Heterotrimeric Gi proteins link Hedgehog signaling to activation of Rho small GTPases to promote fibroblast migration

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.

Hedgehog pathway and cancer: A new area (Review)

In years of research on classical pathways, the composition, information transmission mechanism, crosstalk with other pathways, and physiological and pathological effects of hedgehog (HH) pathway have been gradually clarified. HH also plays a critical role in tumor formation and development. According to the update of interpretation of tumor phenotypes, the latest relevant studies have been sorted out, to explore the specific mechanism of HH pathway in regulating different tumor phenotypes through gene mutation and signal regulation. The drugs and natural ingredients involved in regulating HH pathway were also reviewed; five approved drugs and drugs under research exert efficacy by blocking HH pathway, and at least 22 natural components have potential to treat tumors by HH pathway. Nevertheless, there is a deficiency of existing studies. The present review confirmed the great potential of HH pathway in future cancer treatment with factual basis.

Myosin II mediates Shh signals to shape dental epithelia via control of cell adhesion and movement

The development of ectodermal organs begins with the formation of a stratified epithelial placode that progressively invaginates into the underlying mesenchyme as the organ takes its shape. Signaling by secreted molecules is critical for epithelial morphogenesis, but how that information leads to cell rearrangement and tissue shape changes remains an open question. Using the mouse dentition as a model, we first establish that non-muscle myosin II is essential for dental epithelial invagination and show that it functions by promoting cell-cell adhesion and persistent convergent cell movements in the suprabasal layer. Shh signaling controls these processes by inducing myosin II activation via AKT. Pharmacological induction of AKT and myosin II can also rescue defects caused by the inhibition of Shh. Together, our results support a model in which the Shh signal is transmitted through myosin II to power effective cellular rearrangement for proper dental epithelial invagination.

Therapeutic potential of hedgehog signaling in advanced cancer types

In this chapter, we have made an attempt to elucidate the relevance of hedgehog signaling pathway in tumorigenesis. Here, we have described different types of hedgehog signaling (canonical and non-canonical) with emphasis on the different mechanisms (mutation-driven, autocrine, paracrine and reverse paracrine) it adopts during tumorigenesis. We have discussed the role of hedgehog signaling in regulating cell proliferation, invasion and epithelial-to-mesenchymal transition in both local and advanced cancer types, as reported in different studies based on preclinical and clinical models. We have specifically addressed the role of hedgehog signaling in aggressive neuroendocrine tumors as well. We have also elaborated on the studies showing therapeutic relevance of the inhibitors of hedgehog signaling in cancer. Evidence of the crosstalk of hedgehog signaling components with other signaling pathways and treatment resistance due to tumor heterogeneity have also been briefly discussed. Together, we have tried to put forward a compilation of the studies on therapeutic potential of hedgehog signaling in various cancers, specifically aggressive tumor types with a perspective into what is lacking and demands further investigation.

Non-canonical non-genomic morphogen signaling in anucleate platelets: a critical determinant of prothrombotic function in circulation

Circulating platelets derived from bone marrow megakaryocytes play a central role in thrombosis and hemostasis. Despite being anucleate, platelets express several proteins known to have nuclear niche. These include transcription factors and steroid receptors whose non-genomic functions are being elucidated in platelets. Quite remarkably, components of some of the best-studied morphogen pathways, namely Notch, Sonic Hedgehog (Shh), and Wnt have also been described in recent years in platelets, which regulate platelet function in the context of thrombosis as well as influence their survival. Shh and Notch pathways in stimulated platelets establish feed-forward loops of autocrine/juxtacrine/paracrine non-canonical signaling that helps perpetuate thrombosis. On the other hand, non-canonical Wnt signaling is part of a negative feedback loop for restricting platelet activation and possibly limiting thrombus growth. The present review will provide an overview of these signaling pathways in general. We will then briefly discuss the non-genomic roles of transcription factors and steroid receptors in platelet activation. This will be followed by an elaborate description of morphogen signaling in platelets with a focus on their bearing on platelet activation leading to hemostasis and thrombosis as well as their potential for therapeutic targeting in thrombotic disorders.

Coordination of canonical and noncanonical Hedgehog signalling pathways mediated by WDR11 during primordial germ cell development

WDR11, a gene associated with Kallmann syndrome, is important in reproductive system development but molecular understanding of its action remains incomplete. We previously reported that Wdr11-deficient embryos exhibit defective ciliogenesis and developmental defects associated with Hedgehog (HH) signalling. Here we demonstrate that WDR11 is required for primordial germ cell (PGC) development, regulating canonical and noncanonical HH signalling in parallel. Loss of WDR11 disrupts PGC motility and proliferation driven by the cilia-independent, PTCH2/GAS1-dependent noncanonical HH pathway. WDR11 modulates the growth of somatic cells surrounding PGCs by regulating the cilia-dependent, PTCH1/BOC-dependent canonical HH pathway. We reveal that PTCH1/BOC or PTCH2/GAS1 receptor context dictates SMO localisation inside or outside of cilia, respectively, and loss of WDR11 affects the signalling responses of SMO in both situations. We show that GAS1 is induced by PTCH2-specific HH signalling, which is lost in the absence of WDR11. We also provide evidence supporting a role for WDR11 in ciliogenesis through regulation of anterograde intraflagellar transport potentially via its interaction with IFT20. Since WDR11 is a target of noncanonical SMO signalling, WDR11 represents a novel mechanism by which noncanonical and canonical HH signals communicate and cooperate.

Sonic Hedgehog Signaling Pathway: A Role in Pain Processing

Pain, as one of the most prevalent clinical symptoms, is a complex physiological and psychological activity. Long-term severe pain can become unbearable to the body. However, existing treatments do not provide satisfactory results. Therefore, new mechanisms and therapeutic targets need to be urgently explored for pain management. The Sonic hedgehog (Shh) signaling pathway is crucial in embryonic development, cell differentiation and proliferation, and nervous system regulation. Here, we review the recent studies on the Shh signaling pathway and its action in multiple pain-related diseases. The Shh signaling pathway is dysregulated under various pain conditions, such as pancreatic cancer pain, bone cancer pain, chronic post-thoracotomy pain, pain caused by degenerative lumbar disc disease, and toothache. Further studies on the Shh signaling pathway may provide new therapeutic options for pain patients.

