Pleiotrophin signaling through anaplastic lymphoma kinase is rate-limiting for glioblastoma growth

ALK receptor activation, ligands and therapeutic targeting in glioblastoma and in other cancers

The intracellular anaplastic lymphoma kinase (ALK) fragment shows striking homology with members of the insulin receptor family and was initially identified as an oncogenic fusion protein resulting from a translocation in lymphoma and more recently in a range of cancers. The full-length ALK transmembrane receptor of ~220 kDa was identified based on this initial work. This tyrosine kinase receptor and its ligands, the growth factors pleiotrophin (PTN) and midkine (MK) are highly expressed during development of the nervous system and other organs. Each of these genes has been implicated in malignant progression of different tumor types and shown to alter phenotypes as well as signal transduction in cultured normal and tumor cells. Beyond its role in cancer, the ALK receptor pathway is thought to contribute to nervous system development, function, and repair, as well as metabolic homeostasis and the maintenance of tissue regeneration. ALK receptor activity in cancer can be up-regulated by amplification, overexpression, ligand binding, mutations in the intracellular domain of the receptor and by activity of the receptor tyrosine phosphatase PTPRz. Here we discuss the evidence for ligand control of ALK activity as well as the potential prognostic and therapeutic implications from gene expression and functional studies. An analysis of 18 published gene expression data sets from different cancers shows that overexpression of ALK, its smaller homolog LTK (leukocyte tyrosine kinase) and the ligands PTN and MK in cancer tissues from patients correlate significantly with worse course and outcome of the disease. This observation together with preclinical functional studies suggests that this pathway could be a valid therapeutic target for which complementary targeting strategies with small molecule kinase inhibitors as well as antibodies to ligands or the receptors may be used.

Novel treatment avenues for peripheral T-cell lymphomas

INTRODUCTION

Peripheral T-cell lymphomas (PTCLs) and natural killer (NK) or T-cell non-Hodgkin's lymphomas (NHLs) are a rare and heterogeneous class of diseases with generally poor prognosis. This work intends to provide a focused primer on clinical diagnosis, current treatment regimens, and novel therapeutic approaches. The recent WHO classification has defined 18 different subtypes of PTCL and NK T-cell lymphomas. Diagnosis is mainly based on histology, flow-cytometric analysis of surface molecules in the blood and bone marrow, cytogenetics/fluorescence in situ hybridization (FISH), and T-cell receptor (TCR) rearrangement. Staging as well as follow-up diagnostic procedures rely on imaging techniques such as computerized tomography (CT) and positron emission tomography (PET). Current chemotherapeutic regimens such as CHOP result in a 60 - 70% response rate; however, 5-year survival is only around 30%. Therefore, new treatment strategies are urgently needed. Currently, different drug classes are under scrutiny.

AREAS COVERED

The authors discuss substances that directly target the tumor cells. The article includes such substances as antimetabolites, antibodies, histone deacetylase inhibitors, tyrosine kinase inhibitors, and immunomodulatory substances such as lenalidomide.

EXPERT OPINION

In the future a close collaboration of geneticists, biochemists, and clinicians together with new technologies such as deep sequencing will allow the refinement of treatment strategies in many diseases including PTCLs and NHLs. This refinement will allow treatments to be prepared according to the need of the individual patient.

Targeting ALK: a promising strategy for the treatment of non-small cell lung cancer, non-Hodgkin's lymphoma, and neuroblastoma

Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor that affects a number of biological and biochemical functions through normal ligand-dependent signaling. It has oncogenic functions in a number of tumors including non-small cell lung cancer (NSCLC), anaplastic large cell lymphoma, and neuroblastoma when altered by translocation or amplification or mutation. On August 2011, a small molecule inhibitor against ALK, crizotinib, was approved for therapy against NSCLC with ALK translocations. As we determine the molecular heterogeneity of tumors, the potential of ALK as a relevant therapeutic target in a number of malignancies has become apparent. This review will discuss some of the tumor types with oncogenic ALK alterations. The activity and unique toxicities of crizotinib are described, along with potential mechanisms of resistance and new therapies beyond crizotinib.

Expression analysis of macrodactyly identifies pleiotrophin upregulation

Macrodactyly is a rare family of congenital disorders characterized by the diffuse enlargement of 1 or more digits. Multiple tissue types within the affected digits are involved, but skeletal patterning and gross morphological features are preserved. Not all tissues are equally involved and there is marked heterogeneity with respect to clinical phenotype. The molecular mechanisms responsible for these growth disturbances offer unique insight into normal limb growth and development, in general. To date, no genes or loci have been implicated in the development of macrodactyly. In this study, we performed the first transcriptional profiling of macrodactyly tissue. We found that pleiotrophin (PTN) was significantly overexpressed across all our macrodactyly samples. The mitogenic functions of PTN correlate closely with the clinical characteristics of macrodactyly. PTN thus represents a promising target for further investigation into the etiology of overgrowth phenotypes.

Receptor-type tyrosine phosphatase ligands: looking for the needle in the haystack

Reversible protein phosphorylation plays a pivotal role in intercellular communication. Together with protein tyrosine kinases, protein tyrosine phosphatases (PTPs) are involved in the regulation of key cellular processes by controlling the phosphorylation levels of diverse effectors. Among PTPs, receptor-like protein tyrosine phosphatases (RPTPs) are involved in important developmental processes, particularly in the formation of the nervous system. Until recently, few ligands had been identified for RPTPs, making it difficult to grasp the effects these receptors have on cellular processes, as well as the mechanisms through which their functions are mediated. However, several potential RPTP ligands have now been identified to provide us with unparalleled insights into RPTP function. In this review, we focus on the nature and biological outcomes of these extracellular interactions between RPTPs and their associated ligands.

Inhibitors of the anaplastic lymphoma kinase

INTRODUCTION

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase normally expressed in the developing nervous tissue. Genetic alterations of ALK are associated with a number of cancers, including anaplastic large cell lymphoma (ALCL) and a subset of non-small cell lung cancer (NSCLC). Standard therapies for these diseases include surgery plus unspecific cytotoxic agents, with a low therapeutic window and significant treatment-associated systemic toxicity. A few small-molecule inhibitors of ALK kinase activity have been described in the recent years, some of which are currently undergoing clinical evaluation.

AREAS COVERED

Literature was searched for all ALK inhibitors that have entered clinical investigation, including published research articles and meeting abstracts. Data on pharmacokinetics, safety and efficacy of crizotinib, as well as preliminary clinical data for second-generation compounds, are reviewed. The issue of drug resistance is discussed.

EXPERT OPINION

Understanding the specific genetic aberration that causes cancer development and progression allows major advances in cancer therapy. Along the same way shown by imatinib in chronic myeloid leukemia, compounds that selectively target ALK are bringing a revolution in the treatment of ALK-positive tumors. Crizotinib has just been approved, and new more potent ALK inhibitors will shortly follow. These molecules represent another excellent proof-of-principle for targeted therapy.

Identification of anaplastic lymphoma kinase as a potential therapeutic target in ovarian cancer

Ovarian cancer is the leading cause of death from gynecologic cancer. Improvement in the clinical outcome of patients is likely to be achieved by the identification of molecular events that underlie the oncogenesis of ovarian cancer. Here we show that the anaplastic lymphoma kinase (ALK) is aberrantly activated in ovarian cancer. Using an unbiased and global phosphoproteomic approach, we profiled 69 Chinese primary ovarian tumor tissues and found ALK to be aberrantly expressed and phosphorylated in 4 tumors. Genetic characterization of these ALK-positive tumors indicated that full-length ALK expression in two serous carcinoma patients is consistent with ALK gene copy number gain, whereas a stromal sarcoma patient carries a novel transmembrane ALK fusion gene: FN1-ALK. Biochemical and functional analysis showed that both full-length ALK and FN1-ALK are oncogenic, and tumors expressing ALK or FN1-ALK are sensitive to ALK kinase inhibitors. Furthermore, immunohistochemical analysis of ovarian tumor tissue microarray detected aberrant ALK expression in 2% to 4% serous carcinoma patients. Our findings provide new insights into the pathogenesis of ovarian cancer and identify ALK as a potential therapeutic target in a subset of serous ovarian carcinoma and stromal sarcoma patients.

