasion. Thus, we examined the interactions between EP2/EP4- and IGF-1R-mediated cellular signaling in human pancreatic cancer cells. Selective antagonists against EP2 and EP4 abrogated IGF-1-stimulated cell growth and suppressed MEK/ERK phosphorylation. In subsequent experiments, phospho-antibody arrays indicated increased phosphorylation levels of protein kinase C-θ (PKC-θ) at the Thr538 position following the inhibition of EP2/EP4-mediated signaling. Inhibition of PKC-θ activity impaired cell viability compared with EP2/EP4-antagonized IGF-1-stimulated cells. PKC-θ kinase MAP4K3, which plays a pivotal role in PKC-θ activation, also affected growth signaling in the presence of EP2/EP4 antagonists. Administration of EP2 and EP4 antagonists significantly inhibited the growth of an orthotopic xenograft of IGF-1-secreting pancreatic cancer cells, with increased phospho-PKC-θ and decreased phospho-ERK. Clinico-pathological analyses showed that 17.4% of surgical pancreatic cancer specimens were quadruple-positive for IGF-1R, EP2 (or EP4), MAP4K3, and PKC-θ. These results indicate a novel signaling crosstalk between EP2/EP4 and IGF-1R in cancer cells, and suggest that the MAP4K3-PKC-θ axis is central and could be exploited as a molecular target for cancer therapy.

PKC-Theta in Regulatory and Effector T-cell Functions

One of the major goals in immunology research is to understand the regulatory mechanisms that underpin the rapid switch on/off of robust and efficient effector (Teffs) or regulatory (Tregs) T-cell responses. Understanding the molecular mechanisms underlying the regulation of such responses is critical for the development of effective therapies. T-cell activation involves the engagement of T-cell receptor and co-stimulatory signals, but the subsequent recruitment of serine/threonine-specific protein Kinase C-theta (PKC-θ) to the immunological synapse (IS) is instrumental for the formation of signaling complexes, which ultimately lead to a transcriptional network in T cells. Recent studies demonstrated that major differences between Teffs and Tregs occurred at the IS where its formation induces altered signaling pathways in Tregs. These pathways are characterized by reduced recruitment of PKC-θ, suggesting that PKC-θ inhibits Tregs suppressive function in a negative feedback loop. As the balance of Teffs and Tregs has been shown to be central in several diseases, it was not surprising that some studies revealed that PKC-θ plays a major role in the regulation of this balance. This review will examine recent knowledge on the role of PKC-θ in T-cell transcriptional responses and how this protein can impact on the function of both Tregs and Teffs.

Duodenal gastrointestinal stromal tumor: From clinicopathological features to surgical outcomes

Duodenal gastrointestinal tumors represent an extremely rare subset of stromal tumors arising from interstitial cells of Cajal. In the last 30 years the comprehension of the pathophysiology and natural history of this previously misunderstood clinical entity, in association with developments in endoscopy, imaging technology, and immunohistochemistry has resulted in novel diagnostic and treatment approaches. This is a comprehensive review of the current data of the literature on the various aspects of the diagnosis and treatment of these tumors. The duodenum is the less commonly involved site for these tumors in the digestive tract. Endoscopy and computed tomography can usually establish the diagnosis, confirmed by immunohistochemical staining and occasionally molecular genetic analysis. Endoscopic ultrasound with fine needle aspiration has been recently found to be the gold diagnostic standard with high sensitivity and specificity rates, diagnosing GIST in up to 80% of patients. Due to the complex anatomy of the pancreatico-duodenal region optimal therapeutic strategy of duodenal GISTs are challenging. Nevertheless surgical resection with microscopically clear resection margins seems to be the only potentially curative treatment for non-metastatic primary GISTs of the duodenum. Imatinib mesylate plays a key role in the management of GISTs both as neoadjuvant therapy and in patients with recurrent and metastatic disease. Meanwhile, the advances in the comprehension of the pathophysiology and natural history of this previously misunderstood clinical entity as well as the treatment of these tumors may render feasible, in the near future, the advent of newer and more effective treatment options.