From mesenchymal niches to engineered in vitro model systems: Exploring and exploiting biomechanical regulation of vertebrate hedgehog signalling

Tissue patterning is the result of complex interactions between transcriptional programs and various mechanical cues that modulate cell behaviour and drive morphogenesis. Vertebrate Hedgehog signalling plays key roles in embryogenesis and adult tissue homeostasis, and is central to skeletal development and the osteogenic differentiation of mesenchymal stem cells. The expression of several components of the Hedgehog signalling pathway have been reported to be mechanically regulated in mesodermal tissue patterning and osteogenic differentiation in response to external stimulation. Since a number of bone developmental defects and skeletal diseases, such as osteoporosis, are directly linked to aberrant Hedgehog signalling, a better knowledge of the regulation of Hedgehog signalling in the mechanosensitive bone marrow-residing mesenchymal stromal cells will present novel avenues for modelling these diseases and uncover novel opportunities for extracellular matrix-targeted therapies. In this review, we present a brief overview of the key molecular players involved in Hedgehog signalling and the basic concepts of mechanobiology, with a focus on bone development and regeneration. We also highlight the correlation between the activation of the Hedgehog signalling pathway in response to mechanical cues and osteogenesis in bone marrow-derived mesenchymal stromal cells. Finally, we propose different tissue engineering strategies to apply the expanding knowledge of 3D material-cell interactions in the modulation of Hedgehog signalling in vitro for fundamental and translational research applications.

The role of Hedgehog and Notch signaling pathway in cancer

Notch and Hedgehog signaling are involved in cancer biology and pathology, including the maintenance of tumor cell proliferation, cancer stem-like cells, and the tumor microenvironment. Given the complexity of Notch signaling in tumors, its role as both a tumor promoter and suppressor, and the crosstalk between pathways, the goal of developing clinically safe, effective, tumor-specific Notch-targeted drugs has remained intractable. Drugs developed against the Hedgehog signaling pathway have affirmed definitive therapeutic effects in basal cell carcinoma; however, in some contexts, the challenges of tumor resistance and recurrence leap to the forefront. The efficacy is very limited for other tumor types. In recent years, we have witnessed an exponential increase in the investigation and recognition of the critical roles of the Notch and Hedgehog signaling pathways in cancers, and the crosstalk between these pathways has vast space and value to explore. A series of clinical trials targeting signaling have been launched continually. In this review, we introduce current advances in the understanding of Notch and Hedgehog signaling and the crosstalk between pathways in specific tumor cell populations and microenvironments. Moreover, we also discuss the potential of targeting Notch and Hedgehog for cancer therapy, intending to promote the leap from bench to bedside.

Unraveling the actin cytoskeleton in the malignant transformation of cholangiocyte biology

Correct actin cytoskeleton organization is vital in the liver organ homeostasis and disease control. Rearrangements of the actin cytoskeleton may play a vital role in the bile duct cells cholangiocytes. An abnormal actin network leads to aberrant cell morphology, deregulated signaling networks and ultimately triggering the development of cholangiocarcinoma (CCA) and paving the route for cancer cell dissemination (metastasis). In this review, we will outline alterations of the actin cytoskeleton and the potential role of this dynamic network in initiating CCA, as well as regulating the course of this malignancy. Actin rearrangements not only occur because of signaling pathways, but also regulate and modify cellular signaling. This emphasizes the importance of the actin cytoskeleton itself as cause for aberrant signaling and in promoting tumorigenic phenotypes. We will highlight the impact of aberrant signaling networks on the actin cytoskeleton and its rearrangement as potential cause for CCA. Often, these exact mechanisms in CCA are limited understood and still must be elucidated. Indeed, focusing future research on how actin affects and regulates other signaling pathways may provide more insights into the mechanisms of CCA development, progression, and metastasis. Moreover, manipulation of the actin cytoskeleton organization highlights the potential for a novel therapeutic area.

Molecular pathogenesis and treatment of cavernous nerve injury-induced erectile dysfunction: A narrative review

Introduction: Erectile dysfunction (ED) is a common complication after radical prostatectomy (RP), and it seriously affects the quality of life in patients and their partners. The primary trigger of postoperative ED is surgical injury to the cavernous nerves that control penile erection and run along the anterolateral aspect of the prostate. Despite the introduction and ongoing innovation of nerve-sparing techniques, a significant number of patients still suffer from moderate cavernous nerve injury (CNI), which is thought to be transient and reversible. Therefore, early postoperative penile rehabilitation therapy may salvage patients’ erectile function by promoting cavernous nerve regeneration and preventing penile structural alterations.

Aims: To present a comprehensive overview of the current molecular pathogenesis of CNI-induced ED, as well as novel therapeutic strategies and their potential mechanisms.

Methods: A literature search was performed using PubMed. Search terms included erectile dysfunction, cavernous nerve injury, pathogenesis, pathway, and treatment.

Results: The NOS/NO pathway, oxidative stress-related pathway, RhoA/ROCK pathway, transforming growth factor-β (TGF-β), sonic hedgehog (Shh), and hydrogen sulfide (H2S) are involved in the molecular pathogenesis of CNI-induced ED. Multiple neurotrophins, including brain-derived nerve growth factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and neurturin (NTN), were found to promote cavernous nerve regeneration. Emerging therapeutic approaches can be roughly summarized into four categories, namely small molecule and drug, stem cell-based therapy (SCT), micro-energy therapy and platelet-rich plasma (PRP) therapy.

Conclusion: These pathways collectively lead to the irreversible damage to the penile structure after CNI. The combined early rehabilitation strategies of promoting upstream nerve regeneration and recovering abnormal molecular signals of downstream penis are presumed to save patients’ erectile function after RP. In future studies, the cross-talk between these molecular pathways needs to be further clarified, and the questions of how denervation injury induces the molecular alterations in the penis also need to be addressed.

Towards Precision Oncology: The Role of Smoothened and Its Variants in Cancer

The G protein-coupled receptor Smoothened (Smo) is a central signal transducer of the Hedgehog (Hh) pathway which has been linked to diverse forms of tumours. Stimulated by advancements in structural and functional characterisation, the Smo receptor has been recognised as an important therapeutic target in Hh-driven cancers, and several Smo inhibitors have now been approved for cancer therapy. This receptor is also known to be an oncoprotein itself and its gain-of-function variants have been associated with skin, brain, and liver cancers. According to the COSMIC database, oncogenic mutations of Smo have been identified in various other tumours, although their oncogenic effect remains unknown in these tissues. Drug resistance is a common challenge in cancer therapies targeting Smo, and data analysis shows that healthy individuals also harbour resistance mutations. Based on the importance of Smo in cancer progression and the high incidence of resistance towards Smo inhibitors, this review suggests that detection of Smo variants through tumour profiling could lead to increased precision and improved outcomes of anti-cancer treatments.

Primary cilia and PTH1R interplay in the regulation of osteogenic actions

Primary cilia are subcellular structures specialized in sensing different stimuli in a diversity of cell types. In bone, the primary cilium is involved in mechanical sensing and transduction of signals that regulate the behavior of mesenchymal osteoprogenitors, osteoblasts and osteocytes. To perform its functions, the primary cilium modulates a plethora of molecules including those stimulated by the parathyroid hormone (PTH) receptor type I (PTH1R), a master regulator of osteogenesis. Binding of the agonists PTH or PTH-related protein (PTHrP) to the PTH1R or direct agonist-independent stimulation of the receptor activate PTH1R signaling pathways. In turn, activation of PTH1R leads to regulation of bone formation and remodeling. Herein, we describe the structure, function and molecular partners of primary cilia in the context of bone, playing special attention to those signaling pathways that are mediated directly or indirectly by PTH1R in association with primary cilia during the process of osteogenesis.

