Hedgehog secretion and signal transduction in vertebrates

Targeting signaling pathways in cancer stem cells: A potential approach for developing novel anti-cancer therapeutics

Cancer stem cells (CSCs) have emerged as prime players in the intricate landscape of cancer development, progression, and resistance to traditional treatments. These unique cellular subpopulations own the remarkable capability of self-renewal and differentiation, giving rise to the diverse cellular makeup of tumors and fostering their recurrence following conventional therapies. In the quest for developing more effective cancer therapeutics, the focus has now shifted toward targeting the signaling pathways that govern CSCs behavior. This chapter underscores the significance of these signaling pathways in CSC biology and their potential as pivotal targets for the development of novel chemotherapy approaches. We delve into several key signaling pathways essential for maintaining the defining characteristics of CSCs, including the Wnt, Hedgehog, Notch, JAK-STAT, NF-κB pathways, among others, shedding light on their potential crosstalk. Furthermore, we highlight the latest advancements in CSC-targeted therapies, spanning from promising preclinical models to ongoing clinical trials. A comprehensive understanding of the intricate molecular aspects of CSC signaling pathways and their manipulation holds the prospective to revolutionize cancer treatment paradigms. This, in turn, could lead to more efficacious and personalized therapies with the ultimate goal of eradicating CSCs and enhancing overall patient outcomes. The exploration of CSC signaling pathways represents a key step towards a brighter future in the battle against cancer.

Gestational iron deficiency affects the ratio between interneuron subtypes in the postnatal cerebral cortex in mice

Gestational iron deficiency (gID) is highly prevalent and associated with an increased risk of intellectual and developmental disabilities in affected individuals that are often defined by a disrupted balance of excitation and inhibition (E/I) in the brain. Using a nutritional mouse model of gID, we previously demonstrated a shift in the E/I balance towards increased inhibition in the brains of gID offspring that was refractory to postnatal iron supplementation. We thus tested whether gID affects embryonic progenitor cells that are fated towards inhibitory interneurons. We quantified relevant cell populations during embryonic inhibitory neuron specification and found an increase in the proliferation of Nkx2.1+ interneuron progenitors in the embryonic medial ganglionic eminence at E14 that was associated with increased Shh signaling in gID animals at E12. When we quantified the number of mature inhibitory interneurons that are known to originate from the MGE, we found a persistent disruption of differentiated interneuron subtypes in early adulthood. Our data identify a cellular target that links gID with a disruption of cortical interneurons which play a major role in the establishment of the E/I balance.

Hepatic transcript profiling in beef cattle: Effects of rumen-protected niacin supplementation

The objective of our study was to assess the effect of rumen-protected niacin supplementation on the transcriptome of liver tissue in growing Angus × Simmental steers and heifers through RNA-seq analysis. Consequently, we wanted to assess the known role of niacin in the physiological processes of vasodilation, detoxification, and immune function in beef hepatic tissue. Normal weaned calves (~8 months old) were provided either a control diet or a diet supplemented with rumen-protected niacin (6 g/hd/d) for a 30-day period, followed by a liver biopsy. We observed a significant list of changes at the transcriptome level due to rumen-protected niacin supplementation. Several metabolic pathways revealed potential positive effects to the animal's liver metabolism due to administration of rumen-protected niacin; for example, a decrease in lipolysis, apoptosis, inflammatory responses, atherosclerosis, oxidative stress, fibrosis, and vasodilation-related pathways. Therefore, results from our study showed that the liver transcriptional machinery switched several metabolic pathways to a condition that could potentially benefit the health status of animals supplemented with rumen-protected niacin. In conclusion, based on the results of our study, we can suggest the utilization of rumen-protected niacin supplementation as a nutritional strategy could improve the health status of growing beef cattle in different beef production stages, such as backgrounding operations or new arrivals to a feedlot.

Disruption of hedgehog signaling leads to hyoid bone dysplasia during embryogenesis

The development of the hyoid bone is a complex process that involves the coordination of multiple signaling pathways. Previous studies have demonstrated that disruption of the hedgehog pathway in mice results in a series of structural malformations. However, the specific role and critical period of the hedgehog pathway in the early development of the hyoid bone have not been thoroughly characterized. In this study, we treated pregnant ICR mice with the hedgehog pathway inhibitor vismodegib by oral gavage in order to establish a model of hyoid bone dysplasia. Our results indicate that administration of vismodegib at embryonic days 11.5 (E11.5) and E12.5 resulted in the development of hyoid bone dysplasia. We were able to define the critical periods for the induction of hyoid bone deformity through the use of a meticulous temporal resolution. Our findings suggest that the hedgehog pathway plays a crucial role in the early development of the hyoid bone. Additionally, our research has established a novel and easily established mouse model of synostosis in the hyoid bone using a commercially available pathway-selective inhibitor.

Understanding the Roles of the Hedgehog Signaling Pathway during T-Cell Lymphopoiesis and in T-Cell Acute Lymphoblastic Leukemia (T-ALL)

The Hedgehog (HH) signaling network is one of the main regulators of invertebrate and vertebrate embryonic development. Along with other networks, such as NOTCH and WNT, HH signaling specifies both the early patterning and the polarity events as well as the subsequent organ formation via the temporal and spatial regulation of cell proliferation and differentiation. However, aberrant activation of HH signaling has been identified in a broad range of malignant disorders, where it positively influences proliferation, survival, and therapeutic resistance of neoplastic cells. Inhibitors targeting the HH pathway have been tested in preclinical cancer models. The HH pathway is also overactive in other blood malignancies, including T-cell acute lymphoblastic leukemia (T-ALL). This review is intended to summarize our knowledge of the biological roles and pathophysiology of the HH pathway during normal T-cell lymphopoiesis and in T-ALL. In addition, we will discuss potential therapeutic strategies that might expand the clinical usefulness of drugs targeting the HH pathway in T-ALL.

GRAMD1/ASTER-mediated cholesterol transport promotes Smoothened cholesterylation at the endoplasmic reticulum

Hedgehog (Hh) signaling pathway plays a pivotal role in embryonic development. Hh binding to Patched1 (PTCH1) derepresses Smoothened (SMO), thereby activating the downstream signal transduction. Covalent SMO modification by cholesterol in its cysteine-rich domain (CRD) is essential for SMO function. SMO cholesterylation is a calcium-accelerated autoprocessing reaction, and STIM1-ORAI1-mediated store-operated calcium entry promotes cholesterylation and activation of endosome-localized SMO. However, it is unknown whether the Hh-PTCH1 interplay regulates the activity of the endoplasmic reticulum (ER)-localized SMO. Here, we found that PTCH1 inhibited the COPII-dependent export of SMO from the ER, whereas Hh promoted this process. The RRxWxR amino acid motif in the cytosolic tail of SMO was essential for COPII recognition, ciliary localization, and signal transduction activity. Hh and PTCH1 regulated cholesterol modification of the ER-localized SMO, and SMO cholesterylation accelerated its exit from ER. The GRAMD1/ASTER sterol transport proteins facilitated cholesterol transfer to ER from PM, resulting in increased SMO cholesterylation and enhanced Hh signaling. Collectively, we reveal a regulatory role of GRAMD-mediated cholesterol transport in ER-resident SMO maturation and Hh signaling.

