Dual function of UNC-51-like kinase 3 (Ulk3) in the Sonic hedgehog signaling pathway.

The Sonic hedgehog (Shh) signaling pathway controls a variety of developmental processes and is implicated in tissue homeostasis maintenance and neurogenesis in adults. Recently, we identified Ulk3 as an active kinase able to positively regulate Gli proteins, mediators of the Shh signaling in mammals. Here, we provide several lines of evidence that Ulk3 participates in the transduction of the Shh signal also independently of its kinase activity. We demonstrate that Ulk3 through its kinase domain interacts with Suppressor of Fused (Sufu), a protein required for negative regulation of Gli proteins. Sufu blocks Ulk3 autophosphorylation and abolishes its ability to phosphorylate and positively regulate Gli proteins. We show that Shh signaling destabilizes the Sufu-Ulk3 complex and induces the release of Ulk3. We demonstrate that the Sufu-Ulk3 complex, when co-expressed with Gli2, promotes generation of the Gli2 repressor form, and that reduction of the Ulk3 mRNA level in Shh-responsive cells results in higher potency of the cells to transmit the Shh signal. Our data suggests a dual function of Ulk3 in the Shh signal transduction pathway and propose an additional way of regulating Gli proteins by Sufu, through binding to and suppression of Ulk3.

Hedgehog signalling: how to get from Smo to Ci and Gli.

The secreted morphogens of the Hedgehog family have important roles in normal development as well as in associated pathologies, including cancer. The Hedgehog signalling pathway has been studied in Drosophila and is thought to be conserved in vertebrates. Hedgehog elicits a signalling response that activates Smoothened (Smo). There is evidence of differences between Drosophila and vertebrates concerning signalling downstream of Smo, as well as in Smo itself. Here, we discuss this evidence and its importance for investigations of the pathway and related biology, as well as for the development of drugs targeting components of the pathway for treatment of associated pathologies.

Identification of a novel serine/threonine kinase ULK3 as a positive regulator of Hedgehog pathway.

The Hedgehog (Hh) signaling pathway plays crucial roles in embryonic development and is implicated in tissue homeostasis maintenance and neurogenesis in adults. Aberrant activation of Hh signaling is associated with various developmental abnormalities and several types of cancer. Genetic and biochemical studies ascertain serine/threonine kinase Fused (Fu) as a protein involved in Hh signaling in Drosophila. However, the role of Fu is not fully conserved in mammals suggesting involvement of other kinases in the mammalian Hh signaling pathway. In search of potential homologues to Drosophila and human Fu, we have cloned human serine/threonine kinase ULK3 and assessed its ability to regulate GLI transcription factors, mediators of SHH signaling. We demonstrate that ULK3 enhances endogenous and over-expressed GLI1 and GLI2 transcriptional activity in cultured cells, as assessed by GLI-luciferase reporter assay. Besides that, ULK3 alters subcellular localization of GLI1, as assessed by immunofluorescent staining and immunoblotting assays. We show that ULK3 is an autophosphorylated kinase and phosphorylates GLI proteins in vitro. We also demonstrate that ULK3 catalytical activity is crucial for its function in SHH pathway. We show that ULK3 is widely expressed and its expression is higher in a number of tissues where Shh signaling is known to be active. Our data suggest that serine/threonine kinase ULK3 is involved in the SHH pathway as a positive regulator of GLI proteins.

The tumor suppressor CYLD interacts with TRIP and regulates negatively nuclear factor kappaB activation by tumor necrosis factor.

