SCF (Fbxl17) ubiquitylation of Sufu regulates Hedgehog signaling and medulloblastoma development

P4HA2 hydroxylates SUFU to regulate the paracrine Hedgehog signaling and promote B-cell lymphoma progression

Aberrations in the Hedgehog (Hh) signaling pathway are significantly prevailed in various cancers, including B-cell lymphoma. A critical facet of Hh signal transduction involves the dynamic regulation of the suppressor of fused homolog (SUFU)-glioma-associated oncogene homolog (GLI) complex within the kinesin family member 7 (KIF7)-supported ciliary tip compartment. However, the specific post-translational modifications of SUFU-GLI complex within this context have remained largely unexplored. Our study reveals a novel regulatory mechanism involving prolyl 4-hydroxylase 2 (P4HA2), which forms a complex with KIF7 and is essential for signal transduction of Hh pathway. We demonstrate that, upon Hh pathway activation, P4HA2 relocates alongside KIF7 to the ciliary tip. Here, it hydroxylates SUFU to inhibit its function, thus amplifying the Hh signaling. Moreover, the absence of P4HA2 significantly impedes B lymphoma progression. This effect can be attributed to the suppression of Hh signaling in stromal fibroblasts, resulting in decreased growth factors essential for malignant proliferation of B lymphoma cells. Our findings highlight the role of P4HA2-mediated hydroxylation in modulating Hh signaling and propose a novel stromal-targeted therapeutic strategy for B-cell lymphoma.

Comprehensive data mining reveals RTK/RAS signaling pathway as a promoter of prostate cancer lineage plasticity through transcription factors and CNV

Prostate cancer lineage plasticity is a key driver in the transition to neuroendocrine prostate cancer (NEPC), and the RTK/RAS signaling pathway is a well-established cancer pathway. Nevertheless, the comprehensive link between the RTK/RAS signaling pathway and lineage plasticity has received limited investigation. In particular, the intricate regulatory network governing the interplay between RTK/RAS and lineage plasticity remains largely unexplored. The multi-omics data were clustered with the coefficient of argument and neighbor joining algorithm. Subsequently, the clustered results were analyzed utilizing the GSEA, gene sets related to stemness, multi-lineage state datasets, and canonical cancer pathway gene sets. Finally, a comprehensive exploration of the data based on the ssGSEA, WGCNA, GSEA, VIPER, prostate cancer scRNA-seq data, and the GPSAdb database was conducted. Among the six modules in the clustering results, there are 300 overlapping genes, including 3 previously unreported prostate cancer genes that were validated to be upregulated in prostate cancer through RT-qPCR. Function Module 6 shows a positive correlation with prostate cancer cell stemness, multi-lineage states, and the RTK/RAS signaling pathway. Additionally, the 19 leading-edge genes of the RTK/RAS signaling pathway promote prostate cancer lineage plasticity through a complex network of transcriptional regulation and copy number variations. In the transcriptional regulation network, TP63 and FOXO1 act as suppressors of prostate cancer lineage plasticity, whereas RORC exerts a promoting effect. This study provides a comprehensive perspective on the role of the RTK/RAS pathway in prostate cancer lineage plasticity and offers new clues for the treatment of NEPC.

Transcriptomic Analysis Provides Insights into Candidate Genes and Molecular Pathways Involved in Growth of Mytilus coruscus Larvae

Growth is a fundamental aspect of aquaculture breeding programs, pivotal for successful cultivation. Understanding the mechanisms that govern growth and development differences across various stages can significantly boost seedling production of economically valuable species, thereby enhancing aquaculture efficiency and advancing the aquaculture industry. Mytilus coruscus, a commercially vital marine bivalve, underscores this importance. To decipher the intricate molecular mechanisms dictating growth and developmental disparities in marine shellfish, we conducted transcriptome sequencing and meticulously analyzed gene expression variations and molecular pathways linked to growth traits in M. coruscus. This study delved into the molecular and gene expression variations across five larval development stages, with a specific focus on scrutinizing the differential expression patterns of growth-associated genes using RNA sequencing and quantitative real-time PCR analysis. A substantial number of genes-36,044 differentially expressed genes (DEGs)-exhibited significant differential expression between consecutive developmental stages. These DEGs were then categorized into multiple pathways (Q value < 0.05), including crucial pathways such as the spliceosome, vascular smooth muscle contraction, DNA replication, and apoptosis, among others. In addition, we identified two pivotal signaling pathways-the Hedgehog (Hh) signaling pathway and the TGF-beta (TGF-β) signaling pathway-associated with the growth and development of M. coruscus larvae. Ten key growth-related genes were pinpointed, each playing crucial roles in molecular function and the regulation of growth traits in M. coruscus. These genes and pathways associated with growth provide deep insights into the molecular basis of physiological adaptation, metabolic processes, and growth variability in marine bivalves.

SALL4 is a CRL3REN/KCTD11 substrate that drives Sonic Hedgehog-dependent medulloblastoma

The Sonic Hedgehog (SHH) pathway is crucial regulator of embryonic development and stemness. Its alteration leads to medulloblastoma (MB), the most common malignant pediatric brain tumor. The SHH-MB subgroup is the best genetically characterized, however the molecular mechanisms responsible for its pathogenesis are not fully understood and therapeutic benefits are still limited. Here, we show that the pro-oncogenic stemness regulator Spalt-like transcriptional factor 4 (SALL4) is re-expressed in mouse SHH-MB models, and its high levels correlate with worse overall survival in SHH-MB patients. Proteomic analysis revealed that SALL4 interacts with REN/KCTD11 (here REN), a substrate receptor subunit of the Cullin3-RING ubiquitin ligase complex (CRL3REN) and a tumor suppressor lost in ~30% of human SHH-MBs. We demonstrate that CRL3REN induces polyubiquitylation and degradation of wild type SALL4, but not of a SALL4 mutant lacking zinc finger cluster 1 domain (ΔZFC1). Interestingly, SALL4 binds GLI1 and cooperates with HDAC1 to potentiate GLI1 deacetylation and transcriptional activity. Notably, inhibition of SALL4 suppresses SHH-MB growth both in murine and patient-derived xenograft models. Our findings identify SALL4 as a CRL3REN substrate and a promising therapeutic target in SHH-dependent cancers.