Midkine and Alk signaling in sympathetic neuron proliferation and neuroblastoma predisposition

Neuroblastoma (NB) is the most common extracranial solid tumor in childhood and arises from cells of the developing sympathoadrenergic lineage. Activating mutations in the gene encoding the ALK tyrosine kinase receptor predispose for NB. Here, we focus on the normal function of Alk signaling in the control of sympathetic neuron proliferation, as well as on the effects of mutant ALK. Forced expression of wild-type ALK and NB-related constitutively active ALK mutants in cultures of proliferating immature sympathetic neurons results in a strong proliferation increase, whereas Alk knockdown and pharmacological inhibition of Alk activity decrease proliferation. Alk activation upregulates NMyc and trkB and maintains Alk expression by an autoregulatory mechanism involving Hand2. The Alk-ligand Midkine (Mk) is expressed in immature sympathetic neurons and in vivo inhibition of Alk signaling by virus-mediated shRNA knockdown of Alk and Mk leads to strongly reduced sympathetic neuron proliferation. Taken together, these results demonstrate that the extent and timing of sympathetic neurogenesis is controlled by Mk/Alk signaling. The predisposition for NB caused by activating ALK mutations may thus be explained by aberrations of normal neurogenesis, i.e. elevated and sustained Alk signaling and increased NMyc expression.

Anaplastic lymphoma kinase spares organ growth during nutrient restriction in Drosophila

Developing animals survive periods of starvation by protecting the growth of critical organs at the expense of other tissues. Here, we use Drosophila to explore the as yet unknown mechanisms regulating this privileged tissue growth. As in mammals, we observe in Drosophila that the CNS is more highly spared than other tissues during nutrient restriction (NR). We demonstrate that anaplastic lymphoma kinase (Alk) efficiently protects neural progenitor (neuroblast) growth against reductions in amino acids and insulin-like peptides during NR via two mechanisms. First, Alk suppresses the growth requirement for amino acid sensing via Slimfast/Rheb/TOR complex 1. And second, Alk, rather than insulin-like receptor, primarily activates PI3-kinase. Alk maintains PI3-kinase signaling during NR as its ligand, Jelly belly (Jeb), is constitutively expressed from a glial cell niche surrounding neuroblasts. Together, these findings identify a brain-sparing mechanism that shares some regulatory features with the starvation-resistant growth programs of mammalian tumors.

Emerging importance of ALK in neuroblastoma

Since the original descriptions of gain-of function mutations in anaplastic lymphoma kinase (ALK), interest in the role of this receptor tyrosine kinase in neuroblastoma development and as a potential therapeutic target has escalated. As a group, the activating point mutations in full-length ALK, found in approximately 8% of all neuroblastoma tumors, are distributed evenly across different clinical stages. However, the most frequent somatic mutation, F1174L, is associated with amplification of the MYCN oncogene. This combination of features appears to confer a worse prognosis than MYCN amplification alone, suggesting a cooperative effect on neuroblastoma formation by these two proteins. Indeed, F1174L has shown more potent transforming activity in vivo than the second most common activating mutation, R1275Q, and is responsible for innate and acquired resistance to crizotinib, a clinically relevant ALK inhibitor that will soon be commercially available. These advances cast ALK as a bona fide oncoprotein in neuroblastoma and emphasize the need to understand ALK-mediated signaling in this tumor. This review addresses many of the current issues surrounding the role of ALK in normal development and neuroblastoma pathogenesis, and discusses the prospects for clinically effective targeted treatments based on ALK inhibition.

The receptor tyrosine kinase Alk controls neurofibromin functions in Drosophila growth and learning

Anaplastic Lymphoma Kinase (Alk) is a Receptor Tyrosine Kinase (RTK) activated in several cancers, but with largely unknown physiological functions. We report two unexpected roles for the Drosophila ortholog dAlk, in body size determination and associative learning. Remarkably, reducing neuronal dAlk activity increased body size and enhanced associative learning, suggesting that its activation is inhibitory in both processes. Consistently, dAlk activation reduced body size and caused learning deficits resembling phenotypes of null mutations in dNf1, the Ras GTPase Activating Protein-encoding conserved ortholog of the Neurofibromatosis type 1 (NF1) disease gene. We show that dAlk and dNf1 co-localize extensively and interact functionally in the nervous system. Importantly, genetic or pharmacological inhibition of dAlk rescued the reduced body size, adult learning deficits, and Extracellular-Regulated-Kinase (ERK) overactivation dNf1 mutant phenotypes. These results identify dAlk as an upstream activator of dNf1-regulated Ras signaling responsible for several dNf1 defects, and they implicate human Alk as a potential therapeutic target in NF1.

Neurofibromatosis-1 (NF1) syndrome is a common (1/3,000 births) genetic disorder affecting multiple organ systems, including the nervous system. Its clinical features include short stature, learning disabilities, and several types of benign and malignant tumors. NF1 is caused by mutations that inactivate the NF1 gene, a crucial negative regulator of Ras signaling. Although unregulated Ras signaling is a hallmark of NF1, the specific Ras signaling pathways responsible for disease development remain largely unknown. The Drosophila and human Nf1 genes are highly conserved; and, as in patients, mutant flies are smaller than usual and present deficient learning. Here, we identified the Drosophila Receptor Tyrosine Kinase dAlk as a negative regulator of organismal growth and olfactory learning. We show that excessive dAlk activation results in growth and learning defects similar to those of Nf1 mutants. Genetic suppression studies and pharmacological inhibition indicate dAlk as a critical upstream activator of Nf1-regulated neuronal Ras/ERK signals that contribute to size determination and learning. Importantly, our results strongly suggest that Alk represents a novel, highly specific, and promising therapeutic target in human NF1.

Anaplastic lymphoma kinase in human cancer

The receptor tyrosine kinases (RTKs) play a critical role, controlling cell proliferation, survival, and differentiation of normal cells. Their pivotal function has been firmly established in the pathogenesis of many cancers as well. The anaplastic lymphoma kinase (ALK), a transmembrane RTK, originally identified in the nucleophosmin (NPM)-ALK chimera of anaplastic large cell lymphoma, has emerged as a novel tumorigenic player in several human cancers. In this review, we describe the expression of the ALK-RTK, its related fusion proteins, and their molecular mechanisms of activation. Novel tailored strategies are briefly illustrated for the treatment of ALK-positive neoplasms.

The synthetic peptide P111-136 derived from the C-terminal domain of heparin affin regulatory peptide inhibits tumour growth of prostate cancer PC-3 cells

Background

Heparin affin regulatory peptide (HARP), also called pleiotrophin, is a heparin-binding, secreted factor that is overexpressed in several tumours and associated to tumour growth, angiogenesis and metastasis. The C-terminus part of HARP composed of amino acids 111 to 136 is particularly involved in its biological activities and we previously established that a synthetic peptide composed of the same amino acids (P111-136) was capable of inhibiting the biological activities of HARP. Here we evaluate the ability of P111-136 to inhibit in vitro and in vivo the growth of a human tumour cell line PC-3 which possess an HARP autocrine loop.