Targeting the Hedgehog Pathway in Rhabdomyosarcoma

Aberrant activation of the Hedgehog (Hh) signalling pathway is known to play an oncogenic role in a wide range of cancers; in the particular case of rhabdomyosarcoma, this pathway has been demonstrated to be an important player for both oncogenesis and cancer progression. In this review, after a brief description of the pathway and the characteristics of its molecular components, we describe, in detail, the main activation mechanisms that have been found in cancer, including ligand-dependent, ligand-independent and non-canonical activation. In this context, the most studied inhibitors, i.e., SMO inhibitors, have shown encouraging results for the treatment of basal cell carcinoma and medulloblastoma, both tumour types often associated with mutations that lead to the activation of the pathway. Conversely, SMO inhibitors have not fulfilled expectations in tumours-among them sarcomas-mostly associated with ligand-dependent Hh pathway activation. Despite the controversy existing regarding the results obtained with SMO inhibitors in these types of tumours, several compounds have been (or are currently being) evaluated in sarcoma patients. Finally, we discuss some of the reasons that could explain why, in some cases, encouraging preclinical data turned into disappointing results in the clinical setting.

Targeting crosstalk of signaling pathways in cancer stem cells: a promising approach for development of novel anti-cancer therapeutics

Wnt, Hedgehog (Hh), and Notch signaling pathways are the evolutionarily conserved signaling pathways that regulate the embryonic development and also play crucial role in maintaining stemness properties of cancer stem cells (CSCs) and inducing epithelial-to-mesenchymal transition (EMT), metastasis, and angiogenesis. It has been highly challenging to inhibit the CSCs growth and proliferation as these are capable of evading chemotherapeutic drugs and cause cancer recurrence through multiple signaling pathways. Therefore, novel therapeutic strategies to target the key players involved in the crosstalk of these signaling pathways need to be developed. In this review, we have identified the interacting molecules of Wnt, Hh, and Notch pathways responsible for enhancing the malignant properties of CSCs. Analyzing the functions of these crosstalk molecules will help us to find an approach toward the development of new anti-cancer drugs for inhibition of CSCs growth and progression. Long non-coding RNAs (LncRNAs) play a significant role in various cellular processes, like chromatin remodeling, epigenetic modifications, transcriptional, and post-transcriptional regulations. Here, we have highlighted the research findings suggesting the involvement of LncRNAs in maintenance of the stemness properties of CSCs through modulation of the above-mentioned signaling pathways. We have also discussed about the different therapeutic approaches targeting those key players responsible for mediating the crosstalk between the pathways. Overall, this review article will surely help the cancer biologists to design novel anti-CSCs agents that will open up a new horizon in the field of anti-cancer therapeutics.

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.

Insights Into the Properties, Biological Functions, and Regulation of USP21

Deubiquitylating enzymes (DUBs) antagonize ubiquitination by removing ubiquitin from their substrates. The role of DUBs in controlling various physiological and pathological processes has been extensively studied, and some members of DUBs have been identified as potential therapeutic targets in diseases ranging from tumors to neurodegeneration. Ubiquitin-specific protease 21 (USP21) is a member of the ubiquitin-specific protease family, the largest subfamily of DUBs. Although USP21 was discovered late and early research progress was slow, numerous studies in the last decade have gradually revealed the importance of USP21 in a wide variety of biological processes. In particular, the pro-carcinogenic effect of USP21 has been well elucidated in the last 2 years. In the present review, we provide a comprehensive overview of the current knowledge on USP21, including its properties, biological functions, pathophysiological roles, and cellular regulation. Limited pharmacological interventions for USP21 have also been introduced, highlighting the importance of developing novel and specific inhibitors targeting USP21.

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.

The Hedgehog Signaling Pathway in Idiopathic Pulmonary Fibrosis: Resurrection Time

The hedgehog (Hh) pathway is a sophisticated conserved cell signaling pathway that plays an essential role in controlling cell specification and proliferation, survival factors, and tissue patterning formation during embryonic development. Hh signal activity does not entirely disappear after development and may be reactivated in adulthood within tissue-injury-associated diseases, including idiopathic pulmonary fibrosis (IPF). The dysregulation of Hh-associated activating transcription factors, genomic abnormalities, and microenvironments is a co-factor that induces the initiation and progression of IPF.

A Synopsis of Signaling Crosstalk of Pericytes and Endothelial Cells in Salivary Gland

The salivary gland (SG) microvasculature constitutes a dynamic cellular organization instrumental to preserving tissue stability and homeostasis. The interplay between pericytes (PCs) and endothelial cells (ECs) culminates as a key ingredient that coordinates the development, maturation, and integrity of vessel building blocks. PCs, as a variety of mesenchymal stem cells, enthrall in the field of regenerative medicine, supporting the notion of regeneration and repair. PC-EC interconnections are pivotal in the kinetic and intricate process of angiogenesis during both embryological and post-natal development. The disruption of this complex interlinkage corresponds to SG pathogenesis, including inflammation, autoimmune disorders (Sjögren’s syndrome), and tumorigenesis. Here, we provided a global portrayal of major signaling pathways between PCs and ECs that cooperate to enhance vascular steadiness through the synergistic interchange. Additionally, we delineated how the crosstalk among molecular networks affiliate to contribute to a malignant context. Additionally, within SG microarchitecture, telocytes and myoepithelial cells assemble a labyrinthine companionship, which together with PCs appear to synchronize the regenerative potential of parenchymal constituents. By underscoring the intricacy of signaling cascades within cellular latticework, this review sketched a perceptive basis for target-selective drugs to safeguard SG function.

Cancer Cell-Derived Exosomes Promote HCC Tumorigenesis Through Hedgehog Pathway

Purpose

Hepatocellular carcinoma (HCC) accounts for more than 80% of primary liver cancers and is one of the leading causes of cancer-related death in many countries. Cancer cell-derived exosomes are shown to mediate communications between cancer cells and the microenvironment, promoting tumorigenesis. Hedgehog signaling pathway plays important roles in cancer development of HCC.

Methods

Exosomes were isolated from culture medium of HCC cell lines PLC/PRF/5 and MHCC-97H and were found to promote cancer cell growth measured with cell proliferation and colony formation assay. HCC cells cultured with cancer cell-derived exosome had increased cancer stem cell (CSC) population demonstrated by increased cell sphere formation CSC marker expressions. Hedgehog protein Shh was found to be highly expressed in these two HCC cell lines and preferably carried by exosomes. When Shh was knocked down with shRNA, the resulting exosomes had a reduced effect on promoting cancer cell growth or CSC population increase compared to normal cell-derived exosomes.

Results

The ability of PLC/PRF/5 cells to form tumor in a xenograft model was increased by the addition of the exosomes from control cancer cells but not the exosomes from Shh knocked down cancer cells. Finally, the higher plasma Exo-Shh levels were associated with later tumor stages, higher histological grades, multiple tumors, and higher recurrence rates.

Conclusion

This study demonstrated that HCC cells secreted Shh via exosome and promote tumorigenesis through the activated Hedgehog pathway.

