Veratramine inhibits porcine epidemic diarrhea virus entry through macropinocytosis by suppressing PI3K/Akt pathway.

Porcine epidemic diarrhea (PED) is a contagious intestinal disease caused by α-coronavirus porcine epidemic diarrhea virus (PEDV). At present, no effective vaccine is available to prevent the disease. Therefore, research for novel antivirals is important. This study aimed to identify the antiviral mechanism of Veratramine (VAM), which actively inhibits PEDV replication with a 50 % inhibitory concentration (IC50) of ∼5 µM. Upon VAM treatment, both PEDV-nucleocapsid (N) protein level and virus titer decreased significantly. The time-of-addition assay results showed that VAM could inhibit PEDV replication by blocking viral entry. Importantly, VAM could inhibit PEDV-induced phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) activity and further suppress micropinocytosis, which is required for PEDV entry. In addition, PI3K inhibitor LY294002 showed anti-PEDV activity by blocking viral entry as well. Taken together, VAM possessed anti-PEDV properties against the entry stage of PEDV by inhibiting the macropinocytosis pathway by suppressing the PI3K/Akt pathway. VAM could be considered as a lead compound for the development of anti-PEDV drugs and may be used during the viral entry stage of PEDV infection.

Residue 6.43 defines receptor function in class F GPCRs.

The class Frizzled of G protein-coupled receptors (GPCRs), consisting of ten Frizzled (FZD1-10) subtypes and Smoothened (SMO), remains one of the most enigmatic GPCR families. While SMO relies on cholesterol binding to the 7TM core of the receptor to activate downstream signaling, underlying details of receptor activation remain obscure for FZDs. Here, we aimed to investigate the activation mechanisms of class F receptors utilizing a computational biology approach and mutational analysis of receptor function in combination with ligand binding and downstream signaling assays in living cells. Our results indicate that FZDs differ substantially from SMO in receptor activation-associated conformational changes. SMO manifests a preference for a straight TM6 in both ligand binding and functional readouts. Similar to the majority of GPCRs, FZDs present with a kinked TM6 upon activation owing to the presence of residue P6.43. Functional comparison of FZD and FZD P6.43F mutants in different assay formats monitoring ligand binding, G protein activation, DVL2 recruitment and TOPflash activity, however, underlines further the functional diversity among FZDs and not only between FZDs and SMO.

Cyclopamine sensitizes glioblastoma cells to temozolomide treatment through Sonic hedgehog pathway.

AIM: Glioblastoma is an extremely aggressive glioma, resistant to radio and chemotherapy usually performed with temozolomide. One of the main reasons for glioblastoma resistance to conventional therapies is due to the presence of cancer stem-like cells. These cells could recapitulate some signaling pathways important for embryonic development, such as Sonic hedgehog. Here, we investigated if the inhibitor of the Sonic hedgehog pathway, cyclopamine, could potentiate the temozolomide effect in cancer stem-like cells and glioblastoma cell lines in vitro. MAIN METHODS: The viability of glioblastoma cells exposed to cyclopamine and temozolomide treatment was evaluated by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay while the induction of apoptosis was assessed by western blot. The stemness properties of glioma cells were verified by clonogenic and differentiation assay and the expression of stem cell markers were measured by fluorescence microscopy and western blot. KEY FINDINGS: The glioblastoma viability was reduced by cyclopamine treatment. Cyclopamine potentiated temozolomide treatment in glioblastoma cell lines by inducing apoptosis through activation of caspase-3 cleaved. Conversely, the combined treatment of cyclopamine and temozolomide potentiated the stemness properties of glioblastoma cells by inducing the expression of SOX-2 and OCT-4. SIGNIFICANCE: Cyclopamine plays an effect on glioblastoma cell lines but also sensibilize them to temozolomide treatment. Thus, first-line treatment with Sonic hedgehog inhibitor followed by temozolomide could be used as a new therapeutic strategy for glioblastoma patients.