Methods

A total lysate of PC-3 cells was incubated with biotinylated P111-136 and pulled down for the presence of the HARP receptors in Western blot. In vitro, the P111-136 effect on HARP autocrine loop in PC-3 cells was determined by colony formation in soft agar. In vivo, PC-3 cells were inoculated in the flank of athymic nude mice. Animals were treated with P111-136 (5 mg/kg/day) for 25 days. Tumour volume was evaluated during the treatment. After the animal sacrifice, the tumour apoptosis and associated angiogenesis were evaluated by immunohistochemistry. In vivo anti-angiogenic effect was confirmed using a mouse Matrigel™ plug assay.

Results

Using pull down experiments, we identified the HARP receptors RPTPβ/ζ, ALK and nucleolin as P111-136 binding proteins. In vitro, P111-136 inhibits dose-dependently PC-3 cell colony formation. Treatment with P111-136 inhibits significantly the PC-3 tumour growth in the xenograft model as well as tumour angiogenesis. The angiostatic effect of P111-136 on HARP was also confirmed using an in vivo Matrigel™ plug assay in mice

Conclusions

Our results demonstrate that P111-136 strongly inhibits the mitogenic effect of HARP on in vitro and in vivo growth of PC-3 cells. This inhibition could be linked to a direct or indirect binding of this peptide to the HARP receptors (ALK, RPTPβ/ζ, nucleolin). In vivo, the P111-136 treatment significantly inhibits both the PC-3 tumour growth and the associated angiogenesis. Thus, P111-136 may be considered as an interesting pharmacological tool to interfere with tumour growth that has now to be evaluated in other cancer types.

Stimulation of the midkine/ALK axis renders glioma cells resistant to cannabinoid antitumoral action

Identifying the molecular mechanisms responsible for the resistance of gliomas to anticancer treatments is an issue of great therapeutic interest. Δ(9)-Tetrahydrocannabinol (THC), the major active ingredient of marijuana, and other cannabinoids inhibit tumor growth in animal models of cancer, including glioma, an effect that relies, at least in part, on the stimulation of autophagy-mediated apoptosis in tumor cells. Here, by analyzing the gene expression profile of a large series of human glioma cells with different sensitivity to cannabinoid action, we have identified a subset of genes specifically associated to THC resistance. One of these genes, namely that encoding the growth factor midkine (Mdk), is directly involved in the resistance of glioma cells to cannabinoid treatment. We also show that Mdk mediates its protective effect via the anaplastic lymphoma kinase (ALK) receptor and that Mdk signaling through ALK interferes with cannabinoid-induced autophagic cell death. Furthermore, in vivo Mdk silencing or ALK pharmacological inhibition sensitizes cannabinod-resistant tumors to THC antitumoral action. Altogether, our findings identify Mdk as a pivotal factor involved in the resistance of glioma cells to THC pro-autophagic and antitumoral action, and suggest that selective targeting of the Mdk/ALK axis could help to improve the efficacy of antitumoral therapies for gliomas.

Immunohistochemical surrogates for genetic alterations of CCDN1, PML, ALK, and NPM1 genes in lymphomas and acute myeloid leukemia

The World Health Organization (WHO) classification of lympho-hemopoietic neoplasms is increasingly based on genetic criteria. Detection of tumor-associated primary genetic lesions is usually performed using the polymerase chain reaction (PCR) and/or fluorescence in-situ hybridization (FISH). This review focuses on alternative techniques for detecting genetic lesions in biopsy samples. Immunohistochemical surrogates for the detection of genetic alterations involving the CCND1, PML, anaplastic lymphoma kinase (ALK) and nucleophosmin (NPM1) genes are presented as examples for this approach. Because of their high specificity, rapidity, low costs and ease of performance, these assays have the potential for being extensively applied in developing countries. In some instances (e.g. detection of ALK protein) immunohistochemistry has fully replaced molecular studies for routine diagnosis in paraffin-embedded specimens. Genome wide based discovery of new tumor-associated genetic lesions that are suitable for antibody targeting promises to further expand the application of immunohistochemistry for the molecular classification of hematological neoplasms.

A Pleiotrophin C-terminus peptide induces anti-cancer effects through RPTPβ/ζ

BACKGROUND

Pleiotrophin, also known as HARP (Heparin Affin Regulatory Peptide) is a growth factor expressed in various tissues and cell lines. Pleiotrophin participates in multiple biological actions including the induction of cellular proliferation, migration and angiogenesis, and is involved in carcinogenesis. Recently, we identified and characterized several pleiotrophin proteolytic fragments with biological activities similar or opposite to that of pleiotrophin. Here, we investigated the biological actions of P(122-131), a synthetic peptide corresponding to the carboxy terminal region of this growth factor.

RESULTS

Our results show that P(122-131) inhibits in vitro adhesion, anchorage-independent proliferation, and migration of DU145 and LNCaP cells, which express pleiotrophin and its receptor RPTPβ/ζ. In addition, P(122-131) inhibits angiogenesis in vivo, as determined by the chicken embryo CAM assay. Investigation of the transduction mechanisms revealed that P(122-131) reduces the phosphorylation levels of Src, Pten, Fak, and Erk1/2. Finally, P(122-131) not only interacts with RPTPβ/ζ, but also interferes with other pleiotrophin receptors, as demonstrated by selective knockdown of pleiotrophin or RPTPβ/ζ expression with the RNAi technology.

CONCLUSIONS

In conclusion, our results demonstrate that P(122-131) inhibits biological activities that are related to the induction of a transformed phenotype in PCa cells, by interacing with RPTPβ/ζ and interfering with other pleiotrophin receptors. Cumulatively, these results indicate that P(122-131) may be a potential anticancer agent, and they warrant further study of this peptide.

The application of ribozymes and DNAzymes in muscle and brain

The discovery of catalytic nucleic acids (CNAs) has provided scientists with valuable tools for the identification of new therapies for several untreated diseases through down regulation or modulation of endogenous gene expression involved in these ailments. These CNAs aim either towards the elimination or repair of pathological gene expression. Ribozymes, a class of CNAs, can be mostly used to down-regulate (by RNA cleavage) or repair (by RNA trans-splicing) unwanted gene expression involved in disease. DNAzymes, derived by in vitro selection processes are also able to bind and cleave RNA targets and therefore down-regulate gene expression. The purpose of this review is to present and discuss several applications of ribozymes and DNAzymes in muscle and brain. There are several diseases which affect muscle and brain and catalytic nucleic acids have been used as tools to target specific cellular transcripts involved in these groups of diseases.

The role of pleiotrophin and beta-catenin in fetal lung development

Mammalian lung development is a complex biological process, which is temporally and spatially regulated by growth factors, hormones, and extracellular matrix proteins. Abnormal changes of these molecules often lead to impaired lung development, and thus pulmonary diseases. Epithelial-mesenchymal interactions are crucial for fetal lung development. This paper reviews two interconnected pathways, pleiotrophin and Wnt/β-catenin, which are involved in fibroblast and epithelial cell communication during fetal lung development.