Hedgehog Signaling in Myeloid Malignancies

Simple Summary

The Hedgehog signaling pathway is aberrantly activated in many myeloid malignancies, and pathway inhibition is clinically beneficial in specific patients with acute myeloid leukemia. However, even with the approval of these agents, the role of Hedgehog signaling in other myeloid disorders is less clear. In this review, we summarize the laboratory studies that have examined Hedgehog signaling in normal and malignant hematopoiesis as well as the clinical studies that have been carried out in several myeloid leukemias. Finally, we explore potential strategies to further expand the use of pathway inhibitors as therapies for these diseases.

Abstract

Myeloid malignancies arise from normal hematopoiesis and include several individual disorders with a wide range of clinical manifestations, treatment options, and clinical outcomes. The Hedgehog (HH) signaling pathway is aberrantly activated in many of these diseases, and glasdegib, a Smoothened (SMO) antagonist and HH pathway inhibitor, has recently been approved for the treatment of acute myeloid leukemia (AML). The efficacy of SMO inhibitors in AML suggests that they may be broadly active, but clinical studies in other myeloid malignancies have been largely inconclusive. We will discuss the biological role of the HH pathway in normal hematopoiesis and myeloid malignancies and review clinical studies targeting HH signaling in these diseases. In addition, we will examine SMO-independent pathway activation and highlight potential strategies that may expand the clinical utility of HH pathway antagonists.

Acute Alcohol Intoxication Impairs Sonic Hedgehog-Gli1 Signaling and Activation of Primitive Hematopoietic Precursor Cells in the Early Stage of Host Response to Bacteremia

BACKGROUND

Activation of hematopoietic stem cells [HSCs, lineage(lin)- stem cell growth factor receptor (c-kit)+ stem cell antigen-1(Sca-1)+ , or LKS cells in mice] is critical for initiating the granulopoietic response. This study determined the effect of alcohol exposure on sonic hedgehog (SHH) signaling in the regulation of HSC activation during bacteremia.

METHODS

Acute alcohol intoxication was induced in mice by intraperitoneal (i.p.) injection of 20% alcohol (5 g alcohol/kg body weight). Control mice received i.p. saline. Thirty minutes later, mice were intravenously (i.v.) injected with Escherichia coli (E. coli, 1 to 5 × 107 CFUs/mouse) or saline.

RESULTS

SHH expression by lineage-negative bone marrow cells (BMCs) was significantly increased 24 hours after E. coli infection. Extracellular signal-regulated kinase 1/2 (ERK1/2)-specificity protein 1 (Sp1) signaling promotes SHH expression. ERK1/2 was markedly activated in BMCs 8 hours following E. coli infection. Alcohol suppressed both the activation of ERK1/2 and up-regulation of SHH expression following E. coli infection. E. coli infection up-regulated GLI family zinc finger 1 (Gli1) gene expression by BMCs and increased Gli1 protein content in LKS cells. The extent of Gli1 expression was correlated with the activity of proliferation in LKS cells. Alcohol inhibited up-regulation of Gli1 expression and activation of LKS cells in response to E. coli infection. Alcohol also interrupted the granulopoietic response to bacteremia.

CONCLUSION

These data show that alcohol disrupts SHH-Gli1 signaling and HSC activation in the early stage of the granulopoietic response, which may serve as an important mechanism underlying the impairment of immune defense against bacterial infection in host excessively consuming alcohol.

Large-scale pan-cancer analysis reveals broad prognostic association between TGF-β ligands, not Hedgehog, and GLI1/2 expression in tumors

GLI1 expression is broadly accepted as a marker of Hedgehog pathway activation in tumors. Efficacy of Hedgehog inhibitors is essentially limited to tumors bearing activating mutations of the pathway. GLI2, a critical Hedgehog effector, is necessary for GLI1 expression and is a direct transcriptional target of TGF-β/SMAD signaling. We examined the expression correlations of GLI1/2 with TGFB and HH genes in 152 distinct transcriptome datasets totaling over 23,500 patients and representing 37 types of neoplasms. Their prognostic value was measured in over 15,000 clinically annotated tumor samples from 26 tumor types. In most tumor types, GLI1 and GLI2 follow a similar pattern of expression and are equally correlated with HH and TGFB genes. However, GLI1/2 broadly share prognostic value with TGFB genes and a mesenchymal/EMT signature, not with HH genes. Our results provide a likely explanation for the frequent failure of anti-Hedgehog therapies in tumors, as they suggest a key role for TGF-β, not Hedgehog, ligands, in tumors with elevated GLI1/2-expression.

Recent Insights into Long Bone Development: Central Role of Hedgehog Signaling Pathway in Regulating Growth Plate

The longitudinal growth of long bone, regulated by an epiphyseal cartilaginous component known as the “growth plate”, is generated by epiphyseal chondrocytes. The growth plate provides a continuous supply of chondrocytes for endochondral ossification, a sequential bone replacement of cartilaginous tissue, and any failure in this process causes a wide range of skeletal disorders. Therefore, the cellular and molecular characteristics of the growth plate are of interest to many researchers. Hedgehog (Hh), well known as a mitogen and morphogen during development, is one of the best known regulatory signals in the developmental regulation of the growth plate. Numerous animal studies have revealed that signaling through the Hh pathway plays multiple roles in regulating the proliferation, differentiation, and maintenance of growth plate chondrocytes throughout the skeletal growth period. Furthermore, over the past few years, a growing body of evidence has emerged demonstrating that a limited number of growth plate chondrocytes transdifferentiate directly into the full osteogenic and multiple mesenchymal lineages during postnatal bone development and reside in the bone marrow until late adulthood. Current studies with the genetic fate mapping approach have shown that the commitment of growth plate chondrocytes into the skeletal lineage occurs under the influence of epiphyseal chondrocyte-derived Hh signals during endochondral bone formation. Here, we discuss the valuable observations on the role of the Hh signaling pathway in the growth plate based on mouse genetic studies, with some emphasis on recent advances.

Sonic hedgehog enhances calcium oscillations in hippocampal astrocytes

Sonic hedgehog (SHH) is important for organogenesis during development. Recent studies have indicated that SHH is also involved in the proliferation and transformation of astrocytes to the reactive phenotype. However, the mechanisms underlying these are unknown. Involvement of SHH signaling in calcium (Ca) signaling has not been extensively studied. Here, we report that SHH and Smoothened agonist (SAG), an activator of the signaling receptor Smoothened (SMO) in the SHH pathway, activate Ca oscillations in cultured murine hippocampal astrocytes. The response was rapid, on a minute time scale, indicating a noncanonical pathway activity. Pertussis toxin blocked the SAG effect, indicating an involvement of a G_i coupled to SMO. Depletion of extracellular ATP by apyrase, an ATP-degrading enzyme, inhibited the SAG-mediated activation of Ca oscillations. These results indicate that SAG increases extracellular ATP levels by activating ATP release from astrocytes, resulting in Ca oscillation activation. We hypothesize that SHH activates SMO-coupled Gi in astrocytes, causing ATP release and activation of G_q/11-coupled P2 receptors on the same cell or surrounding astrocytes. Transcription factor activities are often modulated by Ca patterns; therefore, SHH signaling may trigger changes in astrocytes by activating Ca oscillations. This enhancement of Ca oscillations by SHH signaling may occur in astrocytes in the brain in vivo because we also observed it in hippocampal brain slices. In summary, SHH and SAG enhance Ca oscillations in hippocampal astrocytes, G_i mediates SAG-induced Ca oscillations downstream of SMO, and ATP-permeable channels may promote the ATP release that activates Ca oscillations in astrocytes.

