A heparin-binding growth factor secreted from breast cancer cells homologous to a developmentally regulated cytokine

Pleiotrophin and metabolic disorders: insights into its role in metabolism

Pleiotrophin (PTN) is a cytokine which has been for long studied at the level of the central nervous system, however few studies focus on its role in the peripheral organs. The main aim of this review is to summarize the state of the art of what is known up to date about pleiotrophin and its implications in the main metabolic organs. In summary, pleiotrophin promotes the proliferation of preadipocytes, pancreatic β cells, as well as cells during the mammary gland development. Moreover, this cytokine is important for the structural integrity of the liver and the neuromuscular junction in the skeletal muscle. From a metabolic point of view, pleiotrophin plays a key role in the maintenance of glucose and lipid as well as whole-body insulin homeostasis and favors oxidative metabolism in the skeletal muscle. All in all, this review proposes pleiotrophin as a druggable target to prevent from the development of insulin-resistance-related pathologies.

Pleiotrophin drives a prometastatic immune niche in breast cancer

Metastatic cancer cells adapt to thrive in secondary organs. To investigate metastatic adaptation, we performed transcriptomic analysis of metastatic and non-metastatic murine breast cancer cells. We found that pleiotrophin (PTN), a neurotrophic cytokine, is a metastasis-associated factor that is expressed highly by aggressive breast cancers. Moreover, elevated PTN in plasma correlated significantly with metastasis and reduced survival of breast cancer patients. Mechanistically, we find that PTN activates NF-κB in cancer cells leading to altered cytokine production, subsequent neutrophil recruitment, and an immune suppressive microenvironment. Consequently, inhibition of PTN, pharmacologically or genetically, reduces the accumulation of tumor-associated neutrophils and reverts local immune suppression, resulting in increased T cell activation and attenuated metastasis. Furthermore, inhibition of PTN significantly enhanced the efficacy of immune checkpoint blockade and chemotherapy in reducing metastatic burden in mice. These findings establish PTN as a previously unrecognized driver of a prometastatic immune niche and thus represents a promising therapeutic target for the treatment of metastatic breast cancer.

The link between menin and pleiotrophin in the tumor biology of pancreatic neuroendocrine neoplasms

MEN1, which encodes menin protein, is the most frequently mutated gene in pancreatic neuroendocrine neoplasms (pNEN). Pleiotrophin (PTN) was reported being a downstream factor of menin and to promote metastasis in different tumor entities. In this study, the effect of menin and its link to PTN were assessed on features of pNEN cells and outcome of pNEN patients. The expression of menin and PTN in pNEN patient tissues were examined by qRT-PCR and western blot and compared to their metastasis status. Functional assays, including transwell migration/invasion and scratch wound healing assays, were performed on specifically designed CRISPR/Cas9-mediated MEN1-knockout (MEN1-KO) pNEN cell lines (BON1^MEN1-KO and QGP1^MEN1-KO ) to study the metastasis of pNEN. Among 30 menin negative pNEN patients, 21 revealed a strong protein expression of PTN. This combination was associated with metastasis and shorter disease-free survival. Accordingly, in BON1^MEN1-KO and QGP1^MEN1-KO cells, PTN protein expression was positively associated with enhanced cell migration and invasion, which could be reversed by PTN silencing. PTN is a predicting factor of metastatic behavior of menin-deficient-pNEN. In vitro, menin is able to both promote and suppress the metastasis of pNEN by regulating PTN expression depending on the tumoral origin of pNEN cells.

Interactions of Pleiotrophin with a Structurally Defined Heparin Hexasaccharide

Pleiotrophin (PTN) is a potent cytokine that plays an important role in neural generation, angiogenesis, inflammation, and cancers. Its interactions with the polysaccharide glycosaminoglycan (GAG) are crucial to PTN’s biological activities. In this study, we investigated the interaction of selectively protonated PTN with the heparin hexasaccharide ΔUA2S-(GlcNS6S-IdoA2S)₂-GlcNS6S using solution NMR. The use of a structurally defined oligosaccharide and selectively protonated PTN enabled us to obtain intermolecular contacts using unfiltered NOESY experiments, significantly increasing the amount of high-resolution structural information obtainable. Our data showed that PTN’s arginines, lysines, and tryptophans in the two structured domains have strong interactions with the 2-O-sulfated uronate protons in the heparin hexasaccharide. Consistent with the NMR data is the observation that 2-O-desulfation and N-desulfation/N-acetylation significantly decreased heparin hexasaccharides’ affinity for PTN, while 6-O-desulfation only modestly affected the interactions with PTN. These results allowed us to hypothesize that PTN has a preference for sulfate clusters centered on the GlcNS6S-IdoA2S disaccharide. Using these data and the fact that PTN domains mostly bind heparin hexasaccharides independently, models of the PTN-heparin complex were constructed.

Advances in immunological research of amphioxus

Amphioxus, one of the most closely related invertebrates to vertebrates, is an important animal model for studying the origin and evolution of vertebrate immunity, especially the transition from innate immunity to adaptive immunity. The current research progresses of amphioxus in the field of immune organs, immune cells, complement system, cytokines, nuclear factor kappa B, immune-related lectins and enzymes are summarized, and some issues that remain to be understood or are in need of further clarification are highlighted. We hope to provide references for more in-depth study of the amphioxus immune system and lay a solid foundation for the construction of three-dimensional immune network in amphioxus from ontogeny to phylogeny.

Transcriptome profiling of different developmental stages of corpus luteum during the estrous cycle in pigs

To better understand the molecular basis of corpus luteum (CL) development and function RNA-Seq was utilized to identify differentially expressed genes (DEGs) in porcine CL during different physiological stages of the estrous cycle viz. early (EL), mid (ML), late (LL) and regressed (R) luteal. Stage wise comparisons obtained 717 (EL vs. ML), 568 (EL vs. LL), 527 (EL vs. R), 786 (ML vs. LL), 474 (ML vs. R) and 534 (LL vs. R) DEGs with log₂(FC) ≥1 and p < 0.05. The process of angiogenesis, steroidogenesis, signal transduction, translation, cell proliferation and tissue remodelling were significantly (p < 0.05) enriched in EL, ML and LL stages, where as apoptosis was most active in regressed stage. Pathway analysis revealed that most annotated genes were associated with lipid metabolism, translation, immune and endocrine system pathways depicting intra-luteal control of diverse CL function. The network analysis identified genes AR, FOS, CDKN1A, which were likely the novel hub genes regulating CL physiology.