Effect of single-chain antibody targeting of the ligand-binding domain in the anaplastic lymphoma kinase receptor

The tyrosine kinase receptor anaplastic lymphoma kinase (ALK) and its ligand, the growth factor pleiotrophin (PTN), are highly expressed during the development of the nervous system and have been implicated in the malignant progression of different tumor types. Here, we describe human single-chain variable fragment (scFv) antibodies that target the ligand-binding domain (LBD) in ALK and show the effect in vitro and in vivo. The ALK LBD was used as a bait in a yeast two-hybdrid system to select human scFv from a library with randomized complementarity-determining region 3 domains. Surface plasmon resonance showed high-affinity binding of the selected scFv. The anti-ALK scFv competed for binding of PTN to ALK in intact cells and inhibited PTN-dependent signal transduction through endogenous ALK. Invasion of an intact endothelial cell monolayer by U87MG human glioblastoma cells was inhibited by the anti-ALK scFv. In addition, the growth of established tumor xenografts in mice was reversed after the induction of the conditional expression of the anti-ALK scFv. In archival malignant brain tumors expression levels of ALK and PTN were found elevated and appear correlated with poor patient survival. This suggests a rate-limiting function of the PTN/ALK interaction that may be exploited therapeutically.

Suppression of lung adenocarcinoma through menin and polycomb gene-mediated repression of growth factor pleiotrophin

Menin upregulates transcription of cell-cycle inhibitors to suppress endocrine tumors, but it is poorly understood how menin suppresses non-endocrine tumors such as lung cancer. Here, we show that menin inhibits proliferation of human lung cancer cells and growth of lung cancer in mice. The menin-mediated tumor suppression requires repression of growth factor pleiotrophin (PTN), which binds to its cell surface receptor, anaplastic lymphoma kinase (ALK) that is activated in certain lung adenocarcinomas. Menin represses PTN transcription and PTN-induced proliferation of human lung cancer cells, and menin expression is substantially reduced in primary human lung adenocarcinomas. Notably, menin binds the PTN locus and enhances Polycomb gene Enhancer of Zeste homolog 2 (EZH2)-mediated histone H3 lysine 27 trimethylation (H3K27m3), a negative mark for gene transcription but does not affect histone H3K4 methylation that is usually upregulated by menin in endocrine cells. Together, our findings indicate that menin suppresses lung cancer partly through increasing Polycomb gene-mediated H3K27 methylation and repressing PTN transcription, unraveling a novel, epigenetically regulated PTN-ALK signaling pathway in suppressing lung cancer.

Mutation-independent anaplastic lymphoma kinase overexpression in poor prognosis neuroblastoma patients

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase predominantly expressed in the developing nervous system. Recently, mutated ALK has been identified as a major oncogene associated with familial and sporadic neuroblastomas (NBL). Yet, a direct correlation between endogenous expression level of the ALK protein, oncogenic potential, and clinical outcome has not been established. We investigated ALK genetic mutations, protein expression/phosphorylation, and functional inhibition both in NBL-derived cell lines and in 34 localized and 48 advanced/metastatic NBL patients. ALK constitutive phosphorylation/activation was observed in high-ALK expressing cells, harboring either a mutated or a wild-type receptor. No activation was found in cell lines with low expression of wild-type ALK. After 72 hours of treatments, small molecule ALK inhibitor CEP-14083 (60 nmol/L) induced growth arrest and cell death in NBL cells overexpressing wild-type (viability: ALK(high) 12.8%, ALK(low) 73%, P = 0.0035; cell death: ALK(high) 56.4%, ALK(low) 16.2%, P = 0.0001) or mutated ALK. ALK protein expression was significantly up-regulated in advanced/metastatic compared with localized NBLs (ALK overexpressing patients: stage 1-2, 23.5%; stage 3-4, 77%; P < 0.0001). Interestingly, protein levels did not always correlate with ALK genetic alterations and/or mRNA abundance. Both mutated and wild-type ALK receptor can exert oncogenic activity in NBL cells. However, wild-type ALK receptor requires a critical threshold of expression to achieve oncogenic activation. Overexpression of either mutated or wild-type ALK defines poor prognosis patients. Alternative mechanisms other than direct mutations and/or gene amplification regulate the ALK level of expression in NBL cells. Wild-type ALK is a potential therapeutic target for advanced/metastatic NBLs.

Differential expression of receptor protein tyrosine phosphatases accompanies the reorganisation of the retina upon laser lesion

The regulation of protein phosphorylation plays an essential role in virtually all aspects of eukaryotic development. Beginning with the regulation of the cell cycle to cellular proliferation and differentiation, the delicate balance between the phosphorylating activity of kinases and the dephosphorylation by phosphatases controls the outcome of many signal transduction cascades. The generation of cellular diversity occurs in an environment that is structured by the extracellular matrix (ECM) which forms a surrounding niche for stem and progenitor cells. Cell-cell and cell-matrix interactions elicit specific signaling pathways that control cellular behavior. In pathological situations such as neural degenerating diseases, gene expression patterns and finally the composition of the ECM change dramatically. This leads to changes of cell behavior and finally results in the failure of regeneration and functional restoration in the adult central nervous system. In order to study the roles of tyrosine phosphatases and ECM in this context, we analyzed the effects of laser-induced retinal injury on the regulation of the receptor protein tyrosine phosphatases (RPTP) RPTPBr7, Phogrin and RPTPbeta/zeta. The latter occurs in several isoforms, including the soluble released chondroitin sulfate proteoglycan phosphacan that is expressed in the developing retina. The receptor variants RPTPbeta/zeta(long) and RPTPbeta/zeta(short) may serve as receptors of tenascin-proteins and serve as modulators of cell intrinsic signaling in response to the ECM. Using quantitative real-time RT-PCR analysis, we show here a time-dependent pattern of gene expression of these molecules following laser lesions of the retina.

ALK a Novel Lymphoma-associated Tumor Antigen for Vaccination Strategies

The discovery of Tumor Associated Antigens (TAAs) demonstrated that tumor cells can be specifically recognized by the immune system raising the hypothesis that tumors express antigens that Cytotoxic T Lymphocytes (CTLs) can potentially attack. The identification of immunogenic epitopes led to their use as targets to mediate the specific clearance of neoplastic cells by TAA targeting strategies such as vaccination strategies. One of the critical issues in the development of efficient vaccination protocols is the identification of the appropriate TAAs. The TAA should be effective as a "tumor rejection antigen" able to induce an immune response that will affect tumor growth. A distinct pathologic entity characterized by the expression of the Anaplastic Lymphoma Kinase (ALK) protein and named "ALKoma" has recently emerged within the heterogeneous group of CD30+ Anaplastic Large Cell Lymphoma (ALCL). ALK is a receptor tyrosine kinase whose expression is normally restricted to a few scattered cells in the nervous system. Its pathological expression in lymphoma cells is due to a chromosomal translocation that leads to the formation of an ALK-derived oncogenic fusion proteins. ALK fusion proteins ectopically over-expressed and constitutively activated in lymphoid cells play a key role in the neoplastic transformation by the aberrant phosphorylation of intracellular substrates that likely contributes to the molecular pathogenesis of ALCL. The high level of ALK expression in lymphoma cells and its direct role in lymphomagenesis, combined with the fact that normal ALK is expressed at low levels in the immune privileged nervous system, makes ALK an ideal lymphoma-specific target for immunotherapy of ALK+ALCL.

Anaplastic lymphoma kinase: role in cancer pathogenesis and small-molecule inhibitor development for therapy

Anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase in the insulin receptor superfamily, was initially identified in constitutively activated oncogenic fusion forms - the most common being nucleophosmin-ALK - in anaplastic large-cell lymphomas, and subsequent studies have identified ALK fusions in diffuse large B-cell lymphomas, systemic histiocytosis, inflammatory myofibroblastic tumors, esophageal squamous cell carcinomas and non-small-cell lung carcinomas. More recently, genomic DNA amplification and protein overexpression, as well as activating point mutations, of ALK have been described in neuroblastomas. In addition to those cancers for which a causative role for aberrant ALK activity is well validated, more circumstantial links implicate the full-length, normal ALK receptor in the genesis of other malignancies - including glioblastoma and breast cancer - via a mechanism of receptor activation involving autocrine and/or paracrine growth loops with the reported ALK ligands, pleiotrophin and midkine. This review summarizes normal ALK biology, the confirmed and putative roles of ALK in the development of human cancers and efforts to target ALK using small-molecule kinase inhibitors.