Protective effect of sonic hedgehog against oxidized low­density lipoprotein­induced endothelial apoptosis: Involvement of NF­κB and Bcl­2 signaling.

Sonic hedgehog (Shh) is pivotally important in embryonic and adult blood vessel development and homeostasis. However, whether Shh is involved in atherosclerosis and plays a role in endothelial apoptosis induced by oxidized low­density lipoprotein (ox­LDL) has not been reported. The present study used recombinant Shh­N protein (rShh­N) and a plasmid encoding the human Shh gene (phShh) to investigate the role of Shh in ox­LDL­mediated human umbilical vein endothelial cell (HUVEC) apoptosis. The present study found that ox­LDL was able to induce apoptosis in HUVECs and that Shh protein expression was downregulated. Furthermore, pretreatment with rShh­N or transfection with phShh increased anti­apoptosis protein Bcl­2 expression and decreased cell apoptosis. These protective effects of rShh­N could be abolished by cyclopamine, which is a hedgehog signaling inhibitor. Furthermore, a co­immunoprecipitation assay was performed to demonstrate that Shh interacted with NF­κB p65 in HUVECs. Additionally, ox­LDL upregulated the phosphorylation of NF­κB p65 and inhibitor of NF­κB­α (IκBα), and these effects decreased notably following rShh­N and phShh treatment. Together, the present findings suggested that Shh serves an important protective role in alleviating ox­LDL­mediated endothelial apoptosis by inhibiting the NF­κB signaling pathway phosphorylation and Bcl­2 mediated mitochondrial signaling.

Cyclopamine Suppresses Human Esophageal Carcinoma Cell Growth by Inhibiting Glioma-Associated Oncogene Protein-1, a Marker of Human Esophageal Carcinoma Progression.

BACKGROUND Esophageal carcinoma is a common gastrointestinal tumor in humans. Cyclopamine, a Hedgehog (Hh)-pathway-specific inhibitor, is an effective chemotherapeutic drug for suppressing tumor cell differentiation, with unclear mechanisms. We investigated glioma-associated oncogene protein-1 (Gli-1) expression in human esophageal carcinoma tissue and the inhibition of cyclopamine on EC9706 esophageal carcinoma cell growth. MATERIAL AND METHODS Gli-1 in tumor tissue was measured by immunohistochemistry (IHC). EC9706 cells were treated with different concentrations of cyclopamine and incubated for different times. MTT method, flow cytometry, and Acridine orange/ethidium bromide (AO/EB) double-fluorescence staining were applied to detect cell proliferation and apoptosis. Western blot (WB) analysis was performed to assess Gli-1 expression. RESULTS Gli-1 was associated with patient age, gender, lymphatic metastasis, tumor recurrence, and stage, with significantly (P<0.05) positive correlations with age, lymphatic metastasis, tumor recurrence, and stage. At 12 h (F=214.57), 24 h (F=76.832), 48 h (F=236.90), and 72 h (F=164.55), the higher the concentration of cyclopamine, the higher the inhibition rate of suppressing EC9706 proliferation, and this effect was significant (P<0.05). The number of early-apoptosis cells increased as the concentration of cyclopamine increased. Morphology of EC9706 cells appeared as round with rough edges, karyopyknosis, and karyorrhexis. After 48 h, apoptosis rates of EC9706 cells treated with different concentrations of cyclopamine were (7.73±1.25)% at 2.5 µM, (13.37±1.42)% at 5.0 µM, (22.3±2.92)% at 10.0 µM, and (33.57±1.75)% at 20.0 µM, and the effect was dose-dependent. Gli-1 was obviously reduced after cyclopamine treatment and the effect was dose-dependent. CONCLUSIONS Gli-1 is highly expressed in human esophageal carcinoma, and could be a marker for use in assessing tumor stage and the deciding on treatment target.

Sonic hedgehog signalling regulates the self-renewal and proliferation of skin-derived precursor cells in mice.