Cellular and Transcriptional Dynamics during Brown Adipose Tissue Regeneration under Acute Injury

Brown adipose tissue (BAT) is the major site of non-shivering thermogenesis and crucial for systemic metabolism. Under chronic cold exposures and high-fat diet challenges, BAT undergoes robust remodeling to adapt to physiological demands. However, whether and how BAT regenerates after acute injuries are poorly understood. Here, we established a novel BAT injury and regeneration model (BAT-IR) in mice and performed single-cell RNA sequencing (scRNA-seq) and bulk RNA-seq to determine cellular and transcriptomic dynamics during BAT-IR. We further defined distinct fibro-adipogenic and myeloid progenitor populations contributing to BAT regeneration. Cell trajectory and gene expression analyses uncovered the involvement of MAPK, Wnt, and Hedgehog (Hh) signaling pathways in BAT regeneration. We confirmed the role of Hh signaling in BAT development through Myf5Cre-mediated conditional knockout (cKO) of the Sufu gene to activate Hh signaling in BAT and muscle progenitors. Our BAT-IR model therefore provides a paradigm to identify conserved cellular and molecular mechanisms underlying BAT development and remodeling.

Hedgehog signaling in tissue homeostasis, cancers, and targeted therapies

The past decade has seen significant advances in our understanding of Hedgehog (HH) signaling pathway in various biological events. HH signaling pathway exerts its biological effects through a complex signaling cascade involved with primary cilium. HH signaling pathway has important functions in embryonic development and tissue homeostasis. It plays a central role in the regulation of the proliferation and differentiation of adult stem cells. Importantly, it has become increasingly clear that HH signaling pathway is associated with increased cancer prevalence, malignant progression, poor prognosis and even increased mortality. Understanding the integrative nature of HH signaling pathway has opened up the potential for new therapeutic targets for cancer. A variety of drugs have been developed, including small molecule inhibitors, natural compounds, and long non-coding RNA (LncRNA), some of which are approved for clinical use. This review outlines recent discoveries of HH signaling in tissue homeostasis and cancer and discusses how these advances are paving the way for the development of new biologically based therapies for cancer. Furthermore, we address status quo and limitations of targeted therapies of HH signaling pathway. Insights from this review will help readers understand the function of HH signaling in homeostasis and cancer, as well as opportunities and challenges of therapeutic targets for cancer.

FBXL17/spastin axis as a novel therapeutic target of hereditary spastic paraplegia

Background

Spastin significantly influences microtubule regulation in neurons and is implicated in the pathogenesis of hereditary spastic paraplegia (HSP). However, post-translational regulation of the spastin protein remains nebulous. The association between E3 ubiquitin ligase and spastin provides a potential therapeutic strategy.

Results

As evidenced by protein chip analysis, FBXL17 inversely correlated with SPAST-M1 at the protein level in vitro and, also in vivo during embryonic developmental stage. SPAST-M1 protein interacted with FBXL17 specifically via the BTB domain at the N-terminus of SPAST-M1. The SCF^FBXL17 E3 ubiquitin ligase complex degraded SPAST-M1 protein in the nuclear fraction in a proteasome-dependent manner. SPAST phosphorylation occurred only in the cytoplasmic fraction by CK2 and was involved in poly-ubiquitination. Inhibition of SCF^FBXL17 E3 ubiquitin ligase by small chemical and FBXL17 shRNA decreased proteasome-dependent degradation of SPAST-M1 and induced axonal extension. The SPAST Y52C mutant, harboring abnormality in BTB domain could not interact with FBXL17, thereby escaping protein regulation by the SCF^FBXL17 E3 ubiquitin ligase complex, resulting in loss of functionality with aberrant quantity. Although this mutant showed shortening of axonal outgrowth, low rate proliferation, and poor differentiation capacity in a 3D model, this phenotype was rescued by inhibiting SCF^FBXL17 E3 ubiquitin ligase.

Conclusions

We discovered that a novel pathway, FBXL17-SPAST was involved in pathogenicity of HSP by the loss of function and the quantitative regulation. This result suggested that targeting FBXL17 could provide new insight into HSP therapeutics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00851-1.

ERK2 MAP kinase regulates SUFU binding by multisite phosphorylation of GLI1

Crosstalk between the Hedgehog and MAPK signaling pathways occurs in several types of cancer and contributes to clinical resistance to Hedgehog pathway inhibitors. Here we show that MAP kinase-mediated phosphorylation weakens the binding of the GLI1 transcription factor to its negative regulator SUFU. ERK2 phosphorylates GLI1 on three evolutionarily conserved target sites (S102, S116, and S130) located near the high-affinity binding site for SUFU; these phosphorylations cooperate to weaken the affinity of GLI1-SUFU binding by over 25-fold. Phosphorylation of any one, or even any two, of the three sites does not result in the level of SUFU release seen when all three sites are phosphorylated. Tumor-derived mutations in R100 and S105, residues bordering S102, also diminish SUFU binding, collectively defining a novel evolutionarily conserved SUFU affinity-modulating region. In cultured mammalian cells, GLI1 variants containing phosphomimetic substitutions of S102, S116, and S130 displayed an increased ability to drive transcription. We conclude that multisite phosphorylation of GLI1 by ERK2 or other MAP kinases weakens GLI1-SUFU binding, thereby facilitating GLI1 activation and contributing to both physiological and pathological crosstalk.

Hedgehog signaling mechanism and role in cancer

Cell-cell communication through evolutionarily conserved signaling pathways governs embryonic development and adult tissue homeostasis. Deregulation of these signaling pathways has been implicated in a wide range of human diseases including cancer. One such pathway is the Hedgehog (Hh) pathway, which was originally discovered in Drosophila and later found to play a fundamental role in human development and diseases. Abnormal Hh pathway activation is a major driver of basal cell carcinomas (BCC) and medulloblastoma. Hh exerts it biological influence through a largely conserved signal transduction pathway from the activation of the GPCR family transmembrane protein Smoothened (Smo) to the conversion of latent Zn-finger transcription factors Gli/Ci proteins from their repressor (GliR/CiR) to activator (GliA/CiA) forms. Studies from model organisms and human patients have provided deep insight into the Hh signal transduction mechanisms, revealed roles of Hh signaling in a wide range of human cancers, and suggested multiple strategies for targeting this pathway in cancer treatment.

LncRNA RUS shapes the gene expression program towards neurogenesis

The chromatin-associated lncRNA RUS binds in the vicinity to neural differentiation-associated genes and regulates them in a context-dependent manner to enable proper neuron development.