Cylindromas are benign adnexal skin tumors caused by germline mutations in the CYLD gene. In most cases the second wild-type allele is lost in tumor tissue, suggesting that CYLD functions as tumor suppressor. CYLD is a protein of 956 amino acids harboring a functional deubiquitinating domain at the COOH-terminal end. To shed more light on the function of CYLD, we have performed a yeast two hybrid screen using an HaCaT cDNA library that identified the RING finger protein TRIP (TRAF-interacting protein) as interactor with full-length CYLD. Mapping of the interacting domains revealed that the central domain of CYLD binds to the COOH-terminal end of TRIP. Far Western analysis and coimmunoprecipitations in mammalian cells confirmed that full-length CYLD binds to the COOH-terminal domain of TRIP. Because TRIP is an inhibitor of nuclear factor (NF)-kappaB activation by tumor necrosis factor (TNF), the effect of CYLD on NF-kappaB activation was investigated in HeLa cells. The results established that CYLD down-regulates NF-kappaB activation by TNF-alpha. The inhibition by CYLD depends on the presence of the central domain interacting with TRIP and its deubiquitinating activity. These findings indicate that cylindromas arise through constitutive NF-kappaB activation leading to hyperproliferation and tumor growth.

Inhibition of GLI1 gene activation by Patched1.

Patched1 (PTCH1) is a human tumour suppressor that acts as an HH (Hedgehog) receptor protein and is important for embryonic patterning. PTCH1 mediates its effects through SMO (Smoothened) and represses the expression of HH target genes such as the transcription factor GLI1 (glioma 1) as well as PTCH1. Up-regulation of these genes has been observed in several cancer forms, including basal cell carcinoma, digestive track tumours and small cell lung cancer. The fact that PTCH1 down-regulates its own expression via 'negative feedback' is an important feature in HH signalling, as it keeps the balance between HH and PTCH1 activities that are essential for normal development. In the present study, we provide evidence that a novel mechanism allowing PTCH1 to maintain this balance may also exist. We show that gene activation by GLI1, the transcriptional effector of the pathway, can be down-regulated by PTCH1 without involvement of the canonical cascade of HH signalling events. Specifically, the SMO antagonist cyclopamine has no appreciable effects in blocking this PTCH1-mediated inhibition. Moreover, the negative GLI1 regulator SUFU (Suppressor of Fused) was also found to be dispensable. Additionally, deletion mapping of PTCH1 has revealed that the domains encompassed by amino acids 180-786 and 1058-1210 are of highest significance in inhibiting GLI1 gene activation. This contrasts with the importance of the PTCH1 C-terminal domain for HH signalling.

A potential role of alternative splicing in the regulation of the transcriptional activity of human GLI2 in gonadal tissues.

BACKGROUND: Mammalian Gli proteins are important transcription factors involved in the regulation of Sonic hedgehog signal transduction pathway. Association of Gli2 with mammalian development and human disease led us to study the structure and expression of the human GLI2. RESULTS: We show that the region encoding GLI2 repressor domain is subject to alternative splicing in the gonadal tissues and different cell lines. Two major alternatively spliced forms of GLI2 mRNA arise from skipping exon 3 (GLI2Delta3) or exons 4 and 5 (GLI2Delta4-5). Both forms contain premature translational stop codons in the GLI2 open reading frame (ORF) starting from exon 2. Translation of GLI2Delta3 and GLI2Delta4-5 in vitro, initiated from downstream AUG codons, produced N-terminally truncated proteins. In Gli-dependent transactivation assay, expression of GLI2Delta3 induced activation of the reporter gene similar to that of the full-length construct (GLI2fl) containing complete ORF. However, expression of the GLI2Delta4-5 resulted in about 10-fold increase in activation, suggesting that deletion of the major part of repressor domain was responsible for the enhanced activation of GLI2 protein. CONCLUSION: Our data suggest that in addition to proteolytic processing, alternative splicing may be another important regulatory mechanism for the modulation of repressor and activator properties of GLI2 protein.

Recombinant CD44-HABD is a novel and potent direct angiogenesis inhibitor enforcing endothelial cell-specific growth inhibition independently of hyaluronic acid binding.

CD44 is the main cellular receptor for hyaluronic acid (HA). We previously found that overexpression of CD44 inhibited tumor growth of mouse fibrosarcoma cells in mice. Here, we show that soluble recombinant CD44 HA-binding domain (CD44-HABD) acts directly onto endothelial cells by inhibiting endothelial cell proliferation in a cell-specific manner. Consequently, soluble recombinant CD44-HABD also blocked angiogenesis in vivo in chick and mouse, and thereby inhibited tumor growth of various origins at very low doses (0.25 mg/kg x day). The antiangiogenic effect of CD44 is independent of its HA-binding capacity, since mutants deficient in HA binding still maintain their antiangiogenic and antiproliferative properties. Recombinant CD44-HABD represents a novel class of angiogenesis inhibitors based on a cell-surface receptor.