Anaplastic lymphoma kinase: signalling in development and disease

RTKs (receptor tyrosine kinases) play important roles in cellular proliferation and differentiation. In addition, RTKs reveal oncogenic potential when their kinase activities are constitutively enhanced by point mutation, amplification or rearrangement of the corresponding genes. The ALK (anaplastic lymphoma kinase) RTK was originally identified as a member of the insulin receptor subfamily of RTKs that acquires transforming capability when truncated and fused to NPM (nucleophosmin) in the t(2;5) chromosomal rearrangement associated with ALCL (anaplastic large cell lymphoma). To date, many chromosomal rearrangements leading to enhanced ALK activity have been described and are implicated in a number of cancer types. Recent reports of the EML4 (echinoderm microtubule-associated protein like 4)–ALK oncoprotein in NSCLC (non-small cell lung cancer), together with the identification of activating point mutations in neuroblastoma, have highlighted ALK as a significant player and target for drug development in cancer. In the present review we address the role of ALK in development and disease and discuss implications for the future.

Enhanced antitumorigenic effects in glioblastoma on double targeting of pleiotrophin and its receptor ALK

In adults, glioblastomas are the most lethal and most frequent malignant brain tumors, and the poor prognosis despite aggressive treatment indicates the need to establish novel targets for molecular intervention. The secreted growth factor pleiotrophin (PTN, HB-GAM, HBNF, OSF-1) shows mitogenic, chemotactic, and transforming activity. Whereas PTN expression is tightly regulated during embryogenesis and is very limited in normal adult tissues, a marked PTN up-regulation is seen in tumors including glioblastomas. Likewise, the PTN receptor anaplastic lymphoma kinase (ALK) has been shown previously to be upregulated and functionally relevant in glioblastoma. In this study, we explore the antitumorigenic effects of the simultaneous ribozyme-mediated knockdown of both receptor and ligand. Various glioblastoma cell lines are analyzed for PTN and ALK expression. Beyond the individual efficacies of several specific ribozymes against PTN or ALK, respectively, antiproliferative and proapoptotic effects of a single gene targeting approach are strongly enhanced on double knockdown of both genes in vitro. More importantly, this results in the abolishment of tumor growth in an in vivo subcutaneous tumor xenograft model. Finally, the analysis of various downstream signaling pathways by antibody arrays reveals a distinct pattern of changes in the activation of signal transduction molecules on PTN/ALK double knockdown. Beyond the already known ones, it identifies additional pathways relevant for PTN/ALK signaling. We conclude that double targeting of PTN and ALK leads to enhanced antitumorigenic effects over single knockdown approaches, which offers novel therapeutic options owing to increased efficacy also after prolonged knockdown.

Development of anaplastic lymphoma kinase (ALK) small-molecule inhibitors for cancer therapy

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) involved in the genesis of several human cancers; indeed, ALK was initially identified in constitutively activated and oncogenic fusion forms--the most common being nucleophosmin (NPM)-ALK--in a non-Hodgkin's lymphoma (NHL) known as anaplastic large-cell lymphoma (ALCL) and subsequent studies identified ALK fusions in the human sarcomas called inflammatory myofibroblastic tumors (IMTs). In addition, two recent reports have suggested that the ALK fusion, TPM4-ALK, may be involved in the genesis of a subset of esophageal squamous cell carcinomas. While the cause-effect relationship between ALK fusions and malignancies such as ALCL and IMT is very well established, more circumstantial links implicate the involvement of the full-length, normal ALK receptor in the genesis of additional malignancies including glioblastoma, neuroblastoma, breast cancer, and others; in these instances, ALK is believed to foster tumorigenesis following activation by autocrine and/or paracrine growth loops involving the reported ALK ligands, pleiotrophin (PTN) and midkine (MK). There are no currently available ALK small-molecule inhibitors approved for clinical cancer therapy; however, recognition of the variety of malignancies in which ALK may play a causative role has recently begun to prompt developmental efforts in this area. This review provides a succinct summary of normal ALK biology, the confirmed and putative roles of ALK fusions and the full-length ALK receptor in the development of human cancers, and efforts to target ALK using small-molecule kinase inhibitors.

The ligand Jelly Belly (Jeb) activates the Drosophila Alk RTK to drive PC12 cell differentiation, but is unable to activate the mouse ALK RTK

The Drosophila Alk receptor tyrosine kinase (RTK) drives founder cell specification in the developing visceral mesoderm and is crucial for the formation of the fly gut. Activation of Alk occurs in response to the secreted ligand Jelly Belly. No homologues of Jelly Belly are described in vertebrates, therefore we have approached the question of the evolutionary conservation of the Jeb-Alk interaction by asking whether vertebrate ALK is able to function in Drosophila. Here we show that the mouse ALK RTK is unable to rescue a Drosophila Alk mutant, indicating that mouse ALK is unable to recognise and respond to the Drosophila Jeb molecule. Furthermore, the overexpression of a dominant-negative Drosophila Alk transgene is able to block the visceral muscle fusion event, which an identically designed dominant-negative construct for the mouse ALK is not. Using PC12 cells as a model for neurite outgrowth, we show here for the first time that activation of dAlk by Jeb results in neurite extension. However, the mouse Alk receptor is unable to respond in any way to the Drosophila Jeb protein in the PC12 system. In conclusion, we find that the mammalian ALK receptor is unable to respond to the Jeb ligand in vivo or in vitro. These results suggest that either (i) mouse ALK and "mouse Jeb" have co-evolved to the extent that mALK can no longer recognise the Drosophila Jeb ligand or (ii) that the mALK RTK has evolved such that it is no longer activated by a Jeb-like molecule in vertebrates.

The anaplastic lymphoma kinase in the pathogenesis of cancer

Tyrosine kinases are involved in the pathogenesis of most cancers. However, few tyrosine kinases have been shown to have a well-defined pathogenetic role in lymphomas. The anaplastic lymphoma kinase (ALK) is the oncogene of most anaplastic large cell lymphomas (ALCL), driving transformation through many molecular mechanisms. In this Review, we will analyse how translocations or deregulated expression of ALK contribute to oncogenesis and how recent genetic or pharmacological tools, aimed at neutralizing its activity, can represent the basis for the design of powerful combination therapies.

Heparin affin regulatory peptide/pleiotrophin negatively affects diverse biological activities in C6 glioma cells

Heparin affin regulatory peptide (HARP) or pleiotrophin seems to be involved in the progression of several tumors of diverse origin. In this study, we tried to determine the role of HARP in rat C6 glioma cells by using an antisense strategy for inhibition of HARP expression. Decrease of the expression of endogenous HARP in C6 cells (AS-C6 cells) significantly increased proliferation, migration, and anchorage-independent growth of cells. Implantation of AS-C6 cells onto chicken embryo chorioallantoic membranes resulted in a significant increase of tumor-induced angiogenesis compared with that induced by non-transfected or C6 cells transfected with the plasmid alone (PC-C6 cells). In the same line, conditioned medium from AS-C6 cells significantly increased endothelial cell proliferation, migration, and tube formation in vitro compared with the effect of conditioned medium from C6 or PC-C6 cells. Interestingly, vascular endothelial growth factor (VEGF) induced C6 cell proliferation and migration, and SU1496, a selective inhibitor of VEGF receptor 2 (VEGFR2), blocked increased glioma cell growth, migration, and angiogenicity observed in AS-C6 cell cultures. The above results seem to be due to a direct interaction between HARP and VEGF in the culture medium of C6 and PC-C6 cells, while AS-C6 cells secreted comparable amounts of VEGF that do not interact with HARP. Collectively, these data suggest that HARP negatively affects diverse biological activities in C6 glioma cells, mainly due to binding of HARP to VEGF, which may sequester secreted VEGF from signalling through VEGFR2.