The evolution of brain complexity correlates with an increased expression of long, noncoding (lnc) RNAs in neural tissues. Although prominent examples illustrate the potential of lncRNAs to scaffold and target epigenetic regulators to chromatin loci, only few cases have been described to function during brain development. We present a first functional characterization of the lncRNA LINC01322, which we term RUS for “RNA upstream of Slitrk3.” The RUS gene is well conserved in mammals by sequence and synteny next to the neurodevelopmental gene Slitrk3. RUS is exclusively expressed in neural cells and its expression increases during neuronal differentiation of mouse embryonic cortical neural stem cells. Depletion of RUS locks neuronal precursors in an intermediate state towards neuronal differentiation resulting in arrested cell cycle and increased apoptosis. RUS associates with chromatin in the vicinity of genes involved in neurogenesis, most of which change their expression upon RUS depletion. The identification of a range of epigenetic regulators as specific RUS interactors suggests that the lncRNA may mediate gene activation and repression in a highly context-dependent manner.

Disease-associated KBTBD4 mutations in medulloblastoma elicit neomorphic ubiquitylation activity to promote CoREST degradation

Medulloblastoma is the most common malignant brain tumour in children. Genomic studies have identified distinct disease subgroups: wnt/wingless (WNT), sonic hedgehog (SHH), and non-WNT/non-SHH, comprising group 3 and group 4. Alterations in WNT and SHH signalling form the pathogenetic basis for their subgroups, whereas those for non-WNT/non-SHH tumours remain largely elusive. Recent analyses have revealed recurrent in-frame insertions in the E3 ubiquitin ligase adaptor Kelch Repeat and BTB Domain Containing 4 (KBTBD4) in cases of group 3/4 medulloblastoma. Critically, group 3/4 tumours with KBTBD4 mutations typically lack other gene-specific alterations, such as MYC amplification, indicating KBTBD4 insertion mutations as the primary genetic driver. Delineating the role of KBTBD4 mutations thus offers significant opportunities to understand tumour pathogenesis and to exploit the underpinning mechanisms therapeutically. Here, we show a novel mechanism in cancer pathogenesis whereby indel mutations in KBTBD4 drive its recognition of neo-substrates for degradation. We observe that KBTBD4 mutants promote the recruitment and ubiquitylation of the REST Corepressor (CoREST), which forms a complex to modulate chromatin accessibility and transcriptional programmes. The degradation of CoREST promoted by KBTBD4 mutation diverts epigenetic programmes inducing significant alterations in transcription to promote increased stemness of cancer cells. Transcriptional analysis of >200 human group 3 and 4 medulloblastomas by RNA-seq, highlights the presence of CoREST and stem-like signatures in tumours with KBTBD4 mutations, which extend to a further sub-set of non-mutant tumours, suggesting CoREST alterations as a novel pathogenetic mechanism of wide relevance in groups 3 and 4. Our findings uncover KBTBD4 mutation as a novel driver of epigenetic reprogramming in non-WNT/non-SHH medulloblastoma, establish a novel mode of tumorigenesis through gain-of-function mutations in ubiquitin ligases (neo-substrate recruitment) and identify both mutant KBTBD4 and CoREST complexes as new druggable targets for improved tumour-specific therapies.

RNA-seq and ChIP-seq Identification of Unique and Overlapping Targets of GLI Transcription Factors in Melanoma Cell Lines

BACKGROUND

Despite significant progress in therapy, melanoma still has a rising incidence worldwide, and novel treatment strategies are needed. Recently, researchers have recognized the involvement of the Hedgehog-GLI (HH-GLI) signaling pathway in melanoma and its consistent crosstalk with the MAPK pathway. In order to further investigate the link between the two pathways and to find new target genes that could be considered for combination therapy, we set out to find transcriptional targets of all three GLI proteins in melanoma.

METHODS

We performed RNA sequencing on three melanoma cell lines (CHL-1, A375, and MEL224) with overexpressed GLI1, GLI2, and GLI3 and combined them with the results of ChIP-sequencing on endogenous GLI1, GLI2, and GLI3 proteins. After combining these results, 21 targets were selected for validation by qPCR.

RESULTS

RNA-seq revealed a total of 808 differentially expressed genes (DEGs) for GLI1, 941 DEGs for GLI2, and 58 DEGs for GLI3. ChIP-seq identified 527 genes that contained GLI1 binding sites in their promoters, 1103 for GLI2 and 553 for GLI3. A total of 15 of these targets were validated in the tested cell lines, 6 of which were detected by both RNA-seq and ChIP-seq.

CONCLUSIONS

Our study provides insight into the unique and overlapping transcriptional output of the GLI proteins in melanoma. We suggest that our findings could provide new potential targets to consider while designing melanoma-targeted therapy.

SUFU suppresses ferroptosis sensitivity in breast cancer cells via Hippo/YAP pathway

Ferroptosis is a new kind of regulated cell death that is characterized by highly iron-dependent lipid peroxidation. Cancer cells differ in their sensitivity to ferroptosis. Here we showed that the Suppressor of fused homolog (SUFU), a critical component in Hedgehog signaling, regulates ferroptosis sensitivity of breast cancer cells. Ectopic SUFU expression suppressed, whereas depletion of SUFU enhanced the sensitivity of breast cancer cells to RSL3-triggered ferroptosis through deregulation of ACSL4. Moreover, SUFU depletion promoted the activation of Yes-associated protein (YAP), thereby increasing the expression of ACSL4. Mechanistically, SUFU is associated with LATS1. Deletion of a region comprising residues 174-385 in SUFU disrupted SUFU binding to LATS1, thus abrogating SUFU-mediated downregulation of the YAP-ACSL4 axis and sensitivity to ferroptosis. Noteworthy, we showed that vincristine downregulated SUFU, thus increasing breast cancer cell sensitivity to RSL3 in vitro and in vivo. Together, our findings uncover SUFU as a novel regulator in ferroptosis sensitivity.

VCAM-1-targeted MRI Improves Detection of the Tumor-brain Interface

PURPOSE

Despite optimal local therapy, tumor cell invasion into normal brain parenchyma frequently results in recurrence in patients with solid tumors. The aim of this study was to determine whether microvascular inflammation can be targeted to better delineate the tumor-brain interface through vascular cell adhesion molecule-1 (VCAM-1)-targeted MRI.

EXPERIMENTAL DESIGN

Intracerebral xenograft rat models of MDA231Br-GFP (breast cancer) brain metastasis and U87MG (glioblastoma) were used to histologically examine the tumor-brain interface and to test the efficacy of VCAM-1-targeted MRI in detecting this region. Human biopsy samples of the brain metastasis and glioblastoma margins were examined for endothelial VCAM-1 expression.