The immune microenvironment in gastric adenocarcinoma

Like most solid tumours, the microenvironment of epithelial-derived gastric adenocarcinoma (GAC) consists of a variety of stromal cell types, including fibroblasts, and neuronal, endothelial and immune cells. In this article, we review the role of the immune microenvironment in the progression of chronic inflammation to GAC, primarily the immune microenvironment driven by the gram-negative bacterial species Helicobacter pylori. The infection-driven nature of most GACs has renewed awareness of the immune microenvironment and its effect on tumour development and progression. About 75-90% of GACs are associated with prior H. pylori infection and 5-10% with Epstein-Barr virus infection. Although 50% of the world's population is infected with H. pylori, only 1-3% will progress to GAC, with progression the result of a combination of the H. pylori strain, host susceptibility and composition of the chronic inflammatory response. Other environmental risk factors include exposure to a high-salt diet and nitrates. Genetically, chromosome instability occurs in ~50% of GACs and 21% of GACs are microsatellite instability-high tumours. Here, we review the timeline and pathogenesis of the events triggered by H. pylori that can create an immunosuppressive microenvironment by modulating the host's innate and adaptive immune responses, and subsequently favour GAC development.

Sonic Hedgehog Promotes Proliferation and Migration of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis via Rho/ROCK Signaling

Objective. To explore the underlying mechanism of the sonic hedgehog (Shh) signaling pathway in promoting cell proliferation and migration in fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA). Method. FLS were collected from 8 patients with RA and 3 patients with osteoarthritis (OA). The expression of smoothened (Smo, the Shh pathway activator) was quantified by real-time PCR and western blot. FLS were incubated with cyclopamine (a Smo antagonist), purmorphamine (a Smo agonist), Y27632 (a Rho/ROCK signaling inhibitor), or a combination of purmorphamine and Y27632, respectively. Cell proliferation was examined using cell counting kit-8 and cell cycle assays while cell migration was measured with Transwell and wound healing assays. Results. The expression of Smo was higher in FLS from RA patients than from OA patients ( $p<0.05$ ). RA-FLS treated with purmorphamine showed significantly activated proliferation (119.69 vs. 100.0) and migration (252.38 vs. 178.57) compared to untreated cells (both $p<0.001$ ). RA-FLS incubated with cyclopamine or a combination of purmorphamine and Y27632 exhibited significant suppression of proliferation (81.55 vs. 100.0 and 85.84 vs. 100.0) and migration (100 vs. 178.57 and 109.52 vs. 185) ability (all $p<0.001$ ). Conclusion. Our results demonstrated that Shh promoted cell growth and migration of FLS in RA patients through the Rho/ROCK signaling pathway.

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.

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.

Hedgehog signaling and its molecular perspective with cholesterol: a comprehensive review

Hedgehog (Hh) signaling is evolutionarily conserved and plays an instructional role in embryonic morphogenesis, organogenesis in various animals, and the central nervous system organization. Multiple feedback mechanisms dynamically regulate this pathway in a spatiotemporal and context-dependent manner to confer differential patterns in cell fate determination. Hh signaling is complex due to canonical and non-canonical mechanisms coordinating cell-cell communication. In addition, studies have demonstrated a regulatory framework of Hh signaling and shown that cholesterol is vital for Hh ligand biogenesis, signal generation, and transduction from the cell surface to intracellular space. Studies have shown the importance of a specific cholesterol pool, termed accessible cholesterol, which serves as a second messenger, conveying signals between smoothened (Smo) and patched 1 (Ptch1) across the plasma and ciliary membranes. Remarkably, recent high-resolution structural and molecular studies shed new light on the interplay between Hh signaling and cholesterol in membrane biology. These studies elucidated novel mechanistic insight into the release and dispersal of cholesterol-anchored Hh and the basis of Hh recognition by Ptch1. Additionally, the putative model of Smo activation by cholesterol binding and/or modification and Ptch1 antagonization of Smo has been explicated. However, the coupling mechanism of Hh signaling and cholesterol offered a new regulatory principle in cell biology: how effector molecules of the Hh signal network react to and remodel cholesterol accessibility in the membrane and selectively activate Hh signaling proteins thereof. Recognizing the biological importance of cholesterol in Hh signaling activation and transduction opens the door for translational research to develop novel therapeutic strategies. This review looks in-depth at canonical and non-canonical Hh signaling and the distinct proposed model of cholesterol-mediated regulation of Hh signaling components, facilitating a more sophisticated understanding of the Hh signal network and cholesterol biology.

TMED2 binding restricts SMO to the ER and Golgi compartments

Hedgehog (HH) signaling is important for embryonic pattering and stem cell differentiation. The G protein–coupled receptor (GPCR) Smoothened (SMO) is the key HH signal transducer modulating both transcription-dependent and transcription-independent responses. We show that SMO protects naive mouse embryonic stem cells (ESCs) from dissociation-induced cell death. We exploited this SMO dependency to perform a genetic screen in haploid ESCs where we identify the Golgi proteins TMED2 and TMED10 as factors for SMO regulation. Super-resolution microscopy shows that SMO is normally retained in the endoplasmic reticulum (ER) and Golgi compartments, and we demonstrate that TMED2 binds to SMO, preventing localization to the plasma membrane. Mutation of TMED2 allows SMO accumulation at the plasma membrane, recapitulating early events after HH stimulation. We demonstrate the physiologic relevance of this interaction in neural differentiation, where TMED2 functions to repress HH signal strength. Identification of TMED2 as a binder and upstream regulator of SMO opens the way for unraveling the events in the ER–Golgi leading to HH signaling activation.

Hedgehog signals orchestrate tissue patterning by binding the receptor Patched and restricting the signal transducer Smoothened. A genetic screen reveals Tmed2 as a new interactor of Smoothened that is required for regulating Smoothened transport from the endoplasmic reticulum and Golgi to the plasma membrane and hence modulating the strength of Hedgehog signal transduction.