Alternative first exons of PTCH1 are differentially regulated in vivo and may confer different functions to the PTCH1 protein.

The PTCH1 gene is a human tumour suppressor gene frequently mutated in basal cell carcinoma (BCC) and several other tumour types. It encodes a receptor for soluble factors of the hedgehog family. Binding of hedgehog to the receptor relieves its inhibitory action on the transmembrane co-receptor Smoh. In this study we describe alternative first exons of the PTCH1 tumour suppressor gene and show that they are differentially regulated in normal tissues, exon 1B being expressed at very low levels and the major mRNA species containing exon 1 or 1A. Exon 1B transcripts were found to be specifically upregulated in nodular BCCs. The different PTCH1 transcripts all encode proteins that interact with Smoh in doubly transfected cells. Furthermore, functional assays demonstrated that whereas all PTCH1 isoforms can inhibit the activity of SHH, only the PTCH1B isoform is capable of fully inhibiting Smoh activity. The results indicate that in tumour cells the PTCH1B promoter is specifically activated and importantly, that the N-terminal part of PTCH1 including exon 1B is required for full inhibition of Smoh signaling but not for physical interaction with Smoh.

Evaluation of transportan 10 in PEI mediated plasmid delivery assay.

Cell-penetrating peptides (CPPs) are novel high-capacity delivery vectors for different bioactive cargoes. We have evaluated the CPP transportan 10 (TP10) as a delivery vector in different in vitro plasmid delivery assays. Tested methods include: TP10 crosslinked to a plasmid via a peptide nucleic acid (PNA) oligomer, TP10 conjugation with polyethyleneimine (PEI), and addition of unconjugated TP10 to standard PEI transfection assay. We found that without additional DNA condensing agents, TP10 has poor transfection abilities. However, the presence of TP10 increases the transfection efficiency several folds compared to PEI alone. At as low concentrations as 0.6 nM, TP10-PNA constructs were found to enhance plasmid delivery up to 3.7-fold in Neuro-2a cells. Interestingly, the transfection efficiency was most significant at low PEI concentrations, allowing reduced PEI concentration without loss of gene delivery. No increase in cytotoxicity due to TP10 was observed and the uptake mechanism was determined to be endocytosis, as previously reported for PEI mediated transfection. In conclusion, TP10 can enhance PEI mediated transfection at relatively low concentrations and may help to develop future gene delivery systems with reduced toxicity.

A novel metalloprotease from Vipera lebetina venom induces human endothelial cell apoptosis.

A novel endothelial cell apoptosis inducing metalloprotease (VLAIP) was found in the snake venom of Vipera lebetina. This metalloprotease is a heterodimeric glycoprotein with molecular mass of about 106 kDa. The protease hydrolyzes azocasein, fibrinogen and oxidized insulin B-chain. The enzyme readily hydrolyzes the Aalpha-chain and more slowly Bbeta-chain of fibrinogen. VLAIP does not cleave fibrin. The complete amino acid sequences of the two different monomers of VLAIP are deduced from the nucleotide sequences of cDNAs encoding these proteins. The full-length cDNA sequences of the VLAIP-A and VLAIP-B encode open reading frames of 616 and 614 amino acids that include signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. VLAIP belongs to the metalloprotease/disintegrin family of reprolysins and has high identity with the proteins that induce apoptosis of endothelial cells. Treatment of HUVEC cells with VLAIP induces changes in the attachment of cells to the substrate and causes cell death. We demonstrated that VLAIP inhibits endothelial cell adhesion to extracellular matrix proteins: fibrinogen, fibronectin, vitronectin, collagen I, and collagen IV. The induction of apoptosis by VLAIP was shown by means of a typical DNA fragmentation pattern of apoptotic cells as well as by monitoring phosphatidylserine externalization using annexin V-FITC staining and flow cytometric analysis.

