Interaction of urokinase-type plasminogen activator with its receptor rapidly induces activation of glucose transporters

uPAR: An Essential Factor for Tumor Development

Tumorigenesis is closely related to the loss of control of many genes. Urokinase-type plasminogen activator receptor (uPAR), a glycolipid-anchored protein on the cell surface, is controlled by many factors in tumorigenesis and is expressed in many tumor tissues. In this review, we summarize the regulatory effects of the uPAR signaling pathway on processes and factors related to tumor progression, such as tumor cell proliferation, adhesion, metastasis, glycolysis, tumor microenvironment and angiogenesis. Overall, the evidence accumulated to date suggests that uPAR induction by tumor progression may be one of the most important factors affecting therapeutic efficacy. An improved understanding of the interactions between uPAR and its coreceptors in cancer will provide critical biomolecular information that may help to better predict the disease course and response to therapy.

The role of FAK in tumor metabolism and therapy

Focal adhesion kinase (FAK) plays a vital role in tumor cell proliferation, survival and migration. Altered metabolic pathways fuel rapid tumor growth by accelerating glucose, lipid and glutamine processing. Besides the mitogenic effects of FAK, evidence is accumulating supporting the association between hyper-activated FAK and aberrant metabolism in tumorigenesis. FAK can promote glucose consumption, lipogenesis, and glutamine dependency to promote cancer cell proliferation, motility, and survival. Clinical studies demonstrate that FAK-related alterations of tumor metabolism are associated with increased risk of developing solid tumors. Since FAK contributes to the malignant phenotype, small molecule inhibition of FAK-stimulated bioenergetic and biosynthetic processes can provide a novel approach for therapeutic intervention in tumor growth and invasion.

What model organisms and interactomics can reveal about the genetics of human obesity

Genome-wide association studies have identified a number of genes associated with human body weight. While some of these genes are large fields within obesity research, such as MC4R, POMC, FTO and BDNF, the majority do not have a clearly defined functional role explaining why they may affect body weight. Here, we searched biological databases and discovered 33 additional genes associated with human obesity (CADM2, GIPR, GPCR5B, LRP1B, NEGR1, NRXN3, SH2B1, FANCL, GNPDA2, HMGCR, MAP2K5, NUDT3, PRKD1, QPCTL, TNNI3K, MTCH2, DNAJC27, SLC39A8, MTIF3, RPL27A, SEC16B, ETV5, HMGA1, TFAP2B, TUB, ZNF608, FAIM2, KCTD15, LINGO2, POC5, PTBP2, TMEM18, TMEM160). We find that the majority have orthologues in distant species, such as D. melanogaster and C. elegans, suggesting that they are important for the biology of most bilateral species. Intriguingly, signalling cascade genes and transcription factors are enriched among these obesity genes, and several of the genes show properties that could be useful for potential drug discovery. In this review, we demonstrate how information from several distant model species, interactomics and signalling pathway analysis represents an important way to better understand the functional diversity of the surprisingly high number of molecules that seem to be important for human obesity.

SH2B1beta (SH2-Bbeta) enhances expression of a subset of nerve growth factor-regulated genes important for neuronal differentiation including genes encoding urokinase plasminogen activator receptor and matrix metalloproteinase 3/10

Previous work showed that the adapter protein SH2B adapter protein 1beta (SH2B1) (SH2-B) binds to the activated form of the nerve growth factor (NGF) receptor TrkA and is critical for both NGF-dependent neurite outgrowth and maintenance. To identify SH2B1beta-regulated genes critical for neurite outgrowth, we performed microarray analysis of control PC12 cells and PC12 cells stably overexpressing SH2B1beta (PC12-SH2B1beta) or the dominant-negative SH2B1beta(R555E) [PC12-SH2B1beta(R555E)]. NGF-induced microarray expression of Plaur and Mmp10 genes was greatly enhanced in PC12-SH2B1beta cells, whereas NGF-induced Plaur and Mmp3 expression was substantially depressed in PC12-SH2B1beta(R555E) cells. Plaur, Mmp3, and Mmp10 are among the 12 genes most highly up-regulated after 6 h of NGF. Their protein products [urokinase plasminogen activator receptor (uPAR), matrix metalloproteinase 3 (MMP3), and MMP10] lie in the same pathway of extracellular matrix degradation; uPAR has been shown previously to be critical for NGF-induced neurite outgrowth. Quantitative real-time PCR analysis revealed SH2B1beta enhancement of NGF induction of all three genes and the suppression of NGF induction of all three when endogenous SH2B1 was reduced using short hairpin RNA against SH2B1 and in PC12-SH2B1beta(R555E) cells. NGF-induced levels of uPAR and MMP3/10 and neurite outgrowth through Matrigel (MMP3-dependent) were also increased in PC12-SH2B1beta cells. These results suggest that SH2B1beta stimulates NGF-induced neuronal differentiation at least in part by enhancing expression of a specific subset of NGF-sensitive genes, including Plaur, Mmp3, and/or Mmp10, required for neurite outgrowth.