Positive association between PTN polymorphisms and schizophrenia in Northeast Chinese Han population

As a severely and highly heritable psychotic disorder, schizophrenia has become a serious public health problem in modern society. Pleiotrophin (PTN) is a secreted cell cytokine associated with the extracellular matrix and acts as a growth factor. PTN is mainly expressed in neuroectodermal and mesodermal tissues, indicating its effect in neuron migration and epithelium-mesenchyme interactions. Whereas PTN is associated with some neurodegenerative diseases and has modulating effects on them. In this study, we aimed to investigate the association between PTN polymorphisms and schizophrenia in an independent case-control sample-set including 738 schizophrenia patients and 1085 healthy controls. Of the 13 selected single nucleotide polymorphisms (SNPs), five showed significant differences in allele or/and genotype frequencies between patients and controls: rs3959914 (genotype: χ = 11.5217, P = 0.0032); rs11765480 (genotype: χ = 10.6620, P = 0.0049); rs1473355 (genotype: χ = 8.3902, P = 0.0151); rs322246 (allele: χ = 5.5954, P = 0.0180); rs322240 (genotype: χ = 8.8429, P = 0.0121; allele: χ = 8.7802, P = 0.0031). The haplotype analysis of the selected SNPs showed different haplotype frequencies for one block (rs322240, rs322246) between cases and controls (global: χ = 9.0290, P = 0.0110; A-G: χ = 8.985, P = 0.0027; C-A: χ = 5.814, P = 0.0159). Our present results indicate PTN as a susceptibility gene for schizophrenia.

Pleiotrophin: Activity and mechanism

Pleiotrophin (PTN) is a potent mitogenic cytokine with a high affinity for the polysaccharide glycosaminoglycan (GAG). Although it is most strongly associated with neural development during embryogenesis and the neonatal period, its expression has also been linked to a plethora of other physiological events including cancer metastasis, angiogenesis, bone development, and inflammation. A considerable amount of research has been carried out to understand the mechanisms by which PTN regulates these events. In particular, PTN has now been shown to bind a diverse collection of receptors including many GAG-containing proteoglycans. These interactions lead to the activation of many intracellular kinases and, ultimately, activation and transformation of cells. Structural studies of PTN in complex with both GAG and domains from its non-proteoglycan receptors reveal a binding mechanism that relies on electrostatic interactions and points to PTN-induced receptor oligomerization as one of the possible ways PTN uses to control cellular functions.

Role of miR-203 in estrogen receptor-mediated signaling in the rat uterus and endometrial carcinoma

The role of microRNAs (miRNA) in estrogen receptor (ER) signaling in the uterus and in endometrial cancer is not well understood. We therefore analyzed miRNA expression in uterine samples from a standard 3-day uterotrophic assay using young female adult rats to identify E2-regulated miRNAs. Microarray analysis identified 47 E2 down-regulated miRNAs including miR-30a, and 25 E2up-regulated miRNAs including miR-672, miR-203, and miR-146b. The strongly E2-upregulated miR-203 was selected for further analysis. miR-203 was deleted in the rat endometrial adenocarcinoma cell line, RUCA-I, using CRISPR/CAS9. Five clones devoid of miR-203 expression were generated. Proliferation was reduced and G2-arrest was observed in all miR-203 deficient RUCA-I clones. Transfection with a miR-203-3p mimic partially rescues this effect. Comparison of mRNA expression in three miR-203 knockout clones to wild type RUCA-I cells reveals 566 miR-203-upregulated and 592 miR-203-downregulated genes. 43 of the genes that are upregulated by miR-203 knockout in vitro are downregulated in the uterus by E2. Of these Acer2, Zbtb20, Ptn, Rcbtb2, Mum1l1, Hmgn3, and Nfat5 possess one or more seed sequence matches in their 3'-UTR that are predicted to be targets of miR-203. These data demonstrate the importance of E2 regulated miRNAs in general, and miR-203 in particular, for E2 regulated gene expression and physiological processes including proliferation and cell migration, in the uterus as well as in the etiology of endometrial carcinomas.

Neural Precursor-Derived Pleiotrophin Mediates Subventricular Zone Invasion by Glioma

The lateral ventricle subventricular zone (SVZ) is a frequent and consequential site of pediatric and adult glioma spread, but the cellular and molecular mechanisms mediating this are poorly understood. We demonstrate that neural precursor cell (NPC):glioma cell communication underpins this propensity of glioma to colonize the SVZ through secretion of chemoattractant signals toward which glioma cells home. Biochemical, proteomic, and functional analyses of SVZ NPC-secreted factors revealed the neurite outgrowth-promoting factor pleiotrophin, along with required binding partners SPARC/SPARCL1 and HSP90B, as key mediators of this chemoattractant effect. Pleiotrophin expression is strongly enriched in the SVZ, and pleiotrophin knock down starkly reduced glioma invasion of the SVZ in the murine brain. Pleiotrophin, in complex with the binding partners, activated glioma Rho/ROCK signaling, and ROCK inhibition decreased invasion toward SVZ NPC-secreted factors. These findings demonstrate a pathogenic role for NPC:glioma interactions and potential therapeutic targets to limit glioma invasion. PAPERCLIP.

Pleiotrophin as a potential biomarker in breast cancer patients

BACKGROUND

Pleiotrophin (PTN), a multifunctional growth factor, is up-regulated in many tumors. PTN is reported to play an important role in the regulation of several cellular processes. The objective of this study is to evaluate the clinical significance of PTN as a tumor marker in breast cancer (BC).

METHODS

Serum PTN levels were detected in 105 BC patients and 40 healthy volunteers using ELISA. In addition, PTN expression was examined in 80 BC tissues in a nested case-control study by immunohistochemistry.

RESULTS

Serum PTN levels were elevated in BC patients compared to healthy controls. Area under receiver operating characteristic (ROC) curve was 0.878 (95% CI: 0.824-0.932). The sensitivity of serum PTN was superior to CEA and CA15-3. High serum PTN levels were associated with TNM stage, histology grade, and distant metastasis. Moreover, serum PTN levels decreased significantly after surgical treatment. In BC tissues, PTN expression was significantly higher in BC tissues relative to paired paracancerous tissues. Tissue PTN expression proved to be a prognostic factor for breast cancer according to multivariable logistic regression analysis.

CONCLUSION

PTN could be considered as a potential biomarker for the presence of breast cancer.

Pleiotrophin exerts its migration and invasion effect through the neuropilin-1 pathway

Pleiotrophin (PTN) is a pleiotropic growth factor that exhibits angiogenic properties and is involved in tumor growth and metastasis. Although it has been shown that PTN is expressed in tumor cells, few studies have investigated its receptors and their involvement in cell migration and invasion. Neuropilin-1 (NRP-1) is a receptor for multiple growth factors that mediates cell motility and plays an important role in angiogenesis and tumor progression. Here we provide evidence for the first time that NRP-1 is crucial for biological activities of PTN. We found that PTN interacted directly with NRP-1 through its thrombospondin type-I repeat domains. Importantly, binding of PTN to NRP-1 stimulated the internalization and recycling of NRP-1 at the cell surface. Invalidation of NRP-1 by RNA interference in human carcinoma cells inhibited PTN-induced intracellular signaling of the serine-threonine kinase, mitogen-activated protein MAP kinase, and focal adhesion kinase pathways. Accordingly, NRP-1 silencing or blocking by antibody inhibited PTN-induced human umbilical vein endothelial cell migration and tumor cell invasion. These results suggest that NRP-1/PTN interaction provides a novel mechanism for controlling the response of endothelial and tumoral cells to PTN and may explain, at least in part, how PTN contributes to tumor angiogenesis and cancer progression.