OBJECTIVES: The sonic hedgehog (Shh) signalling pathway has an important role in the maintenance of various stem cells and organogenesis during development. However, the effect of Shh in skin-derived precursors (SKPs), which have the capacity for multipotency and self-renewal, is not yet clear. The present study investigated the effects of the Shh signalling pathway on the proliferation and self-renewal of murine SKPs (mSKPs). METHODS: The Shh signalling pathway was activated by treatment with purmorphamine (Shh agonist) or recombinant Shh in mSKPs. Cyclopamine (Shh antagonist) or GANT-61 (Gli inhibitor) was used to inhibit the pathway. Western blot, qPCR, and immunofluorescence were used to analyse the expression of genes related to self-renewal, stemness, epithelial-mesenchymal transition (EMT) and the Shh signalling pathway. In addition, cell proliferation and apoptosis were examined. RESULTS: Inhibiting the Shh signalling pathway reduced mSKP proliferation and sphere formation, but increased apoptosis. Activating this signalling pathway produced opposite results. The Shh signalling pathway also controlled the EMT phenotype in mSKPs. Moreover, purmorphamine recovered the self-renewal and proliferation of aged mSKPs. CONCLUSION: Our results suggest that the Shh signalling pathway has an important role in the proliferation, self-renewal and apoptosis of mSKPs. These findings also provide a better understanding of the cellular mechanisms underlying SKP self-renewal and apoptosis that allow more efficient expansion of SKPs.

Structural Basis of Smoothened Activation in Hedgehog Signaling.

The seven-transmembrane-spanning protein Smoothened is the central transducer in Hedgehog signaling, a pathway fundamental in development and in cancer. Smoothened is activated by cholesterol binding to its extracellular cysteine-rich domain (CRD). How this interaction leads to changes in the transmembrane domain and Smoothened activation is unknown. Here, we report crystal structures of sterol-activated Smoothened. The CRD undergoes a dramatic reorientation, allosterically causing the transmembrane domain to adopt a conformation similar to active G-protein-coupled receptors. We show that Smoothened contains a unique inhibitory π-cation lock, which is broken on activation and is disrupted in constitutively active oncogenic mutants. Smoothened activation opens a hydrophobic tunnel, suggesting a pathway for cholesterol movement from the inner membrane leaflet to the CRD. All Smoothened antagonists bind the transmembrane domain and block tunnel opening, but cyclopamine also binds the CRD, inducing the active transmembrane conformation. Together, these results define the mechanisms of Smoothened activation and inhibition.

Discovery of a Novel Inhibitor of the Hedgehog Signaling Pathway through Cell-based Compound Discovery and Target Prediction.

Cell-based assays enable monitoring of small-molecule bioactivity in a target-agnostic manner and help uncover new biological mechanisms. Subsequent identification and validation of the small-molecule targets, typically employing proteomics techniques, is very challenging and limited, in particular if the targets are membrane proteins. Herein, we demonstrate that the combination of cell-based bioactive-compound discovery with cheminformatic target prediction may provide an efficient approach to accelerate the process and render target identification and validation more efficient. Using a cell-based assay, we identified the pyrazolo-imidazole smoothib as a new inhibitor of hedgehog (Hh) signaling and an antagonist of the protein smoothened (SMO) with a novel chemotype. Smoothib targets the heptahelical bundle of SMO, prevents its ciliary localization, reduces the expression of Hh target genes, and suppresses the growth of Ptch+/- medulloblastoma cells.

Elucidating steroid alkaloid biosynthesis in Veratrum californicum: production of verazine in Sf9 cells.