Isoforms of the orphan nuclear receptor COUP‑TFII differentially modulate pancreatic cancer progression

The expression of the nuclear receptor transcription factor (TF) COUP-TFII is broadly associated with cell differentiation and cancer development, including of pancreatic ductal adenocarcinoma (PDAC), a devastating disease with one of the poorest prognoses among cancers worldwide. Recent studies have started to investigate the pathological and physiological roles of a novel COUP-TFII isoform (COUP-TFII_V2) that lacks the DNA-binding domain. As the role of the canonical COUP-TFII in PDAC was previously demonstrated, the present study evaluated whether COUP-TFII_V2 may have a functional role in PDAC. It was demonstrated that COUP-TFII_V2 naturally occurs in PDAC cells and in primary samples, where its expression is consistent with shorter overall survival and peripheral invasion. Of note, COUP-TFII_V2, exhibiting nuclear and cytosolic expression, is linked to epithelial to mesenchymal transition (EMT) and cancer progression, as confirmed by nude mouse experiments. The present results demonstrated that COUP-TFII_V2 distinctively regulates the EMT of PDAC and, similarly to its sibling, it is associated with tumor aggressiveness. The two isoforms have both overlapping and exclusive functions that cooperate with cancer growth and dissemination. By studying how PDAC cells switch from one isoform to the other, novel insight into cancer biology was gained, indicating that this receptor may serve as a novel possible target for PDAC management.

Regulatory mechanisms of cytoneme-based morphogen transport

During development and tissue homeostasis, cells must communicate with their neighbors to ensure coordinated responses to instructional cues. Cues such as morphogens and growth factors signal at both short and long ranges in temporal- and tissue-specific manners to guide cell fate determination, provide positional information, and to activate growth and survival responses. The precise mechanisms by which such signals traverse the extracellular environment to ensure reliable delivery to their intended cellular targets are not yet clear. One model for how this occurs suggests that specialized filopodia called cytonemes extend between signal-producing and -receiving cells to function as membrane-bound highways along which information flows. A growing body of evidence supports a crucial role for cytonemes in cell-to-cell communication. Despite this, the molecular mechanisms by which cytonemes are initiated, how they grow, and how they deliver specific signals are only starting to be revealed. Herein, we discuss recent advances toward improved understanding of cytoneme biology. We discuss similarities and differences between cytonemes and other types of cellular extensions, summarize what is known about how they originate, and discuss molecular mechanisms by which their activity may be controlled in development and tissue homeostasis. We conclude by highlighting important open questions regarding cytoneme biology, and comment on how a clear understanding of their function may provide opportunities for treating or preventing disease.

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.

The complex web of canonical and non-canonical Hedgehog signaling

Hedgehog (Hh) signaling is a widely studied signaling pathway because of its critical roles during development and in cell homeostasis. Vertebrate canonical and non-canonical Hh signaling are typically assumed to be distinct and occur in different cellular compartments. While research has primarily focused on the canonical form of Hh signaling and its dependency on primary cilia - microtubule-based signaling hubs - an extensive list of crucial functions mediated by non-canonical Hh signaling has emerged. Moreover, amounting evidence indicates that canonical and non-canonical modes of Hh signaling are interlinked, and that they can overlap spatially, and in many cases interact functionally. Here, we discuss some of the many cellular effects of non-canonical signaling and discuss new evidence indicating inter-relationships with canonical signaling. We discuss how Smoothened (Smo), a key component of the Hh pathway, might coordinate such diverse downstream effects. Collectively, pursuit of questions such as those proposed here will aid in elucidating the full extent of Smo function in development and advance its use as a target for cancer therapeutics.

RhoA/ROCK signaling pathway and astrocytes in ischemic stroke

Ischemic stroke is one of the most common and undertreated cerebral diseases with high mortality and disability rate. Various intrinsic and extrinsic factors regulate the onset, severity, and progression of ischemic stroke. As an integral part of the neuronal glia system, astrocytes provide many housekeeping functions in nervous system, and perform multiple functions both beneficial and detrimental for neuronal survival after ischemic stroke. In addition, the small GTPase Rho and its downstream Rho kinase (ROCK) are associated with various neuronal functions such as dendrite development, migration and axonal extension, and numerous central nervous system (CNS) diseases. The aim of this review is to summarize the role of RhoA/ROCK signaling pathway and astrocytes on neurological function after ischemic stroke. We also discuss the interaction of RhoA/ROCK signaling pathway and astrocytes on the tissue repair after brain injury.

Sonic Hedgehog signaling pathway in gynecological and genitourinary cancer (Review)

Cancers of the urinary tract, as well as those of the female and male reproductive systems, account for a large percentage of malignancies worldwide. Mortality is frequently affected by late diagnosis or therapeutic difficulties. The Sonic Hedgehog (SHH) pathway is an evolutionary conserved molecular cascade, which is mainly associated with the development of the central nervous system in fetal life. The present review aimed to provide an in‑depth summary of the SHH signaling pathway, including the characterization of its major components, the mechanism of its upstream regulation and non‑canonical activation, as well as its interactions with other cellular pathways. In addition, the three possible mechanisms of the cellular SHH cascade in cancer tissue are discussed. The aim of the present review was to summarize significant findings with regards to the expression of the SHH pathway components in kidney, bladder, ovarian, cervical and prostate cancer. Reports associated with common deficits and de‑regulations of the SHH pathway were summarized, despite the differences in molecular and histological patterns among these malignancies. However, currently, neither are SHH pathway elements included in panels of prognostic/therapeutic molecular patterns in any of the discussed cancers, nor have the drugs targeting SMO or GLIs been approved for therapy. The findings of the present review may support future studies on the treatment of and/or molecular targets for gynecological and genitourinary cancers.

A non-canonical Hedgehog pathway initiates ciliogenesis and autophagy

Primary cilia function as critical signaling hubs whose absence leads to severe disorders collectively known as ciliopathies; our knowledge of ciliogenesis remains limited. We show that Smo induces ciliogenesis through two distinct yet essential noncanonical Hh pathways in several cell types, including neurons. Surprisingly, ligand activation of Smo induces autophagy via an LKB1-AMPK axis to remove the satellite pool of OFD1. This is required, but not sufficient, for ciliogenesis. Additionally, Smo activates the Gαi-LGN-NuMA-dynein axis, causing accumulation of a portion of OFD1 at centrioles in early ciliogenesis. Both pathways are critical for redistribution of BBS4 from satellites to centrioles, which is also mediated by OFD1 centriolar translocation. Notably, different Smo agonists, which activate Smo distinctly, activate one or the other of these pathways; only in combination they recapitulate the activity of Hh ligand. These studies provide new insight into physiological stimuli (Hh) that activate autophagy and promote ciliogenesis and introduce a novel role for the Gαi-LGN-NuMA-dynein complex in this process.

Regulation of hepatic stellate cell contraction and cirrhotic portal hypertension by Wnt/β-catenin signalling via interaction with Gli1

BACKGROUND AND PURPOSE

Portal hypertension is a lethal complication of cirrhosis. Its mechanism and therapeutic targets remain largely unknown. Hepatic stellate cell (HSC) contraction increases intrahepatic vascular resistance contributing to portal hypertension. We investigated how HSC contraction was regulated by Wnt signalling and the therapeutic implications.