The Novel PKCθ from Benchtop to Clinic

The protein kinases C (PKCs) are a family of serine/threonine kinases involved in regulating multiple essential cellular processes such as survival, proliferation, and differentiation. Of particular interest is the novel, calcium-independent PKCθ which plays a central role in immune responses. PKCθ shares structural similarities with other PKC family members, mainly consisting of an N-terminal regulatory domain and a C-terminal catalytic domain tethered by a hinge region. This isozyme, however, is unique in that it translocates to the immunological synapse between a T cell and an antigen-presenting cell (APC) upon T cell receptor-peptide MHC recognition. Thereafter, PKCθ interacts physically and functionally with downstream effectors to mediate T cell activation and differentiation, subsequently leading to inflammation. PKCθ-specific perturbations have been identified in several diseases, most notably autoimmune disorders, and hence the modulation of its activity presents an attractive therapeutic intervention. To that end, many inhibitors of PKCs and PKCθ have been developed and tested in preclinical and clinical studies. And although selectivity remains a challenge, results are promising for the future development of effective PKCθ inhibitors that would greatly advance the treatment of several T-cell mediated diseases.

Targeting protein kinase C in sarcoma

Protein kinase C (PKC) is a family of serine/threonine tyrosine kinases that regulate many cellular processes including division, proliferation, survival, anoikis and polarity. PKC is abundant in many human cancers and aberrant PKC signalling has been demonstrated in cancer models. On this basis, PKC has become an attractive target for small molecule inhibition within oncology drug development programmes. Sarcoma is a heterogeneous group of mesenchymal malignancies. Due to their relative insensitivity to conventional chemotherapies and the increasing recognition of the driving molecular events of sarcomagenesis, sarcoma provides an excellent platform to test novel therapeutics. In this review we provide a structure-function overview of the PKC family, the rationale for targeting these kinases in sarcoma and the state of play with regard to PKC inhibition in the clinic.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Small gastrointestinal stromal tumor in the stomach: identification of precursor for clinical gastrointestinal stromal tumor using c-kit and α-smooth muscle actin expression

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract. To find precursors for clinical GISTs of the stomach, small gastric stromal tumors of less than 3 cm were collected and examined immunohistochemically with analysis of the KIT mutation. Sixty-eight of 74 lesions were classified into 4 representative groups according to the expression of c-kit and α-smooth muscle actin (αSMA): group A, c-kit diffusely positive and αSMA negative (18 cases); group B, c-kit diffusely positive and αSMA focally positive (13); group C, c-kit focally positive and αSMA diffusely positive (27); and group D, c-kit negative and αSMA diffusely positive (10). Of the 4 groups, groups A and B of c-kit diffuse expression showed higher cellularity and labeling indices of p27(Kip1) and Ki-67 than did groups C and D of diffuse αSMA expression. Incidence of KIT exon 11 mutation in groups A and B was 86% (25/29), whereas that in groups C and D was 0% (0/20). Small gastric stromal tumors with c-kit diffuse expression were considered precursors for clinical GIST because they were significantly different from c-kit focally positive or negative tumors. The mutation of KIT is considered as an early event in tumorigenesis of GIST.

Analysis of induced pluripotent stem cells from a BRCA1 mutant family

Understanding BRCA1 mutant cancers is hampered by difficulties in obtaining primary cells from patients. We therefore generated and characterized 24 induced pluripotent stem cell (iPSC) lines from fibroblasts of eight individuals from a BRCA1 5382insC mutant family. All BRCA1 5382insC heterozygous fibroblasts, iPSCs, and teratomas maintained equivalent expression of both wild-type and mutant BRCA1 transcripts. Although no difference in differentiation capacity was observed between BRCA1 wild-type and mutant iPSCs, there was elevated protein kinase C-theta (PKC-theta) in BRCA1 mutant iPSCs. Cancer cell lines with BRCA1 mutations and hormone-receptor-negative breast cancers also displayed elevated PKC-theta. Genome sequencing of the 24 iPSC lines showed a similar frequency of reprogramming-associated de novo mutations in BRCA1 mutant and wild-type iPSCs. These data indicate that iPSC lines can be derived from BRCA1 mutant fibroblasts to study the effects of the mutation on gene expression and genome stability.

Clinicopathological features of primary leiomyosarcoma of the gastrointestinal tract following recognition of gastrointestinal stromal tumours

AIMS

We aimed to elucidate the clinicopathological and immunohistochemical features of leiomyosarcoma (LMS) of the gastrointestinal (GI) tract.