RESULTS

The interface between tumor and surrounding normal brain tissue exhibited elevated endothelial VCAM-1 expression and increased microvessel density. Tumor proliferation and stemness markers were also significantly upregulated at the tumor rim in the brain metastasis model. T2*-weighted MRI, following intravenous administration of VCAM-MPIO, highlighted the tumor-brain interface of both tumor models more extensively than gadolinium-DTPA-enhanced T1-weighted MRI. Sites of VCAM-MPIO binding, evident as hypointense signals on MR images, correlated spatially with endothelial VCAM-1 upregulation and bound VCAM-MPIO beads detected histologically. These findings were further validated in an orthotopic medulloblastoma model. Finally, the tumor-brain interface in human brain metastasis and glioblastoma samples was similarly characterized by microvascular inflammation, extending beyond the region detectable using conventional MRI.

CONCLUSIONS

This work illustrates the potential of VCAM-1-targeted MRI for improved delineation of the tumor-brain interface in both primary and secondary brain tumors.

Quality control of protein complex composition

Eukaryotic cells possess hundreds of protein complexes that contain multiple subunits and must be formed at the correct time and place during development. Despite specific assembly pathways, cells frequently encounter complexes with missing or aberrant subunits that can disrupt important signaling events. Cells, therefore, employ several ubiquitin-dependent quality control pathways that can prevent, correct, or degrade flawed complexes. In this review, we will discuss our emerging understanding of such quality control of protein complex composition.

Regulation of Hedgehog Signal Transduction by Ubiquitination and Deubiquitination

The Hedgehog (Hh) family of secreted proteins governs embryonic development and adult tissue homeostasis in species ranging from insects to mammals. Deregulation of Hh pathway activity has been implicated in a wide range of human disorders, including congenital diseases and cancer. Hh exerts its biological influence through a conserved signaling pathway. Binding of Hh to its receptor Patched (Ptc), a twelve-span transmembrane protein, leads to activation of an atypical GPCR family protein and Hh signal transducer Smoothened (Smo), which then signals downstream to activate the latent Cubitus interruptus (Ci)/Gli family of transcription factors. Hh signal transduction is regulated by ubiquitination and deubiquitination at multiple steps along the pathway including regulation of Ptc, Smo and Ci/Gli proteins. Here we review the effect of ubiquitination and deubiquitination on the function of individual Hh pathway components, the E3 ubiquitin ligases and deubiquitinases involved, how ubiquitination and deubiquitination are regulated, and whether the underlying mechanisms are conserved from Drosophila to mammals.

Comparative Genomics Sheds Light on the Convergent Evolution of Miniaturized Wasps

Miniaturization has occurred in many animal lineages, including insects and vertebrates, as a widespread trend during animal evolution. Among Hymenoptera, miniaturization has taken place in some parasitoid wasp lineages independently, and may have contributed to the diversity of species. However, the genomic basis of miniaturization is little understood. Diverged approximately 200 Ma, Telenomus wasps (Platygastroidea) and Trichogramma wasps (Chalcidoidea) have both evolved to a highly reduced body size independently, representing a paradigmatic example of convergent evolution. Here, we report a high-quality chromosomal genome of Telenomus remus, a promising candidate for controlling Spodoptera frugiperda, a notorious pest that has recently caused severe crop damage. The T. remus genome (129 Mb) is characterized by a low density of repetitive sequence and a reduction of intron length, resulting in the shrinkage of genome size. We show that hundreds of genes evolved faster in two miniaturized parasitoids Trichogramma pretiosum and T. remus. Among them, 38 genes exhibit extremely accelerated evolutionary rates in these miniaturized wasps, possessing diverse functions in eye and wing development as well as cell size control. These genes also highlight potential roles in body size regulation. In sum, our analyses uncover a set of genes with accelerated evolutionary rates in Tri. pretiosum and T. remus, which might be responsible for their convergent adaptations to miniaturization, and thus expand our understanding on the evolutionary basis of miniaturization. Additionally, the genome of T. remus represents the first genome resource of superfamily Platygastroidea, and will facilitate future studies of Hymenoptera evolution and pest control.

Protein modifications in Hedgehog signaling: Cross talk and feedback regulation confer divergent Hedgehog signaling activity

The complexity of the Hedgehog (Hh) signaling cascade has increased over the course of evolution; however, it does not suffice to accommodate the dynamic yet robust requirements of differential Hh signaling activity needed for embryonic development and adult homeostatic maintenance. One solution to solve this dilemma is to apply multiple forms of post-translational modifications (PTMs) to the core Hh signaling components, modulating their abundance, localization, and signaling activity. This review summarizes various forms of protein modifications utilized to regulate Hh signaling, with a special emphasis on crosstalk between different forms of PTMs and their feedback regulation by Hh signaling.

Hedgehog/GLI Signaling Pathway: Transduction, Regulation, and Implications for Disease

Simple Summary

The Hedgehog/GLI (Hh/GLI) pathway plays a major role during development and it is commonly dysregulated in many diseases, including cancer. This highly concerted series of ligands, receptors, cytoplasmic signaling molecules, transcription factors, and co-regulators is involved in regulating the biological functions controlled by this pathway. Activation of Hh/GLI in cancer is most often through a non-canonical method of activation, independent of ligand binding. This review is intended to summarize our current understanding of the Hh/GLI signaling, non-canonical mechanisms of pathway activation, its implication in disease, and the current therapeutic strategies targeting this cascade.

Abstract

The Hh/GLI signaling pathway was originally discovered in Drosophila as a major regulator of segment patterning in development. This pathway consists of a series of ligands (Shh, Ihh, and Dhh), transmembrane receptors (Ptch1 and Ptch2), transcription factors (GLI1–3), and signaling regulators (SMO, HHIP, SUFU, PKA, CK1, GSK3β, etc.) that work in concert to repress (Ptch1, Ptch2, SUFU, PKA, CK1, GSK3β) or activate (Shh, Ihh, Dhh, SMO, GLI1–3) the signaling cascade. Not long after the initial discovery, dysregulation of the Hh/GLI signaling pathway was implicated in human disease. Activation of this signaling pathway is observed in many types of cancer, including basal cell carcinoma, medulloblastoma, colorectal, prostate, pancreatic, and many more. Most often, the activation of the Hh/GLI pathway in cancer occurs through a ligand-independent mechanism. However, in benign disease, this activation is mostly ligand-dependent. The upstream signaling component of the receptor complex, SMO, is bypassed, and the GLI family of transcription factors can be activated regardless of ligand binding. Additional mechanisms of pathway activation exist whereby the entirety of the downstream signaling pathway is bypassed, and PTCH1 promotes cell cycle progression and prevents caspase-mediated apoptosis. Throughout this review, we summarize each component of the signaling cascade, non-canonical modes of pathway activation, and the implications in human disease, including cancer.

