Mechanism of inhibition of the tumor suppressor Patched by Sonic Hedgehog

Neuroinflammatory Pathways Associated with Chronic Post-Thoracotomy Pain: A Review of Current Literature

Chronic post-thoracotomy pain (CPTP) is a major clinical problem that affects up to 35-55% of patients undergoing thoracic incisions. Evidence suggests that multiple cellular signaling pathways and neuro-inflammatory mediators may play an essential role in the pathogenesis of CPTP. In this comprehensive review, we present the current evidence on the cellular signaling pathways and inflammatory changes associated with the initiation and maintenance of CPTP, focusing on the potential application of these findings in the clinical setting. An electronic search of Medline, EMBASE, Cochrane, Google Scholar, and ClinicalTrials.gov was performed, and 3652 abstracts were identified. After an initial abstract screening, 131 studies underwent a full-text review, and nine papers were eventually included in this review. Studies were included if they assessed the cellular signaling pathways or inflammatory processes associated with the induction and/or maintenance of CPTP. All the identified studies were pre-clinical studies conducted on animal models. Our search identified seven cellular pathways (NK-1 receptor (NK-1), Glutaminase 1, Toll-like receptor 4 (TLR4), Resolvins, Ror-2, Sonic hedgehog signaling (Shh), and Wnt5a/Wnts) and six cytokines (IL-1β, IL-6, IL-8, IL-10, IFN-γ, and TNF-α) that were investigated in the context of CPTP. Multiple cellular signaling pathways and inflammatory cytokines may play an important role in the neuroinflammatory changes associated with the induction and maintenance of chronic post-thoracotomy pain in animal models. However, the clinical impact and therapeutic utility of these neuroinflammatory changes in routine clinical practice have yet to be demonstrated.

Receptor Allostery Promotes Context-Dependent Sonic Hedgehog Signaling During Embryonic Development

Sonic Hedgehog (SHH) signaling functions in temporal- and context-dependent manners to pattern diverse tissues during embryogenesis. The signal transducer Smoothened (SMO) is activated by sterols, oxysterols, and arachidonic acid (AA) through binding pockets in its extracellular cysteine-rich domain (CRD) and 7-transmembrane (7TM) bundle. In vitro analyses suggest SMO signaling is allosterically enhanced by combinatorial ligand binding to these pockets but in vivo evidence of SMO allostery is lacking. Herein, we map an AA binding pocket at the top of the 7TM bundle and show that its disruption attenuates SHH and sterol-stimulated SMO induction. A knockin mouse model of compromised AA binding reveals that homozygous mutant mice are cyanotic, exhibit high perinatal lethality, and show congenital heart disease. Surviving mutants demonstrate pulmonary maldevelopment and fail to thrive. Neurodevelopment is unaltered in these mice, suggesting that context-dependent allosteric regulation of SMO signaling allows for precise tuning of pathway activity during cardiopulmonary development.

Widely-targeted in silico and in vitro evaluation of veratrum alkaloid analogs as FAK inhibitors and dual targeting of FAK and Hh/SMO pathways for cancer therapy: A critical analysis

Focal Adhesive Kinase (FAK), a key player in aggressive cancers, mediates signals crucial for progression, invasion, and metastasis. Despite advances in targeted therapies, drug resistance is still a challenge, and survival rates remain low, particularly for late-stage patients, emphasizing the need for innovative cancer therapeutics. Cyclopamine, a veratrum alkaloid, has shown promising anti-tumor properties, but the search for more potent analogs with enhanced affinity for the biological target continues. This study employs a hybrid virtual screening approach combining pharmacophore model-based virtual screening (PB-VS) and docking-based virtual screening (DB-VS) to identify potential inhibitors of the FAK catalytic domain. PB-VS on the PubChem database yielded a set of hits, which were then docked with the FAK catalytic domain in two stages (1st and 2nd DB-VS). Hits were ranked based on docking scores and interactions with the active site. The top three compounds underwent molecular dynamics simulations, alongside two control compounds (SMO inhibitor(s) and FAK inhibitor(s)), to assess stability through RMSD, RMSF, Rg, and SASA analyses. ADMET properties were evaluated, and compounds were filtered based on drug-likeness criteria. Molecular dynamics simulations demonstrated the stability of compounds when complexed with the FAK catalytic domain. Compounds 16 (-25 kcal/mol), 87 (-27.47 kcal/mol), and 88 (-18.94 kcal/mol) exhibited comparable docking scores, interaction profiles, stability, and binding energies, indicating their potential as lead candidates. However, further validation and optimization through quantitative structure-activity relationship (QSAR) studies are essential to refine their efficacy and therapeutic potential. The in vitro cell-based assay demonstrated that compound 101PF, a FAK inhibitor, significantly inhibited the proliferation and migration of A549 cells. However, the results regarding the combined effects of FAK and SMO inhibitors were inconclusive, highlighting the need for further investigation. This study contributes to developing more effective anti-cancer drugs by improving the understanding of potential cyclopamine-based veratrum alkaloid analogs with enhanced interactions with the FAK catalytic domain.

Identification of small molecule antagonists of sonic hedgehog/heparin binding with activity in hedgehog functional assays

Sonic hedgehog (Shh) is a morphogen with important roles in embryonic development and in the development of a number of cancers. Its activity is modulated by interactions with binding partners and co-receptors including heparin and heparin sulfate proteoglycans (HSPG). To identify antagonists of Shh/heparin binding, a diverse collection of 34,560 chemicals was screened in single point 384-well format. We identified and confirmed twenty six novel small molecule antagonists with diverse structures including four scaffolds that gave rise to multiple hits. Nineteen of the confirmed hits blocked binding of the N-terminal fragment of Shh (ShhN) to heparin with IC50 values < 50 μM. In the Shh-responsive C3H10T1/2 cell model, four of the compounds demonstrated the ability to block ShhN-induced alkaline phosphatase activity. To demonstrate a direct and selective effect on ShhN ligand mediated activity, two of the compounds were able to block induction of Gli1 mRNA, a primary downstream marker for Shh signaling activity, in Shh-mediated but not Smoothened agonist (SAG)-mediated C3H10T1/2 cells. Direct binding of the two compounds to ShhN was confirmed by thermal shift assay and molecular docking simulations, with both compounds docking with the N-terminal heparin binding domain of Shh. Overall, our findings indicate that small molecule compounds that block ShhN binding to heparin and act to inhibit Shh mediated activity in vitro can be identified. We propose that the interaction between Shh and HSPGs provides a novel target for identifying small molecules that bind Shh, potentially leading to novel tool compounds to probe Shh ligand function.

GRK2 kinases in the primary cilium initiate SMOOTHENED-PKA signaling in the Hedgehog cascade

During Hedgehog (Hh) signal transduction in development and disease, the atypical G protein-coupled receptor (GPCR) SMOOTHENED (SMO) communicates with GLI transcription factors by binding the protein kinase A catalytic subunit (PKA-C) and physically blocking its enzymatic activity. Here, we show that GPCR kinase 2 (GRK2) orchestrates this process during endogenous mouse and zebrafish Hh pathway activation in the primary cilium. Upon SMO activation, GRK2 rapidly relocalizes from the ciliary base to the shaft, triggering SMO phosphorylation and PKA-C interaction. Reconstitution studies reveal that GRK2 phosphorylation enables active SMO to bind PKA-C directly. Lastly, the SMO-GRK2-PKA pathway underlies Hh signal transduction in a range of cellular and in vivo models. Thus, GRK2 phosphorylation of ciliary SMO and the ensuing PKA-C binding and inactivation are critical initiating events for the intracellular steps in Hh signaling. More broadly, our study suggests an expanded role for GRKs in enabling direct GPCR interactions with diverse intracellular effectors.