METHODS AND RESULTS

We encountered seven cases of GI-LMS in the colon (n = 4), rectum (n = 1), jejunum (n = 1) and stomach (n = 1). They ranged from 1 to 25 cm (median, 8.5 cm) in size and had high mitotic counts (median 38 per 50 high-power fields). Morphologically, the tumours were composed mainly of spindle cells with eosinophilic cytoplasm and various degrees of nuclear atypia and pleomorphism. Immunohistochemically, the tumours were positive for α-smooth muscle actin (86%), muscle-specific actin (71%), desmin (86%), calponin (71%), h-caldesmon (57%) and smoothelin (71%). All were negative for KIT, CD34, protein kinase C theta and DOG1. Local recurrence and distant metastasis occurred in one and three patients, respectively. We then reviewed 55 cases of GI-LMS from the era following the recognition of gastrointestinal stromal tumours. Among 29 of 55 cases for whom follow-up information was available, the estimated 5-year overall survival rate was 51.6%; tumour size ≥5 cm was correlated significantly with shorter overall survival time (P = 0.0016), while mitotic count (≥50 or ≥100 per 50 high-power fields) proved to be no prognostic factor.

CONCLUSIONS

GI-LMSs have distinctive clinicopathological and immunohistochemical features and exhibit aggressive biological behaviour.

Autocrine role for Gas6 with Tyro3 and Axl in leiomyosarcomas

Leiomyosarcoma (LMS) represent 15 % of adult sarcomas. The aim of this work was to identify novel altered pathways in LMS, which may be of therapeutic value for patients. Thirteen fresh frozen samples of soft tissue and visceral LMS were analyzed and compared with normal smooth muscle uterine tissue (NSM) for phosphoproteomic profile. Four proteins were found differentially expressed including Tyro3. The functional role of Tyro3 and its ligand Gas6 was investigated in two LMS cell lines, SK-LMS-1 and CNIO-AA. Four proteins and phosphoproteins were differentially expressed in LMS samples vs NSM: A loss of FAK Y397 phosphorylation was observed in all LMSs, while Tyro3, MSH2 and PKC theta were consistently overexpressed. Gas6, the major ligand of Tyro3, was expressed in 8 of the 13 LMS samples, and Gas6 expression highly correlated to Akt Y473 phosphorylation and to a lesser extent to Erk1/2 phosphorylation. SK-LMS-1 and CNIO-AA LMS expressed Tyro3, Axl and Gas6 at high level in CNIO-AA while at low levels in SK-LMS-1. Exposure of both cell lines to foretinib, a tyrosine kinase inhibitor of Met, Axl and Tyro3, reduced cell viability and induced caspase 3/7 activation. Transfection of CNIO-AA with small interfering RNA directed against Tyro3 and Axl genes induced a reduction of the expression of the specific proteins and, when combined, significantly reduced CNIO-AA cell viability. Leiomyosarcomas overexpress Tyro3. Gas6, a ligand of Tyro3, exerts an autocrine activities though Tyro3 and Axl in a subgroup of LMS.

The yin and yang of protein kinase C-theta (PKCθ): a novel drug target for selective immunosuppression

Protein kinase C-theta (PKCθ) is a protein kinase C (PKC) family member expressed predominantly in T lymphocytes, and extensive studies addressing its function have been conducted. PKCθ is the only T cell-expressed PKC that localizes selectively to the center of the immunological synapse (IS) following conventional T cell antigen stimulation, and this unique localization is essential for PKCθ-mediated downstream signaling. While playing a minor role in T cell development, early in vitro studies relying, among others, on the use of PKCθ-deficient (Prkcq(-/-)) T cells revealed that PKCθ is required for the activation and proliferation of mature T cells, reflecting its importance in activating the transcription factors nuclear factor kappa B, activator protein-1, and nuclear factor of activated T cells, as well as for the survival of activated T cells. Upon subsequent analysis of in vivo immune responses in Prkcq(-/-) mice, it became clear that PKCθ has a selective role in the immune system: it is required for experimental Th2- and Th17-mediated allergic and autoimmune diseases, respectively, and for alloimmune responses, but is dispensable for protective responses against pathogens and for graft-versus-leukemia responses. Surprisingly, PKCθ was recently found to be excluded from the IS of regulatory T cells and to negatively regulate their suppressive function. These attributes of PKCθ make it an attractive target for catalytic or allosteric inhibitors that are expected to selectively suppress harmful inflammatory and alloimmune responses without interfering with beneficial immunity to infections. Early progress in developing such drugs is being made, but additional studies on the role of PKCθ in the human immune system are urgently needed.