Antisense oligodeoxynucleotides for urokinase-plasminogen activator receptor have anti-invasive and anti-proliferative effects in vitro and inhibit spontaneous metastases of human melanoma in mice

We have targeted the urokinase-type plasminogen activator receptor (uPAR) with phosphorothioate antisense oligonucleotides (aODN) in vitro to evaluate the anti-invasive and anti-proliferative effects of uPAR down-regulation, as well as in vivo to evaluate anti-tumor and anti-metastatic activity. aODN-dependent uPAR downregulation in vitro was induced in cells of human melanoma, mammary carcinoma, ovarian carcinoma and SV-40-transformed embryonic lung fibroblasts. uPAR was determined by an antibody-based assay and by semiquantitative polymerase chain reaction. Cell invasion was evaluated by Matrigel invasion assay and cell proliferation by direct cell counting. aODN reduced uPAR, invasion and proliferation in all the treated cell lines. Following aODN treatment, human melanoma cells exhibited a strong decrease of uPAR-dependent ERK1/2 activation and were used in vivo to control metastasis in CD-1 male nude (nu/nu) mice by uPAR aODN injection. 60 mice were injected in the hind leg muscles with a suspension of 10(6) melanoma cells. After 4 days, when a tumor mass of about 350 mg was evident in all the mice injected, 20 mice were treated i.v. with aODN and 20 with dODN at 0.5 mg/day for 5 consecutive days. Twenty control mice were not treated. A second and third cycle of treatment was administered at 2-day intervals. Treatment with aODN resulted into a 78% reduction of lung metastases and 45% reduction of the primary tumor mass with no loss of body weight. Our results suggest to evaluate the utility of uPAR aODN in controlling the metastatic spreading of human melanoma.

Novel interactions between urokinase and its receptor

Urokinase-type plasminogen activator (uPA) binds to its receptor (uPAR) with a K(d) of about 1 nm. The catalytic activity of the complex is apparent at uPA concentrations close to K(d). Other functions of the complex, such as signal transduction, are apparent at much higher concentrations (35-60 nm). In the present study, we show that uPA and recombinant soluble uPAR (suPAR), at concentrations that exceed the K(d) and the theoretical saturation levels (10-80 nm), establish novel interactions that lead to a further increase in the activity of the single-chain uPA (scuPA)/suPAR and two-chain uPA (tcuPA)/suPAR complexes. Experiments performed using dynamic light scattering, gel filtration, and electron microscopy techniques indicate that suPAR forms dimers and oligomers. The three techniques provide evidence that the addition of an equimolar concentration of scuPA leads to the dissociation of these dimers and oligomers. Biacore data show that suPAR dimers and oligomers bind scuPA with decreased affinity when compared with monomers. We postulate that uPAR is present in equilibrium between oligomer/dimer/monomer forms. The binding of uPA to suPAR dimers and oligomers occurs with lower affinity than the binding to monomer. These novel interactions regulate the activity of the resultant complexes and may be involved in uPA/uPAR mediated signal transduction.