Structural studies reveal an important role for the pleiotrophin C-terminus in mediating interactions with chondroitin sulfate

Pleiotrophin (PTN) is a potent glycosaminoglycan-binding cytokine that is important in neural development, angiogenesis and tissue regeneration. Much of its activity is attributed to its interactions with the chondroitin sulfate (CS) proteoglycan, receptor type protein tyrosine phosphatase ζ (PTPRZ). However, there is little high resolution structural information on the interactions between PTN and CS, nor is it clear why the C-terminal tail of PTN is necessary for signaling through PTPRZ, even though it does not contribute to heparin binding. We determined the first structure of PTN and analyzed its interactions with CS. Our structure shows that PTN possesses large basic surfaces on both of its structured domains and also that residues in the hinge segment connecting the domains have significant contacts with the C-terminal domain. Our analysis of PTN-CS interactions showed that the C-terminal tail of PTN is essential for maintaining stable interactions with chondroitin sulfate A, the type of CS commonly found on PTPRZ. These results offer the first possible explanation of why truncated PTN missing the C-terminal tail is unable to signal through PTPRZ. NMR analysis of the interactions of PTN with CS revealed that the C-terminal domain and hinge of PTN make up the major CS-binding site in PTN, and that removal of the C-terminal tail weakened the affinity of the site for CSA but not for other high sulfation density CS.

DATABASE

Coordinates of the ensemble of ten PTN structures have been deposited in RCSB under accession number 2n6f. Chemical shifts assignments and structural constraints have been deposited in BMRB under accession number 25762.

Increased Pleiotrophin Concentrations in Papillary Thyroid Cancer

Background

Thyroid nodules are common, and approximately 5% of these nodules are malignant. Pleiotrophin (PTN) is a heparin-binding growth factor which is overexpressed in many cancers. The expression of PTN in papillary thyroid cancer (PTC) is unknown.

Method and Findings

74 subjects (age 47 ± 12 y, 15 males) who had thyroidectomy with a histological diagnosis: 79 benign nodules and 23 PTCs (10 classic, 6 tall cell, 6 follicular variant and 1 undetermined). Fine-needle aspiration (FNA) samples were obtained ex vivo from surgically excised tissue and assayed for PTN and thyroglobulin (Tg). Immunohistochemistry (IHC) was performed on tissue sections. In FNA samples, PTN concentration normalized to Tg was significantly higher in PTC than in benign nodules (16 ± 6 vs 0.3 ± 0.1 ng/mg, p < 0.001). In follicular variant of PTC (n = 6), the PTN/Tg ratio was also higher than in benign nodules (1.3 ± 0.6 vs 0.3 ± 0.1 ng/mg, P < 0.001, respectively). IHC showed cytoplasmic localization of PTN in PTC cells.

Conclusion

In ex vivo FNA samples, the PTN to thyroglobulin ratio was higher in PTCs, including follicular variant PTC, than in benign thyroid nodules. The findings raise the possibility that measurement of the PTN to Tg ratio may provide useful diagnostic and/or prognostic information in the evaluation of thyroid nodules.

The heparin-binding growth factor midkine: the biological activities and candidate receptors

The heparin-binding growth factor midkine (MK) comprises a family with pleiotrophin/heparin-binding growth-associated molecule. The biological phenomena in which MK is involved can be categorized into five areas: (i) cancer, (ii) inflammation/immunity, (iii) blood pressure, (iv) development and (v) tissue protection. The phenotypes are clear in vivo, but the mechanisms by which MK exerts these actions are not fully understood. Candidate receptors for MK include anaplastic lymphoma kinase, protein tyrosine phosphatase ζ, Notch2, LDL receptor-related protein 1, integrins and proteoglycans. Some physical associations between these candidate receptors are also known. Because of the striking in vivo phenotypes after manipulation of MK, MK could be an important molecular target for the treatment of various diseases. To this end, it will be important to pursue studies to fully understand the mechanisms of MK action.

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.

Delivery systems for the direct application of siRNAs to induce RNA interference (RNAi) in vivo

RNA interference (RNAi) is a powerful method for specific gene silencing which may also lead to promising novel therapeutic strategies. It is mediated through small interfering RNAs (siRNAs) which sequence-specifically trigger the cleavage and subsequent degradation of their target mRNA. One critical factor is the ability to deliver intact siRNAs into target cells/organs in vivo. This review highlights the mechanism of RNAi and the guidelines for the design of optimal siRNAs. It gives an overview of studies based on the systemic or local application of naked siRNAs or the use of various nonviral siRNA delivery systems. One promising avenue is the the complexation of siRNAs with the polyethylenimine (PEI), which efficiently stabilizes siRNAs and, upon systemic administration, leads to the delivery of the intact siRNAs into different organs. The antitumorigenic effects of PEI/siRNA-mediated in vivo gene-targeting of tumor-relevant proteins like in mouse tumor xenograft models are described.

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.

Pleiotrophin regulates lung epithelial cell proliferation and differentiation during fetal lung development via beta-catenin and Dlk1

The role of pleiotrophin in fetal lung development was investigated. We found that pleiotrophin and its receptor, protein-tyrosine phosphatase receptor beta/zeta, were highly expressed in mesenchymal and epithelial cells of the fetal lungs, respectively. Using isolated fetal alveolar epithelial type II cells, we demonstrated that pleiotrophin promoted fetal type II cell proliferation and arrested type II cell trans-differentiation into alveolar epithelial type I cells. Pleiotrophin also increased wound healing of injured type II cell monolayer. Knockdown of pleiotrophin influenced lung branching morphogenesis in a fetal lung organ culture model. Pleiotrophin increased the tyrosine phosphorylation of beta-catenin, promoted beta-catenin translocation into the nucleus, and activated T cell factor/lymphoid enhancer factor transcription factors. Dlk1, a membrane ligand that initiates the Notch signaling pathway, was identified as a downstream target of the pleiotrophin/beta-catenin pathway by endogenous dlk1 expression, promoter assay, and chromatin immunoprecipitation. These results provide evidence that pleiotrophin regulates fetal type II cell proliferation and differentiation via integration of multiple signaling pathways including pleiotrophin, beta-catenin, and Notch pathways.

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.

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.