An intrapelvic extraintestinal gastrointestinal stromal tumor of undetermined origin: diagnosis by prostate needle biopsy

We herein report a case of intrapelvic gastrointestinal stromal tumor (GIST) of undetermined origin in a 48-year-old male who presented with dysuria. An enlarged tumor was detected on digital rectal examination. Imaging studies showed a solid and lobular homogenous tumor of 7.0 cm in diameter. The tumor was attached to the right dorsal aspect of the prostate with compression of the seminal vesicles and rectum. It was considered that the tumor had arisen from the prostate, although the patient's serum prostate-specific antigen level was low (0.436 ng/mL). The histological diagnosis by prostate needle biopsy was a spindle cell tumor. At cystoprostatectomy, the tumor was confirmed to be separated from the prostate by a fibrous band, and showed spindle cells with a fascicular growth pattern, but without necrotic areas. Mitotic figures were noted in 12 of 50 high-power fields. The tumor cells were immunoreactive for the KIT protein (CD117), CD34, Discovered on GIST-1 (DOG-1), and vimentin. In contrast, they were negative for desmin, α-smooth muscle actin, pancytokeratin (AE1/AE3), and S100 protein. The Ki-67 labeling index was 5%. The genetic analyses targeting the c-kit gene revealed a point mutation at codon 559 (GTT→GAT). The diagnosis of GIST was confirmed on the basis of the morphological features, immunoprofile, and results of the molecular analyses. Since extraintestinal GIST can resemble a prostatic tumor clinically, KIT (CD117) and DOG-1 should be considered for inclusion in the immunohistochemical panel for spindle cell tumors obtained by prostate needle biopsy.

Clinical features and treatment of gastrointestinal stromal tumors: Recent advances

Gastrointestinal stromal tumors (GISTs) are the most common gastrointestinal mesenchymal tumors. The development of molecular biology, pathology and clinical medicine in recent years has deepened our understanding of GISTs. The combination of traditional surgery and molecular targeted drugs is particularly important for the treatment of GISTs. Multi-target and multi-kinase inhibitors such as imatinib and sunitinib have been used for the treatment of unresectable and recurrent GISTs. This paper provides a brief review of gene analysis, pathological characteristics, operational and adjuvant therapy of GISTs.

Current management of gastrointestinal stromal tumors--a comprehensive review

BACKGROUND

Gastrointestinal stromal tumors (GISTs) comprise < 1% of all gastrointestinal (GI) tumors, but GISTs are the most common mesenchymal tumors of the GI tract. Dramatic changes in clinical practice have been observed in the last decade. This review highlights the overall management of GIST and its recent developments.

METHOD

We identified literature by searching Medline and PubMed from January 1995 to December 2011 using the keywords "gastrointestinal stromal tumors", "GIST", "imatinib" and "tyrosine kinase inhibitor". Additional papers were identified by a manual search of the references from the key articles. There were no exclusion criteria for published information to the topics.

RESULTS

For localized primary GISTs, surgical resection is the mainstay of therapy. The 5-year survival rate after complete resection of GISTs is approximately 50%-65%. Many factors including tumor size, mitotic rate, tumor location, kinase mutational status and occurrence of tumor rupture have been extensively studied and proposed to be predictors of survival outcomes. Adjuvant imatinib is proposed as an option for those patients with a substantial risk of relapse. Unresectable metastatic or recurrent GIST can be treated with a tyrosine kinase inhibitor, imatinib, with a remarkable response (50%-70%) and prolonged survival (median progression-free survival: 18-20 months; median overall survival: 51-57 months). The standard approach in the case of tumor progression on 400 mg once per day is to increase the imatinib dose to 400 mg twice per day as permitted by toxicity. Use of a second-line targeted agent, sunitinib, in patients with advanced GIST who fail (or are intolerant of) imatinib therapy is advised.

CONCLUSION

Treatment for GISTs has become increasingly complex because of the growing understanding of its biology. A multidisciplinary team that includes radiologists, medical oncologists, pathologists, and surgeons is paramount for the effective treatment of GIST.

The PKCθ pathway participates in the aberrant accumulation of Fra-1 protein in invasive ER-negative breast cancer cells

Fra-1 is aberrantly expressed in a large number of cancer cells and tissues, and emerging evidence suggests an important role for this Fos family protein in both oncogenesis and the progression or maintenance of many tumour types. Here, we show that the concentration of Fra-1 is high in invasive oestrogen receptor (ER)-negative (ER-) breast cancer cell lines, regardless of their Ras pathway status. All of the ER- cells express high levels of activated PKCθ, and the inhibition of PKCθ activity using RNA interference or the expression of a dominant-negative mutant results in a dramatic reduction in Fra-1 abundance. Conversely, the ectopic expression of constitutively active PKCθ leads to Fra-1 phosphorylation and accumulation in poorly invasive ER+ cells. This accumulation is due to the stabilisation of the Fra-1 protein through PKCθ signalling, whereas other members of the PKC family are ineffective. Both Ste20-related proline-alanine-rich kinase (SPAK) and ERK1/2, whose activities are upregulated by PKCθ, participate in PKCθ-driven Fra-1 stabilisation. Interestingly, their relative contributions appear to be different depending on the cell line studied. ERK1/2 signalling has a major role in ER- MDA-MB-231 cells, whereas Fra-1 accumulation occurs mainly through SPAK signalling in ER- BT549 cells. Fra-1 mutational analysis shows that the phosphorylation of S265, T223 and T230 is critical for PKCθ-driven Fra-1 stabilisation. Phosphorylation of the protein was confirmed using specific antisera against Fra-1 phosphorylated on T223 or S265. In addition, Fra-1 participates in PKCθ-induced cell invasion and is necessary for PKCθ-induced cell migration. In summary, we identified PKCθ signalling as an important regulator of Fra-1 accumulation in ER- breast cancer cells. Moreover, our results suggest that PKCθ could participate in progression of some breast cancers and could be a new therapeutic target.