Steroid alkaloids have been shown to elicit a wide range of pharmacological effects that include anticancer and antifungal activities. Understanding the biosynthesis of these molecules is essential to bioengineering for sustainable production. Herein, we investigate the biosynthetic pathway to cyclopamine, a steroid alkaloid that shows promising antineoplastic activities. Supply of cyclopamine is limited, as the current source is solely derived from wild collection of the plant Veratrum californicum. To elucidate the early stages of the pathway to cyclopamine, we interrogated a V. californicum RNA-seq dataset using the cyclopamine accumulation profile as a predefined model for gene expression with the pattern-matching algorithm Haystack. Refactoring candidate genes in Sf9 insect cells led to discovery of four enzymes that catalyze the first six steps in steroid alkaloid biosynthesis to produce verazine, a predicted precursor to cyclopamine. Three of the enzymes are cytochromes P450 while the fourth is a γ-aminobutyrate transaminase; together they produce verazine from cholesterol.

Metabolism Study of Veratramine Associated with Neurotoxicity by Using HPLC-MSn.

Veratramine (VAM) is the major lipid-soluble alkaloid existing in Veratrum nigrum L. that has been demonstrated to exert neurotoxic effects. To better understand the potential mechanism of neurotoxicity of VAM, VAM-induced DNA damage was measured in the cerebellum and cerebral cortex of mice after a 7-day repetitive oral dose by using single-cell gel electrophoresis (comet assay). A method based on high-performance liquid chromatography-electrospray ionization tandem mass spectrometry was developed for the determination of VAM and its in vivo and in vitro metabolites, to establish the potential correlation between metabolites and neurotoxicity. In vitro experiment was carried out using rat liver microsomes, whereas the in vivo study was conducted on rats at a single dose of 3 mg/kg. The results showed that VAM caused DNA damage in the cerebellum and cerebral cortex of mice in a dose-dependent manner. Phenyl mono-oxidation, sulfate conjugation and phenyl di-oxidation were proposed to be the main in vivo metabolic pathways of VAM, whereas the major in vitro metabolic pathways were phenyl mono-oxidation, hydroxylation and methylation. Phenyl-oxidation reaction was likely to be associated with reactive oxygen species production, leading to the DNA damage in the mouse brain.

The pre-clinical absorption, distribution, metabolism and excretion properties of IPI-926, an orally bioavailable antagonist of the hedgehog signal transduction pathway.

1. IPI-926 is a novel semisynthetic cyclopamine derivative that is a potent and selective Smoothened inhibitor that blocks the hedgehog signal transduction pathway. 2. The in vivo clearance of IPI-926 is low in mouse and dog and moderate in monkey. The volume of distribution is high across species. Oral bioavailability ranges from moderate in monkey to high in mouse and dog. Predicted human clearance using simple allometry is low (24 L h(-1)), predicted volume of distribution is high (469 L) and predicted half-life is long (20 h). 3. IPI-926 is highly bound to plasma proteins and has minimal interaction with human α-1-acid glycoprotein. 4. In vitro metabolic stability ranges from stable to moderately stable. Twelve oxidative metabolites were detected in mouse, rat, dog, monkey and human liver microsome incubations and none were unique to human. 5. IPI-926 is not a potent reversible inhibitor of CYP1A2, 2C8, 2C9 or 3A4 (testosterone). IPI-926 is a moderate inhibitor of CYP2C19, 2D6 and 3A4 (midazolam) with KI values of 19, 16 and 4.5 µM, respectively. IPI-926 is both a substrate and inhibitor (IC50 = 1.9 µM) of P-glycoprotein. 6. In summary, IPI-926 has desirable pre-clinical absorption, distribution, metabolism and excretion properties.