Inhibition of δ-catenin palmitoylation slows the progression of prostate cancer

Prostate cancer (PCa) is the second leading cause of death in males. It has been reported that δ-catenin expression is upregulated during the late stage of prostate cancer. Palmitoylation promotes protein transport to the cytomembrane and regulates protein localization and function. However, the effect of δ-catenin palmitoylation on the regulation of cancer remains unknown. In this study, we utilized prostate cancer cells overexpressing mutant δ-catenin (J6A cells) to induce a depalmitoylation phenotype and investigate its effect on prostate cancer. Our results indicated that depalmitoylation of δ-catenin not only reduced its membrane expression but also promoted its degradation in the cytoplasm, resulting in a decrease in the effect of EGFR and E-cadherin signaling. Consequently, depalmitoylation of δ-catenin reduced the proliferation and metastasis of prostate cancer cells. Our findings provide novel insights into potential therapeutic strategies for controlling the progression of prostate cancer through palmitoylation-based targeting of δ-catenin.

Numb positively regulates Hedgehog signaling at the ciliary pocket

Hedgehog (Hh) signaling relies on the primary cilium, a cell surface organelle that serves as a signaling hub for the cell. Using proximity labeling and quantitative proteomics, we identify Numb as a ciliary protein that positively regulates Hh signaling. Numb localizes to the ciliary pocket and acts as an endocytic adaptor to incorporate Ptch1 into clathrin-coated vesicles, thereby promoting Ptch1 exit from the cilium, a key step in Hh signaling activation. Numb loss impedes Sonic hedgehog (Shh)-induced Ptch1 exit from the cilium, resulting in reduced Hh signaling. Numb loss in spinal neural progenitors reduces Shh-induced differentiation into cell fates reliant on high Hh activity. Genetic ablation of Numb in the developing cerebellum impairs the proliferation of granule cell precursors, a Hh-dependent process, resulting in reduced cerebellar size. This study highlights Numb as a regulator of ciliary Ptch1 levels during Hh signal activation and demonstrates the key role of ciliary pocket-mediated endocytosis in cell signaling.

GRK2 Kinases in the Primary Cilium Initiate SMOOTHENED-PKA Signaling in the Hedgehog Cascade

During Hedgehog (Hh) signal transduction in development and disease, the atypical G protein-coupled receptor (GPCR) SMOOTHENED (SMO) communicates with GLI transcription factors by binding the protein kinase A catalytic subunit (PKA-C) and physically blocking its enzymatic activity. Here we show that GPCR kinase 2 (GRK2) orchestrates this process during endogenous Hh pathway activation in the vertebrate primary cilium. Upon SMO activation, GRK2 rapidly relocalizes from the ciliary base to the shaft, triggering SMO phosphorylation and PKA-C interaction. Reconstitution studies reveal that GRK2 phosphorylation enables active SMO to bind PKA-C directly. Lastly, the SMO-GRK2-PKA pathway underlies Hh signal transduction in a range of cellular and in vivo models. Thus, GRK2 phosphorylation of ciliary SMO, and the ensuing PKA-C binding and inactivation, are critical initiating events for the intracellular steps in Hh signaling. More broadly, our study suggests an expanded role for GRKs in enabling direct GPCR interactions with diverse intracellular effectors.

A Residual N-Terminal Peptide Enhances Signaling of Depalmitoylated Hedgehog to the Patched Receptor

During their biosynthesis, Sonic hedgehog (Shh) morphogens are covalently modified by cholesterol at the C-terminus and palmitate at the N-terminus. Although both lipids initially anchor Shh to the plasma membrane of producing cells, it later translocates to the extracellular compartment to direct developmental fates in cells expressing the Patched (Ptch) receptor. Possible release mechanisms for dually lipidated Hh/Shh into the extracellular compartment are currently under intense debate. In this paper, we describe the serum-dependent conversion of the dually lipidated cellular precursor into a soluble cholesteroylated variant (ShhC) during its release. Although ShhC is formed in a Dispatched- and Scube2-dependent manner, suggesting the physiological relevance of the protein, the depalmitoylation of ShhC during release is inconsistent with the previously postulated function of N-palmitate in Ptch receptor binding and signaling. Therefore, we analyzed the potency of ShhC to induce Ptch-controlled target cell transcription and differentiation in Hh-sensitive reporter cells and in the Drosophila eye. In both experimental systems, we found that ShhC was highly bioactive despite the absence of the N-palmitate. We also found that the artificial removal of N-terminal peptides longer than eight amino acids inactivated the depalmitoylated soluble proteins in vitro and in the developing Drosophila eye. These results demonstrate that N-depalmitoylated ShhC requires an N-peptide of a defined minimum length for its signaling function to Ptch.

Gene expression analyses reveal potential mechanism of inorganic arsenic-induced apoptosis in zebrafish

Our previous study showed that sodium arsenite (200 mg/L) affected the nervous system and induced motor neuron development via the Sonic hedgehog pathway in zebrafish larvae. To gain more insight into the effects of arsenite on other signaling pathways, including apoptosis, we have performed quantitative polymerase chain reaction array-based gene expression analyses. The 96-well array plates contained primers for 84 genes representing 10 signaling pathways that regulate several biological functions, including apoptosis. We exposed eggs at 5 h postfertilization until the 72 h postfertilization larval stage to 200 mg/L sodium arsenite. In the Janus kinase/signal transducers and activators of transcription, nuclear factor κ-light-chain-enhancer of activated B cells, and Wingless/Int-1 signaling pathways, the expression of only one gene in each pathway was significantly altered. The expression of multiple genes was altered in the p53 and oxidative stress pathways. Sodium arsenite induced excessive apoptosis in the larvae. This compelled us to analyze specific genes in the p53 pathway, including cdkn1a, gadd45aa, and gadd45ba. Our data suggest that the p53 pathway is likely responsible for sodium arsenite-induced apoptosis. In addition, sodium arsenite significantly reduced global DNA methylation in the zebrafish larvae, which may indicate that epigenetic factors could be dysregulated after arsenic exposure. Together, these data elucidate potential mechanisms of arsenic toxicity that could improve understanding of arsenic's effects on human health.