Gastrointestinal stromal tumors (GISTs): CD117, DOG-1 and PKCθ expression. Is there any advantage in using several markers?

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract. Expression of CD117, DOG1 and PKCθ was investigated immunohistochemically in a series of 99 paraffin-embedded GISTs in order to determine the sensitivity and diagnostic value of these markers. KIT exons 9, 11, 13 and 17 and PDGFRA exons 12 and 18 were amplified by PCR and sequenced. A total of 94/99 (94%) GISTs stained positive for CD117, 81/99 (82%) for PKCθ and 90/99 (91%) for DOG-1. A significant correlation was noted between CD117 and DOG-1 expression (p=0.0001). All three markers were expressed in 74% (73/99) of GISTs. Of the five CD117-negative cases, two were PKCθ-negative/DOG1-negative and had mutations in KIT exon 11. Two were PKCθ-positive/DOG1-positive and had mutations in PDGFRA (one each in exons 12 and 18), and one was DOG1-negative/PKCθ-positive, with a PDGFRA exon 18 mutation. The most sensitive marker was CD117, followed by DOG-1 and PKCθ. Although PKCθ was less sensitive, and its staining is more challenging and difficult to interpret, the use of this marker is highly recommended, particularly in CD117-negative/DOG-1-negative GISTs.

Histopathology of gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST), generally driven by oncogenic KIT or PDGFRA mutations, is the most common mesenchymal tumor of the gastrointestinal (GI) tract. GIST is most common in the stomach (60%) and small intestine (30%), but can occur anywhere in the GI-tract and the intra-abdominal soft tissues. GIST can show spindle cell or epithelioid morphology, and mitotic count and tumor size are most important prognostic parameters. GISTs in NF1 patients and children are distinctive clinicopathologic groups. Immunohistochemical testing for KIT and sometimes for DOG1/Ano 1 is essential in confirming the diagnosis.

Gastrointestinal stromal tumor: advances in diagnosis and management

CONTEXT

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract and should be differentiated from other mesenchymal tumors. They harbor specific activating mutations in the KIT or platelet-derived growth factor receptor α ( PDGFRA ) receptor tyrosine kinases, which makes them responsive to pharmacologic inhibitors, such as imatinib mesylate and sunitinib malate.

OBJECTIVES

To provide a comprehensive review of the pathogenesis of GIST and the underlying principles of targeted therapy, to review the salient histologic and immunohistochemical features that facilitate the distinction of GIST from other mesenchymal neoplasms of the gastrointestinal tract, and to present the prognostic parameters for risk stratification that guide clinical management.

DATA SOURCES

Review of the English literature through PubMed as well as personal experience. Photographs were taken from cases encountered at the Cleveland Clinic.

CONCLUSIONS

The discovery of the KIT -GIST connection has not only improved the diagnostic accuracy of GISTs but also provided us with a better understanding of the histogenesis and molecular pathogenesis of these neoplasms.

Malignant gastrointestinal stromal tumor of the tongue: case report and review of the literature

A case of malignant gastrointestinal stromal tumor (GIST) of the tongue is reported. The patient was a 60-year-old woman. She underwent extended hemiglossectomy, neck dissection and reconstruction of the defect with radial forearm microvascular free flap. Etiology, histopathology, differential diagnosis, clinical presentation, and treatment of GISTs are discussed. The absence of any previous report in the English-language literature about the occurrence of GIST in the tongue is emphasized.