Aberrant activation of hedgehog pathway in nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC) is a very common head and neck cancer in southern china. Despite advances in surgical and chemotherapeutic approaches, its prognosis is still not promising. Hedgehog signaling pathway was reported to be involved in a number of cancers including head and neck. However, it remains unclear regarding the role of this pathway in NPC. By real-time PCR, we found Ptch1, Smo, and Gli-1 were expressed in all human nasopharyngeal epithelial tissues and cell lines. Compared with nasopharyngeal normal epithelial tissues, the mRNA expression level of Gli-1 was higher in carcinoma and nasopharyngitis (NPI) epithelial tissues. While compared with nasopharyngitis epithelia, the mRNA expression level of Ptch1 was lower in carcinoma epithelia and normal epithelia. The expressions of Smo mRNA were not significantly different among these epithelial tissues. Immunohistochemistry analysis revealed that the expression level of Gli-1 was higher in NPC than NPI. Thus, our data indicated that aberrant activation of hedgehog pathway in NPC. Furthermore, blocking the pathway with cyclopamine inhibited the proliferation of NPC epithelia cell lines. In addition, blockade of the pathway in three NPC cell lines with cyclopamine-induced tumor cell apoptosis. The transcription of hedgehog target genes also is inhibited by cyclopamine. These data suggested that hedgehog pathway may sustain nasopharyngeal tumor growth. Our data demonstrated that hedgehog signaling pathway was involved in NPC pathogenesis and might be a novel therapeutic target for NPC.

The insecticide synergist piperonyl butoxide inhibits hedgehog signaling: assessing chemical risks.

The spread of chemicals, including insecticides, into the environment often raises public health concerns, as exemplified by a recent epidemiologic study associating in utero piperonyl butoxide (PBO) exposure with delayed mental development. The insecticide synergist PBO is listed among the top 10 chemicals detected in indoor dust; a systematic assessment of risks from PBO exposure, as for many toxicants unfortunately, may be underdeveloped when important biological targets that can cause toxicity are unknown. Hedgehog/Smoothened signaling is critical in neurological development. This study was designed to use novel high-throughput in vitro drug screening technology to identify modulators of Hedgehog signaling in environmental chemicals to assist the assessment of their potential risks. A directed library of 1408 environmental toxicants was screened for Hedgehog/Smoothened antagonist activity using a high-content assay that evaluated the interaction between Smoothened and ßarrestin2 green fluorescent protein. PBO was identified as a Hedgehog/Smoothened antagonist capable of inhibiting Hedgehog signaling. We found that PBO bound Smoothened and blocked Smoothened overexpression-induced Gli-luciferase reporter activity but had no effect on Gli-1 downstream transcriptional factor-induced Gli activity. PBO inhibited Sonic Hedgehog ligand-induced Gli signaling and mouse cerebellar granular precursor cell proliferation. Moreover, PBO disrupted zebrafish development. Our findings demonstrate the value of high-throughput target-based screening strategies that can successfully evaluate large numbers of environmental toxicants and identify key targets and unknown biological activity that is helpful in properly assessing potential risks.

Full regeneration of the tribasal Polypterus fin.

Full limb regeneration is a property that seems to be restricted to urodele amphibians. Here we found that Polypterus, the most basal living ray-finned fish, regenerates its pectoral lobed fins with a remarkable accuracy. Pectoral Polypterus fins are complex, formed by a well-organized endoskeleton to which the exoskeleton rays are connected. Regeneration initiates with the formation of a blastema similar to that observed in regenerating amphibian limbs. Retinoic acid induces dose-dependent phenotypes ranging from inhibition of regeneration to apparent anterior-posterior duplications. As in all developing tetrapod limbs and regenerating amphibian blastema, Sonic hedgehog is expressed in the posterior mesenchyme during fin regeneration. Hedgehog signaling plays a role in the regeneration and patterning processes: an increase or reduction of fin bony elements results when this signaling is activated or disrupted, respectively. The tail fin also regenerates but, in contrast with pectoral fins, regeneration can resume after release from the arrest caused by hedgehog inhibition. A comparative analysis of fin phenotypes obtained after retinoic acid treatment or altering the hedgehog signaling levels during regeneration allowed us to assign a limb tetrapod equivalent segment to Polypterus fin skeletal structures, thus providing clues to the origin of the autopod. We propose that appendage regeneration was a common property of vertebrates during the fin to limb transition.

The Hedgehog morphogen in myocardial ischemia-reperfusion injury.