Expression of the PTCH1 tumor suppressor gene is regulated by alternative promoters and a single functional Gli-binding site.

The PTCH1 tumor suppressor gene encodes a receptor for secreted hedgehog (HH) ligands and is important for proper proliferation, differentiation and patterning in almost every tissue and organ during embryogenesis. The PTCH1 protein works as a negative regulator of the HH-signaling pathway by repressing downstream signaling by the coreceptor smoothened (SMOH). Mutations in PTCH1 lead to constitutive expression of HH target genes and a relationship between mutated PTCH1 and the most common tumor form in the Western world, Basal Cell Carcinoma (BCC) has been clearly established. We here show that PTCH1 is transcriptionally regulated by three independent promoters generating transcripts with alternative first exons. We demonstrate that only one of two putative Gli-binding sites that were identified in the promoter region of PTCH1 is functional, and that the transactivating Gli proteins, GLI1, Gli2 and GLI3, bind and enhance transcription through this site. Moreover, a strong repression of both basal and induced PTCH1 transcription was observed following expression of a truncated version of GLI3. Most interestingly, the upstream components in the HH-signaling cascade, Sonic HH (SHH) and SMOH, solely operate through the functional Gli-binding site because mutation of the Gli-binding site resulted in the disappearance of the enhanced transcription induced by the Gli proteins, as well as by SHH or SMOH. This finding suggests that transcriptional activation of the PTCH1 gene mediated via the HH-signaling pathway is dependent on the single functional Gli-binding site.

Purification, characterization and plasma half-life of PEGylated soluble recombinant non-HA-binding CD44.

BACKGROUND AND OBJECTIVES: The aim of this study was to increase the serum half-life of recombinant CD44 hyaluronan (HA) binding domain by PEGylation. We have previously found that recombinant soluble CD44 HA binding domain (CD44HABD) and its non-HA-binding triple mutant CD44HABD(R41AY78SY79S) (CD44-3MUT) inhibits angiogenesis and subcutaneous tumor growth. However, this ~12 kDa recombinant protein displays a high serum clearance rate. METHODS: Here, we report the purification of monomeric CD44-3MUT from urea solubilized inclusion bodies using weak anion exchange chromatography and gel filtration. To increase the serum residence time of CD44-3MUT we PEGylated the resulting protein using 20 kDa methoxy-PEG-propionaldehyde. RESULTS: PEGylation of CD44-3MUT prolonged its in vivo serum half-life about 70-fold from 0.03 to 1.8 hours. Along with extended plasma residence time, PEGylation also increased the systemic exposure. By cell impedance assay we confirmed that PEGylated CD44-3MUT maintained its in vitro function. The results from the impedance assay additionally demonstrate that the CD44-3MUT effect on endothelial cells is mediated by vimentin. CONCLUSIONS: In summary, we have developed a purification protocol for large-scale production of CD44-3MUT and generated a PEGylated form of CD44-3MUT. HA binding domain of CD44(CD44HABD) and its modified non-HA binding form (CD44-3MUT) inhibit angiogenesis and tumor growth in vivo without disturbing HA-binding functions. CD44-3MUT has been PEGylated for use as a new type of anti-angiogenic human drug. PEGylation of CD44-3MUT improved pharmacokinetic properties but retains its functional activity.

The transcriptional repressor domain of Gli3 is intrinsically disordered.

The transcription factor Gli3 is acting mainly as a transcriptional repressor in the Sonic hedgehog signal transduction pathway. Gli3 contains a repressor domain in its N-terminus from residue G106 to E236. In this study we have characterized the intracellular structure of the Gli3 repressor domain using a combined bioinformatics and experimental approach. According to our findings the Gli3 repressor domain while being intrinsically disordered contains predicted anchor sites for partner interactions. The obvious interaction partners to test were Ski and DNA; however, with both of these the structure of Gli3 repressor domain remained disordered. To locate residues important for the repressor function we mutated several residues within the Gli3 repressor domain. Two of these, H141A and H157N, targeting predicted helical regions, significantly decreased transcriptional repression and thus identify important functional parts of the domain.