High nuclear protein kinase Cθ expression may correlate with disease recurrence and poor survival in oral squamous cell carcinoma

Protein kinase Cs play important roles in many biological processes and tumorigenesis. This study examined the expression of protein kinase Cθ and assessed its significance in patients with oral squamous cell carcinoma. Immunohistochemical staining was carried out to investigate the expression of protein kinase Cθ in 59 cases of oral squamous cell carcinoma. The results were correlated with clinical characteristics and outcome of patients. Diffuse cytoplasmic protein kinase Cθ was identified in 53 (89.8%) of the 59 oral squamous cell carcinoma cases, and the expression was not statistically associated with any clinicopathologic parameter. Twenty (40.7%) of the 59 oral squamous cell carcinoma cases exhibited nuclear expression of protein kinase Cθ with different grade of intensity. χ(2) analysis indicated that high nuclear protein kinase Cθ expression correlated significantly with shorter 24-month survival (P = .043) and disease recurrence (P = .019). The Kaplan-Meier method also showed that high nuclear expression of protein kinase Cθ was significantly associated with poor overall survival (P = .034) and shorter time to recurrence (P = .003). Univariate analysis revealed that high nuclear protein kinase Cθ expression (P = .046; hazard ratio, 2.2), tumor size less than 2 cm (P = .049; hazard ratio, 4.7), lymph node metastasis (P = .003; hazard ratio, 3.0), and higher stage (P = .002; hazard ratio, 8.7) were each associated with shorter overall survival. We identified the aberrant nuclear expression of protein kinase Cθ in oral squamous cell carcinoma. High nuclear protein kinase Cθ expression may correlate with disease recurrence and poor survival in patients with oral squamous cell carcinoma.

Evaluation of prognostic factors and their capacity to predict biological behavior in gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are c-KIT-signaling-driven mesenchymal tumors of the human digestive tract, many of which have c-KIT or PDGFRα activating mutations. The authors studied the immunohistochemical markers, c-KIT and PDGFRα mutations, in GISTs and their association with the clinicopathological and clinical follow-up in 145 GISTs. Tumors were located mainly in the stomach, the median tumor size being 7.5 cm. The mitotic index was ≤5 mitoses per 50 high-power fields in 61% of cases, 96% expressed CD117, and c-KIT or PDGFRα mutations were detected in 68% of cases. The median follow-up of the series was 52 months (range = 1 to 244.9 months). Tumor size, cell morphology, mitotic index, incomplete resection, Fletcher's risk classification, Ki-67 overexpression, and c-KIT mutations were associated with progression-free survival. Incomplete resection and mitotic activity also provide information about overall survival. In conclusion, complete clinicopathological, immunohistochemical, and genetic descriptions are necessary to characterize this disease and optimize its clinical management.

PKCθ activation in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors is needed for stimulation of numerous important cellular signaling cascades

The novel PKCθ isoform is highly expressed in T-cells, brain and skeletal muscle and originally thought to have a restricted distribution. It has been extensively studied in T-cells and shown to be important for apoptosis, T-cell activation and proliferation. Recent studies showed its presence in other tissues and importance in insulin signaling, lung surfactant secretion, intestinal barrier permeability, platelet and mast-cell functions. However, little information is available for PKCθ activation by gastrointestinal (GI) hormones/neurotransmitters and growth factors. In the present study we used rat pancreatic acinar cells to explore their ability to activate PKCθ and the possible interactions with important cellular mediators of their actions. Particular attention was paid to cholecystokinin (CCK), a physiological regulator of pancreatic function and important in pathological processes affecting acinar function, like pancreatitis. PKCθ-protein/mRNA was present in the pancreatic acini, and T538-PKCθ phosphorylation/activation was stimulated only by hormones/neurotransmitters activating phospholipase C. PKCθ was activated in time- and dose-related manner by CCK, mediated 30% by high-affinity CCK(A)-receptor activation. CCK stimulated PKCθ translocation from cytosol to membrane. PKCθ inhibition (by pseudostrate-inhibitor or dominant negative) inhibited CCK- and TPA-stimulation of PKD, Src, RafC, PYK2, p125(FAK) and IKKα/β, but not basal/stimulated enzyme secretion. Also CCK- and TPA-induced PKCθ activation produced an increment in PKCθ's direct association with AKT, RafA, RafC and Lyn. These results show for the first time the PKCθ presence in pancreatic acinar cells, its activation by some GI hormones/neurotransmitters and involvement in important cell signaling pathways mediating physiological responses (enzyme secretion, proliferation, apoptosis, cytokine expression, and pathological responses like pancreatitis and cancer growth).