Anaplastic lymphoma kinase is activated through the pleiotrophin/receptor protein-tyrosine phosphatase beta/zeta signaling pathway: an alternative mechanism of receptor tyrosine kinase activation

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) first discovered as the constitutively active nucleophosmin-ALK oncoprotein in anaplastic large cell lymphomas (ALCL). Full-length ALK has a critical role in normal development and differentiation. Activated full-length ALK also is found in different malignant cancers. Nevertheless, the ligand to activate ALK remained unknown until recently, when ALK was proposed to be the physiological receptor of the cytokine pleiotrophin (PTN, Ptn). However, earlier studies had demonstrated that receptor protein tyrosine phosphatase (RPTP) beta/zeta is a physiological PTN receptor. We now demonstrate that phosphorylation of ALK in PTN-stimulated cells is mediated through the PTN/RPTPbeta/zeta signaling pathway. ALK is phosphorylated independently of a direct interaction of PTN with ALK. The data thus support a unique model of ALK activation. In cells not stimulated by PTN, RPTPbeta/zeta dephosphorylates ALK at the site(s) in ALK that is undergoing autophosphorylation through autoactivation. In contrast, when RPTPbeta/zeta is inactivated in PTN-stimulated cells, the sites that are autophosphorylated in ALK no longer can be dephosphorylated by RPTPbeta/zeta; thus, autoactivation and tyrosine phosphorylation of ALK rapidly increase. The data indicate that the PTN/RPTPbeta/zeta signaling pathway is a critical regulator of the steady state levels of tyrosine phosphorylation and activation of ALK; the data support the conclusion that ALK phosphorylation and activation in PTN-stimulated cells are increased through a unique "alternative mechanism of RTK activation."

In contrast to agonist monoclonal antibodies, both C-terminal truncated form and full length form of Pleiotrophin failed to activate vertebrate ALK (anaplastic lymphoma kinase)?

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase essentially and transiently expressed during development in specific regions of the central and peripheral nervous system. ALK expression persists at a lower level in the adult brain. Thus, it might play an important role in both the normal development and function of the nervous system. The nature of the cognate ligand of this receptor in vertebrates is still a matter of debate. Pleiotrophin and midkine have been proposed as ligands of ALK but several independent studies do not confirm this hypothesis. Interestingly, a recent study proposed that a C-terminal truncated form of Pleiotrophin (Pleiotrophin.15) and not the full length form (Pleiotrophin.18) promotes glioblastoma proliferation in an ALK-dependent fashion. These data were obviously a strong basis to conciliate the conflicting results so far reported in the literature. In the present study, we first purified to homogeneity the two forms of Pleiotrophin secreted by HEK 293 cells. In contrast to agonist monoclonal antibodies, both Pleiotrophin.15 and Pleiotrophin.18 failed to activate ALK in neuroblastoma and glioblastoma cells expressing this receptor. Thus, for our point of view, ALK is still an orphan receptor in vertebrates.

Targeting pleiotropin to treat osteoarthritis

Pleiotropin (PTN) is a secreted heparin-binding peptide expressed in mesodermal and neuroectodermal cells during development, but rarely in adult tissues. Although PTN is abundant in fetal or juvenile cartilage, it is undectable in mature cartilage. However, PTN is re-expressed in chondrocytes in early stages of osteoarthritis where it is detectable in situ and in synovial fluids from patients. PTN enhances chondrogenesis by stimulation of extra-cellular matrix synthesis, reduction of degrading matrix metalloproteases and induction of their inhibitors; PTN also slightly reduces pro-inflammatory factors, such as nitric oxide and vascular endothelial growth factor. Furthermore, PTN stimulates chondrocyte clustering and proliferation. Thus, PTN appears to mediate repair and protective processes in osteoarthritic cartilage and appears to be a promising factor to treat osteoarthritis.

The receptor protein tyrosine phosphatase (RPTP)beta/zeta is expressed in different subtypes of human breast cancer

Increasing evidence suggests mutations in human breast cancer cells that induce inappropriate expression of the 18-kDa cytokine pleiotrophin (PTN, Ptn) initiate progression of breast cancers to a more malignant phenotype. Pleiotrophin signals through inactivating its receptor, the receptor protein tyrosine phosphatase (RPTP)beta/zeta, leading to increased tyrosine phosphorylation of different substrate proteins of RPTPbeta/zeta, including beta-catenin, beta-adducin, Fyn, GIT1/Cat-1, and P190RhoGAP. PTN signaling thus has wide impact on different important cellular systems. Recently, PTN was found to activate anaplastic lymphoma kinase (ALK) through the PTN/RPTPbeta/zeta signaling pathway; this discovery potentially is very important, since constitutive ALK activity of nucleophosmin (NPM)-ALK fusion protein is causative of anaplastic large cell lymphomas, and, activated ALK is found in other malignant cancers. Recently ALK was identified in each of 63 human breast cancers from 22 subjects. We now demonstrate that RPTPbeta/zeta is expressed in each of these same 63 human breast cancers that previously were found to express ALK and in 10 additional samples of human breast cancer. RPTPbeta/zeta furthermore was localized not only in its normal association with the cell membrane but also scattered in cytoplasm and in nuclei in different breast cancer cells and, in the case of infiltrating ductal carcinomas, the distribution of RPTPbeta/zeta changes as the breast cancer become more malignant. The data suggest that the PTN/RPTPbeta/zeta signaling pathway may be constitutively activated and potentially function to constitutively activate ALK in human breast cancer.

Anaplastic lymphoma kinase is expressed in different subtypes of human breast cancer

Pleiotrophin (PTN, Ptn) is an 18kDa cytokine expressed in human breast cancers. Since inappropriate expression of Ptn stimulates progression of breast cancer in transgenic mice and a dominant negative PTN reverses the transformed phenotype of human breast cancer cells that inappropriately express Ptn, it is suggested that constitutive PTN signaling in breast cancer cells that inappropriately express Ptn activates pathways that promote a more aggressive breast cancer phenotype. Pleiotrophin signals by inactivating its receptor, the receptor protein tyrosine phosphatase (RPTP)beta/zeta, and, recently, PTN was found to activate anaplastic lymphoma kinase (ALK) through the PTN/RPTPbeta/zeta signaling pathway in PTN-stimulated cells, not through a direct interaction of PTN with ALK and thus not through the PTN-enforced dimerization of ALK. Since full-length ALK is activated in different malignant cancers and activated ALK is a potent oncogenic protein, we examined human breast cancers to test the possibility that ALK may be expressed in breast cancers and potentially activated through the PTN/RPTPbeta/zeta signaling pathway; we now demonstrate that ALK is strongly expressed in different histological subtypes of human breast cancer; furthermore, ALK is expressed in both nuclei and cytoplasm and, in the ;;dotted" pattern characteristic of ALK fusion proteins in anaplastic large cell lymphoma. This study thus supports the possibility that activated ALK may be important in human breast cancers and potentially activated either through the PTN/RPTPbeta/zeta signaling pathway, or, alternatively, as an activated fusion protein to stimulate progression of breast cancer in humans.