Capillary electrophoresis with LED-induced native fluorescence detection for determination of isoquinoline alkaloids and their cytotoxicity in extracts of Chelidonium majus L.

In this study, we introduced a simple and sensitive method of capillary electrophoresis with ultraviolet light-emitting diode-induced native fluorescence (UV-LEDIF) detection for the determination of isoquinoline alkaloids in extracts of Chelidonium majus L. Samples were extracted with acidic methanol and the extracts were directly analysed by CE. Simultaneous determination of protopine, chelidonine, coptisine, sanguinarine, allocryptopine, chelerythrine and stylopine was performed in 20mM phosphate buffer (pH 3.1). The baseline separation of these alkaloids was finished within 20 min. As these alkaloids have native fluorescence, they were directly detected using the commercially available UV light emitting diode without troublesome fluorescent derivatisation. Satisfactory LOD values were obtained for the studied compounds considering their appearance in natural extracts. Lower limits of detection were 0.05 µg/mL for protopine, 0.06 µg/mL for stylopine and allocryptopine, 0.07 µg/mL for chelidonine, 0.22 µg/mL for sanguinarine, 1.7 µg/mL for chelerythrine and 5.5 µg/mL for coptisine. The developed method was successfully applied to determine the contents of seven alkaloids in the aerial parts of Chelidonium majus L, which varied from 0.025 to 0.763% (w/w). Also, to demonstrate the potential of the proposed CE method, an estimation of the cytotoxic properties of selected Celandine alkaloids in a natural extract was carried out.

Soluble CD44 interacts with intermediate filament protein vimentin on endothelial cell surface.

CD44 is a cell surface glycoprotein that functions as hyaluronan receptor. Mouse and human serum contain substantial amounts of soluble CD44, generated either by shedding or alternative splicing. During inflammation and in cancer patients serum levels of soluble CD44 are significantly increased. Experimentally, soluble CD44 overexpression blocks cancer cell adhesion to HA. We have previously found that recombinant CD44 hyaluronan binding domain (CD44HABD) and its non-HA-binding mutant inhibited tumor xenograft growth, angiogenesis, and endothelial cell proliferation. These data suggested an additional target other than HA for CD44HABD. By using non-HA-binding CD44HABD Arg41Ala, Arg78Ser, and Tyr79Ser-triple mutant (CD443MUT) we have identified intermediate filament protein vimentin as a novel interaction partner of CD44. We found that vimentin is expressed on the cell surface of human umbilical vein endothelial cells (HUVEC). Endogenous CD44 and vimentin coprecipitate from HUVECs, and when overexpressed in vimentin-negative MCF-7 cells. By using deletion mutants, we found that CD44HABD and CD443MUT bind vimentin N-terminal head domain. CD443MUT binds vimentin in solution with a Kd in range of 12-37 nM, and immobilised vimentin with Kd of 74 nM. CD443MUT binds to HUVEC and recombinant vimentin displaces CD443MUT from its binding sites. CD44HABD and CD443MUT were internalized by wild-type endothelial cells, but not by lung endothelial cells isolated from vimentin knock-out mice. Together, these data suggest that vimentin provides a specific binding site for soluble CD44 on endothelial cells.

Sonic Hedgehog pathway activity in prostate cancer.

Abnormal activation of the Sonic hedgehog (Shh) signaling pathway has been demonstrated in a number of human tumors, including prostate cancer. The study aimed to assess the activity of Shh pathway components (Shh, Gli1, Gli2 and Gli3), as well as the proliferation markers FoxA1 and Notch1 during cancer progression in the transgenic adenocarcinoma of the mouse prostate (TRAMP). We evaluated changes in respective proteins by immunohistochemistry at three time points (12, 17 and 21 weeks of age) in the tissue of TRAMP and C57Bl/6 mice. Moreover, the expression of mRNA of these proteins was assessed. The present study shows a significant age-dependent increase in the number of Shh, Gli1, Gli3 and FoxA1-positive prostate cells and a decrease in Gli2-positive cells in TRAMP. The study also supports the hypothesis that the development of prostate cancer and its metastasis is associated with activation of the Shh signaling pathway.