Cellular and molecular mechanisms of Hedgehog signalling

The Hedgehog signalling pathway has crucial roles in embryonic tissue patterning, postembryonic tissue regeneration, and cancer, yet aspects of Hedgehog signal transmission and reception have until recently remained unclear. Biochemical and structural studies surprisingly reveal a central role for lipids in Hedgehog signalling. The signal - Hedgehog protein - is modified by cholesterol and palmitate during its biogenesis, thereby necessitating specialized proteins such as the transporter Dispatched and several lipid-binding carriers for cellular export and receptor engagement. Additional lipid transactions mediate response to the Hedgehog signal, including sterol activation of the transducer Smoothened. Access of sterols to Smoothened is regulated by the apparent sterol transporter and Hedgehog receptor Patched, whose activity is blocked by Hedgehog binding. Alongside these lipid-centric mechanisms and their relevance to pharmacological pathway modulation, we discuss emerging roles of Hedgehog pathway activity in stem cells or their cellular niches, with translational implications for regeneration and restoration of injured or diseased tissues.

The energetics and ion coupling of cholesterol transport through Patched1

Patched1 (PTCH1) is a tumor suppressor protein of the mammalian Hedgehog (HH) signaling pathway, implicated in embryogenesis and tissue homeostasis. PTCH1 inhibits the G protein-coupled receptor Smoothened (SMO) via a debated mechanism involving modulating ciliary cholesterol accessibility. Using extensive molecular dynamics simulations and free energy calculations to evaluate cholesterol transport through PTCH1, we find an energetic barrier of ~15 to 20 kilojoule per mole for cholesterol export. In silico data are coupled to in vivo biochemical assays of PTCH1 mutants to probe coupling between cation binding sites, transmembrane motions, and PTCH1 activity. Using complementary simulations of Dispatched1, we find that transition between "inward-open" and solvent "occluded" states is accompanied by Na+-induced pinching of intracellular helical segments. Thus, our findings illuminate the energetics and ion coupling stoichiometries of PTCH1 transport mechanisms, whereby one to three Na+ or two to three K+ couple to cholesterol export, and provide the first molecular description of transitions between distinct transport states.

The Inseparable Relationship Between Cholesterol and Hedgehog Signaling

Ligands of the Hedgehog (HH) pathway are paracrine signaling molecules that coordinate tissue development in metazoans. A remarkable feature of HH signaling is the repeated use of cholesterol in steps spanning ligand biogenesis, secretion, dispersal, and reception on target cells. A cholesterol molecule covalently attached to HH ligands is used as a molecular baton by transfer proteins to guide their secretion, spread, and reception. On target cells, a signaling circuit composed of a cholesterol transporter and sensor regulates transmission of HH signals across the plasma membrane to the cytoplasm. The repeated use of cholesterol in signaling supports the view that the HH pathway likely evolved by coopting ancient systems to regulate the abundance or organization of sterol-like lipids in membranes.

The Hedgehog Pathway as a Therapeutic Target in Chronic Myeloid Leukemia

Despite the development of therapeutic agents that selectively target cancer cells, relapse driven by acquired drug resistance and resulting treatment failure remains a significant issue. The highly conserved Hedgehog (HH) signaling pathway performs multiple roles in both development and tissue homeostasis, and its aberrant regulation is known to drive the pathogenesis of numerous human malignancies. However, the role of HH signaling in mediating disease progression and drug resistance remains unclear. This is especially true for myeloid malignancies. The HH pathway, and in particular the protein Smoothened (SMO), has been shown to be essential for regulating stem cell fate in chronic myeloid leukemia (CML). Evidence suggests that HH pathway activity is critical for maintaining the drug-resistant properties and survival of CML leukemic stem cells (LSCs), and that dual inhibition of BCR-ABL1 and SMO may comprise an effective therapeutic strategy for the eradication of these cells in patients. This review will explore the evolutionary origins of HH signaling, highlighting its roles in development and disease, which are mediated by canonical and non-canonical HH signaling. Development of small molecule inhibitors of HH signaling and clinical trials using these inhibitors as therapeutic agents in cancer and their potential resistance mechanisms, are also discussed, with a focus on CML.

The Energetics and Ion Coupling of Cholesterol Transport Through Patched1

Patched1 (PTCH1) is the principal tumour suppressor protein of the mammalian Hedgehog (HH) signalling pathway, implicated in embryogenesis and tissue homeostasis. PTCH1 inhibits the Class F G protein-coupled receptor Smoothened (SMO) via a debated mechanism involving modulating accessible cholesterol levels within ciliary membranes. Using extensive molecular dynamics (MD) simulations and free energy calculations to evaluate cholesterol transport through PTCH1, we find an energetic barrier of ~15-20 kJ mol -1 for cholesterol export. In simulations we identify cation binding sites within the PTCH1 transmembrane domain (TMD) which may provide the energetic impetus for cholesterol transport. In silico data are coupled to in vivo biochemical assays of PTCH1 mutants to probe coupling between transmembrane motions and PTCH1 activity. Using complementary simulations of Dispatched1 (DISP1) we find that transition between 'inward-open' and solvent 'occluded' states is accompanied by Na + induced pinching of intracellular helical segments. Thus, our findings illuminate the energetics and ion-coupling stoichiometries of PTCH1 transport mechanisms, whereby 1-3 Na + or 2-3 K + couple to cholesterol export, and provide the first molecular description of transitions between distinct transport states.

Hedgehog acyltransferase catalyzes a random sequential reaction and utilizes multiple fatty acyl-CoA substrates

Sonic hedgehog (Shh) signaling is a key component of embryonic development and is a driving force in several cancers. Hedgehog acyltransferase (Hhat), a member of the membrane-bound O-acyltransferase family of enzymes, catalyzes the attachment of palmitate to the N-terminal cysteine of Shh, a posttranslation modification critical for Shh signaling. The activity of Hhat has been assayed in cells and in vitro, and cryo-EM structures of Hhat have been reported, yet several unanswered questions remain regarding the enzyme’s reaction mechanism, substrate specificity, and the impact of the latter on Shh signaling. Here, we present an in vitro acylation assay with purified Hhat that directly monitors attachment of a fluorescently tagged fatty acyl chain to Shh. Our kinetic analyses revealed that the reaction catalyzed by Hhat proceeds through a random sequential mechanism. We also determined that Hhat can utilize multiple fatty acyl-CoA substrates for fatty acid transfer to Shh, with comparable affinities and turnover rates for myristoyl-CoA, palmitoyl-CoA, palmitoleoyl-CoA, and oleoyl-CoA. Furthermore, we investigated the functional consequence of differential fatty acylation of Shh in a luciferase-based Shh reporter system. We found that the potency of the signaling response in cells was higher for Shh acylated with saturated fatty acids compared to monounsaturated fatty acids. These findings demonstrate that Hhat can attach fatty acids other than palmitate to Shh and suggest that heterogeneous fatty acylation has the potential to impact Shh signaling in the developing embryo and/or cancer cells.

Application of Small Molecules in the Central Nervous System Direct Neuronal Reprogramming

The lack of regenerative capacity of neurons leads to poor prognoses for some neurological disorders. The use of small molecules to directly reprogram somatic cells into neurons provides a new therapeutic strategy for neurological diseases. In this review, the mechanisms of action of different small molecules, the approaches to screening small molecule cocktails, and the methods employed to detect their reprogramming efficiency are discussed, and the studies, focusing on neuronal reprogramming using small molecules in neurological disease models, are collected. Future research efforts are needed to investigate the in vivo mechanisms of small molecule-mediated neuronal reprogramming under pathophysiological states, optimize screening cocktails and dosing regimens, and identify safe and effective delivery routes to promote neural regeneration in different neurological diseases.