Sufu negatively regulates both initiations of centrosome duplication and DNA replication

Centrosome duplication and DNA replication are two pivotal events that higher eukaryotic cells use to initiate proliferation. While DNA replication is initiated through origin licensing, centrosome duplication starts with cartwheel assembly and is partly controlled by CP110. However, the upstream coordinator for both events has been, until now, a mystery. Here, we report that suppressor of fused protein (Sufu), a negative regulator of the Hedgehog (Hh) pathway playing a significant role in restricting the trafficking and function of glioma-related (Gli) proteins, acts as an upstream switch by facilitating CP110 phosphorylation by CDK2, promoting intranuclear Cdt1 degradation and excluding prereplication complex (pre-RC) components from chromosomes, independent of its canonical function in the Hh pathway. We found that Sufu localizes to both the centrosome and the nucleus and that knockout of Sufu induces abnormalities including centrosome amplification, increased nuclear size, multipolar spindle formation, and polyploidy. Serum stimulation promotes the elimination of Sufu from the centrosome by vesicle release at the ciliary tip and from the nucleus via protein degradation, which allows centrosome duplication and DNA replication to proceed. Collectively, this work reveals a mechanism through which Sufu negatively regulates the G1-S transition.

Positive feedback of SuFu negating protein 1 on Hedgehog signaling promotes colorectal tumor growth

Hedgehog (Hh) signaling plays a critical role in embryogenesis and tissue homeostasis, and its deregulation has been associated with tumor growth. The tumor suppressor SuFu inhibits Hh signaling by preventing the nuclear translocation of Gli and suppressing cell proliferation. Regulation of SuFu activity and stability is key to controlling Hh signaling. Here, we unveil SuFu Negating Protein 1 (SNEP1) as a novel Hh target, that enhances the ubiquitination and proteasomal degradation of SuFu and thus promotes Hh signaling. We further show that the E3 ubiquitin ligase LNX1 plays a critical role in the SNEP1-mediated degradation of SuFu. Accordingly, SNEP1 promotes colorectal cancer (CRC) cell proliferation and tumor growth. High levels of SNEP1 are detected in CRC tissues and are well correlated with poor prognosis in CRC patients. Moreover, SNEP1 overexpression reduces sensitivity to anti-Hh inhibitor in CRC cells. Altogether, our findings demonstrate that SNEP1 acts as a novel feedback regulator of Hh signaling by destabilizing SuFu and promoting tumor growth and anti-Hh resistance.

Regulator of cullins-1 (ROC1) negatively regulates the Gli2 regulator SUFU to activate the hedgehog pathway in bladder cancer

BACKGROUND

The regulator of cullins-1 (ROC1) is an essential subunit in the cullin-RING ligase (CRL) protein complex and has been shown to be critical in bladder cancer cell survival and progression. This study aimed to explore the molecular mechanism of ROC1 action in the malignant progression of bladder cancer.

METHODS

This study utilized ex vivo, in vitro, and in vivo nude mouse experiments to assess the underlying mechanisms of ROC1 in bladder cancer cells. The expression of the components of the sonic hedgehog (SHH) pathway was determined by western blot analysis. ROC1 expression in human tumors was evaluated by immunohistochemistry.

RESULTS

ROC1 overexpression promoted the growth of bladder cancer cells, whereas knockdown of ROC1 expression had the opposite effect in bladder cancer cells. Mechanistically, ROC1 was able to target suppressor of fused homolog (SUFU) for ubiquitin-dependent degradation, allowing Gli2 release from the SUFU complex to activate the SHH pathway. Furthermore, knockdown of SUFU expression partially rescued the ROC1 knockdown-suppressed SHH activity as well as cancer cell growth inhibition. In ex vivo experiments, tissue microarray analysis of human bladder cancer specimens revealed a positive association of ROC1 expression with the SHH pathway activity.

CONCLUSION

This study demonstrated that dysregulation of the ROC1-SUFU-GLI2 axis plays an important role in bladder cancer progression and that targeting ROC1 expression is warranted in further investigations as a novel strategy for the future control of bladder cancer.

The FBXL family of F-box proteins: variations on a theme

The ubiquitin–proteasome system (UPS) is responsible for the rapid targeting of proteins for degradation at 26S proteasomes and requires the orchestrated action of E1, E2 and E3 enzymes in a well-defined cascade. F-box proteins (FBPs) are substrate-recruiting subunits of Skp1-cullin1-FBP (SCF)-type E3 ubiquitin ligases that determine which proteins are ubiquitinated. To date, around 70 FBPs have been identified in humans and can be subdivided into distinct families, based on the protein-recruiting domains they possess. The FBXL subfamily is defined by the presence of multiple leucine-rich repeat (LRR) protein-binding domains. But how the 22 FBPs of the FBXL family achieve their individual specificities, despite having highly similar structural domains to recruit their substrates, is not clear. Here, we review and explore the FBXL family members in detail highlighting their structural and functional similarities and differences and how they engage their substrates through their LRRs to adopt unique interactomes.

Ubiquitin ligases and medulloblastoma: genetic markers of the four consensus subgroups identified through transcriptome datasets

The ubiquitin proteasome system regulates key cellular processes in normal and in cancer cells. Herein, we review published data on the role of ubiquitin ligases in the four major subgroups of medulloblastoma (MB). While conventional literature serves as an initial source of information on cellular pathways in MB, large publicly available datasets of gene expression can be used to add information not previously identified in the literature. By analysing the publicly available Cavalli dataset, we show that increased expression of ZNRF3 characterizes the WNT subgroup of MB. The ZNRF3 gene codes for an E3 ligase associated with WNT receptors. Loss of a copy of chromosome 6 in a subtype of the WNT group was associated with decreased expression of the gene encoding the E3 ligase RNF146. While the E3 ligase SMURF regulates SHH receptors, increased expression of the gene encoding the Cullin Ring E3 adaptor PPP2R2C was statistically a better genetic marker of the SHH group. Genes whose expression was statistically strongly related to Group 3 included the E3 ligase gene TRIM58, and the gene for the E3 ligase adaptor, PPP2R2B. Group 4 MB was associated with expression of genes encoding several E3 ligases and E3 ligase adaptors involved in ribosome biogenesis. Increased expression of the genes encoding the E3 ligase adaptors and transcription repressors ZBTB18 and ZBTB38 were also noted in subgroup 4. These data suggest that several E3 ligases and their adaptors should be investigated as therapeutic targets for subgroup specific MB brain tumors.