Smoothened agonist augments proliferation and survival of neural cells.

Sonic hedgehog signaling pathway is important in developmental processes like dorsoventral neural tube patterning, neural stem cell proliferation and neuronal and glial cell survival. Shh is also implicated in the regulation of the adult hippocampal neurogenesis. Recently, nonpeptidyl Smoothened activators of the Shh pathway have been identified. The aim of this study was to investigate the effects of chlorobenzothiophene-containing molecule, Smo agonist (SAG), which has been shown to activate Shh signaling pathway, in neurogenesis and neuronal survival in in vitro and in vivo models. Our in vitro experiments showed that SAG induces increased expression of Gli1 mRNA, transcriptional target and mediator of Shh signal. In vitro experiments also demonstrated that SAG in low-nanomolar concentrations induces proliferation of neuronal and glial precursors without affecting the differentiation pattern of newly produced cells. In contrast to Shh, SAG did not induce neurotoxicity in neuronal cultures. The SAG and Shh treatment also promoted the survival of newly generated neural cells in the dentate gyrus after their intracerebroventricular administration to adult rats. We propose that SAG and similar compounds represent attractive molecules to be developed for treatment of disorders where stimulation of the generation and survival of new neural cells would be beneficial.

Identification of the gene transcription repressor domain of Gli3.

Gli transcription factors are downstream targets of the Hedgehog signaling pathway. Two of the three Gli proteins harbor gene transcription repressor function in the N-terminal half. We have analyzed the sequences and identified a potential repressor domain in Gli2 and Gli3 and have tested this experimentally. Overexpression studies confirm that the N-terminal parts harbor gene repression activity and we mapped the minimal repressor to residues 106 till 236 in Gli3. Unlike other mechanisms that inhibit Gli induced gene transcription, the repressor domain identified here does not utilize Histone deacetylases (HDACs) to achieve repression, as confirmed by HDAC inhibition studies and pull-down assays. This distinguishes the identified domain from other regulatory parts with negative influence on transcription.

Generation and characterization of a single-chain Fv antibody against G, a hedgehog signaling pathway transcription factor.

Gli3 is a key regulator of development, controlling multiple patterning steps. Here we report the generation of a scFv antibody specific to the repressor domain of human Gli3. We show that this scFv retains the binding capacity of its parent anti-Gli3 monoclonal antibody derived from hybridoma clone 5E1. When expressed in mammalian cells, the anti-Gli3 scFv co-localizes with intracellular Gli3. Immunocytochemical staining of the intrabody in Gli3-positive TM4 cells shows a distinct perinuclear cytoplasmic localization. Such a scFv constitutes a useful tool for studying transcriptional regulation of the hedgehog pathway in mammals and offers a starting point for developing novel Gli-related therapeutic intrabodies.

A possible role of mouse Fused (STK36) in Hedgehog signaling and Gli transcription factor regulation.

The segment polarity gene Fused (Fu) encodes a putative serine-threonine kinase Fu, which has been shown to play a key role in the Hedgehog signaling pathway of Drosophila. Human FU (hFU) has been shown to enhance the activity of Gli transcription factors, targets of the signaling pathway. However, Fu ( -/- ) mice do not show aberrant embryonic development indicating that mouse Fu (mFu) is dispensable for Hedgehog signaling until birth. In order to investigate if there are important differences between hFU and mFu, we cloned the cDNA, analyzed expression and tested the ability of mFu to regulate Gli proteins. Of the tested tissues only brain and testis showed significant expression. However, in transient overexpression analyses mFu was able to enhance Gli induced transcription in a manner similar to hFU. Thus, we turned to RNAi in order to test if mFu would be important for Hedgehog signaling after all. In one cell line with reduced mFu expression the Hedgehog signaling was severely hampered, indicating that mFu may have a role in Hedgehog signaling and Gli regulation in some cellular situations.