Non-canonical Sonic Hedgehog signaling amplifies platelet reactivity and thrombogenicity

Sonic Hedgehog signaling amplifies platelet activation.

Targeting Shh signaling attenuates hemostasis and thrombosis.

Sonic Hedgehog (Shh) is a morphogen in vertebrate embryos that is also associated with organ homeostasis in adults. We report here that human platelets, though enucleate, synthesize Shh from preexisting mRNAs upon agonist stimulation, and mobilize it for surface expression and release on extracellular vesicles, thus alluding to its putative role in platelet activation. Shh, in turn, induced a wave of noncanonical signaling in platelets leading to activation of small GTPase Ras homolog family member A and phosphorylation of myosin light chain in activated protein kinase-dependent manner. Remarkably, agonist-induced thrombogenic responses in platelets, which include platelet aggregation, granule secretion, and spreading on immobilized fibrinogen, were significantly attenuated by inhibition of Hedgehog signaling, thus, implicating inputs from Shh in potentiation of agonist-mediated platelet activation. In consistence, inhibition of the Shh pathway significantly impaired arterial thrombosis in mice. Taken together, the above observations strongly support a feed-forward loop of platelet stimulation triggered locally by Shh, similar to ADP and thromboxane A2, that contributes significantly to the stability of occlusive arterial thrombus and that can be investigated as a potential therapeutic target in thrombotic disorders.

Hedgehog Autoprocessing: From Structural Mechanisms to Drug Discovery

Hedgehog (Hh) signaling plays pivotal roles in embryonic development. In adults, Hh signaling is mostly turned off but its abnormal activation is involved in many types of cancer. Hh signaling is initiated by the Hh ligand, generated from the Hh precursor by a specialized autocatalytic process called Hh autoprocessing. The Hh precursor consists of an N-terminal signaling domain (HhN) and a C-terminal autoprocessing domain (HhC). During Hh autoprocessing, the precursor is cleaved between N- and C-terminal domain followed by the covalent ligation of cholesterol to the last residue of HhN, which subsequently leads to the generation of Hh ligand for Hh signaling. Hh autoprocessing is at the origin of canonical Hh signaling and precedes all downstream signaling events. Mutations in the catalytic residues in HhC can lead to congenital defects such as holoprosencephaly (HPE). The aim of this review is to provide an in-depth summary of the progresses and challenges towards an atomic level understanding of the structural mechanisms of Hh autoprocessing. We also discuss drug discovery efforts to inhibit Hh autoprocessing as a new direction in cancer therapy.

Sonic Hedgehog Signaling in Cerebellar Development and Cancer

The sonic hedgehog (SHH) pathway regulates the development of the central nervous system in vertebrates. Aberrant regulation of SHH signaling pathways often causes neurodevelopmental diseases and brain tumors. In the cerebellum, SHH secreted by Purkinje cells is a potent mitogen for granule cell progenitors, which are the most abundant cell type in the mature brain. While a reduction in SHH signaling induces cerebellar structural abnormalities, such as hypoplasia in various genetic disorders, the constitutive activation of SHH signaling often induces medulloblastoma (MB), one of the most common pediatric malignant brain tumors. Based on the existing literature on canonical and non-canonical SHH signaling pathways, emerging basic and clinical studies are exploring novel therapeutic approaches for MB by targeting SHH signaling at distinct molecular levels. In this review, we discuss the present consensus on SHH signaling mechanisms, their roles in cerebellar development and tumorigenesis, and the recent advances in clinical trials for MB.

Cholesterol and Hedgehog Signaling: Mutual Regulation and Beyond

The Hedgehog (HH) signaling is one of the key agents that govern the precisely regulated developmental processes of multicellular organisms in vertebrates and invertebrates. The HH pathway in the receiving cell includes Patched1, a twelve-pass transmembrane receptor, and Smoothened, a seven-transmembrane G-protein coupled receptor (GPCR), and the downstream GLI family of three transcriptional factors (GLI1-GLI3). Mutations of HH gene and the main components in HH signaling are also associated with numerous types of diseases. Before secretion, the HH protein undergoes post-translational cholesterol modification to gain full activity, and cholesterol is believed to be essential for proper HH signaling transduction. In addition, results from recent studies show the reciprocal effect that HH signaling functions in cholesterol metabolism as well as in cholesterol homeostasis, which provides feedback to HH pathway. Here, we hope to provide new insights into HH signaling function by discussing the role of cholesterol in HH protein maturation, secretion and HH signaling transduction, and the potential role of HH in regulation of cholesterol as well.

Hedgehog pathway modulation by glypican 3-conjugated heparan sulfate

Glypicans are a family of cell surface heparan sulfate proteoglycans that play critical roles in multiple cell signaling pathways. Glypicans consist of a globular core, an unstructured stalk modified with sulfated glycosaminoglycan chains, and a glycosylphosphatidylinositol anchor. Though these structural features are conserved, their individual contribution to glypican function remains obscure. Here, we investigate how glypican 3 (GPC3), which is mutated in Simpson-Golabi-Behmel tissue overgrowth syndrome, regulates Hedgehog signaling. We find that GPC3 is necessary for the Hedgehog response, surprisingly controlling a downstream signal transduction step. Purified GPC3 ectodomain rescues signaling when artificially recruited to the surface of GPC3-deficient cells but has dominant-negative activity when unattached. Strikingly, the purified stalk, modified with heparan sulfate but not chondroitin sulfate, is necessary and sufficient for activity. Our results demonstrate a novel function for GPC3-associated heparan sulfate and provide a framework for the functional dissection of glycosaminoglycans by in vivo biochemical complementation. This article has an associated First Person interview with the first author of the paper.

Structural basis for catalyzed assembly of the Sonic hedgehog-Patched1 signaling complex

The dually lipidated Sonic hedgehog (SHH) morphogen signals through the tumor suppressor membrane protein Patched1 (PTCH1) to activate the Hedgehog pathway, which is fundamental in development and cancer. SHH engagement with PTCH1 requires the GAS1 coreceptor, but the mechanism is unknown. We demonstrate a unique role for GAS1, catalyzing SHH-PTCH1 complex assembly in vertebrate cells by direct SHH transfer from the extracellular SCUBE2 carrier to PTCH1. Structure of the GAS1-SHH-PTCH1 transition state identifies how GAS1 recognizes the SHH palmitate and cholesterol modifications in modular fashion and how it facilitates lipid-dependent SHH handoff to PTCH1. Structure-guided experiments elucidate SHH movement from SCUBE2 to PTCH1, explain disease mutations, and demonstrate that SHH-induced PTCH1 dimerization causes its internalization from the cell surface. These results define how the signaling-competent SHH-PTCH1 complex assembles, the key step triggering the Hedgehog pathway, and provide a paradigm for understanding morphogen reception and its regulation.