Concomitant targeting of Hedgehog signaling and MCL-1 synergistically induces cell death in Hedgehog-driven cancer cells

In the present study, we show that concomitant inhibition of Hedgehog (HH) signaling by the glioma-associated oncogene homolog1 (GLI1)-targeting agent GANT61 and the antiapoptotic BCL-2 protein family member MCL-1 by A-1210477 synergistically induces cell death in HH-driven cancers, i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB) cells. Combined genetic and pharmacological inhibition emphasized that co-treatment of GANT61 and A-1210477 indeed relies on inhibition of GLI1 (by GANT61) and MCL-1 (by A-1210477). Mechanistic studies revealed that A-1210477 triggers the release of BIM from MCL-1 and its shuttling to BCL-x_L and BCL-2. Indeed, BIM proved to be required for GANT61/A-1210477-induced cell death, as genetic silencing of BIM using siRNA significantly rescues cell death upon GANT61/A-1210477 co-treatment. Similarly, genetic silencing of NOXA results in a significant reduction of GANT61/A-1210477-mediated cell death. Also, overexpression of MCL-1 or BCL-2 significantly protects RMS cells from GANT61/A-1210477-triggered cell death. Addition of the pan-caspase inhibitor zVAD.fmk significantly decreases GANT61/A-1210477-stimulated cell demise, indicating apoptotic cell death. In conclusion, GANT61 and A-1210477 synergize to engage mitochondrial apoptosis. These findings provide the rationale for further evaluation of dual inhibition of HH signaling and MCL-1 in HH-driven cancers.

Wnt, Notch, and TGF-β Pathways Impinge on Hedgehog Signaling Complexity: An Open Window on Cancer

Constitutive activation of the Hedgehog (Hh) signaling pathway is associated with increased risk of developing several malignancies. The biological and pathogenic importance of Hh signaling emphasizes the need to control its action tightly, both physiologically and therapeutically. Evidence of crosstalk between Hh and other signaling pathways is reported in many tumor types. Here, we provide an overview of the current knowledge about the communication between Hh and major signaling pathways, such as Notch, Wnt, and transforming growth factor β (TGF-β), which play critical roles in both embryonic and adult life. When these pathways are unbalanced, impaired crosstalk contributes to disease development. It is reported that more than one of these pathways are active in different type of tumors, at the same time. Therefore, starting from a plethora of stimuli that activate multiple signaling pathways, we describe the signals that preferentially converge on the Hh signaling cascade that influence its activity. Moreover, we highlight several connection points between Hh and Notch, Wnt, or TGF-β pathways, showing a reciprocal synergism that contributes to tumorigenesis, supporting a more malignant behavior by tumor cells, such as in leukemia and brain tumors. Understanding the importance of these molecular interlinking networks will provide a rational basis for combined anticancer drug development.

Targeting the crosstalks of Wnt pathway with Hedgehog and Notch for cancer therapy

Wnt pathway is an evolutionarily conserved signaling pathway determining patterning of animal embryos, cell fate, cell polarity, and a substantial role in the origin and maintenance of stem cells. It has been found to crosstalk with two other major developmental pathways, Hedgehog and Notch, in many embryological development cascades and in maintaining stemness of stem cells Research has shown that all the three pathways are potent in inducing tumorigenesis, driving tumor progression and aiding epithelial to mesenchymal transition in malignant cells, apart from maintaining cancer stem cells population inside the tumor tissue. Cancer stem cells are thought to aid in the process of tumor relapse, as they survive therapy by displaying drug resistance and then repopulating tumor tissues. Hence the role of these crosstalks in cancer is under intensive research. Inhibition of all the three pathways individually have resulted in tumor regression, but not optimally, as treatment failure and cancer relapse have been found to occur. Hence, instead of targeting a single pathway, targeting the crosstalk network could be a better alternative to conventional cancer treatment. Also, elimination of both tumor cells as well as cancer stem cells implies a reduced chance of relapse. Drugs developed to target these crosstalking networks, when used in combinatorial therapy, can potentially increase the efficacy of the therapy to a very large extent.

Defining a critical period in calvarial development for Hedgehog pathway antagonist-induced frontal bone dysplasia in mice

The Hedgehog (Hh) signalling pathway is essential for cellular proliferation and differentiation during embryonic development. Gain and loss of function of Hh signalling are known to result in an array of craniofacial malformations. To determine the critical period for Hh pathway antagonist-induced frontal bone hypoplasia, we examined patterns of dysmorphology caused by Hh signalling inhibition. Pregnant mice received a single oral administration of Hh signalling inhibitor GDC-0449 at 100 mg•kg⁻¹ or 150 mg•kg⁻¹ body weight at preselected time points between embryonic days (E)8.5 and 12.5. The optimal teratogenic concentration of GDC-0449 was determined to be 150 mg•kg⁻¹. Exposure between E9.5 and E10.5 induced frontal bone dysplasia, micrognathia and limb defects, with administration at E10.5 producing the most pronounced effects. This model showed decreased ossification of the frontal bone with downregulation of Hh signalling. The osteoid thickness of the frontal bone was significantly reduced. The amount of neural crest-derived frontal bone primordium was reduced after GDC-0449 exposure owing to a decreased rate of cell proliferation and increased cell death.

During embryonic development, the Hedgehog signalling pathway regulates the migration, proliferation and differentiation of cranial neural crest cells in the early frontal bone. The Hedgehog signalling pathway transmits information to embryonic cells for their proper cell differentiation, and increased or reduced function of that signalling results in various craniofacial malformations. A team headed by Weihui Chen at Fujian Medical University in China investigated the patterns of abnormalities caused by inhibition of Hedgehog signalling in pregnant mice at preselected embryonic time points. The team was able to identify the critical period for sensitivity to GDC-0449, a potent Hedgehog signalling inhibitor. The authors believe that their mouse model can be effective in further investigating the mechanisms of craniofacial malformations and will have a profound impact on identifying candidate human disease genes and associated environmental factors.