EXPERIMENTAL APPROACH

Liver tissues from cirrhotic patients were examined. Cirrhotic mice with genetic or pharmacological treatments were used for in vivo assessments, and their primary cells were isolated. Cellular functions and signalling pathways were analysed in human HSC-LX2 cells using real-time PCR, Western blotting, siRNA, luciferase reporter assay, chromatin immunoprecipitation, co-immunoprecipitation and site-directed mutagenesis.

KEY RESULTS

Wnt/β-catenin correlated with HSC contraction in human cirrhotic liver. Wnt3a stimulated Smo-independent Gli1 nuclear translocation followed by LARG-mediated RhoA activation leading to HSC contraction. Suppressor of fused (Sufu) negatively mediated Wnt3a-induced Gli1 nuclear translocation. Wnt/β-catenin repressed transcription of Sufu dependent on β-catenin/TCF4 interaction and TCF4 binding to Sufu promoter. Molecular simulation and site-directed mutagenesis identified the β-catenin residues Lys312 and Lys435 critically involved in this interaction. TCF4 binding to the sequence CACACCTTCC at Sufu promoter was required for transrepression of Sufu. In cirrhotic mice, short-term liver-targeting β-catenin deficiency or acute treatment with β-catenin inhibitors reduced portal pressure via restriction of HSC contraction rather than inhibiting HSC activation. Long-term deficiency or treatments also ameliorated liver injury, fibrosis and inflammation.

CONCLUSION AND IMPLICATIONS

Interaction between Wnt/β-catenin and Smo-independent Gli1 pathways promoted HSC contraction via TCF4-dependent transrepression of Sufu. HSC-specific inhibition of β-catenin may have therapeutic benefits for cirrhotic portal hypertension.

Ubiquitin-protein ligase Ubr5 cooperates with hedgehog signalling to promote skeletal tissue homeostasis

Mammalian Hedgehog (HH) signalling pathway plays an essential role in tissue homeostasis and its deregulation is linked to rheumatological disorders. UBR5 is the mammalian homologue of the E3 ubiquitin-protein ligase Hyd, a negative regulator of the Hh-pathway in Drosophila. To investigate a possible role of UBR5 in regulation of the musculoskeletal system through modulation of mammalian HH signaling, we created a mouse model for specific loss of Ubr5 function in limb bud mesenchyme. Our findings revealed a role for UBR5 in maintaining cartilage homeostasis and suppressing metaplasia. Ubr5 loss of function resulted in progressive and dramatic articular cartilage degradation, enlarged, abnormally shaped sesamoid bones and extensive heterotopic tissue metaplasia linked to calcification of tendons and ossification of synovium. Genetic suppression of smoothened (Smo), a key mediator of HH signalling, dramatically enhanced the Ubr5 mutant phenotype. Analysis of HH signalling in both mouse and cell model systems revealed that loss of Ubr5 stimulated canonical HH-signalling while also increasing PKA activity. In addition, human osteoarthritic samples revealed similar correlations between UBR5 expression, canonical HH signalling and PKA activity markers. Our studies identified a crucial function for the Ubr5 gene in the maintenance of skeletal tissue homeostasis and an unexpected mode of regulation of the HH signalling pathway.

Hedgehog Signaling: Implications in Cancers and Viral Infections

The hedgehog (SHH) signaling pathway is primarily involved in embryonic gut development, smooth muscle differentiation, cell proliferation, adult tissue homeostasis, tissue repair following injury, and tissue polarity during the development of vertebrate and invertebrate organisms. GLIoma-associated oncogene homolog (GLI) family of zinc-finger transcription factors and smoothened (SMO) are the signal transducers of the SHH pathway. Both SHH ligand-dependent and independent mechanisms activate GLI proteins. Various transcriptional mechanisms, posttranslational modifications (phosphorylation, ubiquitination, proteolytic processing, SUMOylation, and acetylation), and nuclear-cytoplasmic shuttling control the activity of SHH signaling pathway proteins. The dysregulated SHH pathway is associated with bone and soft tissue sarcomas, GLIomas, medulloblastomas, leukemias, and tumors of breast, lung, skin, prostate, brain, gastric, and pancreas. While extensively studied in development and sarcomas, GLI family proteins play an essential role in many host-pathogen interactions, including bacterial and viral infections and their associated cancers. Viruses hijack host GLI family transcription factors and their downstream signaling cascades to enhance the viral gene transcription required for replication and pathogenesis. In this review, we discuss a distinct role(s) of GLI proteins in the process of tumorigenesis and host-pathogen interactions in the context of viral infection-associated malignancies and cancers due to other causes. Here, we emphasize the potential of the Hedgehog (HH) pathway targeting as a potential anti-cancer therapeutic approach, which in the future could also be tested in infection-associated fatalities.

The Role of Smoothened in Cancer

Smoothened (SMO) belongs to the Hedgehog (HH) signaling pathway, which regulates cell growth, migration, invasion and stem cells in cancer. The HH signaling pathway includes both canonical and noncanonical pathways. The canonical HH pathway functions through major HH molecules such as HH ligands, PTCH, SMO and GLI, whereas the noncanonical HH pathway involves the activation of SMO or GLI through other pathways. The role of SMO has been discussed in different types of cancer, including breast, liver, pancreatic and colon cancers. SMO expression correlates with tumor size, invasiveness, metastasis and recurrence. In addition, SMO inhibitors can suppress cancer formation, reduce the proliferation of cancer cells, trigger apoptosis and suppress cancer stem cell activity. A better understanding of the role of SMO in cancer could contribute to the development of novel therapeutic approaches.

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.

Crosstalk Between Signaling Pathways Involved in the Regulation of Airway Smooth Muscle Cell Hyperplasia

Increased ASM mass, primarily due to ASM hyperplasia, has been recognized as a hallmark of airway remodeling in asthma. Increased ASM mass is the major contributor to the airway narrowing, thus worsening the bronchoconstriction in response to stimuli. Inflammatory mediators and growth factors released during inflammation induce increased ASM mass surrounding airway wall via increased ASM proliferation, diminished ASM apoptosis and increased ASM migration. Several major pathways, such as MAPKs, PI3K/AKT, JAK2/STAT3 and Rho kinase, have been reported to regulate these cellular activities in ASM and were reported to be interrelated at certain points. This article aims to provide an overview of the signaling pathways/molecules involved in ASM hyperplasia as well as the mapping of the interplay/crosstalk between these major pathways in mediating ASM hyperplasia. A more comprehensive understanding of the complexity of cellular signaling in ASM cells will enable more specific and safer drug development in the control of asthma.