Hedgehog Pathway Inhibitors as Targeted Cancer Therapy and Strategies to Overcome Drug Resistance

Hedgehog (Hh) signaling is a highly conserved pathway that plays a vital role during embryonic development. Recently, uncontrolled activation of this pathway has been demonstrated in various types of cancer. Therefore, Hh pathway inhibitors have emerged as an important class of anti-cancer agents. Unfortunately, however, their reputation has been tarnished by the emergence of resistance during therapy, necessitating clarification of mechanisms underlying the drug resistance. In this review, we briefly overview canonical and non-canonical Hh pathways and their inhibitors as targeted cancer therapy. In addition, we summarize the mechanisms of resistance to Smoothened (SMO) inhibitors, including point mutations of the drug binding pocket or downstream molecules of SMO, and non-canonical mechanisms to reinforce Hh pathway output. A distinct mechanism involving loss of primary cilia is also described to maintain GLI activity in resistant tumors. Finally, we address the main strategies to circumvent the drug resistance. These strategies include the development of novel and potent inhibitors targeting different components of the canonical Hh pathway or signaling molecules of the non-canonical pathway. Further studies are necessary to avoid emerging resistance to Hh inhibitors and establish an optimal customized regimen with improved therapeutic efficacy to treat various types of cancer, including basal cell carcinoma.

Primary Cilia in Pancreatic β- and α-Cells: Time to Revisit the Role of Insulin-Degrading Enzyme

The primary cilium is a narrow organelle located at the surface of the cell in contact with the extracellular environment. Once underappreciated, now is thought to efficiently sense external environmental cues and mediate cell-to-cell communication, because many receptors, ion channels, and signaling molecules are highly or differentially expressed in primary cilium. Rare genetic disorders that affect cilia integrity and function, such as Bardet-Biedl syndrome and Alström syndrome, have awoken interest in studying the biology of cilium. In this review, we discuss recent evidence suggesting emerging roles of primary cilium and cilia-mediated signaling pathways in the regulation of pancreatic β- and α-cell functions, and its implications in regulating glucose homeostasis.

Structure, mechanism, and inhibition of Hedgehog acyltransferase

The Sonic Hedgehog (SHH) morphogen pathway is fundamental for embryonic development and stem cell maintenance and is implicated in various cancers. A key step in signaling is transfer of a palmitate group to the SHH N terminus, catalyzed by the multi-pass transmembrane enzyme Hedgehog acyltransferase (HHAT). We present the high-resolution cryo-EM structure of HHAT bound to substrate analog palmityl-coenzyme A and a SHH-mimetic megabody, revealing a heme group bound to HHAT that is essential for HHAT function. A structure of HHAT bound to potent small-molecule inhibitor IMP-1575 revealed conformational changes in the active site that occlude substrate binding. Our multidisciplinary analysis provides a detailed view of the mechanism by which HHAT adapts the membrane environment to transfer an acyl chain across the endoplasmic reticulum membrane. This structure of a membrane-bound O-acyltransferase (MBOAT) superfamily member provides a blueprint for other protein-substrate MBOATs and a template for future drug discovery.

Hedgehog-Interacting Protein is a multimodal antagonist of Hedgehog signalling

Hedgehog (HH) morphogen signalling, crucial for cell growth and tissue patterning in animals, is initiated by the binding of dually lipidated HH ligands to cell surface receptors. Hedgehog-Interacting Protein (HHIP), the only reported secreted inhibitor of Sonic Hedgehog (SHH) signalling, binds directly to SHH with high nanomolar affinity, sequestering SHH. Here, we report the structure of the HHIP N-terminal domain (HHIP-N) in complex with a glycosaminoglycan (GAG). HHIP-N displays a unique bipartite fold with a GAG-binding domain alongside a Cysteine Rich Domain (CRD). We show that HHIP-N is required to convey full HHIP inhibitory function, likely by interacting with the cholesterol moiety covalently linked to HH ligands, thereby preventing this SHH-attached cholesterol from binding to the HH receptor Patched (PTCH1). We also present the structure of the HHIP C-terminal domain in complex with the GAG heparin. Heparin can bind to both HHIP-N and HHIP-C, thereby inducing clustering at the cell surface and generating a high-avidity platform for SHH sequestration and inhibition. Our data suggest a multimodal mechanism, in which HHIP can bind two specific sites on the SHH morphogen, alongside multiple GAG interactions, to inhibit SHH signalling.

Noncoding RNAs: emerging players in skin cancers pathogenesis

Skin malignancies form in tissues of the skin and are the most frequent cancers in the world, with an increasing incidence and a steady fatality rate. They are classified as melanoma or nonmelanoma cancers, which include basal cell carcinoma and squamous cell carcinoma. Noncoding RNA transcripts have received increased attention after the thorough analysis of the human genome revealed that most of the genomic components are not encoded to protein. MicroRNAs, long noncoding RNAs, and circular RNAs are some of the well-studied types of these noncoding regions. The alteration in any of these members' expression is associated intrinsically with human cancers, including skin malignancies, due to their critical functions in cell processes for normal development. As a result, investigating the noncoding component of the transcriptome opens up the possibility of discovering new therapeutic and diagnostic targets. This review discusses current studies on the involvement of microRNAs, long noncoding RNAs, and circular RNAs in the pathogenesis of human skin cancers.

Full-length Dhh and N-terminal Shh act as competitive antagonists to regulate angiogenesis and vascular permeability

AIMS

The therapeutic potential of Hedgehog (Hh) signalling agonists for vascular diseases is of growing interest. However, molecular and cellular mechanisms underlying the role of the Hh signalling in vascular biology remain poorly understood. The purpose of the present article is to clarify some conflicting literature data.

METHODS AND RESULTS

With this goal, we have demonstrated that, unexpectedly, ectopically administered N-terminal Sonic Hh (N-Shh) and endogenous endothelial-derived Desert Hh (Dhh) induce opposite effects in endothelial cells (ECs). Notably, endothelial Dhh acts under its full-length soluble form (FL-Dhh) and activates Smoothened in ECs, while N-Shh inhibits it. At molecular level, N-Shh prevents FL-Dhh binding to Patched-1 (Ptch1) demonstrating that N-Shh acts as competitive antagonist to FL-Dhh. Besides, we found that even though FL-Hh ligands and N-Hh ligands all bind Ptch1, they induce distinct Ptch1 localization. Finally, we confirmed that in a pathophysiological setting, i.e. brain inflammation, astrocyte-derived N-Shh acts as a FL-Dhh antagonist.

CONCLUSION

The present study highlights for the first time that FL-Dhh and N-Hh ligands have antagonistic properties especially in ECs.

When Viruses Cross Developmental Pathways

Aberrant regulation of developmental pathways plays a key role in tumorigenesis. Tumor cells differ from normal cells in their sustained proliferation, replicative immortality, resistance to cell death and growth inhibition, angiogenesis, and metastatic behavior. Often they acquire these features as a consequence of dysregulated Hedgehog, Notch, or WNT signaling pathways. Human tumor viruses affect the cancer cell hallmarks by encoding oncogenic proteins, and/or by modifying the microenvironment, as well as by conveying genomic instability to accelerate cancer development. In addition, viral immune evasion mechanisms may compromise developmental pathways to accelerate tumor growth. Viruses achieve this by influencing both coding and non-coding gene regulatory pathways. Elucidating how oncogenic viruses intersect with and modulate developmental pathways is crucial to understanding viral tumorigenesis. Many currently available antiviral therapies target viral lytic cycle replication but with low efficacy and severe side effects. A greater understanding of the cross-signaling between oncogenic viruses and developmental pathways will improve the efficacy of next-generation inhibitors and pave the way to more targeted antiviral therapies.