Searching for depolarization-induced genes that modulate synaptic plasticity and neurotrophin-induced genes that mediate neuronal differentiation

We identify and characterize two classes of immediate-early genes: (i) genes, induced by depolarization in neurons, that play a role in depolarization-induced neuronal plasticity and (ii) genes, induced in neuronal precursors by neurotrophins, that play a causal role in neurotrophin-directed neuronal differentiation. We use rat PC12 pheochromocytoma cells to identify (i) genes preferentially induced by [depolarization or forskolin] versus [Nerve Growth Factor (NGF) or Epidermal Growth Factor (EGF)] and (ii) genes preferentially induced by NGF versus EGF. We describe (i) a collection of genes preferentially induced by depolarization/forskolin in PC12 cells and by kainic acid in vivo, and (ii) a collection of genes preferentially induced by NGF. The synaptotagmin IV gene encodes a synaptic vesicle protein whose level is modulated by depolarization. NGF preferentially induces the urokinase-plasminogen activator receptor in PC12 cells. Antisense oligonucleotide and anti-UPAR antibody experiments demonstrate that NGF-induced UPAR expression is required for NGF-driven PC12 cell differentiation.

The urokinase plasminogen activator receptor (UPAR) is preferentially induced by nerve growth factor in PC12 pheochromocytoma cells and is required for NGF-driven differentiation

Nerve growth factor (NGF)-driven differentiation of PC12 pheochromocytoma cells is a well studied model used both to identify molecular, biochemical, and physiological correlates of neurotrophin-driven neuronal differentiation and to determine the causal nature of specific events in this differentiation process. Although epidermal growth factor (EGF) elicits many of the same early biochemical and molecular changes in PC12 cells observed in response to NGF, EGF does not induce molecular or morphological differentiation of PC12 cells. The identification of genes whose expression is differentially regulated by NGF versus EGF in PC12 cells has, therefore, been considered a source of potential insight into the molecular specificity of neurotrophin-driven neuronal differentiation. A "second generation" representational difference analysis procedure now identifies the urokinase plasminogen activator receptor (UPAR) as a gene that is much more extensively induced by NGF than by EGF in PC12 cells. Both an antisense oligonucleotide for the UPAR mRNA and an antibody directed against UPAR protein block NGF-induced morphological and biochemical differentiation of PC12 cells; NGF-induced UPAR expression is required for subsequent NGF-driven differentiation.

Urokinase Receptor (CD87) Aggregation Triggers Phosphoinositide Hydrolysis and Intracellular Calcium Mobilization in Mononuclear Phagocytes

Leukocytes utilize urokinase receptors (uPAR; CD87) in adhesion, migration, and matrix proteolysis. uPAR aggregate at cell-substratum interfaces and at leading edges of migrating cells, so this study was undertaken to determine whether uPAR aggregation is capable of initiating activation signaling. Monocyte-like U937 cells were labeled with fluo-3-acetoxymethyl ester to quantitate intracellular Ca2+ concentrations ([Ca2+]i) by spectrofluorometry, and uPAR was aggregated by mAb cross-linking. uPAR aggregation induced highly reproducible increases in [Ca2+]i of 103.0 ± 10.9 nM (p < 0.0001) and >3-fold increases in cellular d-myoinositol 1,4,5-trisphosphate (Ins(1,4,5)P3) levels. Similar increases in [Ca2+]i were also elicited by uPAR aggregation in human monocytes, but cross-linking a control IgG2a had no effect on [Ca2+]i. Selectively cross-linking uPA-occupied uPAR with an anti-uPA mAb produced smaller increases in [Ca2+]i, but fully saturating uPAR with exogenous uPA enhanced the [Ca2+]i response to equal the effect of aggregating uPAR directly. Increased [Ca2+]i was inhibited by thapsigargin, herbimycin A, and U73122, but only partially reduced by low extracellular [Ca2+], indicating that uPAR aggregation increases [Ca2+]i by activating phospholipase C through a tyrosine kinase-dependent mechanism, generating Ins(1,4,5)P3 and releasing Ca2+ from Ins(1,4,5)P3-sensitive intracellular stores. Cross-linking the β2 integrin CR3 could not duplicate the effect of uPAR cross-linking, and uPAR-triggered Ca2+ mobilization was not blocked by anti-CR3 mAbs. These results indicate that uPAR aggregation initiates phosphoinositide hydrolysis by mechanisms that are not strictly dependent on associated uPA or CR3.