The Importance of the Hedgehog Signaling Pathway in Tumorigenesis of Spinal and Cranial Chordoma

Chordomas is rare malignant bone tumors thought to arise from remnants of embryonic notochord along the spine, frequently at the skull base and sacrum. Although chordoma is slow growing tumors, while are extremely recurrent, and aggressive, as well as the rate of prognosis remains poorly. Radical surgery and high-dose radiation are the most used treatments. Currently, there is no effective chemotherapeutic standard for chordomas. The Hedgehog (HH) pathway adjusts various processes included in expansion and differentiation of tissues and organs throughout the fetus’s life, furthermore cell growth and differentiation in the adult organism, of the cell in an adult organism, in which acute anesthesia is involved in multiple cancers. To study the role of signaling the hedgehog in the base of the skull and sacrum chordomas, the expression of SHH and GLI-1 levels were detected immuno histochemically, Additionally, PTCH-1 and GLI-1 expressions were distinguished by in- Situ- hybridization. Based on the findings presented herein, it is likely that the HH signal cascade was revealed even in cranial, where consecoently spinal chordoma and their recurrences play an important role. Our staining exhibited a canonical, ligand- dependent and autocrine Hedgehog signaling in skull base and sacrum chordomas including relapse. Due to the high levels of SHH and GLI-1 expression in all investigated chordoma samples, the study suggests a possible autocrine ligand-dependent activation of the canonical HH signaling cascade. A paracrine or non-canonical pathway cannot be excluded. Our results suggest that Hedgehog-inhibitors, like SHH-, GLI- and SMO- inhibitors, might serve as a potential and effective target for the treatment of chordomas.

Mitogen-activated kinase kinase kinase 1 inhibits hedgehog signaling and medulloblastoma growth through GLI1 phosphorylation

The aberrant activation of hedgehog (HH) signaling is a leading cause of the development of medulloblastoma, a pediatric tumor of the cerebellum. The FDA-approved HH inhibitor, Vismodegib, which targets the transmembrane transducer SMO, has shown limited efficacy in patients with medulloblastoma, due to compensatory mechanisms that maintain an active HH-GLI signaling status. Thus, the identification of novel actionable mechanisms, directly affecting the activity of the HH-regulated GLI transcription factors is an important goal for these malignancies. In this study, using gene expression and reporter assays, combined with biochemical and cellular analyses, we demonstrate that mitogen-activated kinase kinase kinase 1 (MEKK1), the most upstream kinase of the mitogen-activated protein kinase (MAPK) phosphorylation modules, suppresses HH signaling by associating and phosphorylating GLI1, the most potent HH-regulated transcription factor. Phosphorylation occurred at multiple residues in the C-terminal region of GLI1 and was followed by an increased association with the cytoplasmic proteins 14-3-3. Of note, the enforced expression of MEKK1 or the exposure of medulloblastoma cells to the MEKK1 activator, Nocodazole, resulted in a marked inhibitory effect on GLI1 activity and tumor cell proliferation and viability. Taken together, the results of this study shed light on a novel regulatory mechanism of HH signaling, with potentially relevant implications in cancer therapy.

Novel Familial Variant of the Desert Hedgehog Gene: Clinical Findings in Two Sisters with 46,XY Gonadal Dysgenesis or 46,XX Karyotype and Literature Review

BACKGROUND

In humans, Desert Hedgehog (DHH) gene mutations are a very rare cause of 46,XY gonadal dysgenesis (GD), eventually associated with peripheral neuropathy.

PATIENTS AND METHODS

Clinical records of 12 patients with 46,XY GD and unknown genetic background were reviewed and a 46,XY woman with peripheral neuropathy was individuated. Her 46,XX sister affected by similar neuropathy was also investigated. Genomic DNA was extracted and DHH exons sequenced and analyzed. A comparative genomic hybridization array was also performed.

RESULTS

In both the 46,XY and 46,XX sisters, a homozygous c.554C>A mutation in exon 2 of the DHH gene was found, determining a premature termination codon (p.Ser 185*). Heterozygous consanguineous carrier parents showed neither reproductive problems nor peripheral neuropathy. In the proband and her sister, a 499-kb duplication in 9p22.1 was also found.

CONCLUSION

A 46,XY European woman with 46,XY GD and a novel homozygous DHH pathogenic variant is reported, confirming that this gene plays a key role in male gonadal development. Her 46,XX sister, harboring the same mutation, showed normal internal and external female phenotype. Thus, DHH seems not to be involved in the ovarian development pathway or its postpubertal function. Homozygous DHH mutations cause a specific peripheral neuropathy in humans with both 46,XY and 46,XX karyotypes.

Widespread Expression of Hedgehog Pathway Components in a Large Panel of Human Tumor Cells and Inhibition of Tumor Growth by GANT61: Implications for Cancer Therapy

The sonic Hedgehog/GLI signaling pathway (HH) is critical for maintaining tissue polarity in development and contributes to tumor stemness. Transcription factors GLI1–3 are the downstream effectors of HH and activate oncogenic targets. To explore the completeness of the expression of HH components in tumor cells, we performed a screen for all HH proteins in a wide spectrum of 56 tumor cell lines of various origin using Western blot analysis. Generally, all HH proteins were expressed. Important factors GLI1 and GLI2 were always expressed, only exceptionally one of them was lowered, suggesting the functionality of HH in all tumors tested. We determined the effect of a GLI inhibitor GANT61 on proliferation in 16 chosen cell lines. More than half of tumor cells were sensitive to GANT61 to various extents. GANT61 killed the sensitive cells through apoptosis. The inhibition of reporter activity containing 12xGLI consensus sites by GANT61 and cyclopamine roughly correlated with cell proliferation influenced by GANT61. Our results recognize the sensitivity of tumor cell types to GANT61 in cell culture and support a critical role for GLI factors in tumor progression through restraining apoptosis. The use of GANT61 in combined targeted therapy of sensitive tumors, such as melanomas, seems to be immensely helpful.

Common genetic causes of holoprosencephaly are limited to a small set of evolutionarily conserved driver genes of midline development coordinated by TGF-β, hedgehog, and FGF signaling

Here, we applied targeted capture to examine 153 genes representative of all the major vertebrate developmental pathways among 333 probands to rank their relative significance as causes for holoprosencephaly (HPE). We now show that comparisons of variant transmission versus nontransmission among 136 HPE Trios indicates some reported genes now lack confirmation, while novel genes are implicated. Furthermore, we demonstrate that variation of modest intrinsic effect can synergize with these driver mutations as gene modifiers.

Hedgehog signaling negatively co-regulates BH3-only protein Noxa and TAp73 in TP53-mutated cells

In the present study, we show that pharmacological repression by the Hedgehog (Hh) pathway inhibitor (HPI) GANT61 induces expression of the proapoptotic protein Noxa in TP53-mutated embryonal pediatric tumor cells driven by Hh signaling (i.e. rhabdomyosarcoma (RMS) and medulloblastoma (MB)). Similarly, genetic silencing of Gli1 by siRNA causes increased Noxa mRNA and protein levels, while overexpression of Gli1 results in decreased Noxa expression. Furthermore, TAp73 mRNA and protein levels are increased upon Gli1 knockdown, while Gli1 overexpression reduces TAp73 mRNA and protein levels. However, knockdown of TAp73 fails to block Noxa induction in GANT61-treated cells, suggesting that Noxa is not primarily regulated by TAp73. Interestingly, mRNA levels of the transcription factor EGR1 correlate with those of Noxa and TAp73. Silencing of EGR1 results in decreased Noxa and TAp73 mRNA levels, indicating that EGR1 is involved in regulating transcriptional activity of Noxa and TAp73. These findings suggest that Gli1 represses Noxa and TAp73, possibly via EGR1. These findings could be exploited for the treatment of Hh-driven tumors, e.g. for their sensitization to chemotherapeutic agents.