The developmental Hedgehog (Hh) protein family is known to be pivotal in many embryonic patterning events and the number of processes in which Hh plays an essential role is expanding persistently. Recently, it has become clear that the Hh pathway is not only active in the developing embryo but also in the adult organism. For example, Hh has been suggested to salvage ischemia-induced tissue damage although endogenous Hh might be deleterious during the early phase of myocardial ischemia-reperfusion. The current review provides an overview of the history of Hh biology and discusses some novel insights on Hh cell biology. Hh function in pathophysiology as well as recent findings concerning Hh signaling in ischemia models, especially in light of cardiovascular disease, is discussed in more detail and future perspectives are proposed.

BMP7 and SHH regulate Pax2 in mouse retinal astrocytes by relieving TLX repression.

Pax2 is essential for development of the neural tube, urogenital system, optic vesicle, optic cup and optic tract. In the eye, Pax2 deficiency is associated with coloboma, a loss of astrocytes in the optic nerve and retina, and abnormal axonal pathfinding of the ganglion cell axons at the optic chiasm. Thus, appropriate expression of Pax2 is essential for astrocyte determination and differentiation. Although BMP7 and SHH have been shown to regulate Pax2 expression, the molecular mechanism by which this regulation occurs is not well understood. In this study, we determined that BMP7 and SHH activate Pax2 expression in mouse retinal astrocyte precursors in vitro. SHH appeared to play a dual role in Pax2 regulation; 1) SHH may regulate BMP7 expression, and 2) the SHH pathway cooperates with the BMP pathway to regulate Pax2 expression. BMP and SHH pathway members can interact separately or together with TLX, a repressor protein in the tailless transcription factor family. Here we show that the interaction of both pathways with TLX relieves the repression of Pax2 expression in mouse retinal astrocytes. Together these data reveal a new mechanism for the cooperative actions of signaling pathways in astrocyte determination and differentiation and suggest interactions of regulatory pathways that are applicable to other developmental programs.

Sonic hedgehog: its expression in a healing cornea and its role in neovascularization.

PURPOSE: To examine if sonic hedgehog (Shh) is involved in tissue neovascularization by using cell culture and an animal cornea. METHODS: The effects of exogenous Shh (5.0 nM), vascular endothelial growth factor (VEGF), and/or a Shh signal inhibitor (2.5 or 10.0 muM cyclopamine) on vessel-like tube formation of vascular endothelial cells were examined in vitro. The effects of Shh on the expression of angiogenic cytokines in cultured cell types were examined in cultured cells. The expression of Shh and its receptor, Patched 1 (Ptc), was examined in a vascularized mouse cornea during post-alkali burn healing. The effect of exogenous Shh on corneal neovascularization in vivo was assayed using a rat cornea system. The effect of a topical injection of cyclopamine on cauterization-induced corneal neovascularization was then studied. RESULTS: Adding Shh promoted vessel-like tube formation of vascular endothelial cells. This effect was counteracted by addition of cyclopamine. Cyclopamine did not affect VEGF-enhanced tube formation. Shh did not affect the expression levels of angiogenic cytokines in cultured cell types. mRNA and protein expression levels of Shh and Ptc were under the detection limit in an uninjured cornea, but Shh but not Ptc was upregulated in a healing, alkali-burned, vascularized cornea. Exogenous Shh promoted neovascularization (NV) formation in vivo in a rat cornea. Topical cyclopmine blocked Gli signaling (blocked translocation of Gli3) and the length of neovascularization in the peripheral cornea post-cauterization as compared with the control vehicle-treated cornea. CONCLUSIONS: Shh enhances endothelial tube formation independently through VEGF signaling in vitro. Shh signaling is involved in the development of unfavorable corneal neovascularization in animal corneas.

Smoothened adopts multiple active and inactive conformations capable of trafficking to the primary cilium.