Mechanism and ultrasensitivity in Hedgehog signaling revealed by Patched1 disease mutations

Hedgehog signaling is fundamental in animal embryogenesis, and its dysregulation causes cancer and birth defects. The pathway is triggered when the Hedgehog ligand inhibits the Patched1 membrane receptor, relieving repression that Patched1 exerts on the GPCR-like protein Smoothened. While it is clear how loss-of-function Patched1 mutations cause hyperactive Hedgehog signaling and cancer, how other Patched1 mutations inhibit signaling remains unknown. Here, we develop quantitative single-cell functional assays for Patched1, which, together with mathematical modeling, indicate that Patched1 inhibits Smoothened enzymatically, operating in an ultrasensitive regime. Based on this analysis, we propose that Patched1 functions in cilia, catalyzing Smoothened deactivation by removing cholesterol bound to its extracellular, cysteine-rich domain. Patched1 mutants associated with holoprosencephaly dampen signaling by three mechanisms: reduced affinity for Hedgehog ligand, elevated catalytic activity, or elevated affinity for the Smoothened substrate. Our results clarify the enigmatic mechanism of Patched1 and explain how Patched1 mutations lead to birth defects.

Small molecules in targeted cancer therapy: advances, challenges, and future perspectives

Due to the advantages in efficacy and safety compared with traditional chemotherapy drugs, targeted therapeutic drugs have become mainstream cancer treatments. Since the first tyrosine kinase inhibitor imatinib was approved to enter the market by the US Food and Drug Administration (FDA) in 2001, an increasing number of small-molecule targeted drugs have been developed for the treatment of malignancies. By December 2020, 89 small-molecule targeted antitumor drugs have been approved by the US FDA and the National Medical Products Administration (NMPA) of China. Despite great progress, small-molecule targeted anti-cancer drugs still face many challenges, such as a low response rate and drug resistance. To better promote the development of targeted anti-cancer drugs, we conducted a comprehensive review of small-molecule targeted anti-cancer drugs according to the target classification. We present all the approved drugs as well as important drug candidates in clinical trials for each target, discuss the current challenges, and provide insights and perspectives for the research and development of anti-cancer drugs.

Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation

Hedgehog (HH) is a highly conserved secretory signalling protein family mainly involved in embryonic development, homeostasis, and tumorigenesis. HH is generally synthesised as a precursor, which subsequently undergoes autoproteolytic cleavage to generate an amino-terminal fragment (HH-N), mediating signalling, and a carboxyl-terminal fragment (HH-C), catalysing the auto-processing reaction. The N-terminal region of HH-N is required for HH multimer formation to promote signal transduction, whilst the functions of the C-terminal region of HH-N remain ambiguous. This study focused on Indian Hedgehog (IHH), a member of the HH family, to explore the functions of the C-terminal region of the amino-terminal fragment of IHH (IHH-N) via protein truncation, cell-based assays, and 3D structure prediction. The results revealed that three amino acids, including S195, A196, and A197, were crucial for the multimer formation by inserting the mutual binding of IHH-N proteins. K191, S192, E193, and H194 had an extremely remarkable effect on IHH self-cleavage. In addition, A198, K199, and T200 evidently affected the stability of IHH-N. This work suggested that the C-terminus of IHH-N played an important role in the physiological function of IHH at multiple levels, thus deepening the understanding of HH biochemical properties.

Association of Sonic Hedgehog with the extracellular matrix requires its zinc-coordination center

Background

Sonic Hedgehog (Shh) has a catalytic cleft characteristic for zinc metallopeptidases and has significant sequence similarities with some bacterial peptidoglycan metallopeptidases defining a subgroup within the M15A family that, besides having the characteristic zinc coordination motif, can bind two calcium ions. Extracellular matrix (ECM) components in animals include heparan-sulfate proteoglycans, which are analogs of bacterial peptidoglycan and are involved in the extracellular distribution of Shh.

Results

We found that the zinc-coordination center of Shh is required for its association to the ECM as well as for non-cell autonomous signaling. Association with the ECM requires the presence of at least 0.1 μM zinc and is prevented by mutations affecting critical conserved catalytical residues. Consistent with the presence of a conserved calcium binding domain, we find that extracellular calcium inhibits ECM association of Shh.

Conclusions

Our results indicate that the putative intrinsic peptidase activity of Shh is required for non-cell autonomous signaling, possibly by enzymatically altering ECM characteristics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00359-5.

Palmitoylation of Hedgehog proteins by Hedgehog acyltransferase: roles in signalling and disease

Hedgehog acyltransferase (Hhat), a member of the membrane-bound O-acyltransferase (MBOAT) family, catalyses the covalent attachment of palmitate to the N-terminus of Hedgehog proteins. Palmitoylation is a post-translational modification essential for Hedgehog signalling. This review explores the mechanisms involved in Hhat acyltransferase enzymatic activity, similarities and differences between Hhat and other MBOAT enzymes, and the role of palmitoylation in Hedgehog signalling. In vitro and cell-based assays for Hhat activity have been developed, and residues within Hhat and Hedgehog essential for palmitoylation have been identified. In cells, Hhat promotes the transfer of palmitoyl-CoA from the cytoplasmic to the luminal side of the endoplasmic reticulum membrane, where Shh palmitoylation occurs. Palmitoylation is required for efficient delivery of secreted Hedgehog to its receptor Patched1, as well as for the deactivation of Patched1, which initiates the downstream Hedgehog signalling pathway. While Hhat loss is lethal during embryogenesis, mutations in Hhat have been linked to disease states or abnormalities in mice and humans. In adults, aberrant re-expression of Hedgehog ligands promotes tumorigenesis in an Hhat-dependent manner in a variety of different cancers, including pancreatic, breast and lung. Targeting hedgehog palmitoylation by inhibition of Hhat is thus a promising, potential intervention in human disease.

C-Terminal Peptide Modifications Reveal Direct and Indirect Roles of Hedgehog Morphogen Cholesteroylation

Hedgehog (Hh) morphogens are involved in embryonic development and stem cell biology and, if misregulated, can contribute to cancer. One important post-translational modification with profound impact on Hh biofunction is its C-terminal cholesteroylation during biosynthesis. The current hypothesis is that the cholesterol moiety is a decisive factor in Hh association with the outer plasma membrane leaflet of producing cells, cell-surface Hh multimerization, and its transport and signaling. Yet, it is not decided whether the cholesterol moiety is directly involved in all of these processes, because their functional interdependency raises the alternative possibility that the cholesterol initiates early processes directly and that these processes can then steer later stages of Hh signaling independent of the lipid. We generated variants of the C-terminal Hh peptide and observed that these cholesteroylated peptides variably impaired several post-translational processes in producing cells and Hh biofunction in Drosophila melanogaster eye and wing development. We also found that substantial Hh amounts separated from cholesteroylated peptide tags in vitro and in vivo and that tagged and untagged Hh variants lacking their C-cholesterol moieties remained bioactive. Our approach thus confirms that Hh cholesteroylation is essential during the early steps of Hh production and maturation but also suggests that it is dispensable for Hh signal reception at receiving cells.