Pleiotrophin expression in astrocytic and oligodendroglial tumors and it’s correlation with histological diagnosis, microvascular density, cellular proliferation and overall survival

BACKGROUND

Pleiotrophin (PTN) is a secreted cytokine with several properties related with tumor development, including differentiation, angiogenesis, invasion, apoptosis and metastasis. There is evidence that PTN has also a relevant role in primary brain neoplasms and its inactivation could be important to treatment response. Astrocytic and oligodendroglial tumors are the most frequent primary brain neoplasms. Astrocytic tumors are classified as pilocytic astrocytoma (PA), diffuse astrocytoma (DA), anaplastic astrocytoma (AA) and glioblastoma (GBM). Oligodendroglial tumors are classified as oligodendroglioma (O) and anaplastic oligodendroglioma (AO). The aim of the present study was to compare PTN expression, in astrocytomas and oligodendrogliomas and its association with the histological diagnosis, microvascular density, proliferate potential and clinical outcome.

METHODS

Seventy-eight central nervous system tumors were analyzed. The histological diagnosis in accordance with WHO classification was: 13PA, 18DA, 8AA, 15GBM, 16O and 8AO. Immunohistochemistry was realized with these specific antibodies: pleiotrophin, CD31 to microvascular density and Ki-67 to cell proliferation.

RESULTS

PTN expression was significantly higher in GBM and AA when compared to PA and higher in GBM compared to DA. PTN expression did not differ between O and AO. Proliferate index and microvascular density were evaluated only in high grade tumors (AA, GBM and AO) divided in three groups according to PTN expression (low, intermediate and high). These results showed no statistical difference between PTN expression and index of cellular proliferation and neither to PTN expression and microvascular density. Overall survival (OS) analysis (months) showed similar results in high grade gliomas with different levels of PTN expression.

CONCLUSIONS

Our results suggest that PTN expression is associated with histopathological grade of astrocytomas. Proliferation rate, microvascular density and overall survival do not seem to be associated with PTN expression.

Role of heparin binding growth factors in nigrostriatal dopamine system development and Parkinson's disease

The developmental biology of the dopamine (DA) system may hold important clues to its reconstruction. We hypothesized that factors highly expressed during nigrostriatal development and re-expressed after injury and disease may play a role in protection and reconstruction of the nigrostriatal system. Examination of gene expression in the developing striatum suggested an important role for the heparin binding growth factor family at time points relevant to establishment of dopaminergic innervation. Midkine, pleiotrophin (PTN), and their receptors syndecan-3 and receptor protein tyrosine phosphatase beta/zeta, were highly expressed in the striatum during development. Furthermore, PTN was up-regulated in the degenerating substantia nigra of Parkinson's patients. The addition of PTN to ventral mesencephalic cultures augmented DA neuron survival and neurite outgrowth. Thus, PTN was identified as a factor that plays a role in the nigrostriatal system during development and in response to disease, and may therefore be useful for neuroprotection or reconstruction of the DA system.

Effects of pleiotrophin, a heparin-binding growth factor, on human primary and immortalized chondrocytes

OBJECTIVE

Pleiotrophin (PTN) is a secreted heparin-binding peptide expressed in mesodermal and neuroectodermal cells during development, but rarely in adult tissues. In fetal and juvenile, but not in mature cartilage, PTN is abundant. Furthermore, PTN is re-expressed in chondrocytes in early stages of osteoarthritis (OA). Since little is known about the functions of PTN in cartilage, we investigated the occurrence of PTN receptors in human articular cartilage in situ and PTN effects on human primary and immortalized chondrocytes in vitro.

METHODS

Receptor expression and regulation was monitored by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. PTN effects and signal transduction were studied by electrophoretic mobility shift, Boyden chamber cell migration and proliferation assays, effects on gene expression by real time RT-PCR and that on nitric oxide (NO) by the Griess reaction.

RESULTS

Of the putative PTN signaling receptors, immortalized and primary chondrocytes (pc) expressed the anaplastic lymphoma kinase (ALK), less the receptor-type protein tyrosine phosphatase zeta/beta (PTPzeta). ALK expression was upregulated upon ligand exposure. PTN stimulation activated the AP-1 (activator protein-1) transcription factor and altered gene expression. Prolonged stimulation induced PTN mRNA expression slightly, reduced vascular endothelial growth factor (VEGF) mRNA as well as NO production. Whereas mRNA expression of matrix metalloproteinases (MMPs) MMP-1 and MMP-13 was reduced, their inhibitors TIMP-1 and TIMP-2 were induced. Furthermore, PTN stimulated chondrocyte migration and proliferation.

CONCLUSIONS

These results show that PTN is an autocrine growth factor in cartilage. We suggest that PTN may be involved in the clustering and proliferation of chondrocytes observed in the early stages of OA.

Anaplastic lymphoma kinase and its signalling molecules as novel targets in lymphoma therapy

A crucial issue in the development of molecularly-targeted anticancer therapies is the identification of appropriate molecules whose targeting would result in tumour regression with a minimal level of systemic toxicity. Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase, normally expressed at low levels in the nervous system. As a consequence of chromosomal translocations involving the alk gene (2p23), ALK is also aberrantly expressed and constitutively activated in approximately 60% of CD30+ anaplastic large cell lymphomas (ALCLs). Due to the selective overexpression of ALK in tumour cells, its direct involvement in the process of malignant transformation and its frequent expression in ALCL patients, the authors recognise ALK as a suitable candidate for the development of molecularly targeted strategies for the therapeutic treatment of ALK-positive lymphomas. Strategies targeting ALK directly or indirectly via the inhibition of the protein networks responsible for ALK oncogenic signalling are discussed.

The effect of pleiotrophin signaling on adipogenesis

Pleiotrophin (PTN) plays diverse roles in cell growth and differentiation. In this investigation, we demonstrate that PTN plays a negative role in adipogensis and that glycogen synthase kinase 3beta (GSK-3beta) and beta-catenin are involved in the regulation of PTN-mediated preadipocyte differentiation. Knocking down the expression of PTN using siRNA resulted in an increase in phospho-GSK-3beta expression, and the accumulation of nuclear beta-catenin, which are critical downstream signaling proteins for both the PTN and Wnt signaling pathways. Our investigation suggests that there is a PTN/PI3K/AKT/GSK-3beta/beta-catenin signaling pathway, which cross-talks with the Wnt/Fz/GSK-3beta/beta-catenin pathway and negatively regulates adipogenesis.

Pleiotrophin disrupts calcium-dependent homophilic cell-cell adhesion and initiates an epithelial-mesenchymal transition

Regulation of the levels of tyrosine phosphorylation is essential to maintain the functions of proteins in different signaling pathways and other cellular systems, but how the steady-state levels of tyrosine phosphorylation are coordinated in different cellular systems to initiate complex cellular functions remains a formidable challenge. The receptor protein tyrosine phosphatase (RPTP)beta/zeta is a transmembrane tyrosine phosphatase whose substrates include proteins important in intracellular and transmembrane protein-signaling pathways, cytoskeletal structure, cell-cell adhesion, endocytosis, and chromatin remodeling. Pleiotrophin (PTN the protein and Ptn the gene) is a ligand for RPTPbeta/zeta; PTN inactivates RPTPbeta/zeta, leaving unchecked the continued endogenous activity of tyrosine kinases that increase phosphorylation of the substrates of RPTPbeta/zeta at sites dephosphorylated by RPTPbeta/zeta in cells not stimulated by PTN. Thus, through the regulation of the tyrosine phosphatase activity of RPTPbeta/zeta, the PTN/RPTPbeta/zeta signaling pathway coordinately regulates the levels of tyrosine phosphorylation of proteins in many cellular systems. We now demonstrate that PTN disrupts cytoskeletal protein complexes, ablates calcium-dependent homophilic cell-cell adhesion, stimulates ubiquitination and degradation of N-cadherin, reorganizes the actin cytoskeleton, and induces a morphological epithelial-mesenchymal transition (EMT) in PTN-stimulated U373 cells. The data suggest that increased tyrosine phosphorylation of the different substrates of RPTPbeta/zeta in PTN-stimulated cells alone is sufficient to coordinately stimulate the different functions needed for an EMT; it is possible that PTN initiates an EMT in cells at sites where PTN is expressed in development and in malignant cells that inappropriately express Ptn.