Protein phosphatase 4 promotes Hedgehog signaling through dephosphorylation of Suppressor of fused

Reversible phosphorylation of Suppressor of fused (Sufu) is essential for Sonic Hedgehog (Shh) signal transduction. Sufu is stabilized under dual phosphorylation of protein kinase A (PKA) and glycogen synthase kinase 3β (GSK3β). Its phosphorylation is reduced with the activation of Shh signaling. However, the phosphatase in this reversible phosphorylation has not been found. Taking advantage of a proteomic approach, we identified Protein phosphatase 4 regulatory subunit 2 (Ppp4r2), an interacting protein of Sufu. Shh signaling promotes the interaction of these two proteins in the nucleus, and Ppp4 also promotes dephosphorylation of Sufu, leading to its degradation and enhancing the Gli1 transcriptional activity. Finally, Ppp4-mediated dephosphorylation of Sufu promotes proliferation of medulloblastoma tumor cells, and expression of Ppp4 is positively correlated with up-regulation of Shh pathway target genes in the Shh-subtype medulloblastoma, underscoring the important role of this regulation in Shh signaling.

Fbxl17 is rearranged in breast cancer and loss of its activity leads to increased global O-GlcNAcylation

In cancer, many genes are mutated by genome rearrangement, but our understanding of the functional consequences of this remains rudimentary. Here we report the F-box protein encoded by FBXL17 is disrupted in the region of the gene that encodes its substrate-binding leucine rich repeat (LRR) domain. Truncating Fbxl17 LRRs impaired its association with the other SCF holoenzyme subunits Skp1, Cul1 and Rbx1, and decreased ubiquitination activity. Loss of the LRRs also differentially affected Fbxl17 binding to its targets. Thus, genomic rearrangements in FBXL17 are likely to disrupt SCFFbxl17-regulated networks in cancer cells. To investigate the functional effect of these rearrangements, we performed a yeast two-hybrid screen to identify Fbxl17-interacting proteins. Among the 37 binding partners Uap1, an enzyme involved in O-GlcNAcylation of proteins was identified most frequently. We demonstrate that Fbxl17 binds to UAP1 directly and inhibits its phosphorylation, which we propose regulates UAP1 activity. Knockdown of Fbxl17 expression elevated O-GlcNAcylation in breast cancer cells, arguing for a functional role for Fbxl17 in this metabolic pathway.

Prostaglandin E1 Inhibits GLI2 Amplification-Associated Activation of the Hedgehog Pathway and Drug Refractory Tumor Growth

Aberrant activation of the Hedgehog (HH) signaling pathway underlines the initiation and progression of a multitude of cancers. The effectiveness of the leading drugs vismodegib (GDC-0449) and sonidegib (LDE225), both Smoothened (SMO) antagonists, is compromised by acquisition of mutations that alter pathway components, notably secondary mutations in SMO and amplification of GLI2, a transcriptional mediator at the end of the pathway. Pharmacologic blockade of GLI2 activity could ultimately overcome these diversified refractory mechanisms, which would also be effective in a broader spectrum of primary tumors than current SMO antagonists. To this end, we conducted a high-content screening directly analyzing the ciliary translocation of GLI2, a key event for GLI2 activation in HH signal transduction. Several prostaglandin compounds were shown to inhibit accumulation of GLI2 within the primary cilium (PC). In particular, prostaglandin E1 (PGE1), an FDA-approved drug, is a potent GLI2 antagonist that overcame resistance mechanisms of both SMO mutagenesis and GLI2 amplification. Consistent with a role in HH pathway regulation, EP4 receptor localized to the PC. Mechanistically, PGE1 inhibited HH signaling through the EP4 receptor, enhancing cAMP-PKA activity, which promoted phosphorylation and degradation of GLI2 via the ubiquitination pathway. PGE1 also effectively inhibited the growth of drug refractory human medulloblastoma xenografts. Together, these results identify PGE1 and other prostaglandins as potential templates for complementary therapeutic development to circumvent resistance to current generation SMO antagonists in use in the clinic. SIGNIFICANCE: These findings show that PGE1 exhibits pan-inhibition against multiple drug refractory activities for Hedgehog-targeted therapies and elicits significant antitumor effects in xenograft models of drug refractory human medulloblastoma mimicking GLI2 amplification.

F-box proteins and cancer: an update from functional and regulatory mechanism to therapeutic clinical prospects

E3 ubiquitin ligases play a critical role in cellular mechanisms and cancer progression. F-box protein is the core component of the SKP1-cullin 1-F-box (SCF)-type E3 ubiquitin ligase and directly binds to substrates by various specific domains. According to the specific domains, F-box proteins are further classified into three sub-families: 1) F-box with leucine rich amino acid repeats (FBXL); 2) F-box with WD 40 amino acid repeats (FBXW); 3) F-box only with uncharacterized domains (FBXO). Here, we summarize the substrates of F-box proteins, discuss the important molecular mechanism and emerging role of F-box proteins especially from the perspective of cancer development and progression. These findings will shed new light on malignant tumor progression mechanisms, and suggest the potential role of F-box proteins as cancer biomarkers and therapeutic targets for future cancer treatment.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells (CSCs) were first identified in leukemia in 1994, they have been considered promising therapeutic targets for cancer therapy. These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies, such as recurrence, metastasis, heterogeneity, multidrug resistance, and radiation resistance. The biological activities of CSCs are regulated by several pluripotent transcription factors, such as OCT4, Sox2, Nanog, KLF4, and MYC. In addition, many intracellular signaling pathways, such as Wnt, NF-κB (nuclear factor-κB), Notch, Hedgehog, JAK-STAT (Janus kinase/signal transducers and activators of transcription), PI3K/AKT/mTOR (phosphoinositide 3-kinase/AKT/mammalian target of rapamycin), TGF (transforming growth factor)/SMAD, and PPAR (peroxisome proliferator-activated receptor), as well as extracellular factors, such as vascular niches, hypoxia, tumor-associated macrophages, cancer-associated fibroblasts, cancer-associated mesenchymal stem cells, extracellular matrix, and exosomes, have been shown to be very important regulators of CSCs. Molecules, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) cells have been developed to specifically target CSCs, and some of these factors are already undergoing clinical trials. This review summarizes the characterization and identification of CSCs, depicts major factors and pathways that regulate CSC development, and discusses potential targeted therapy for CSCs.