Sonic hedgehog signaling in astrocytes

Astrocytes are complex cells that perform a broad array of essential functions in the healthy and injured nervous system. The recognition that these cells are integral components of various processes, including synapse formation, modulation of synaptic activity, and response to injury, underscores the need to identify the molecular signaling programs orchestrating these diverse functional properties. Emerging studies have identified the Sonic hedgehog (Shh) signaling pathway as an essential regulator of the molecular identity and functional properties of astrocytes. Well established as a powerful regulator of diverse neurodevelopmental processes in the embryonic nervous system, its functional significance in astrocytes is only beginning to be revealed. Notably, Shh signaling is active only in discrete subpopulations of astrocytes distributed throughout the brain, a feature that has potential to yield novel insights into functional specialization of astrocytes. Here, we discuss Shh signaling and emerging data that point to essential roles for this pleiotropic signaling pathway in regulating various functional properties of astrocytes in the healthy and injured brain.

Activation barriers in Class F G protein-coupled receptors revealed by umbrella sampling simulations

The Class F G protein-coupled receptors (GPCRs) include Smoothened and the ten Frizzled receptors, which are major cell membrane receptors in the Hedgehog and Wnt signalling pathways respectively and of enormous interest in embryonic development and as therapeutic targets in cancer. Recent crystal structures of Smoothened provide the opportunity to investigate the structural biology of Class F GPCRs in more detail, in turn, informing the development of therapeutics. A key question in this area is how one receptor may trigger distinct pathways - particularly relevant for Wnt signalling, in which signals may be transduced from a Frizzled via Dishevelled or G proteins, depending on the context. In this study, we employ adiabatic biased molecular dynamics and umbrella sampling to investigate the activation of Smoothened and Frizzled-7 in both the native state and bound to endogenous ligands, as well as how the clinically used Smoothened antagonist vismodegib alters this signalling. The results highlight key energetic barriers in the activation of these receptors, and the molecular features of the receptors mediating these barriers, demonstrating our approach as a robust means of investigating signalling through these receptors.

Sterols in an intramolecular channel of Smoothened mediate Hedgehog signaling

Smoothened (SMO), a class Frizzled G protein-coupled receptor (class F GPCR), transduces the Hedgehog signal across the cell membrane. Sterols can bind to its extracellular cysteine-rich domain (CRD) and to several sites in the seven transmembrane helices (7-TMs) of SMO. However, the mechanism by which sterols regulate SMO via multiple sites is unknown. Here we determined the structures of SMO-Gi complexes bound to the synthetic SMO agonist (SAG) and to 24(S),25-epoxycholesterol (24(S),25-EC). A novel sterol-binding site in the extracellular extension of TM6 was revealed to connect other sites in 7-TMs and CRD, forming an intramolecular sterol channel from the middle side of 7-TMs to CRD. Additional structures of two gain-of-function variants, SMOD384R and SMOG111C/I496C, showed that blocking the channel at its midpoints allows sterols to occupy the binding sites in 7-TMs, thereby activating SMO. These data indicate that sterol transport through the core of SMO is a major regulator of SMO-mediated signaling.

A peptidic inhibitor for PD-1 palmitoylation targets its expression and functions

Programmed cell death protein 1 (PD-1) is a crucial anticancer target, but the relatively low response rate and acquired resistance to existing antibody drugs highlight an urgent need to develop alternative targeting strategies. Here, we report the palmitoylation of PD-1, discover the main DHHC enzyme for this modification, reveal the mechanism of its effect on PD-1 protein stability, and rationally develop a peptide for targeting PD-1 expression. Palmitoylation promoted the trafficking of PD-1 to the recycling endosome, thus preventing its lysosome-dependent degradation. Palmitoylation of PD-1, but not of PD-L1, promoted mTOR signaling and tumor cell proliferation, and targeting palmitoylation displayed significant anti-tumor effects in a three-dimensional culture system. A peptide was designed to competitively inhibit PD-1 palmitoylation and expression, opening a new route for developing PD-1 inhibitors and combinatorial cancer immunotherapy.

We show for the first time that PD-1 is palmitoylated, identify DHHC9 as the predominant enzyme for its palmitoylation, and reveal the molecular mechanisms underlying its effects on PD-1 stability and functions. Importantly, we also designed PD1-PALM, a competitive inhibitor of PD-1 palmitoylation, and this first-in-class molecule may inspire the development of new checkpoint inhibitors.

Hedgehog Pathway Activation Requires Coreceptor-Catalyzed, Lipid-Dependent Relay of the Sonic Hedgehog Ligand

Hedgehog signaling governs critical processes in embryogenesis, adult stem cell maintenance, and tumorigenesis. The activating ligand, Sonic hedgehog (SHH), is highly hydrophobic because of dual palmitate and cholesterol modification, and thus, its release from cells requires the secreted SCUBE proteins. We demonstrate that the soluble SCUBE-SHH complex, although highly potent in cellular assays, cannot directly signal through the SHH receptor, Patched1 (PTCH1). Rather, signaling by SCUBE-SHH requires a molecular relay mediated by the coreceptors CDON/BOC and GAS1, which relieves SHH inhibition by SCUBE. CDON/BOC bind both SCUBE and SHH, recruiting the complex to the cell surface. SHH is then handed off, in a dual lipid-dependent manner, to GAS1, and from GAS1 to PTCH1, initiating signaling. These results define an essential step in Hedgehog signaling, whereby coreceptors activate SHH by chaperoning it from a latent extracellular complex to its cell-surface receptor, and point to a broader paradigm of coreceptor function.

Hedgehog Signaling and Truncated GLI1 in Cancer

The hedgehog (HH) signaling pathway regulates normal cell growth and differentiation. As a consequence of improper control, aberrant HH signaling results in tumorigenesis and supports aggressive phenotypes of human cancers, such as neoplastic transformation, tumor progression, metastasis, and drug resistance. Canonical activation of HH signaling occurs through binding of HH ligands to the transmembrane receptor Patched 1 (PTCH1), which derepresses the transmembrane G protein-coupled receptor Smoothened (SMO). Consequently, the glioma-associated oncogene homolog 1 (GLI1) zinc-finger transcription factors, the terminal effectors of the HH pathway, are released from suppressor of fused (SUFU)-mediated cytoplasmic sequestration, permitting nuclear translocation and activation of target genes. Aberrant activation of this pathway has been implicated in several cancer types, including medulloblastoma, rhabdomyosarcoma, basal cell carcinoma, glioblastoma, and cancers of lung, colon, stomach, pancreas, ovarian, and breast. Therefore, several components of the HH pathway are under investigation for targeted cancer therapy, particularly GLI1 and SMO. GLI1 transcripts are reported to undergo alternative splicing to produce truncated variants: loss-of-function GLI1ΔN and gain-of-function truncated GLI1 (tGLI1). This review covers the biochemical steps necessary for propagation of the HH activating signal and the involvement of aberrant HH signaling in human cancers, with a highlight on the tumor-specific gain-of-function tGLI1 isoform.