Gain-of-Function Mutations of Receptor Tyrosine Kinases in Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in human gastrointestinal tract. We first found that most GISTs expressed KIT, a receptor tyrosine kinase encoded by protooncogene c-kit and that approximately 90% of the sporadic GISTs had somatic gain-of-function mutations of the c-kit gene. Since both GISTs and interstitial cells of Cajal (ICCs) were double-positive for KIT and CD34, GISTs were considered to originate from ICCs or their precursor cells. We also found that germline gain-of-function mutations of the c-kit gene resulted in familial and multiple GISTs with diffuse hyperplasia of ICCs as the preexisting lesion. Moreover, we found that about half of the sporadic GISTs without c-kit gene mutations had gain-of-function mutations of platelet-derived growth factor receptor alpha (PDGFRA) gene that encodes another receptor tyrosine kinase. Imatinib which is known to inhibit constitutively activated BCR-ABL tyrosine kinase in chronic myelogenous leukemia also inhibits constitutive activation of mutated KIT and PDGFRA, and is now being used for metastatic or unresectable GISTs as a molecular target drug. Mutational analyses of c-kit and PDGFRA genes are considered to be significant for prediction of effectiveness of imatinib and newly developed/developing other agents on GISTs. Some mouse models of familial and multiple GISTs have been genetically created, and may be useful for further investigation of GIST biology.

Gastrointestinal stromal tumor markers in cutaneous melanomas: relationship to prognostic factors and outcome

Melanoma expresses c-kit, a gastrointestinal stromal tumor marker, but has not been extensively evaluated for protein kinase C θ (PKCθ) or DOG1, and these stains have not been correlated with prognostic factors. We immunostained 62 primary cutaneous and 15 metastatic melanomas for polyclonal c-kit (pc-kit), monoclonal c-kit (mc-kit), PKCθ, and DOG1 and correlated results with prognostic parameters and survival. Of the cutaneous melanomas, 34 (55%) stained for pc-kit, 30 (48%) for mc-kit, 11 (18%) for PKCθ, and 2 (3%) for DOG1. The Breslow depth was 1.00 mm or less in 21 (68%) of 31 pc-kit+ cutaneous melanomas compared with 7 (27%) of 26 pc-kit- melanomas (P = .002). The pc-kit+ melanomas had less nodal disease (1/31 [3%] vs 9/25 [36%]; P = .001) and local recurrence (1/33 [3%] vs 6/27 [22%]; P = .021) but no statistically significant difference in the rate of distant metastases (13/32 [41%] vs 14/27 [52%]; P = .388) or survival (10/34 [29%] vs 16/39 [41%]; P = .301). We found that pc-kit correlates better with prognostic parameters than does mc-kit.

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.

Neurotensin receptor 1 is expressed in gastrointestinal stromal tumors but not in interstitial cells of Cajal

Gastrointestinal stromal tumors (GIST) are thought to derive from the interstitial cells of Cajal (ICC) or an ICC precursor. Oncogenic mutations of the KIT or PDGFRA receptor tyrosine kinases are present in the majority of GIST, leading to ligand-independent activation of the intracellular signal transduction pathways. We previously investigated the gene expression profile in the murine Kit^K641E GIST model and identified Ntsr1 mRNA, encoding the Neurotensin receptor 1, amongst the upregulated genes. Here we characterized Ntsr1 mRNA and protein expression in the murine Kit^K641E GIST model and in tissue microarrays of human GIST. Ntsr1 mRNA upregulation in Kit^K641E animals was confirmed by quantitative PCR. Ntsr1 immunoreactivity was not detected in the Kit positive ICC of WT mice, but was present in the Kit positive hyperplasia of Kit^K641E mice. In the normal human gut, NTSR1 immunoreactivity was detected in myenteric neurons but not in KIT positive ICC. Two independent tissue microarrays, including a total of 97 GIST, revealed NTSR1 immunoreactivity in all specimens, including the KIT negative GIST with PDGFRA mutation. NTSR1 immunoreactivity exhibited nuclear, cytoplasmic or mixed patterns, which might relate to variable levels of NTSR1 activation. As studies using radio-labeled NTSR1 ligand analogues for whole body tumor imaging and for targeted therapeutic interventions have already been reported, this study opens new perspectives for similar approaches in GIST.