Sonic hedgehog selectively promotes lymphangiogenesis after kidney injury through noncanonical pathway

Kidney fibrosis is associated with an increased lymphangiogenesis, characterized by the formation and expansion of new lymphatic vessels. However, the trigger and underlying mechanism responsible for the growth of lymphatic vessels in diseased kidney remain poorly defined. Here, we report that tubule-derived sonic hedgehog (Shh) ligand is a novel lymphangiogenic factor that plays a crucial role in mediating lymphatic endothelial cell proliferation and expansion. Shh was induced in renal tubular epithelium in various models of fibrotic chronic kidney disease, and this was accompanied by an expansion of lymphatic vessels in adjacent areas. In vitro, Shh selectively promoted the proliferation of human dermal lymphatic endothelial cells (HDLECs) but not human umbilical vein endothelial cells, as assessed by cell counting, MTT assay, and bromodeoxyuridine incorporation. Shh also induced the expression of vascular endothelial growth factor receptor-3, cyclin D1, and proliferating cell nuclear antigen in HDLECs. Shh did not affect the expression of Gli1, the downstream target and readout of canonical hedgehog signaling, but activated ERK-1/2 in HDLECs. Inhibition of Smoothened with small-molecule inhibitor or blockade of ERK-1/2 activation abolished the lymphatic endothelial cell proliferation induced by Shh. In vivo, inhibition of Smoothened also repressed lymphangiogenesis and attenuated renal fibrosis. This study identifies Shh as a novel mitogen that selectively promotes lymphatic, but not vascular, endothelial cell proliferation and suggests that tubule-derived Shh plays an essential role in mediating lymphangiogenesis after kidney injury.

Role of Hedgehog Signaling in Vasculature Development, Differentiation, and Maintenance

The role of Hedgehog (Hh) signaling in vascular biology has first been highlighted in embryos by Pepicelli et al. in 1998 and Rowitch et al. in 1999. Since then, the proangiogenic role of the Hh ligands has been confirmed in adults, especially under pathologic conditions. More recently, the Hh signaling has been proposed to improve vascular integrity especially at the blood–brain barrier (BBB). However, molecular and cellular mechanisms underlying the role of the Hh signaling in vascular biology remain poorly understood and conflicting results have been reported. As a matter of fact, in several settings, it is currently not clear whether Hh ligands promote vessel integrity and quiescence or destabilize vessels to promote angiogenesis. The present review relates the current knowledge regarding the role of the Hh signaling in vasculature development, maturation and maintenance, discusses the underlying proposed mechanisms and highlights controversial data which may serve as a guideline for future research. Most importantly, fully understanding such mechanisms is critical for the development of safe and efficient therapies to target the Hh signaling in both cancer and cardiovascular/cerebrovascular diseases.

RhoGTPase in Vascular Disease

Ras-homologous (Rho)A/Rho-kinase pathway plays an essential role in many cellular functions, including contraction, motility, proliferation, and apoptosis, inflammation, and its excessive activity induces oxidative stress and promotes the development of cardiovascular diseases. Given its role in many physiological and pathological functions, targeting can result in adverse effects and limit its use for therapy. In this review, we have summarized the role of RhoGTPases with an emphasis on RhoA in vascular disease and its impact on endothelial, smooth muscle, and heart and lung fibroblasts. It is clear from the various studies that understanding the regulation of RhoGTPases and their regulators in physiology and pathological conditions is required for effective targeting of Rho.

Signalling networks in cholangiocarcinoma: Molecular pathogenesis, targeted therapies and drug resistance

Cholangiocarcinoma (CCA) is a deadly disease. While surgery may attain cure in a minor fraction of cases, therapeutic options in either the adjuvant or advanced setting are limited. The possibility of advancing the efficacy of therapeutic approaches to CCA relies on understanding its molecular pathogenesis and developing rational therapies aimed at interfering with oncogenic signalling networks that drive and sustain cholangiocarcinogenesis. These efforts are complicated by the intricate biology of CCA, which integrates not only the driving force of tumour cell-intrinsic alterations at the genetic and epigenetic level but also pro-tumorigenic cues conveyed to CCA cells by different cell types present in the rich tumour stroma. Herein, we review our current understanding of the mechanistic bases underpinning the activation of major oncogenic pathways causative of CCA pathogenesis. We subsequently discuss how this knowledge is being exploited to implement rationale-based and genotype-matched therapeutic approaches that predictably will radically transform CCA clinical management in the next decade. We conclude by highlighting the mechanisms of therapeutic resistance in CCA and reviewing innovative approaches to combat resistance at the preclinical and clinical level.

Gi/o-Protein Coupled Receptors in the Aging Brain

Cells translate extracellular signals to regulate processes such as differentiation, metabolism and proliferation, via transmembranar receptors. G protein-coupled receptors (GPCRs) belong to the largest family of transmembrane receptors, with over 800 members in the human species. Given the variety of key physiological functions regulated by GPCRs, these are main targets of existing drugs. During normal aging, alterations in the expression and activity of GPCRs have been observed. The central nervous system (CNS) is particularly affected by these alterations, which results in decreased brain functions, impaired neuroregeneration, and increased vulnerability to neuropathologies, such as Alzheimer's and Parkinson diseases. GPCRs signal via heterotrimeric G proteins, such as G_o, the most abundant heterotrimeric G protein in CNS. We here review age-induced effects of GPCR signaling via the G_i/o subfamily at the CNS. During the aging process, a reduction in protein density is observed for almost half of the G_i/o-coupled GPCRs, particularly in age-vulnerable regions such as the frontal cortex, hippocampus, substantia nigra and striatum. G_i/o levels also tend to decrease with aging, particularly in regions such as the frontal cortex. Alterations in the expression and activity of GPCRs and coupled G proteins result from altered proteostasis, peroxidation of membranar lipids and age-associated neuronal degeneration and death, and have impact on aging hallmarks and age-related neuropathologies. Further, due to oligomerization of GPCRs at the membrane and their cooperative signaling, down-regulation of a specific G_i/o-coupled GPCR may affect signaling and drug targeting of other types/subtypes of GPCRs with which it dimerizes. G_i/o-coupled GPCRs receptorsomes are thus the focus of more effective therapeutic drugs aiming to prevent or revert the decline in brain functions and increased risk of neuropathologies at advanced ages.

Structure, function and disease relevance of Wnt inhibitory factor 1, a secreted protein controlling the Wnt and hedgehog pathways

Wnts and Hedgehogs (Hh) are large, lipid-modified extracellular morphogens that play key roles in embryonic development and stem cell proliferation of Metazoa. Both morphogens signal through heptahelical Frizzled-type receptors of the G-Protein Coupled Receptor family and there are several other similarities that suggest a common evolutionary origin of the Hh and Wnt pathways. There is evidence that the secreted protein, Wnt inhibitory factor 1 (WIF1) modulates the activity of both Wnts and Hhs and may thus contribute to the intertwining of these pathways. In this article, we review the structure, evolution, molecular interactions and functions of WIF1 with major emphasis on its role in carcinogenesis.