Extrinsic regulation of T-type Ca(2+) channel expression in chick nodose ganglion neurons

Functional expression of T-type Ca(2+) channels is developmentally regulated in chick nodose neurons. In this study we have tested the hypothesis that extrinsic factors regulate the expression of T-type Ca(2+) channels in vitro. Voltage-gated Ca(2+) currents were measured using whole-cell patch clamp recordings in E7 nodose neurons cultured under various conditions. Culture of E7 nodose neurons for 48 h with a heart extract induced the expression of T-type Ca(2+) channels without any significant effect on HVA currents. T-type Ca(2+) channel expression was not stimulated by survival promoting factors such as BDNF. The stimulatory effect of heart extract was mediated by a heat-labile, trypsin-sensitive factor. Various hematopoietic cytokines including CNTF and LIF mimic the stimulatory effect of heart extract on T-type Ca(2+) channel expression. The stimulatory effect of heart extract and CNTF requires at least 12 h continuous exposure to reach maximal expression and is not altered by culture of nodose neurons with the protein synthesis inhibitor anisomycin, suggesting that T-type Ca(2+) channel expression is regulated by a posttranslational mechanism. Disruption of the Golgi apparatus with brefeldin-A inhibits the stimulatory effect of heart extract and CNTF suggesting that protein trafficking regulates the functional expression of T-type Ca(2+) channels. Heart extract- or CNTF-evoked stimulation of T-type Ca(2+) channel expression is blocked by the Jak/STAT and MAP kinase blockers, AG490 and U0126, respectively. This study provides new insights into the electrical differentiation of placode-derived sensory neurons and the role of extrinsic factors in regulating the functional expression of Ca(2+) channels.

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.

The presence of pleiotrophin in the human intervertebral disc is associated with increased vascularization: an immunohistologic study

STUDY DESIGN

An immunohistological study of surgical specimens of human intervertebral disc.

OBJECTIVE

To examine the presence of pleiotrophin in diseased or damaged intervertebral disc tissue and the association between its presence and the extent of tissue vascularization and innervation.

SUMMARY OF BACKGROUND DATA

Increased levels of pleiotrophin, a growth and differentiation factor that is active in various pathophysiologic processes, including angiogenesis, has been associated with osteoarthritic changes of human articular cartilage. The association between pleiotrophin expression and pathologic conditions of the human intervertebral disc is unknown.

METHODS

Specimens of human lumbar intervertebral discs, obtained following surgical discectomy, were divided into 3 groups: non-degenerated discs (n = 7), degenerated discs (n = 6), and prolapsed discs (n = 11). Serial tissue sections of each specimen were immunostained to determine the presence of pleiotrophin, blood vessels (CD34-positive endothelial cells), and nerves (neurofilament 200 kDa [NF200]-positive nerve fibers).

RESULTS

Pleiotrophin immunoreactivity was seen in disc cells, endothelial cells, and in the extracellular matrix in most specimens of intervertebral disc but was most prevalent in vascularized tissue in prolapsed discs. There was a significant correlation between the presence of pleiotrophin-positive disc cells and that of CD34-positive blood vessels. NF200-positive nerves were seen in vascularized areas of more degenerated discs, but nerves did not appear to codistribute with blood vessels or pleiotrophin positivity in prolapsed discs.

CONCLUSIONS

Pleiotrophin is present in pathologic human intervertebral discs, and its prevalence and distribution suggest that it may play a role in neovascularization of diseased or damaged disc tissue.

Midkine is an autocrine activator of signal transducer and activator of transcription 3 in 3T3-L1 cells

Mitotic clonal expansion is believed to be necessary for 3T3-L1 adipocyte formation. Signal transducer and activator of transcription 3 (STAT3), a mitogenic signaling protein, is activated through tyrosine phosphorylation during the proliferative phases of adipogenesis. We hypothesize that this signaling protein plays a key role in mitotic clonal expansion and differentiation. Here we determined that the adipocyte differentiation cocktail containing isobutylmethylxanthine, dexamethasone, and insulin (MDI) induced STAT3 tyrosine phosphorylation indirectly through the synthesis of an autocrine/paracrine factor. We further determined that the factor has heparin binding properties and identified the factor as midkine, a pleiotrophic growth factor previously associated with neuronal development and oncogenesis. Recombinant midkine induced STAT3 tyrosine phosphorylation in a time- and dose-dependent manner and stimulated the proliferation of postconfluent 3T3-L1 cells. Midkine neutralizing antibodies inhibited differentiation-induced STAT3 tyrosine phosphorylation as well as adipogenesis. These results show that MDI-induced synthesis and release of midkine explains the delayed activation of STAT3 during adipogenesis and that the midkine-STAT3 signaling pathway plays a necessary role in mitotic clonal expansion and differentiation.

The pluripotent cytokine pleiotrophin is induced by wounding in human mesangial cells

Mesangial re-modeling and mesangial cell (MC) migration are features of several glomerular diseases including mesangiocapillary glomerulonephritis. In vitro investigations have recently identified ADAM-15, a multidomain adamalysin, as central to the migration of MC. The current study used array technology to investigate the expression of other genes in migrating cells and identified pleiotrophin (PTN), platelet-derived growth factor alpha polypeptide chain, colony stimulating factor, and four members of the tumor necrosis factor-alpha superfamily as major genes that were upregulated. Transcriptional induction of PTN was confirmed by reverse transcription-polymerase chain reaction and Northern blotting and induction of the protein by Western blotting and immunohistochemical localization. PTN was observed associated with mesangial 'hillocks' in confluent MC cultures. In contrast, in models of migration, migrating cells had the highest expression of cell-associated PTN. PTN protein was less evident, however, in the conditioned medium of MCs. Treatment of MC with heparanase removed PTN from the cells suggesting that its localization was owing to an association with heparan sulfates on the cell surface or in the extracellular matrix. This is the first description of the expression of PTN by human MCs and the data suggest that it is rapidly induced in cells that are triggered to migrate. The result of this induction is currently under investigation.

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.

Gene silencing through RNA interference (RNAi) in vivo: strategies based on the direct application of siRNAs

RNA interference (RNAi) offers great potential not only for in vitro target validation, but also as a novel therapeutic strategy based on the highly specific and efficient silencing of a target gene, e.g. in tumor therapy. Since it relies on small interfering RNAs (siRNAs), which are the mediators of RNAi-induced specific mRNA degradation, a major issue is the delivery of therapeutically active siRNAs into the target tissue/target cells in vivo. For safety reasons, strategies based on (viral) vector delivery may be of only limited clinical use. The more desirable approach is to directly apply catalytically active siRNAs. This review highlights the recent knowledge on the guidelines for the selection of siRNAs which show high activity in the absence of non-specific siRNA effects. It then focuses on approaches to directly use siRNA molecules in vivo and gives a comprehensive overview of in vivo studies based on the direct application of siRNAs to induce RNAi. One promising approach is the in vivo siRNA delivery through complexation of chemically unmodified siRNAs with polyethylenimine (PEI). The anti-tumoral effects of PEI/siRNA-based targeting of tumor-relevant genes in vivo are described.