Role and inhibition of GLI1 protein in cancer

GLI1 is a transcriptional regulator involved in the development of different types of cancer. GLI1 transcriptional activity is regulated within the Hedgehog pathway (canonical activity), but can also be controlled independently (non-canonical activity) in the context of other signaling pathways. Experimental evidences show GLI1 involvement in both small- and non–small-cell lung cancers. Direct inhibition of the protein, in combination with other chemotherapeutic agents, represents a promising strategy for the treatment of different malignancies.

Sonic Hedgehog Signaling Regulates Hematopoietic Stem/Progenitor Cell Activation during the Granulopoietic Response to Systemic Bacterial Infection

Activation and reprogramming of hematopoietic stem/progenitor cells play a critical role in the granulopoietic response to bacterial infection. Our current study determined the significance of Sonic hedgehog (SHH) signaling in the regulation of hematopoietic precursor cell activity during the host defense response to systemic bacterial infection. Bacteremia was induced in male Balb/c mice via intravenous injection (i.v.) of Escherichia coli (5 × 10⁷ CFUs/mouse). Control mice received i.v. saline. SHH protein level in bone marrow cell (BMC) lysates was markedly increased at both 24 and 48 h of bacteremia. By contrast, the amount of soluble SHH ligand in marrow elutes was significantly reduced. These contrasting alterations suggested that SHH ligand release from BMCs was reduced and/or binding of soluble SHH ligand to BMCs was enhanced. At both 12 and 24 h of bacteremia, SHH mRNA expression by BMCs was significantly upregulated. This upregulation of SHH mRNA expression was followed by a marked increase in SHH protein expression in BMCs. Activation of the ERK1/2–SP1 pathway was involved in mediating the upregulation of SHH gene expression. The major cell type showing the enhancement of SHH expression in the bone marrow was lineage positive cells. Gli1 positioned downstream of the SHH receptor activation serves as a key component of the hedgehog (HH) pathway. Primitive hematopoietic precursor cells exhibited the highest level of baseline Gli1 expression, suggesting that they were active cells responding to SHH ligand stimulation. Along with the increased expression of SHH in the bone marrow, expression of Gli1 by marrow cells was significantly upregulated at both mRNA and protein levels following bacteremia. This enhancement of Gli1 expression was correlated with activation of hematopoietic stem/progenitor cell proliferation. Mice with Gli1 gene deletion showed attenuation in activation of marrow hematopoietic stem/progenitor cell proliferation and inhibition of increase in blood granulocytes following bacteremia. Our results indicate that SHH signaling is critically important in the regulation of hematopoietic stem/progenitor cell activation and reprogramming during the granulopoietic response to serious bacterial infection.

Aspirin inhibits the SHH/GLI1 signaling pathway and sensitizes malignant glioma cells to temozolomide therapy

Aberrant activation of sonic hedgehog (SHH)/glioma-associated oncogene homolog 1 (GLI1) pathway plays an important role in the tumorigenicity of malignant glioma cells and resistance to temozolomide (TMZ). Here we investigated the aspirin's antineoplastic molecular route by targeting SHH/GLI1 pathway and examined the feasibility of aspirin combined with TMZ therapy. Western blot and quantitative real-time polymerase chain reaction (qRT-PCR) revealed that the activity of the SHH/GLI1 pathway was strongly inhibited by aspirin. Aspirin acted as the glioma growth-inhibitory and pro-apoptosis roles by inhibiting the SHH/GLI1 pathway and reprogramming the epithelial to mesenchymal transition (EMT). The immunofluorescence assay showed aspirin could prevent the nuclear translocation of GLI1 to inhibit its transcriptional regulation. The stable lentiviral overexpression of GLI1 reversed the DNA double strand breaks (DSBs) caused by the GANT61 and TMZ. Furthermore, aspirin combined with TMZ enhanced chemosensitivity and GLI1-induced chemoprotection was partly blocked by aspirin in vitro and in vivo. Collectively, aspirin has a therapeutic potential for SHH/GLI1 targeted therapy against glioma cells. Acquired activation of GLI1 protects glioma cells against TMZ therapy. Impairment of DNA DSBs repair activity might be involved in the route of aspirin-induced chemosensitivity. Combined aspirin with TMZ may be a promising strategy against malignant glioma.

Taking the Occam's Razor Approach to Hedgehog Lipidation and Its Role in Development

All Hedgehog (Hh) proteins signal from producing cells to distant receiving cells despite being synthesized as N-and C-terminally lipidated, membrane-tethered molecules. To explain this paradoxical situation, over the past 15 years, several hypotheses have been postulated that tie directly into this property, such as Hh transport on cellular extensions called cytonemes or on secreted vesicles called lipophorins and exosomes. The alternative situation that tight membrane association merely serves to prevent unregulated Hh solubilization has been addressed by biochemical and structural studies suggesting Hh extraction from the membrane or proteolytic Hh release. While some of these models may act in different organisms, tissues or developmental programs, others may act together to specify Hh short- and long-range signaling in the same tissues. To test and rank these possibilities, we here review major models of Hh release and transport and hypothesize that the (bio)chemical and physical properties of firmly established, homologous, and functionally essential biochemical Hh modifications are adapted to specify and determine interdependent steps of Hh release, transport and signaling, while ruling out other steps. This is also described by the term “congruence”, meaning that the logical combination of biochemical Hh modifications can reveal their true functional implications. This combined approach reveals potential links between models of Hh release and transport that were previously regarded as unrelated, thereby expanding our view of how Hhs can steer development in a simple, yet extremely versatile, manner.

Lkb1 regulates granule cell migration and cortical folding of the cerebellar cortex

Cerebellar growth and foliation require the Hedgehog-driven proliferation of granule cell precursors (GCPs) in the external granule layer (EGL). However, that increased or extended GCP proliferation generally does not elicit ectopic folds suggests that additional determinants control cortical expansion and foliation during cerebellar development. Here, we find that genetic loss of the serine-threonine kinase Liver Kinase B1 (Lkb1) in GCPs increased cerebellar cortical size and foliation independent of changes in proliferation or Hedgehog signaling. This finding is unexpected given that Lkb1 has previously shown to be critical for Hedgehog pathway activation in cultured cells. Consistent with unchanged proliferation rate of GCPs, the cortical expansion of Lkb1 mutants is accompanied by thinning of the EGL. The plane of cell division, which has been implicated in diverse processes from epithelial surface expansions to gyrification of the human cortex, remains unchanged in the mutants when compared to wild-type controls. However, we find that Lkb1 mutants display delayed radial migration of post-mitotic GCPs that coincides with increased cortical size, suggesting that aberrant cell migration may contribute to the cortical expansion and increase foliation. Taken together, our results reveal an important role for Lkb1 in regulating cerebellar cortical size and foliation in a Hedgehog-independent manner.

Human germline hedgehog pathway mutations predispose to fatty liver

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease. Activation of hedgehog (Hh) signaling has been implicated in the progression of NAFLD and proposed as a therapeutic target; however, the effects of Hh signaling inhibition have not been studied in humans with germline mutations that affect this pathway.