[Current situation of researches on a sensor organelle, primary cilium, to understand the pathogenesis of ciliopathy]

Primary cilium is a membrane-protruding immotile sensory organelle. It had been supposed that the cilium was a static organelle for long periods. However, recent studies have uncovered that the cilium is dynamically organized organelle in a cell cycle-dependent manner; it is formed during G₀/G₁ phase and resorbed when the cells enter cell division cycle. Despite the primary cilium is very short and its surface area is extremely small, the cilium possesses a few kinds of G protein-coupled receptors, growth factor receptors and ion channels. Therefore, it can function as a signaling receptor for selective bioactive ligands and mechanical stresses. Dysregulation of the ciliary dynamics is linked with hereditary disorders, so called "ciliopathy", with clinical manifestations of microcephaly, polycystic kidney, situs inversus, polydactyly, and so on. No effective medical treatment for the ciliopathies has been available. Increasing evidences about the molecular mechanisms of ciliary dynamics and ciliary functions have revealed that enormous number of molecules regulate a cycle of ciliogenesis, cilium-derived signaling, ciliary resorption and elimination. However, it is a fact that research progress is far inferior to the full disclosure of the molecular mechanisms. Further studies are required to clarify the pathogenesis of the cilipathies. Moreover, efficient medical treatments are expected to be developed by pharmacological approaches.

DYRK1B regulates Hedgehog-induced microtubule acetylation

The posttranslational modification (PTM) of tubulin subunits is important for the physiological functions of the microtubule (MT) cytoskeleton. Although major advances have been made in the identification of enzymes carrying out MT-PTMs, little knowledge is available on how intercellular signaling molecules and their associated pathways regulate MT-PTM-dependent processes inside signal-receiving cells. Here we show that Hedgehog (Hh) signaling, a paradigmatic intercellular signaling system, affects the MT acetylation state in mammalian cells. Mechanistically, Hh pathway activity increases the levels of the MT-associated DYRK1B kinase, resulting in the inhibition of GSK3β through phosphorylation of Serine 9 and the subsequent suppression of HDAC6 enzyme activity. Since HDAC6 represents a major tubulin deacetylase, its inhibition increases the levels of acetylated MTs. Through the activation of DYRK1B, Hh signaling facilitates MT-dependent processes such as intracellular mitochondrial transport, mesenchymal cell polarization or directed cell migration. Taken together, we provide evidence that intercellular communication through Hh signals can regulate the MT cytoskeleton and contribute to MT-dependent processes by affecting the level of tubulin acetylation.

Hedgehog Signaling in Cancer: A Prospective Therapeutic Target for Eradicating Cancer Stem Cells

The Hedgehog (Hh) pathway is a signaling cascade that plays a crucial role in many fundamental processes, including embryonic development and tissue homeostasis. Moreover, emerging evidence has suggested that aberrant activation of Hh is associated with neoplastic transformations, malignant tumors, and drug resistance of a multitude of cancers. At the molecular level, it has been shown that Hh signaling drives the progression of cancers by regulating cancer cell proliferation, malignancy, metastasis, and the expansion of cancer stem cells (CSCs). Thus, a comprehensive understanding of Hh signaling during tumorigenesis and development of chemoresistance is necessary in order to identify potential therapeutic strategies to target various human cancers and their relapse. In this review, we discuss the molecular basis of the Hh signaling pathway and its abnormal activation in several types of human cancers. We also highlight the clinical development of Hh signaling inhibitors for cancer therapy as well as CSC-targeted therapy.

Potential use of CXCL12/CXCR4 and sonic hedgehog pathways as therapeutic targets in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor occurring in children, and although high long-term survival rates have been reached with current therapeutic protocols, several neurological injuries are still observed among survivors. It has been shown that the development of MB is highly dependent on the microenvironment surrounding it and that the CXCL12 chemokine and its receptor, CXCR4 and the Sonic Hedgehog (SHH) pathway are crucial for cerebellar development, coordinating proliferation and migration of embryonic cells and malfunctions in these axes can lead to MB development. Indeed, the concomitant overactivation of these axes was suggested to define a new MB molecular subgroup. New molecules are being studied, aiming to inhibit either CXCR4 or the SHH pathways and have been tested in preclinical settings for the treatment of cancers. The use of these molecules could improve MB treatment and save patients from aggressive surgery, chemotherapy and radiotherapy regimens, which are responsible for severe neurological consequences. This review aims to summarize current data about the experimental inhibition of CXCR4 and SHH pathways in MB and its potential implications in treatment of this cancer.

Activation of the Gi protein-RHOA axis by non-canonical Hedgehog signaling is independent of primary cilia

Primary cilia are solitary organelles that emanate from the plasma membrane during growth arrest in almost all mammalian cells. The canonical Hedgehog (HH) pathway requires trafficking of the G protein-coupled receptor SMOOTHENED (SMO) and the GLI transcription factors to the primary cilium upon binding of a HH ligand to PATCHED1. However, it is unknown if activation of the small GTPase RHOA by SMO coupling to heterotrimeric Gi proteins, a form of non-canonical HH signaling, requires localization of SMO in the primary cilium. In this study, we compared RHOA and Gi protein stimulation by activation of SMO or sphingosine 1-phosphate receptor (S1P) receptors in WT and KIF3A-deficient mouse embryonic fibroblasts that lack primary cilia. We found that activation of SMO in response to Sonic HH (SHH) or purmorphamine (PUR), a small molecule agonist of SMO, stimulates Gi proteins and RHOA independently of the presence of primary cilia, similar to the effects of S1P. However, while S1P induced a fast activation of AKT that is sensitive to the Gi inhibitor pertussis toxin, HH pathway activators did not significantly activate AKT, suggesting that RHOA activation is not downstream of AKT. Our findings demonstrate that early events in some forms of non-canonical HH signaling occur in extraciliary membranes, which might be particularly relevant for actively-cycling cells, for some cancers characterized by loss of primary cilia, and in ciliopathies.

Sonic Hedgehog Medulloblastoma Cancer Stem Cells Mirnome and Transcriptome Highlight Novel Functional Networks

Molecular classification has improved the knowledge of medulloblastoma (MB), the most common malignant brain tumour in children, however current treatments cause severe side effects in patients. Cancer stem cells (CSCs) have been described in MB and represent a sub population characterised by self-renewal and the ability to generate tumour cells, thus representing the reservoir of the tumour. To investigate molecular pathways that characterise this sub population, we isolated CSCs from Sonic Hedgehog Medulloblastoma (SHH MB) arisen in Patched 1 (Ptch1) heterozygous mice, and performed miRNA- and mRNA-sequencing. Comparison of the miRNA-sequencing of SHH MB CSCs with that obtained from cerebellar Neural Stem Cells (NSCs), allowed us to obtain a SHH MB CSC miRNA differential signature. Pathway enrichment analysis in SHH MB CSCs mirnome and transcriptome was performed and revealed a series of enriched pathways. We focused on the putative targets of the SHH MB CSC miRNAs that were involved in the enriched pathways of interest, namely pathways in cancer, PI3k-Akt pathway and protein processing in endoplasmic reticulum pathway. In silico analysis was performed in SHH MB patients and identified several genes, whose expression was associated with worse overall survival of SHH MB patients. This study provides novel candidates whose functional role should be further investigated in SHH MB.