Role of fibroblast growth factor-binding protein in the pathogenesis of HIV-associated hemolytic uremic syndrome

A characteristic finding of childhood HIV-associated hemolytic uremic syndrome (HIV-HUS) is the presence of endothelial injury and microcystic tubular dilation, leading to a rapid progression of the renal disease. We have previously shown that a secreted fibroblast growth factor-binding protein (FGF-BP) is upregulated in kidneys from children affected with HIV-HUS and HIV nephropathy. Here, we sought to determine the potential role of FGF-BP in the pathogenesis of HIV-HUS. By immunohistochemical and in situ hybridization studies, we observed FGF-BP protein and mRNA upregulation in regenerating renal tubular epithelial cells from kidneys of HIV-Tg26mice with late-stage renal disease, that is, associated with the development of microcystic tubular dilatation and accumulation of FGF-2. Moreover, FGF-BP increased the FGF-2-dependent growth and survival of cultured primary human renal glomerular endothelial cells and enhanced FGF-2-induced MAPK/ERK2 activation, as well as the proliferation of immortalized GM7373 endothelial cells. We propose that HIV-Tg26mice are a clinically relevant model system to study the role of FGF-BP in the pathogenesis of HIV-associated renal diseases. Furthermore, the upregulation of FGF-BP by regenerating renal tubular epithelial cells may provide a mechanism by which the regenerative and angiogenic activity of FGF-2 in renal capillaries can be modulated in children with HIV-HUS and other renal disease.

Differential induction of glioblastoma migration and growth by two forms of pleiotrophin

Glioblastoma is the most common malignant brain tumor of adults and one of the most lethal cancers. The secreted growth factor pleiotrophin (PTN) promotes glioblastoma migration and proliferation, initiating its oncogenic activities through two cell surface receptors, the protein tyrosine phosphatase receptor zeta (PTPRZ1) and the anaplastic lymphoma kinase (ALK), respectively. Here, we report on the presence and purification of two naturally occurring forms of PTN (18 and 15 kDa) that differentially promote glioblastoma migration and proliferation. Using a panel of glioblastoma cell lines, including low passage patient-derived cultures, we demonstrate that PTN15 promotes glioblastoma proliferation in an ALK-dependent fashion, whereas immobilized PTN18 promotes haptotactic migration of glioblastoma cells in a PTPRZ1-dependent fashion. Mass spectrometric analysis indicated that PTN15 differs from PTN18 by processing of 12 C-terminal amino acids. To demonstrate clinical relevance, we show that PTN15, PTN18, and PTPRZ1 are significantly overexpressed in glioblastoma relative to normal brain at both mRNA and protein levels using microarray, Western blot, and tissue microarray analyses on human tumors. These results indicate that the PTN18-PTPRZ1 and the PTN15-ALK signaling pathways represent potentially important therapeutic targets for glioblastoma invasion and growth.

Overexpression of heparin-binding growth-associated molecule in malignant glioma cells

The highly invasive and angiogenic characteristics of malignant gliomas depend on the production of growth factors and angiogenic factors. Heparin-binding growth-associated molecule (HB-GAM) is a secreted growth factor that is mitogenic for endothelial cells. To examine the expression profile of HB-GAM in malignant glioma cells, messenger ribonucleic acid (mRNA) expression was analyzed in 10 malignant glioma cell lines, two glioblastoma tissue specimens, and two normal brain tissue specimens by the reverse transcription-polymerase chain reaction. HB-GAM mRNA was expressed in all specimens including normal brain tissue specimens. Western blot analysis revealed that HB-GAM protein contents in glioma cell lines and glioblastoma tissues were 1.8 to 6.3 times higher than those in normal brain tissues. The effect of neutralizing anti-platelet-derived growth factor (PDGF) antibody was also examined on the production of HB-GAM in malignant glioma cells, since malignant glioma cells secrete PDGF that upregulates HB-GAM expression. Treatment of U251 and T98G glioblastoma cells with the anti-PDGF antibody did not affect the HB-GAM production. These results suggest that HB-GAM is overexpressed in malignant glioma cells and is involved in tumor growth.

Receptor protein tyrosine phosphatase ζ as a therapeutic target for glioblastoma therapy

Astrocytomas are the most frequent brain tumour type in adults. The most common astrocytoma is the glioblastoma (GBM), which is also the most malignant and refractory to treatment--ultimately leading to the patient's death within a year of diagnosis. Neither the classical nor more experimental therapeutic approaches have significantly improved the clinical outcome of this disease. Expression profile analysis of primary tumours has provided recent insight into the identification of new GBM therapeutic targets. These proteins serve as excellent candidates to either inhibit the target molecule's functions (e.g., angiogenesis, migration or proliferation) or, coupled with a toxin or radionucleotide, to bind and exterminate the tumour cells. The receptor protein tyrosine phosphatase zeta (RPTPzeta) and one of its main ligands, pleiotropin (Ptn), are overexpressed in GBMs, thus making them potentially very good targets for the development of new immunotherapeutics. This review will summarise recent advances in GBM therapies focusing on RPTPzeta as a target for immunotherapeutics.

Ribozyme-targeting reveals the rate-limiting role of pleiotrophin in glioblastoma

Glioblastomas (GBMs) are the most frequent malignant brain tumors with very limited treatment options and nearly all GBM patients dying within 1 year. Pleiotrophin (PTN, HB-GAM, HBNF, OSF-1) is a secreted growth factor that shows mitogenic, chemotactic and transforming activity. While PTN expression is tightly regulated during embryogenesis and very limited in normal adult tissues, a marked PTN upregulation is seen in tumors including glioblastomas. Targeting of the PTN receptors, ALK and RPTP-zeta, indicates a contribution of PTN-activated signaling pathways in glioblastomas. However, the relevance of PTN expression itself is unknown especially since, besides PTN, at least one more growth factor, midkine (MK), signals through ALK and is expressed in glioblastoma. Here we demonstrate the biologic relevance of PTN in 2 glioblastoma cell lines in vitro and in vivo. We show that stable ribozyme-targeting leads to a robust reduction of PTN mRNA and protein levels. This results in decreased cell proliferation, cell migration and soft agar colony formation in vitro. Comparing clonal ribozyme-transfected cells with different residual PTN levels, we establish a PTN gene-dose effect of glioblastoma cell proliferation. In a subcutaneous tumor xenograft mouse model, in vivo growth is markedly reduced upon PTN depletion, which is paralleled by decreased PTN serum levels. Furthermore, the immunohistochemical analysis of the tumors shows reduced angiogenesis in PTN-depleted tumors. We conclude that PTN is a rate-limiting growth factor in glioblastoma. Since PTN is overexpressed in glioblastomas but rarely found in normal tissue, PTN may represent an attractive therapeutic target.

Ribozyme targeting of the growth factor pleiotrophin in established tumors: a gene therapy approach

The growth and metastasis of solid tumors relies on the activities of polypeptide growth factors to recruit stromal tissue and expand the tumor mass. Pleiotrophin (PTN) is a secreted growth factor with angiogenic activity that has been found to contribute to the growth and metastasis of tumors including melanoma. Here, we present a gene therapy approach of targeting PTN in established tumors using ribozymes. Tetracycline-regulated ribozyme expression vectors were used to deplete conditionally PTN mRNA from melanoma xenograft tumors in vivo. We found that tetracycline-mediated initiation of ribozyme expression in established tumors reduced further tumor growth. Next, we generated synthetic anti-PTN ribozymes that inhibit PTN-dependent colony formation of cells in soft agar. Intraperitoneal administration of these synthetic ribozymes into nude mice inhibited growth of PTN-positive, subcutaneous melanoma. Furthermore, PTN released from the tumors into the circulation of mice was reduced after ribozyme treatment. These data show that ribozyme targeting of rate-limiting tumor growth factors could provide an efficient tool for cancer therapy and that the efficacy may be reflected in the reduction of the serum levels of the targeted protein, PTN.