Emerging roles of F-box proteins in cancer drug resistance

Chemotherapy continues to be a major treatment strategy for various human malignancies. However, the frequent emergence of chemoresistance compromises chemotherapy efficacy leading to poor prognosis. Thus, overcoming drug resistance is pivotal to achieve enhanced therapy efficacy in various cancers. Although increased evidence has revealed that reduced drug uptake, increased drug efflux, drug target protein alterations, drug sequestration in organelles, enhanced drug metabolism, impaired DNA repair systems, and anti-apoptotic mechanisms, are critically involved in drug resistance, the detailed resistance mechanisms have not been fully elucidated in distinct cancers. Recently, F-box protein (FBPs), key subunits in Skp1-Cullin1-F-box protein (SCF) E3 ligase complexes, have been found to play critical roles in carcinogenesis, tumor progression, and drug resistance through degradation of their downstream substrates. Therefore, in this review, we describe the functions of FBPs that are involved in drug resistance and discuss how FBPs contribute to the development of cancer drug resistance. Furthermore, we propose that targeting FBPs might be a promising strategy to overcome drug resistance and achieve better treatment outcome in cancer patients. Lastly, we state the limitations and challenges of using FBPs to overcome chemotherapeutic drug resistance in various cancers.

β-TrCP- and Casein Kinase II-Mediated Degradation of Cyclin F Controls Timely Mitotic Progression

Orderly progressions of events in the cell division cycle are necessary to ensure the replication of DNA and cell division. Checkpoint systems allow the accurate execution of each cell-cycle phase. The precise regulation of the levels of cyclin proteins is fundamental to coordinate cell division with checkpoints, avoiding genome instability. Cyclin F has important functions in regulating the cell cycle during the G2 checkpoint; however, the mechanisms underlying the regulation of cyclin F are poorly understood. Here, we observe that cyclin F is regulated by proteolysis through β-TrCP. β-TrCP recognizes cyclin F through a non-canonical degron site (TSGXXS) after its phosphorylation by casein kinase II. The degradation of cyclin F mediated by β-TrCP occurs at the G2/M transition. This event is required to promote mitotic progression and favors the activation of a transcriptional program required for mitosis.

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β-TrCP1 and β-TrCP2 interact with cyclin F and control cyclin F levels during mitosis

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A TSGXXS motif is necessary for β-TrCP1 and β-TrCP2 binding to cyclin F

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CKIIα phosphorylates cyclin F at S704 within the TSGXXS motif

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β-TrCP-mediated degradation of cyclin F promotes mitotic progression via B-Myb

ERAP1 promotes Hedgehog-dependent tumorigenesis by controlling USP47-mediated degradation of βTrCP

The Hedgehog (Hh) pathway is essential for embryonic development and tissue homeostasis. Aberrant Hh signaling may occur in a wide range of human cancers, such as medulloblastoma, the most common brain malignancy in childhood. Here, we identify endoplasmic reticulum aminopeptidase 1 (ERAP1), a key regulator of innate and adaptive antitumor immune responses, as a previously unknown player in the Hh signaling pathway. We demonstrate that ERAP1 binds the deubiquitylase enzyme USP47, displaces the USP47-associated βTrCP, the substrate-receptor subunit of the SCF^βTrCP ubiquitin ligase, and promotes βTrCP degradation. These events result in the modulation of Gli transcription factors, the final effectors of the Hh pathway, and the enhancement of Hh activity. Remarkably, genetic or pharmacological inhibition of ERAP1 suppresses Hh-dependent tumor growth in vitro and in vivo. Our findings unveil an unexpected role for ERAP1 in cancer and indicate ERAP1 as a promising therapeutic target for Hh-driven tumors.

ERAP1 is an endoplasmic reticulum aminopeptidase that trims MHC Class-I peptides for antigen presentation. Here, the authors show that ERAP1 enhances Hedgehog signalling by sequestering USP47 from  βTrCP and promoting tumorigenesis through βTrCP degradation and increased Gli protein stability.

Dimerization quality control ensures neuronal development and survival

Aberrant complex formation by recurrent interaction modules, such as BTB domains, leucine zippers, or coiled coils, can disrupt signal transduction, yet whether cells detect and eliminate complexes of irregular composition is unknown. By searching for regulators of the BTB family, we discovered a quality control pathway that ensures functional dimerization [dimerization quality control (DQC)]. Key to this network is the E3 ligase SCF^FBXL17, which selectively binds and ubiquitylates BTB dimers of aberrant composition to trigger their clearance by proteasomal degradation. Underscoring the physiological importance of DQC, SCF^FBXL17 is required for the differentiation, function, and survival of neural crest and neuronal cells. We conclude that metazoan organisms actively monitor BTB dimerization, and we predict that distinct E3 ligases similarly control complex formation by other recurrent domains.

Tumorigenic Cell Reprogramming and Cancer Plasticity: Interplay between Signaling, Microenvironment, and Epigenetics

Accumulating evidences indicate that many tumors rely on subpopulations of cancer stem cells (CSCs) with the ability to propagate malignant clones indefinitely and to produce an overt cancer. Of importance, CSCs seem to be more resistant to the conventional cytotoxic treatments, driving tumor growth and contributing to relapse. CSCs can originate from normal committed cells which undergo tumor-reprogramming processes and reacquire a stem cell-like phenotype. Increasing evidences also show how tumor homeostasis and progression strongly rely on the capacity of nontumorigenic cancer cells to dedifferentiate to CSCs. Both tumor microenvironment and epigenetic reprogramming drive such dynamic mechanisms, favoring cancer cell plasticity and tumor heterogeneity. Here, we report new developments which led to an advancement in the CSC field, elucidating the concepts of cancer cell of origin and CSC plasticity in solid tumor initiation and maintenance. We further discuss the main signaling pathways which, under the influence of extrinsic environmental factors, play a critical role in the formation and maintenance of CSCs. Moreover, we propose a review of the main epigenetic mechanisms whose deregulation can favor the onset of CSC features both in tumor initiation and tumor maintenance. Finally, we provide an update of the main strategies that could be applied to target CSCs and cancer cell plasticity.