Activation of Hedgehog (Hh) signaling requires the transmembrane protein Smoothened (Smo), a member of the G-protein coupled receptor superfamily. In mammals, Smo translocates to the primary cilium upon binding of Hh ligands to their receptor, Patched (Ptch1), but it is unclear if ciliary trafficking of Smo is sufficient for pathway activation. Here, we demonstrate that cyclopamine and jervine, two structurally related inhibitors of Smo, force ciliary translocation of Smo. Treatment with SANT-1, an unrelated Smo antagonist, abrogates cyclopamine- and jervine-mediated Smo translocation. Further, activation of protein kinase A, either directly or through activation of Galphas, causes Smo to translocate to a proximal region of the primary cilium. We propose that Smo adopts multiple inactive and active conformations, which influence its localization and trafficking on the primary cilium.

Evidence for allosteric interactions of antagonist binding to the smoothened receptor.

The Smoothened receptor (Smo) mediates hedgehog (Hh) signaling critical for development, cell growth, and migration, as well as stem cell maintenance. Aberrant Hh signaling pathway activation has been implicated in a variety of cancers, and small-molecule antagonists of Smo have entered human clinical trials for the treatment of cancer. Here, we report the biochemical characterization of allosteric interactions of agonists and antagonists for Smo. Binding of two radioligands, [(3)H]3-chloro-N-[trans-4-(methylamino)cyclohexyl]-N-{[3-(4-pyridinyl)-phenyl]methyl}-1-benzothiophene-2-carboxamide (SAG-1.3) (agonist) and [(3)H]cyclopamine (antagonist), was characterized using human Smo expressed in human embryonic kidney 293F membranes. We observed full displacement of [(3)H]cyclopamine by all Smo agonist and antagonist ligands examined. N-[(1E)-(3,5-Dimethyl-1-phenyl-1H-pyrazol-4-yl)methylidene]-4-(phenylmethyl)-1-piperazinamine (SANT-1), an antagonist, did not fully inhibit the binding of [(3)H]SAG-1.3. In a functional cell-based beta-lactamase reporter gene assay, SANT-1 and N-[3-(1H-benzimidazol-2-yl)-4-chlorophenyl]-3,4,5-tris(ethyloxy)-benzamide (SANT-2) fully inhibited 3-chloro-4,7-difluoro-N-[trans-4-(methylamino)cyclohexyl]-N-{[3-(4-pyridinyl)phenyl]methyl}-1-benzothiophene-2-carboxamide (SAG-1.5)-induced Hh pathway activation. Detailed "Schild-type" radioligand binding analysis with [(3)H]SAG-1.3 revealed that two structurally distinct Smoothened receptor antagonists, SANT-1 and SANT-2, bound in a manner consistent with that of allosteric modulation. Our mechanism of action characterization of radioligand binding to Smo combined with functional data provides a better understanding of small-molecule interactions with Smo and their influence on the Hh pathway.

ER71 acts downstream of BMP, Notch, and Wnt signaling in blood and vessel progenitor specification.

FLK1-expressing (FLK1(+)) mesoderm generates blood and vessels. Here, we show that combined BMP, Notch, and Wnt signaling is necessary for efficient FLK1(+) mesoderm formation from embryonic stem cells (ESCs). Inhibition of BMP, Notch, and Wnt signaling pathways greatly decreased the generation of FLK1(+) mesoderm and expression of the Ets transcription factor Er71. Enforced expression of ER71 in ESCs resulted in a robust induction of FLK1(+) mesoderm; rescued the generation of FLK1(+) mesoderm when blocked by BMP, Notch, and Wnt inhibition; and enhanced hematopoietic and endothelial cell generation. Er71-deficient mice had greatly reduced FLK1 expression, died early in gestation, and displayed severe blood and vessel defects that are highly reminiscent of the Flk1 null mouse phenotype. Collectively, we provide compelling evidence that ER71 functions downstream of BMP, Notch, and Wnt signals and regulates FLK1(+) mesoderm, blood, and vessel development.