Anaplastic lymphoma kinase proteins in growth control and cancer

The normal functions of full-length anaplastic lymphoma kinase (ALK) remain to be completely elucidated. Although considered to be important in neural development, recent studies in Drosophila also highlight a role for ALK in gut muscle differentiation. Indeed, the Drosophila model offers a future arena for the study of ALK, its ligands and signalling cascades. The discovery of activated fusion forms of the ALK tyrosine kinase in anaplastic large cell lymphoma (ALCL) has dramatically improved our understanding of the pathogenesis of these lymphomas and enhanced the pathological diagnosis of this subtype of non-Hodgkin's lymphoma (NHL). Likewise, the realisation that a high percentage of inflammatory myofibroblastic tumours express activated-ALK fusion proteins has clarified the causation of these mesenchymal neoplasms and provided for their easier discrimination from other mesenchymal-derived inflammatory myofibroblastic tumour (IMT) mimics. Recent reports of ALK expression in a range of carcinoma-derived cell lines together with its apparent role as a receptor for PTN and MK, both of which have been implicated in tumourigenesis, raise the possibility that ALK-mediated signalling could play a role in the development and/or progression of a number of common solid tumours. The therapeutic targeting of ALK may prove to have efficacy in the treatment of many of these neoplasms.

Development of parenteral formulation for a novel angiogenesis inhibitor, CKD-732 through complexation with hydroxypropyl-β-cyclodextrin

The effect of hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) on the aqueous solubility and chemical stability of O-(4-Dimethylaminoethoxycinnamoyl)fumagillol (CKD-732), a new angiogenesis inhibitor, was investigated with an aim of preparing a stable and effective parenteral formulation. The CKD-732/HP-beta-CyD inclusion complex was obtained in solid state by freeze-drying and characterized in solution by proton nuclear magnetic resonance (1H NMR). Then, the pharmacokinetic profile in rats and the in vivo tumor growth inhibitory activity in mice following the parenteral administration of aqueous CKD-732/HP-beta-CyD complex were compared to those of CKD-732.hemioxalate solution having an equivalent concentration. The aqueous solubility of CKD-732 was markedly increased by the combination of pH adjustment and HP-beta-CyD complexation through a soluble 1:1 inclusion complex formation, which was supported by NMR spectroscopy. The hydrolysis of CKD-732 following pseudo first-order kinetics was decelerated moderately but significantly in acidic and basic solutions in the presence of HP-beta-CyD. The stability of lyophilized CKD-732/HP-beta-CyD complex was also drastically improved after storage in various conditions. The intravenous pharmacokinetic profile and the subcutaneous in vivo tumor growth inhibitory activity of aqueous CKD-732/HP-beta-CyD complex were not significantly different from those of CKD-732.hemioxalate solution with the favorable reduction of irritation. These results demonstrate that the CKD-732/HP-beta-CyD complex is an attractive formulation for use in the parenteral delivery of CKD-732.

Effect of estradiol on estrogen receptor-alpha gene expression and activity can be modulated by the ErbB2/PI 3-K/Akt pathway

Epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and heregulin-beta1 (HRG-beta1), can modulate the expression and activity of the estrogen receptor-alpha (ER-alpha) via the phosphatidylinositol 3-kinase (PI 3-K)/Akt pathway in the ER-alpha-positive breast cancer cell line, MCF-7. Estradiol can also rapidly activate PI 3-K/Akt in these cells (nongenomic effect). The recent study examines whether Akt is involved in the ER-alpha regulation by estradiol (genomic effect). Stable transfection of parental MCF-7 cells with a dominant-negative Akt mutant, as well as the PI 3-K inhibitors wortmannin and LY 294,002, blocked the effect of estradiol on ER-alpha expression and activity by 70-80 and 55-63%, respectively. Stable transfection of MCF-7 cells with a constitutively active Akt mimicked the effect of estradiol. The changes in ER-alpha expression and activity were abrogated in response to estradiol by an arginine to cysteine mutation in the pleckstrin homology (PH) domain of Akt (R25C), suggesting the involvement of this amino acid in the interaction between Akt and ER-alpha. Experiments employing selective ErbB inhibitors demonstrate that the effect of estradiol on ER-alpha expression and activity is mediated by ErbB2 and not by EGFR. Moreover, anchorage-dependent and -independent growth assays, cell cycle and membrane ruffling analyses showed that Akt exerts estrogen-like activity on cell growth and membrane ruffling and that a selective ErbB2 inhibitor, but not anti-ErbB2 antibodies directed to the extracellular domain, can block these effects. In the presence of constitutively active Akt, tamoxifen only partially inhibits cell growth. In contrast, in cells stably transfected with either a dominant-negative Akt or with R25C-Akt, as well as in parental cells in the presence of a selective ErbB2 inhibitor, the effect of estradiol on anchorage-dependent and -independent cell growth was inhibited by 50-75 and 100%, respectively. Dominant-negative Akt inhibited membrane ruffling by 54%; however, R25C-Akt did not have any effect, suggesting that kinase activity plays an important role in this process. Scatchard analysis demonstrated a 67% reduction in estrogen-binding capacity in cells transfected with constitutively active Akt. No change in binding affinity of estradiol to the receptor was observed upon transfection with either Akt mutant. Taken together, our results suggest that estradiol treatment results in binding to membrane ER-alpha and interaction with a heterodimer containing ErbB2, leading to tyrosine phosphorylation. This results in the activation of PI 3-K and Akt. Akt, in turn, may interact with nuclear ER-alpha, altering its expression and activity.

HB-GAM/Pleiotrophin and Midkine are differently expressed and distributed during retinoic acid-induced neural differentiation of P19 cells

HB-GAM/Pleiotrophin and Midkine (MK) are developmentally-regulated proteins with putative functions during cell growth and differentiation. Using the P19 cell which is a model to study the events associated with early development, we examined the expression and cellular localization of HB-GAM and MK during neural differentiation of P19 cells induced by retinoic acid (RA). The temporal expressions of HB-GAM and MK transcripts and both the levels and cellular localizations of the corresponding proteins appeared dramatically different. MK mRNA, already expressed in untreated P19 cells, was transiently increased by exposure to RA and then largely down regulated. More interestingly, HB-GAM which was not detected in untreated P19 cells was strongly expressed after 2 days of RA treatment and this expression persists throughout the duration of the culture suggesting that it could be involved in different aspects of this differentiation process.