METHODS

Patients with holoprosencephaly (HPE), a disorder associated with germline mutations disrupting Sonic hedgehog (SHH) signaling, were clinically evaluated for NAFLD. A combined mouse model of Hh signaling attenuation (Gli2 heterozygous null: Gli2^+/-) and diet-induced NAFLD was used to examine aspects of NAFLD and hepatic gene expression profiles, including molecular markers of hepatic fibrosis and inflammation.

RESULTS

Patients with HPE had a higher prevalence of liver steatosis compared to the general population, independent of obesity. Exposure of Gli2^+/- mice to fatty liver-inducing diets resulted in increased liver steatosis compared to wild-type mice. Similar to humans, this effect was independent of obesity in the mutant mice and was associated with decreased expression of pro-fibrotic and pro-inflammatory genes, and increased expression of PPARγ, a potent anti-fibrogenic and anti-inflammatory regulator. Interestingly, tumor suppressors p53 and p16INK4 were found to be downregulated in the Gli2^+/- mice exposed to a high-fat diet.

CONCLUSIONS

Our results indicate that germline mutations disrupting Hh signaling promotes liver steatosis, independent of obesity, with reduced fibrosis. While Hh signaling inhibition has been associated with a better NAFLD prognosis, further studies are required to evaluate the long-term effects of mutations affecting this pathway. Lay summary: Non-alcoholic fatty liver disease (NAFLD) is characterized by excess fat deposition in the liver predominantly due to high calorie intake and a sedentary lifestyle. NAFLD progression is usually accompanied by activation of the Sonic hedgehog (SHH) pathway leading to fibrous buildup (scar tissue) and inflammation of the liver tissue. For the first time patients with holoprosencephaly, a disease caused by SHH signaling mutations, are shown to have increased liver steatosis independent of obesity. This observation was recapitulated in a mouse model of attenuated SHH signaling that also showed increased liver steatosis but with decreased fibrosis and inflammation. While SHH inhibition is associated with a good NAFLD prognosis, this increase in liver fat accumulation in the context of SHH signaling inhibition must be studied prospectively to evaluate its long-term effects, especially in individuals with Western-type dietary habits.

DeSUMOylation of Gli1 by SENP1 Attenuates Sonic Hedgehog Signaling

The transcriptional output of the Sonic Hedgehog morphogenic pathway is orchestrated by three Krüppel family transcription factors, Gli1 to -3, which undergo extensive posttranslational modifications, including ubiquitination and SUMOylation. Here, we report that the sentrin-specific peptidase SENP1 is the specific deSUMOylation enzyme for Gli1. We show that SUMOylation stabilizes Gli1 by competing with ubiquitination at conserved lysine residues and that SUMOylated Gli1 is enriched in the nucleus, suggesting that SUMOylation is a nuclear localization signal for Gli1. Finally, we show that small interfering RNA (siRNA)-mediated knockdown of SENP1 augments the ability of Shh to sustain the proliferation of cerebellar granule cell precursors, demonstrating the physiological significance of the negative regulation of Shh signaling by SENP1.

Oroxyloside A Overcomes Bone Marrow Microenvironment-Mediated Chronic Myelogenous Leukemia Resistance to Imatinib via Suppressing Hedgehog Pathway

Imatinib (IM), as first inhibitor of the oncogenic tyrosine kinase BCR-ABL, has been widely used to treat chronic myeloid leukemia (CML) for decades in clinic. However, resistance to IM usually occurs in CML patients. The bone marrow (BM), as the predominant microenvironment of CML, secretes an abundant amount of cytokines, which may contribute to drug resistance. In current study, we utilized in vitro K562 co-culture model with BM stroma to investigate IM resistance. As a result, co-culturing of K562 with BM stroma was sufficient to cause resistance to IM, which was accompanied with the activation of hedgehog (Hh) signaling pathway and upregulation of BCR-ABL as well as its downstream proteins like phosphorylated Akt, Bcl-xL and survivin, etc. On the other hand, oroxyloside A (OAG), a metabolite of oroxylin A from the root of Scutellaria baicalensis Georgi, which had low toxic effect on K562 cells, was able to sensitize K562 cells co-cultured with BM stroma to IM treatment in vitro and in vivo. We observed that OAG suppressed Hh pathway and subsequently nuclear translocation of GLI1, followed by downregulation of BCR-ABL and its downstream effectors, thus facilitating IM to induce apoptosis of K562 cells. Together, BM microenvironment rendered K562 cells drug resistance through activating Hh signaling, however, OAG could overcome IM resistance of CML cells through inhibiting Hh-BCR-ABL axis in vitro and in vivo.

Development of anticancer agents targeting the Hedgehog signaling

Hedgehog signaling is an evolutionarily conserved pathway which is essential in embryonic and postnatal development as well as adult organ homeostasis. Abnormal regulation of Hedgehog signaling is implicated in many diseases including cancer. Consequently, substantial efforts have made in the past to develop potential therapeutic agents that specifically target the Hedgehog signaling for cancer treatment. Here, we review the therapeutic agents for inhibition of the Hedgehog signaling and their clinical advances in cancer treatment.

Glypican-6 promotes the growth of developing long bones by stimulating Hedgehog signaling

Autosomal-recessive omodysplasia (OMOD1) is caused by mutations in glypican-6. Capurro et al. show that glypican-6 stimulates Hedgehog (Hh) signaling, and reduced Hh signaling may contribute to the pathogenesis of OMOD1.

Autosomal-recessive omodysplasia (OMOD1) is a genetic condition characterized by short stature, shortened limbs, and facial dysmorphism. OMOD1 is caused by loss-of-function mutations of glypican 6 (GPC6). In this study, we show that GPC6-null embryos display most of the abnormalities found in OMOD1 patients and that Hedgehog (Hh) signaling is significantly reduced in the long bones of these embryos. The Hh-stimulatory activity of GPC6 was also observed in cultured cells, where this GPC increased the binding of Hh to Patched 1 (Ptc1). Consistent with this, GPC6 interacts with Hh through its core protein and with Ptc1 through its glycosaminoglycan chains. Hh signaling is triggered at the primary cilium. In the absence of Hh, we observed that GPC6 is localized outside of the cilium but moves into the cilium upon the addition of Hh. We conclude that GPC6 stimulates Hh signaling by binding to Hh and Ptc1 at the cilium and increasing the interaction of the receptor and ligand.

Targeting Signaling Pathways in Cancer Stem Cells for Cancer Treatment

The Wnt, Hedgehog, and Notch pathways are inherent signaling pathways in normal embryogenesis, development, and hemostasis. However, dysfunctions of these pathways are evident in multiple tumor types and malignancies. Specifically, aberrant activation of these pathways is implicated in modulation of cancer stem cells (CSCs), a small subset of cancer cells capable of self-renewal and differentiation into heterogeneous tumor cells. The CSCs are accountable for tumor initiation, growth, and recurrence. In this review, we focus on roles of Wnt, Hedgehog, and Notch pathways in CSCs' stemness and functions and summarize therapeutic studies targeting these pathways to eliminate CSCs and improve overall cancer treatment outcomes.