Sonic hedgehog-dependent activation of adventitial fibroblasts promotes neointima formation

Aims

Adventitial cells have been suggested to contribute to neointima formation, but the functional relevance and the responsible signalling pathways are largely unknown. Sonic hedgehog (Shh) is a regulator of vasculogenesis and promotes angiogenesis in the adult.

Methods and results

Here we show that proliferation of vascular smooth muscle cells (SMC) after wire-induced injury in C57BL/6 mice is preceded by proliferation of adventitial fibroblasts. Simultaneously, the expression of Shh and its downstream signalling protein smoothened (SMO) were robustly increased within injured arteries. In vitro, combined stimulation with Shh and platelet-derived growth factor (PDGF)-BB strongly induced proliferation and migration of human adventitial fibroblasts. The supernatant of these activated fibroblasts contained high levels of interleukin-6 and -8 and strongly induced proliferation and migration of SMC. Inhibition of SMO selectively prevented fibroblast proliferation, cytokine release, and paracrine SMC activation. Mechanistically, we found that PDGF-BB activates protein kinase A in fibroblasts and thereby induces trafficking of SMO to the plasma membrane, where it can be activated by Shh. In vivo, SMO-inhibition significantly prevented the proliferation of adventitial fibroblasts and neointima formation following wire-induced injury.

Conclusions

The initial activation of adventitial fibroblasts is essential for the subsequent proliferation of SMC and neointima formation. We identified SMO-dependent Shh signalling as a specific process for the activation of adventitial fibroblasts.

Coupling of Smoothened to inhibitory G proteins reduces voltage-gated K+ currents in cardiomyocytes and prolongs cardiac action potential duration

SMO (Smoothened), the central transducer of Hedgehog signaling, is coupled to heterotrimeric G_i proteins in many cell types, including cardiomyocytes. In this study, we report that activation of SMO with SHH (Sonic Hedgehog) or a small agonist, purmorphamine, rapidly causes a prolongation of the action potential duration that is sensitive to a SMO inhibitor. In contrast, neither of the SMO agonists prolonged the action potential in cardiomyocytes from transgenic G_iCT/TTA mice, in which G_i signaling is impaired, suggesting that the effect of SMO is mediated by G_i proteins. Investigation of the mechanism underlying the change in action potential kinetics revealed that activation of SMO selectively reduces outward voltage-gated K⁺ repolarizing (Kv) currents in isolated cardiomyocytes and that it induces a down-regulation of membrane levels of Kv4.3 in cardiomyocytes and intact hearts from WT but not from GiCT/TTA mice. Moreover, perfusion of intact hearts with Shh or purmorphamine increased the ventricular repolarization time (QT interval) and induced ventricular arrhythmias. Our data constitute the first report that acute, noncanonical Hh signaling mediated by G_i proteins regulates K⁺ currents density in cardiomyocytes and sensitizes the heart to the development of ventricular arrhythmias.

Overlap in signaling between Smoothened and the α subunit of the heterotrimeric G protein G13

The Hedgehog family of morphogens has long been known to utilize, through the 7-transmembrane protein Smoothened (Smo), the heterotrimeric G protein Gi in both canonical and noncanonical forms of signaling. Other G proteins, while not specifically utilized by Smo, may nonetheless provide access to some of the events controlled by it. We reported several years ago that the G protein G13 activates one or more forms of the Gli family of transcription factors. While the Gli transcription factors are well known targets for Smo, the uncertain mechanism of activation by G13 and the identity of the targeted Gli(s) limited predictions as to the extent to which G13 might mimic Smo's actions. We evaluate here the potential for overlap in G13 and Smo signaling using C3H10T1/2 and 3T3-L1 cells as models of osteogenesis and adipogenesis, respectively. We find in C3H10T1/2 cells that a constitutively active form of Gα13 (Gα13QL) increases Gli1 mRNA, as does a constitutively active form of Smo (SmoA1). We find as well that Gα13QL induces alkaline phosphatase activity, a marker of osteogenesis, albeit the induction is far less substantial than that achieved by SmoA1. In 3T3-L1 cells both Gα13QL and SmoA1 markedly suppress adipogenic differentiation as determined by triglyceride accumulation. RNA sequencing reveals that Gα13QL and SmoA1 regulate many of the same genes but that quantitative and qualitative differences exist. Differences also exist, we find, between SmoA1 and purmorphamine, an agonist for Smo. Therefore, while comparisons of constitutively active proteins are informative, extrapolations to the setting of agonists require care.

Autophagic Flux Is Regulated by Interaction Between the C-terminal Domain of PATCHED1 and ATG101

The Hedgehog (Hh) receptor Patched1 (PTCH1) is a well-known tumor suppressor that in its active form represses Smoothened (SMO) activity, inhibits proliferation, and induces apoptosis. The cytoplasmic C-terminal domain (CTD) regulates PTCH1 turnover and nucleates a proapoptotic complex. In this study, it was mechanistically determined that Autophagy-related 101 (ATG101), essential for mammalian autophagy, physically interacts with the CTD of PTCH1 and connects it to the ULK complex, which stimulates the autophagy machinery in response to changes in nutrient availability. This interaction results in a blockade of basal autophagic flux and accumulation of autophagosomes with undegraded cargo. Remarkably, this function of PTCH1 is independent of its repressive activity on SMO, as shown in SMO-deficient cells or in the presence of a SMO inhibitor, but is opposed by Sonic Hedgehog (SHH). These findings reveal a novel noncanonical function of PTCH1 that limits autophagy, mediated by ATG101, which could have therapeutic implications in Hh-dependent cancers.Implications: Loss-of-function of the tumor suppressor Patched1 might promote cancer cell fitness by increasing autophagic flux in response to metabolic or environmental stresses. Mol Cancer Res; 16(5); 909-19. ©2018 AACR.

The cholangiocyte primary cilium in health and disease

Cholangiocytes, like most cells, express primary cilia extending from their membranes. These organelles function as antennae which detect stimuli from bile and transmit the information into cells regulating several signaling pathways involved in secretion, proliferation and apoptosis. The ability of primary cilia to detect different signals is provided by ciliary associated proteins which are expressed in its membrane. Defects in the structure and/or function of these organelles lead to cholangiociliopathies that result in cholangiocyte hyperproliferation, altered fluid secretion and absorption. Since primary cilia dysfunction has been observed in several epithelial tumors, including cholangiocarcinoma (CCA), primary cilia have been proposed as tumor suppressor organelles. In addition, the loss of cilia is associated with dysregulation of several molecular pathways resulting in CCA development and progression. Thus, restoration of the primary cilia may be a potential therapeutic approach for several ciliopathies and CCA.