Anti-apoptotic signaling of pleiotrophin through its receptor, anaplastic lymphoma kinase

The secreted growth factor pleiotrophin (PTN) can induce mitogenesis in cells that express the receptor for this growth factor, anaplastic lymphoma kinase (ALK). Here we examine the ability of PTN to produce anti-apoptotic signals. We demonstrate that PTN is a survival factor for SW-13 epithelial cells and show that ribozyme-mediated depletion of ALK from SW-13 cells abolishes this effect of PTN. Furthermore, in serum-starved NIH3T3 fibroblasts PTN prevents apoptosis (measured by annexin V staining) with an EC(50) of 0.2 ng/ml and induces cell growth at higher concentrations of PTN. A polyclonal antibody against the PTN ligand-binding domain of the ALK receptor (alpha-LBD) was a partial agonist for ALK in NIH3T3 cells. This alpha-LBD antibody showed high agonist activity for anti-apoptosis (56 +/- 9% relative to PTN), low agonist activity for cell growth (21 +/- 1% relative to PTN), and was an antagonist of PTN-induced cell growth (61 +/- 2% inhibition). Both MAP kinase and phosphatidylinositol (PI) 3-kinase cascades in NIH3T3 cells were activated by PTN, and this effect persisted for up to 3 h. Surprisingly, the anti-apoptotic effect of PTN was completely blocked by the MAP kinase inhibitor UO126, but was not affected by the PI 3-kinase inhibitor LY294002. In contrast, PTN-dependent cell growth required both MAPK and PI 3-kinase activity. We conclude that anti-apoptotic signaling of PTN through ALK in NIH3T3 fibroblasts is via the MAP kinase pathway.

Midkine binds to anaplastic lymphoma kinase (ALK) and acts as a growth factor for different cell types

Midkine (MK) is a developmentally regulated, secreted growth factor homologous to pleiotrophin (PTN). To investigate the potential role of MK in tumor growth, we expressed MK in human SW-13 cells and studied receptor binding, signal transduction, and activity of MK. The MK protein stimulates soft agar colony formation in vitro and tumor growth of SW-13 cells in athymic nude mice, as well as proliferation of human endothelial cells from brain microvasculature and umbilical vein (HUVEC) in the low ng/ml range. MK binds to anaplastic lymphoma kinase (ALK), the receptor for PTN, with an apparent K(d) of 170 pm in intact cells, and this receptor binding of MK is competed by PTN with an apparent K(d) of approximately 20 pm. Monoclonal antibodies raised against the extracellular ligand-binding domain of ALK inhibit ALK receptor binding of MK as well as MK-stimulated colony formation of SW-13 cells. Furthermore, MK stimulates ALK phosphorylation in WI-38 human fibroblasts and activates PI3-kinase and MAP kinase signal transduction in WI-38, HUVEC, neuroblastoma (SH SY-5Y) and glioblastoma (U87MG) cells that express the ALK protein. We conclude that MK can act as a growth, survival, and angiogenic factor during tumorigenesis and signals through the ALK receptor.

Dominant negative effectors of heparin affin regulatory peptide (HARP) angiogenic and transforming activities

Heparin affin regulatory peptide (HARP) is an heparin-binding growth factor, highly expressed in several primary human tumors and considered as a rate-limiting angiogenic factor in tumor growth, invasion, and metastasis. Implication of this protein in carcinogenesis is linked to its mitogenic, angiogenic, and transforming activities. Recently, we have demonstrated that the C-terminal residues 111-136 of HARP are required for its mitogenic and transforming activities (Bernard-Pierrot, I., Delbe, J., Caruelle, D., Barritault, D., Courty, J., and Milhiet, P. E. (2001) J. Biol. Chem. 276, 12228-12234). In this paper, HARP deleted of its last 26 amino acids was shown to act as a dominant negative effector for its mitogenic, angiogenic, transforming, and tumor-formation activities by heterodimerizing with the wild type protein. Similarly, the synthetic corresponding peptide P111-136 displayed in vitro inhibition of wild type HARP activities, but in this case, the inhibition was mainly explained by the competition of the peptide with HARP for the binding to the extracellular domain of the high affinity ALK receptor.

Serum levels of the angiogenic factor pleiotrophin in relation to disease stage in lung cancer patients

Pleiotrophin is a heparin-binding growth factor involved in the differentiation and proliferation of neuronal tissue during embryogenesis, and also secreted by melanoma and breast carcinoma cells. Pleiotrophin exhibits mitogenic and angiogenic properties and has been shown to influence the vascular supply, expansion and metastasis of tumour cells. Our aim was to study the serum and plasma concentrations of pleiotrophin and the classical angiogenic growth factor vascular endothelial growth factor. Using a specific ELISA-test we studied patients with small cell lung cancer (n=63), and patients with non-small cell lung cancer (n=22) in comparison to healthy control subjects (n=41). In most of the lung cancer patients (81%), we found serum levels of pleiotrophin above those of control subjects (P<0.001). Of the 63 small cell lung cancer patients in the study pleiotrophin serum levels were elevated in 55 cases (87%) and in 14 cases (63%) of the 22 non-small cell lung cancer patients. Pleiotrophin mean serum concentrations were 10.8-fold higher in the tumour patient group as compared to the control group (P<0.001). Furthermore, pleiotrophin serum levels correlated positively with the stage of disease and inversely with the response to therapy. Plasma vascular endothelial growth factor concentrations were elevated in only in 28.6% of small cell lung cancer and 45.5% of non-small cell lung cancer patients by an average of 2.3-fold. Quite strikingly, there was no apparent correlation between the plasma vascular endothelial growth factor concentration and the stage of disease. Our study suggests that pleiotrophin may be an early indicator of lung cancer and might be of use in monitoring the efficacy of therapy, which needs to be confirmed by larger studies.

Pleiotrophin: a cytokine with diverse functions and a novel signaling pathway

Pleiotrophin (PTN the protein, Ptn the gene) is a 136 amino acid secreted heparin-binding cytokine that signals diverse functions, including lineage-specific differentiation of glial progenitor cells, neurite outgrowth, and angiogenesis. Pleiotrophin gene expression is found in cells in early differentiation during different development periods and upregulated in cells with an early differentiation phenotype in wound repair. The Ptn gene is a protooncogene. It is strongly expressed in different human tumor cells and expression of the Ptn gene in tumor cells in vivo accelerates growth and stimulates tumor angiogenesis. Separate independent domains have been identified in PTN to signal transformation and tumor angiogenesis. Pleiotrophin is the first ligand of any of the known transmembrane tyrosine phosphatases. Pleiotrophin inactivates the receptor protein tyrosine phosphatase (RPTP) beta/zeta. The interaction of PTN and RPTP beta/zeta increases steady-state tyrosine phosphorylation of beta-catenin. Pleiotrophin thus regulates both normal cell functions and different pathological conditions at many levels. It signals these functions through a transmembrane tyrosine phosphatase.