Hedgehog pathway mediates early acceleration of liver regeneration induced by a novel two-staged hepatectomy in mice

BACKGROUND & AIMS

ALPPS, a novel two-staged approach for the surgical removal of large/multiple liver tumors, combines portal vein ligation (PVL) with parenchymal transection. This causes acceleration of compensatory liver growth, enabling faster and more extensive tumor removal. We sought to identify the plasma factors thought to mediate the regenerative acceleration following ALPPS.

METHODS

We compared a mouse model of ALPPS against PVL and additional control surgeries (n=6 per group). RNA deep sequencing was performed to identify candidate molecules unique to ALPPS liver (n=3 per group). Recombinant protein and a neutralizing antibody combined with appropriate surgeries were used to explore candidate functions in ALPPS (n=6 per group). Indian hedgehog (IHH/Ihh) levels were assessed in human ALPPS patient plasma (n=6).

RESULTS

ALPPS in mouse confirmed significant acceleration of liver regeneration relative to PVL (p<0.001). Ihh mRNA, coding for a secreted ligand inducing hedgehog signaling, was uniquely upregulated in ALPPS liver (p<0.001). Ihh plasma levels rose 4h after surgery (p<0.01), along with hedgehog pathway activation and subsequent cyclin D1 induction in the liver. When combined with PVL, Ihh alone was sufficient to induce ALPPS-like acceleration of liver growth. Conversely, blocking Ihh markedly inhibited the accelerating effects of ALPPS. In the small cohort of ALPPS patients, IHH tended to be elevated early after surgery.

CONCLUSIONS

Ihh and hedgehog pathway activation provide the first mechanistic insight into the acceleration of liver regeneration triggered by ALPPS surgery. The accelerating potency of recombinant Ihh, and its potential effect in human ALPPS may lead to a clinical role for this protein.

LAY SUMMARY

ALPPS, a novel two-staged hepatectomy, accelerates liver regeneration, thereby helping to treat patients with otherwise unresectable liver tumors. The molecular mechanisms behind this accelerated regeneration are unknown. Here, we elucidate that Indian hedgehog, a secreted ligand important for fetal development, is a crucial mediator of the regenerative acceleration triggered by ALPPS surgery.

Smoothened Regulates Migration of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis via Activation of Rho GTPase Signaling

Fibroblast-like synoviocytes (FLSs) acquire aggressive phenotypes characterized with enhanced migration abilities and inherent invasive qualities in rheumatoid arthritis (RA). Smoothened (Smo) is a key component of sonic hedgehog (Shh) signaling and contributes to tumor cell invasion and metastasis. The objective of this study is to investigate the role of Smo in the modulation of cell migration and explore the underlying molecular mechanism(s). FLSs were isolated from RA synovium. Shh levels were regulated by a Smo agonist (purmorphamine), Smo antagonist (KAAD-cyclopamine), or small interfering RNA targeting the Smo gene (Smo-siRNA) in RA-FLSs. Expression of Smo was detected by real-time PCR and western blot analysis. Cell migration was examined by Transwell assay and activation of Rho GTPases was measured by pull-down assays. Incubation with purmorphamine resulted in a significant increase of cell migration and activation of Rho GTPase signaling compared to controls (P < 0.05). However, treatment with KAAD-cyclopamine or transfection with Smo-siRNA suppressed migration of RA-FLSs and showed an inhibitory effect of Rho GTPase signaling. Together, these results suggest that Smo plays an important role in RA-FLSs migration through activation of Rho GTPase signaling and may contribute to progression of RA, thus, targeting Shh signal may have a therapeutic potential in patients with RA.

Gene expression profiling of tumor-initiating stem cells from mouse Krebs-2 carcinoma using a novel marker of poorly differentiated cells

Using the ability of poorly differentiated cells to natively internalize fragments of extracellular double-stranded DNA as a marker, we isolated a tumorigenic subpopulation present in Krebs-2 ascites that demonstrated the features of tumor-inducing cancer stem cells. Having combined TAMRA-labeled DNA probe and the power of RNA-seq technology, we identified a set of 168 genes specifically expressed in TAMRA-positive cells (tumor-initiating stem cells), these genes remaining silent in TAMRA-negative cancer cells. TAMRA+ cells displayed gene expression signatures characteristic of both stem cells and cancer cells. The observed expression differences between TAMRA+ and TAMRA- cells were validated by Real Time PCR. The results obtained corroborated the biological data that TAMRA+ murine Krebs-2 tumor cells are tumor-initiating stem cells. The approach developed can be applied to profile any poorly differentiated cell types that are capable of immanent internalization of double-stranded DNA.

Suppressor of Fused Chaperones Gli Proteins To Generate Transcriptional Responses to Sonic Hedgehog Signaling

Cellular responses to the graded Sonic Hedgehog (Shh) morphogenic signal are orchestrated by three Gli genes that give rise to both transcription activators and repressors. An essential downstream regulator of the pathway, encoded by the tumor suppressor gene Suppressor of fused (Sufu), plays critical roles in the production, trafficking, and function of Gli proteins, but the mechanism remains controversial. Here, we show that Sufu is upregulated in active Shh responding tissues and accompanies Gli activators translocating into and Gli repressors out of the nucleus. Trafficking of Sufu to the primary cilium, potentiated by Gli activators but not repressors, was found to be coupled to its nuclear import. We have identified a nuclear export signal (NES) motif of Sufu in juxtaposition to the protein kinase A (PKA) and glycogen synthase kinase 3 (GSK3) dual phosphorylation sites and show that Sufu binds the chromatin with both Gli1 and Gli3. Close comparison of neural tube development among individual Ptch1-/-, Sufu-/-, and Ptch1-/-; Sufu-/- double mutant embryos indicates that Sufu is critical for the maximal activation of Shh signaling essential to the specification of the most-ventral neurons. These data define Sufu as a novel class of molecular chaperone required for every aspect of Gli regulation and function.

Protein lipid modifications--More than just a greasy ballast

Covalent lipid modifications of proteins are crucial for regulation of cellular plasticity, since they affect the chemical and physical properties and therefore protein activity, localization, and stability. Most recently, lipid modifications on proteins are increasingly attracting important regulatory entities in diverse signaling events and diseases. In all cases, the lipid moiety of modified proteins is essential to allow water-soluble proteins to strongly interact with membranes or to induce structural changes in proteins that are critical for elemental processes such as respiration, transport, signal transduction, and motility. Until now, roughly about ten lipid modifications on different amino acid residues are described at the UniProtKB database and even well-known modifications are underrepresented. Thus, it is of fundamental importance to develop a better understanding of this emerging and so far under-investigated type of protein modification. Therefore, this review aims to give a comprehensive and detailed overview about enzymatic and nonenzymatic lipidation events, will report their role in cellular biology, discuss their relevancy for diseases, and describe so far available bioanalytical strategies to analyze this highly challenging type of modification.

Consensus Paper: Cerebellar Development

The development of the mammalian cerebellum is orchestrated by both cell-autonomous programs and inductive environmental influences. Here, we describe the main processes of cerebellar ontogenesis, highlighting the neurogenic strategies used by developing progenitors, the genetic programs involved in cell fate specification, the progressive changes of structural organization, and some of the better-known abnormalities associated with developmental disorders of the cerebellum.