Perspective on updated treatment guidelines for patients with gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract and present predominantly in middle-aged and older individuals. Historically, the outlook for patients with GISTs was very poor because of the general lack of efficacy of conventional chemotherapy and the often limited surgical options. However, the recognition of the role of mutations of the v-kit Hardy/Zuckerman 4 feline sarcoma viral oncogene homolog KIT and the platelet derived growth factor receptor alpha gene PDGFRα in the development of GISTs led to the evaluation of potential antitumor effects of the tyrosine kinase inhibitors imatinib and, more recently, sunitinib. Consequently, these molecularly targeted therapies were introduced into clinical practice, and the outcome for patients with GISTs improved considerably. In the last few years, the European Society of Medical Oncology, the National Comprehensive Cancer Network, and the Canadian Advisory Committee on GIST each published a major set of guidelines or practice recommendations for the management of patients with GIST. In the current review, the latest recommendations from each organization are summarized in terms of diagnosis and risk assessment, tumor staging, surgical and/or drug treatment of primary resectable and recurrent metastatic disease, and patient follow-up and assessment. In addition, areas of consensus and points of divergence among the guidelines are highlighted along with any unresolved issues.

Specificity of DOG1 (K9 clone) and protein kinase C theta (clone 27) as immunohistochemical markers of gastrointestinal stromal tumour

AIMS

DOG1 and protein kinase C (PKC) theta are both sensitive immunohistochemical markers of gastrointestinal stromal tumour (GIST). However, there are conflicting data regarding the specificity of the most commonly used PKC theta antibody (clone 27), and there are no existing data regarding the specificity of the only known commercially available DOG1 antibody (K9 clone) at the time of writing. This study's aim was to characterize the immunoreactivity patterns of both monoclonal antibodies amongst a wide range of neoplasm types including, in particular, histological mimics of GIST.

METHODS AND RESULTS

Immunohistochemistry for DOG1 and PKC theta was performed on whole tissue sections from 23 different neoplasm types (total of 125 cases). Ten of these neoplasm types showed CD117 immunopositivity. Only three (Ewing's sarcoma, glomus tumour and synovial sarcoma) of the 23 neoplasm types showed DOG1 immunopositivity, and such positivity was often focal and weak in intensity. In contrast, all but four (ganglioneuromas, leiomyomas, desmoplastic small round cell tumours and PEComa/angiomyolipomas) of the 23 neoplasm types showed PKC theta immunopositivity.

CONCLUSIONS

Compared with CD117, DOG1 (using the K9 antibody) is a more specific marker, whereas PKC theta (using the clone 27 antibody) is a considerably less specific immunohistochemical marker for GIST.

DOG1 and CD117 are the antibodies of choice in the diagnosis of gastrointestinal stromal tumours

AIMS

The histopathological diagnosis of gastrointestinal stromal tumours (GIST) is typically made based on a combination of clinical and morphological features supported by immunohistochemistry studies. The aim of this study was to examine the staining quality, sensitivity, specificity and utility of antibodies used commonly in GIST diagnosis.

METHODS AND RESULTS

Immunohistochemistry with a panel of antibodies [CD117, DOG1, protein kinase C (PKC)-theta, nestin, CD34, smooth muscle actin (SMA), desmin, S100 and CD171] was performed on whole sections from 187 GIST and 29 gastrointestinal mesenchymal tumours, and on several microarrays including 355 GISTs and 120 soft tissue sarcomas. Results showed that DOG1 and CD117 were the most sensitive and specific antibodies used in GIST diagnosis. PKC-theta and nestin were sensitive, but less specific, also staining other spindle cell tumours commonly considered in the differential diagnosis of GIST. CD34 staining was less sensitive than many of the other antibodies and of limited aid in diagnosis. The smooth muscle markers SMA and desmin, together with the neural marker S100, were unhelpful in confirming a diagnosis of GIST, but were particularly useful in the exclusion/diagnosis of other gastrointestinal mesenchymal tumour types.

CONCLUSIONS

In the majority of histologically suspected GISTs a combination of CD117 and DOG1 immunostaining is sufficient to confirm the histological diagnosis.

Gastrointestinal stromal tumors (GISTs): an updated experience

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are relatively common mesenchymal tumors of the digestive tract characterized by c-KIT mutations. This is a comprehensive review of the current data of the literature on the various aspects of the diagnosis and treatment of these tumors.

METHODS

The stomach is the most commonly involved site for these tumors in the digestive tract. Computed tomography and endoscopy can usually establish the diagnosis. The study of certain specific immunohistochemical markers may contribute to better characterization of these tumors.

RESULTS

Surgical resection of GISTs has been the most effective therapy. In addition, targeted therapy with tyrosine kinase inhibitors may reduce the development of recurrence or decrease the disease progression in patients with metastatic disease.

CONCLUSIONS

The introduction of tyrosine kinase inhibitors has resulted in significant improvement in the overall prognosis of these patients. Furthermore, preoperative imatinib can decrease tumor volume and is associated with complete surgical resection in locally advanced primary GISTs.