Functions of the fibrinolytic system in human Ito cells and its control by basic fibroblast and platelet-derived growth factor

During liver fibrogenesis, hepatic stellate cells (HSC) proliferate and migrate under the influence of growth factors, including platelet-derived growth factor (PDGF) and basic-fibroblast growth factor (b-FGF). The plasminogen activation system regulates extracellular matrix (ECM) catabolism and cell movement. We evaluated the expression and biological functions of the plasminogen activation system in human HSC and its interaction with PDGF and b-FGF. Urokinase-plasminogen activator receptors (u-PAR) were measured by radioligand binding, cell cross-linking, immunoassay, and RNAse protection assay. u-PA and plasminogen activator inhibitors (PAIs) expression and activities were analyzed by zymography, immunoassay, and RNase protection assay. Cell migration and proliferation, studied in Boyden chambers and by microscopic counting, were evaluated after the addition of PDGF, b-FGF, and blockade with anti-u-PA, anti-u-PAR antibodies, and antisense oligodeoxynucleotides (aODN) against u-PAR mRNA. We have shown that HSC produce u-PAR, u-PA, and PAI-1. PDGF and b-FGF up-regulate u-PA and u-PAR, but not PAI-1, and exogenous addition of u-PA stimulates HSC proliferation, chemotaxis, and chemoinvasion. Inhibition of u-PA/u-PAR with antibodies against u-PA or u-PAR and with u-PAR aODN inhibit the proliferative, chemotactic, and chemoinvasive activity of PDGF and b-FGF. These findings indicate that u-PA and u-PAR are required for the mitogenic and chemoinvasive activity of PDGF and b-FGF on HSC.

Defective Internalization and Sustained Activation of Truncated Granulocyte Colony-Stimulating Factor Receptor Found in Severe Congenital Neutropenia/Acute Myeloid Leukemia

Acquired mutations truncating the C-terminal domain of the granulocyte colony-stimulating factor receptor (G-CSF-R) are found in about 20% of severe congenital neutropenia (SCN) patients, with this cohort of patients predisposed to acute myeloid leukemia (AML). In myeloid cells, such mutations act in a dominant-negative manner leading to hyperproliferation and lack of differentiation in response to G-CSF. However, why these truncated receptors are dominant in function over wild-type receptors has remained unclear. We report that ligand-induced internalization of truncated G-CSF-R is severely impaired compared with the wild-type receptor, which results in sustained activation of STAT proteins. Strikingly, in cells coexpressing both truncated and wild-type forms, the truncated receptors acted dominantly with regard to both internalization and sustained activation. Site-directed mutagenesis of the C-terminus showed that receptor tyrosines in this region were dispensable for internalization, whereas a di-leucine–containing motif in Box B3 played some role. However, loss of the di-leucine motif was not the critical determinant of the sustained activation status of truncated receptors. These data suggest that defective internalization, leading to extended receptor activation, is a major cause of the dominant hyperproliferative effect of truncated G-CSF receptors, which is only partially due to the loss of a di-leucine motif present in the Box B3 region of the full-length receptor.

Defective Internalization and Sustained Activation of Truncated Granulocyte Colony-Stimulating Factor Receptor Found in Severe Congenital Neutropenia/Acute Myeloid Leukemia

Acquired mutations truncating the C-terminal domain of the granulocyte colony-stimulating factor receptor (G-CSF-R) are found in about 20% of severe congenital neutropenia (SCN) patients, with this cohort of patients predisposed to acute myeloid leukemia (AML). In myeloid cells, such mutations act in a dominant-negative manner leading to hyperproliferation and lack of differentiation in response to G-CSF. However, why these truncated receptors are dominant in function over wild-type receptors has remained unclear. We report that ligand-induced internalization of truncated G-CSF-R is severely impaired compared with the wild-type receptor, which results in sustained activation of STAT proteins. Strikingly, in cells coexpressing both truncated and wild-type forms, the truncated receptors acted dominantly with regard to both internalization and sustained activation. Site-directed mutagenesis of the C-terminus showed that receptor tyrosines in this region were dispensable for internalization, whereas a di-leucine–containing motif in Box B3 played some role. However, loss of the di-leucine motif was not the critical determinant of the sustained activation status of truncated receptors. These data suggest that defective internalization, leading to extended receptor activation, is a major cause of the dominant hyperproliferative effect of truncated G-CSF receptors, which is only partially due to the loss of a di-leucine motif present in the Box B3 region of the full-length receptor.