Mass Spectrometry-based Proteomic Studies of Human Anaplastic Large Cell Lymphoma

Malignant lymphomas are a diverse group of malignant neoplasms that arise as a result of a complex interplay of multiple factors including genetic aberrations, immunosuppression, and exposure to noxious agents such as ionizing radiation and chemical agents. Anaplastic large cell lymphoma (ALCL) is an aggressive T-lineage lymphoma harboring chromosomal translocations involving the anaplastic lymphoma kinase (ALK) tyrosine kinase. The most common translocation in ALCL is the t(2;5)(p23;q35). This results in the formation of a chimeric fusion kinase, nucleophosmin/ALK. Nucleophosmin/ALK activates numerous downstream signaling pathways resulting in enhanced survival and proliferation. Using a variety of mass spectrometry-driven proteomic strategies, we have studied several aspects of the ALCL proteome. In this review, we provide a summary of mass spectrometry-based proteomic studies that expands the current understanding of the molecular pathogenesis of ALCL and provides the basis for the identification of biomarkers and targets for novel therapeutic agents.

Expression of nine tumour antigens in a series of human glioblastoma multiforme: interest of EGFRvIII, IL-13Ralpha2, gp100 and TRP-2 for immunotherapy

In this study, we investigated the mRNA and protein expression of nine tumour antigens in human glioblastoma multiforme with a view to their possible use in dendritic cell-based immunotherapy. Expression of ALK, EGFRvIII, GALT3, gp100, IL-13Ralpha2, MAGE-A3, NA17-A, TRP-2 and tyrosinase were studied by real-time RT-PCR on frozen tissues using a series of 47 tumour samples from patients with glioblastoma. Results were compared with non-neoplastic brain expression or glioblastoma samples with very low levels of expression near the limits of detection for EGFRvIII and MAGE-A3, as these latter two antigens were not detected in non-neoplastic brain. Tumour antigens showing a 5-fold increase in mRNA expression were considered as positive, and only antigens displaying an mRNA over-expression in a significant number of cases were analysed by immunohistochemistry on paraffin-embedded sections. Using real time RT-PCR, we found EGFRvIII, gp100, IL-13Ralpha2 and TRP-2 to be positive in 64, 38, 32 and 21% of cases, respectively. While we observed no over-expression for ALK, GALT3 and tyrosinase, 3 samples out of 47 were positive for MAGE-3 and 1 sample for NA17-A. More than 25% of tumour cells showed strong protein expression in 13, 34, 85 and 96% of GBM samples for gp100, TRP-2, EGFRvIII and IL-13Ralpha2, respectively. Interestingly, protein expression of at least 3 antigens was observed in 38% of cases. These results point out the importance of EGFRvIII, IL-13Ralpha2 and, to a less extent gp100 and TRP-2, for developing an immunotherapy strategy against glioblastoma.

Sodium chloride regulates Extracellular Regulated Kinase 1/2 in different tumor cell lines

Perturbations of the extracellular ionic content by different hypo- or hyperosmolar stimuli initiate stress responses to maintain cell viability that include activation of Mitogen Activated Protein Kinases (MAPK) in cell lines derived from kidney epithelium. When hyperosmolar conditions induced by different salts occurred in the extracellular environment of tumor-derived cell lines, they activated the Extracellular Regulated Kinase 1/2 by increasing its phosphorylation steady-state on Thr202/Tyr204 in a time- and dose-dependent manner. It was found that Extracellular Regulated Kinase 1/2 activation is a consequence of selective phosphorylation by mitogen-activated protein kinase/ERK kinase. Changes in cell shape or in tubulin or actin cytoskeletal structure were not found, although cell growth arrest was observed as well as induction of apoptosis and modified cell migration ability that were dependent upon Extracellular Regulated Kinase 1/2 activation evidencing a critical role for the Extracellular Regulated Kinase 1/2 in mediating survival of cells in hyperosmotic conditions.

RNA interference-mediated gene silencing of pleiotrophin through polyethylenimine-complexed small interfering RNAs in vivo exerts antitumoral effects in glioblastoma xenografts

RNA interference (RNAi) is a powerful strategy to inhibit gene expression through specific mRNA degradation mediated by small interfering RNAs (siRNAs). In vivo, however, the application of siRNAs is severely limited by their instability and poor delivery into target cells and target tissues. Glioblastomas are the most frequent and malignant brain tumors with, so far, limited treatment options. To develop novel and more efficacious therapies, advanced targeting strategies against glioblastoma multiforme (GBM)-relevant target genes must be established in vivo. Here we use RNAi-based targeting of the secreted growth factor pleiotrophin (PTN), employing a polyethylenimine (PEI)/siRNA complex strategy. We show that the complexation of chemically unmodified siRNAs with PEI leads to the formation of complexes that condense and completely cover siRNAs as determined by atomic force microscopy (AFM). On the efficient cellular delivery of these PEI/siRNA complexes, the PTN downregulation in U87 glioblastoma cells in vitro results in decreased proliferation and soft agar colony formation. More importantly, in vivo treatment of nude mice through systemic application (subcutaneous or intraperitoneal) of PEI-complexed PTN siRNAs leads to the delivery of intact siRNAs into subcutaneous tumor xenografts and a significant inhibition of tumor growth without a measurable induction of siRNA-mediated immunostimulation. Likewise, in a clinically more relevant orthotopic mouse glioblastoma model with U87 cells growing intracranially, the injection of PEI-complexed PTN siRNAs into the CNS exerts antitumoral effects. In conclusion, we present the PEI complexation of siRNAs as a universally applicable platform for RNAi in vitro and in vivo and establish, also in a complex and relevant orthotopic tumor model, the potential of PEI/siRNA-mediated PTN gene targeting as a novel therapeutic option in GBM.

Recruitment of insulin receptor substrate-1 and activation of NF-kappaB essential for midkine growth signaling through anaplastic lymphoma kinase

Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase in the insulin receptor superfamily. We recently demonstrated that the growth factors pleiotrophin (PTN) and midkine (MK) are ligands for ALK and that upon ALK activation, insulin receptor substrate-1 (IRS-1) and other substrates are phosphorylated. Here, the role of IRS-1 in ligand-mediated ALK signaling is investigated in interleukin-3 (IL-3)-dependent 32D murine myeloid cells. These cells do not express ALK and IRS family members, and do not respond to exogenously added PTN or MK. We show that expression of ALK plus IRS-1 renders these cells independent of IL-3 owing to the activation of ALK by endogenous MK. Mutational analysis reveals that this transformed phenotype of 32D cells requires kinase-active ALK as well as the interaction of ALK with IRS-1. Furthermore, 32D/IRS-1/ALK cells display an enhanced activation of mitogen-activated protein kinase and PI3-kinase pathways, and a selective transcriptional activation of nuclear factor (NF)-kappaB. Small interfering RNA-mediated knockdown of the endogenous MK or p65/NF-kappaB revealed that both these are rate limiting for the transformed phenotype induced by ALK plus IRS-1. We conclude that the recruitment of IRS-1 to activated ALK and the activation of NF-kappaB are essential for the autocrine growth and survival signaling of MK.