Distinct Cation Gradients Power Cholesterol Transport at Different Key Points in the Hedgehog Signaling Pathway

Cholesterol plays two critical roles in Hedgehog signaling, a fundamental pathway in animal development and cancer: it covalently modifies the Sonic hedgehog (SHH) ligand, restricting its release from producing cells, and directly activates Smoothened in responding cells. In both contexts, a membrane protein related to bacterial RND transporters regulates cholesterol: Dispatched1 controls release of cholesterylated SHH, and Patched1 antagonizes Smoothened activation by cholesterol. The mechanism and driving force for eukaryotic RND proteins, including Dispatched1 and Patched1, are unknown. Here, we show that Dispatched1 acts enzymatically to catalyze SHH release. Dispatched1 uses the energy of the plasma membrane Na⁺ gradient, thus functioning as an SHH/Na⁺ antiporter. In contrast, Patched1 repression of Smoothened requires the opposing K⁺ gradient. Our results clarify the transporter activity of essential eukaryotic RND proteins and demonstrate that the two main cation gradients of animal cells differentially power cholesterol transport at two crucial steps in the Hedgehog pathway.

<p>Sonic Hedgehog Signaling Contributes to Chronic Post-Thoracotomy Pain via Activating BDNF/TrkB Pathway in Rats</p>

Purpose

Some patients undergoing thoracotomy may suffer from chronic post-thoracotomy pain (CPTP). Treatment of CPTP has been a clinical challenge and the underlying mechanisms of CPTP remain elusive. Recently, sonic hedgehog (Shh) signaling has been shown to be associated with various pain states but its role in the pathogenesis of CPTP is still unclear.

Methods

CPTP was induced in rats by thoracotomy. Rats were divided into CPTP group and non-CPTP group based on the mechanical withdrawal threshold (MWT). Rats were administered with Shh signaling inhibitor cyclopamine and activator smoothened agonist (SAG), and then evaluated by MWT and cold allodynia testing. The expressions of Shh signaling (Shh ligand, patched and smoothened receptor, Gli transcription factors), brain-derived neurotrophic factor (BDNF), tropomyosin-related kinase receptor B (Trk-B), phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt) in rat T4-5 spinal cord dorsal horn (SDH) were detected by Western blotting and immunohistochemistry.

Results

The expression of Shh signaling significantly increased and the BDNF/TrkB pathway was activated in T4-5 SDH of CPTP rats. Cyclopamine attenuated hyperalgesia and down-regulated the expressions of Gil1, BDNF, p-TrkB, p-PI3K and p-Akt in CPTP rats. SAG induced hyperalgesia in non-CPTP rats and elevated the expressions of Gil1, BDNF, p-TrkB, p-PI3K and p-Akt.

Conclusion

Shh signaling may contribute to CPTP via activating BDNF/TrkB signaling pathway, and inhibition of Shh signaling may effectively alleviate CPTP.

Mechanistic Insights into the Generation and Transduction of Hedgehog Signaling

Cell differentiation and proliferation require Hedgehog (HH) signaling and aberrant HH signaling causes birth defects or cancers. In this signaling pathway, the N-terminally palmitoylated and C-terminally cholesterylated HH ligand is secreted into the extracellular space with help of the Dispatched-1 (DISP1) and Scube2 proteins. The Patched-1 (PTCH1) protein releases its inhibition of the oncoprotein Smoothened (SMO) after binding the HH ligand, triggering downstream signaling events. In this review, we discuss the recent structural and biochemical studies on four major components of the HH pathway: the HH ligand, DISP1, PTCH1, and SMO. This research provides mechanistic insights into how HH signaling is generated and transduced from the cell surface into the intercellular space and will aid in facilitating the treatment of HH-related diseases.

GLI3: a mediator of genetic diseases, development and cancer

The transcription factor GLI3 is a member of the Hedgehog (Hh/HH) signaling pathway that can exist as a full length (Gli3-FL/GLI3-FL) or repressor (Gli3-R/GLI3-R) form. In response to HH activation, GLI3-FL regulates HH genes by targeting the GLI1 promoter. In the absence of HH signaling, GLI3 is phosphorylated leading to its partial degradation and the generation of GLI3-R which represses HH functions. GLI3 is also involved in tissue development, immune cell development and cancer. The absence of Gli3 in mice impaired brain and lung development and GLI3 mutations in humans are the cause of Greig cephalopolysyndactyly (GCPS) and Pallister Hall syndromes (PHS). In the immune system GLI3 regulates B, T and NK-cells and may be involved in LPS-TLR4 signaling. In addition, GLI3 was found to be upregulated in multiple cancers and was found to positively regulate cancerous behavior such as anchorage-independent growth, angiogenesis, proliferation and migration with the exception in acute myeloid leukemia (AML) and medulloblastoma where GLI plays an anti-cancerous role. Finally, GLI3 is a target of microRNA. Here, we will review the biological significance of GLI3 and discuss gaps in our understanding of this molecule. Video Abstract.

Novel HDAC11 inhibitors suppress lung adenocarcinoma stem cell self-renewal and overcome drug resistance by suppressing Sox2

Non-small cell lung cancer (NSCLC) is known to have poor patient outcomes due to development of resistance to chemotherapy agents and the EGFR inhibitors, which results in recurrence of highly aggressive lung tumors. Even with recent success in immunotherapy using the checkpoint inhibitors, additional investigations are essential to identify novel therapeutic strategies for efficacious treatment for NSCLC. Our finding that high levels of histone deacetylase 11 (HDAC11) in human lung tumor tissues correlate with poor patient outcome and that depletion or inhibition of HDAC11 not only significantly reduces self-renewal of cancer stem cells (CSCs) from NSCLC but also decreases Sox2 expression that is essential for maintenance of CSCs, indicates that HDAC11 is a potential target to combat NSCLC. We find that HDAC11 suppresses Sox2 expression through the mediation of Gli1, the Hedgehog pathway transcription factor. In addition, we have used highly selective HDAC11 inhibitors that not only target stemness and adherence independent growth of lung cancer cells but these inhibitors could also efficiently ablate the growth of drug-insensitive stem-like cells as well as therapy resistant lung cancer cells. These inhibitors were found to be efficacious even in presence of cancer associated fibroblasts which have been shown to contribute in therapy resistance. Our study presents a novel role of HDAC11 in lung adenocarcinoma progression and the potential use of highly selective inhibitors of HDAC11 in combating lung cancers.

Recent Findings in the Posttranslational Modifications of PD-L1

Immune checkpoint therapy, such as the reactivation of T-cell activity by targeting programmed cell death 1 (PD-1) and its ligand PD-L1 (also called B7-H1 and CD274) has been found pivotal in changing the historically dim prognoses of malignant tumors by causing durable objective responses. However, the response rate of immune checkpoint therapy required huge improvements. It has been shown that the expression of PD-L1 on cancer cells and immune cell membranes is correlated with a more durable objective response rate to PD-L1 antibodies, which highlights the importance of deeply understanding how this protein is regulated. Posttranslational modifications such as phosphorylation, N-glycosylation, and ubiquitination of PD-L1 have emerged as important regulatory mechanisms that modulate immunosuppression in patients with cancer. In this review, we summarized the latest findings of PD-L1 protein modification and their clinical applications.