Translocations involving anaplastic lymphoma kinase (ALK)

Anaplastic large-cell lymphoma (ALCL) comprises a group of non-Hodgkin's lymphomas (NHLs) that were first described in 1985 by Stein and co-workers and are characterized by the expression of the CD30/Ki-1 antigen (Stein et al., 1985). Approximately half of these lymphomas are associated with a typical chromosomal translocation, t(2;5)(p23;q35). Much confusion about the exact classification and clinicopathological features of this subgroup of NHL was clarified with the identification of NPM-ALK (nucleophosmin-anaplastic lymphoma kinase) as the oncogene created by the t(2;5) (Morris et al., 1994). With the discovery of NPM-ALK as the specific lymphoma gene mutation, this NHL subtype could be redefined on the molecular level. This achievement was enhanced by the availability of specific antibodies that recognize ALK fusion proteins in paraffin-embedded lymphoma tissues. Several excellent recent reviews have summarized the histopathological and molecular findings of ALCL and their use in the classification of this lymphoma entity (Anagnostopoulos and Stein, 2000; Benharroch et al., 1998; Drexler et al., 2000; Foss et al., 2000; Gogusev and Nezelof, 1998; Kadin and Morris, 1998; Ladanyi, 1997; Morris et al., 2001; Shiota and Mori, 1996; Skinnider et al., 1999; Stein et al., 2000). This review will focus on the molecular function and signal transduction pathways activated by ALK fusion oncogenes, with recent advances and possible clinical implications to be discussed.

Selective thrombosis of tumor blood vessels in mammary adenocarcinoma implants in rats

Adenocarcinomas in rats and humans frequently contain perivascular, degranulating mast cells that release heparin. Protamine is a low-molecular weight, cationic polypeptide that binds avidly to heparin and neutralizes its anticoagulant properties. We hypothesized that mast-cell heparin functions as a localized anticoagulant that modulates hemostasis and blood perfusion in tumors. Consequently, systemically administered protamine should be able to neutralize the endogenous heparin within tumors, thereby inducing selective thrombosis of blood vessels within tumors. Here we demonstrate with magnetic resonance imaging (MRI) that an intravenous dose of protamine labeled with gadolinium accumulated within the parenchyma of subcutaneous implants of a mammary adenocarcinoma in Fischer 344 rats. Moreover, we show with dynamic contrast enhanced MRI that sequential intravenous doses of protamine in 12 tumor-bearing rats resulted in significantly decreased signal enhancement kinetics (blood perfusion) of the tumor. This functional impairment of MRI signal enhancement was accompanied by histological evidence of thrombosis in the blood vessels within the tumor. There was no histological evidence of thrombosis within normal liver, kidney, lung, spleen, or adjacent muscle of tumor-bearing animals that received protamine treatment or in the tumors of animals that had not been pretreated with protamine. On the basis of these results, we conclude that protamine accumulates within adenocarcinoma implants and induces selective thrombosis of blood vessels within the tumor, probably by neutralizing the endogenous heparin within tumors.

Identification of anaplastic lymphoma kinase as a receptor for the growth factor pleiotrophin

Pleiotrophin (PTN) is a secreted growth factor that induces neurite outgrowth and is mitogenic for fibroblasts, epithelial, and endothelial cells. During tumor growth PTN can serve as an angiogenic factor and drive tumor invasion and metastasis. To identify a receptor for PTN, we panned a phage display human cDNA library against immobilized PTN protein as a bait. From this we isolated a phage insert that was homologous to an amino acid sequence stretch in the extracellular domain (ECD) of the orphan receptor tyrosine kinase anaplastic lymphoma kinase (ALK). In parallel with PTN, ALK is highly expressed during perinatal development of the nervous system and down-modulated in the adult. Here we show in cell-free assays as well as in radioligand receptor binding studies in intact cells that PTN binds to the ALK ECD with an apparent Kd of 32 +/- 9 pm. This receptor binding is inhibited by an excess of PTN, by the ALK ECD, and by anti-PTN and anti-ECD antibodies. PTN added to ALK-expressing cells induces phosphorylation of both ALK and of the downstream effector molecules IRS-1, Shc, phospholipase C-gamma, and phosphatidylinositol 3-kinase. Furthermore, the growth stimulatory effect of PTN on different cell lines in culture coincides with the endogenous expression of ALK mRNA, and the effect of PTN is enhanced by ALK overexpression. From this we conclude that ALK is a receptor that transduces PTN-mediated signals and propose that the PTN-ALK axis can play a significant role during development and during disease processes.

The lysine-rich C-terminal tail of heparin affin regulatory peptide is required for mitogenic and tumor formation activities

Heparin affin regulatory peptide (HARP) is a 18-kDa heparin-binding polypeptide that is highly expressed in developing tissues and in several primary human tumors. It seems to play a key role in cellular growth and differentiation. In vitro, HARP displays mitogenic, angiogenic, and neurite outgrowth activities. It is a secreted protein that is organized in two beta-sheet domains, each domain containing a cluster of basic residues. To assess determinants involved in the biological activities of HARP, C-terminally truncated proteins were produced in Chinese hamster ovary-K1 cells and tested for their mitogenic, tumor formation in nude mice and neurite outgrowth activities. Our data clearly indicate that the residues 111-136 of the lysine-rich C-terminal domain are involved in the mitogenic and tumor formation activities of HARP. Correlatively, no signal transduction was detected using the corresponding mutant, suggesting the absence of HARP binding to its high affinity receptor. However, this C-terminal domain of HARP is not involved in the neurite outgrowth activity. We also demonstrate that HARP signal peptide cleavage could led to two maturated forms that are both but differentially mitogenic.

Influence of the human endogenous retrovirus-like element HERV-E.PTN on the expression of growth factor pleiotrophin: a critical role of a retroviral Sp1-binding site

Germ line insertion of a human endogenous retrovirus-like element (HERV-E.PTN) into the growth factor pleiotrophin (PTN) gene generated a phylogenetically new promoter driving the expression of functional HERV-PTN fusion transcripts. Here we show by in situ hybridization, that HERV-PTN fusion transcripts are expressed in malignant trophoblasts (i.e. choriocarcinoma) and in the proliferative and in the invasive trophoblasts of gestational trophoblastic tissue. Additionally, a 1.9 kb fragment of the HERV-derived PTN promoter was analysed which has strong activity when transiently transfected into choriocarcinoma JEG-3 cells in contrast to HeLa cells. Deletion of the retrovirally-derived promoter portion abolished its activity and an enhancer (+443 to +486) was identified in this region. Electrophoretic mobility shift and supershift experiments identified a Sp1 binding site in this enhancer and site specific mutation of this site abolished its activity in choriocarcinoma cells. Sp1 overexpression in Drosophila SL2 cells showed that the enhancer activity is mediated via Sp1 binding in vivo. Furthermore, mutation of the Sp1 binding site reduced the activity of a promoter test fragment in choriocarcinoma cells by 80%. Our result shows that a retroviral Sp1 binding site in the PTN promoter is important for the expression of growth factor pleiotrophin in human choriocarcinoma cells. Oncogene (2000) 19, 3988 - 3998.