Itch/β-arrestin2-dependent non-proteolytic ubiquitylation of SuFu controls Hedgehog signalling and medulloblastoma tumorigenesis

Suppressor of Fused (SuFu), a tumour suppressor mutated in medulloblastoma, is a central player of Hh signalling, a pathway crucial for development and deregulated in cancer. Although the control of Gli transcription factors by SuFu is critical in Hh signalling, our understanding of the mechanism regulating this key event remains limited. Here, we show that the Itch/β-arrestin2 complex binds SuFu and induces its Lys63-linked polyubiquitylation without affecting its stability. This process increases the association of SuFu with Gli3, promoting the conversion of Gli3 into a repressor, which keeps Hh signalling off. Activation of Hh signalling antagonises the Itch-dependent polyubiquitylation of SuFu. Notably, different SuFu mutations occurring in medulloblastoma patients are insensitive to Itch activity, thus leading to deregulated Hh signalling and enhancing medulloblastoma cell growth. Our findings uncover mechanisms controlling the tumour suppressive functions of SuFu and reveal that their alterations are implicated in medulloblastoma tumorigenesis.

SuFu is a tumour suppressor in medulloblastoma and regulates Gli proteins in the Sonic Hedgehog pathway; however, the molecular mechanisms behind this regulation are unclear. Here, the authors show that the Itch/β-arrestin2 complex binds and ubiquitylates SuFu, facilitating the interaction with Gli3 and its conversion into the repressive form, thus counteracting medulloblastoma formation.

Molecular mechanisms of suppressor of fused in regulating the hedgehog signalling pathway

Highly conserved throughout evolution, the hedgehog (Hh) signalling pathway has been demonstrated to be involved in embryonic development, stem cell maintenance and tissue homeostasis in animals ranging from invertebrates to vertebrates. In the human body, a variety of cancer types are associated with the aberrantly activated Hh signalling pathway. Multiple studies have revealed suppressor of fused (Sufu) as a key negative regulator of this signalling pathway. In vertebrates, Sufu primarily functions as a tumor suppressor factor by interacting with and inhibiting glioma-associated oncogene homologues (GLIs), which are the terminal transcription factors of the Hh signalling pathway and belong to the Kruppel family of zinc finger proteins; by contrast, the regulation of Sufu itself remains relatively unclear. In the present review article, we focus on the effects of Sufu on the Hh signalling pathway in tumourigenesis and the molecular mechanisms underlying the regulation of GLI by Sufu. In addition, the factors modulating the activity of Sufu at post-transcriptional levels are also discussed.

FBXL13 directs the proteolysis of CEP192 to regulate centrosome homeostasis and cell migration

Aberrant centrosome organisation with ensuing alterations of microtubule nucleation capacity enables tumour cells to proliferate and invade despite increased genomic instability. CEP192 is a key factor in the initiation process of centrosome duplication and in the control of centrosome microtubule nucleation. However, regulatory means of CEP192 have remained unknown. Here, we report that FBXL13, a binding determinant of SCF (SKP1-CUL1-F-box)-family E3 ubiquitin ligases, is enriched at centrosomes and interacts with the centrosomal proteins Centrin-2, Centrin-3, CEP152 and CEP192. Among these, CEP192 is specifically targeted for proteasomal degradation by FBXL13. Accordingly, induced FBXL13 expression downregulates centrosomal γ-tubulin and disrupts centrosomal microtubule arrays. In addition, depletion of FBXL13 induces high levels of CEP192 and γ-tubulin at the centrosomes with the consequence of defects in cell motility. Together, we characterise FBXL13 as a novel regulator of microtubule nucleation activity and highlight a role in promoting cell motility with potential tumour-promoting implications.

Ubiquitylation at the crossroads of development and disease

Human development requires intricate cell specification and communication pathways that allow an embryo to generate and appropriately connect more than 200 different cell types. Key to the successful completion of this differentiation programme is the quantitative and reversible regulation of core signalling networks, and post-translational modification with ubiquitin provides embryos with an essential tool to accomplish this task. Instigated by E3 ligases and reversed by deubiquitylases, ubiquitylation controls many processes that are fundamental for development, such as cell division, fate specification and migration. As aberrant function or regulation of ubiquitylation enzymes is at the roots of developmental disorders, cancer, and neurodegeneration, modulating the activity of ubiquitylation enzymes is likely to provide strategies for therapeutic intervention.

Lipopolysaccharide modulates p300 and Sirt1 to promote PRMT1 stability via an SCFFbxl17-recognized acetyldegron

E3 ubiquitin ligase recognizes its protein substrates via specific molecular signatures for ubiquitin proteasomal degradation. However, the role of acetylation/deacetylation in the process of E3 ubiquitin ligase recognizing its protein substrates is not fully studied. Here, we report that a tandem IK motif in protein arginine methyltransferase 1 (PRMT1) forms an acetyldegron to recruit the F-box/LRR-repeat protein 17 (FBXL17), a component of the SKP1-CUL1-F-box protein (SCF)-type E3 ubiquitin ligase complex. PRMT1 is polyubiquitylated for proteasome degradation with a half-life of approximately 4 h in lung epithelial cells. SCF^Fbxl17 mediates PRMT1 polyubiquitylation at K117. SCF^Fbxl17 specifically binds PRMT1 via a unique motif IKxxxIK. Strikingly, the acetylation/deacetylation status of the lysine residues within the motif determines Fbxl17 binding. Deacetylation on both K200 and K205 by Sirtuin 1 (Sirt1) and acetylation of p300 (EP300) on K205 collaboratively prepare the motif for SCF^Fbxl17 binding thereby triggering PRMT1 protein degradation. Pathogen-derived lipopolysaccharide (LPS) downregulates Sirt1 and p300 to protect PRMT1 from degradation. This study demonstrates that LPS promotes PRMT1 stability by blockade of PRMT1 and SCF^Fbxl17 binding via an acetylation/deacetylation-modified acetyldegron; and LPS-elevated levels of PRMT1 lead to bronchial epithelial cell overgrowth in pulmonary inflammatory diseases.

Cerebrospinal fluid from patients with amyotrophic lateral sclerosis inhibits sonic hedgehog function

Sonic hedgehog (Shh) is a morphogen essential to the developing nervous system that continues to play an important role in adult life by contributing to cell proliferation and differentiation, maintaining blood-brain barrier integrity, and being cytoprotective against oxidative and excitotoxic stress, all features of importance in amyotrophic lateral sclerosis (ALS). ALS is a fatal disease characterized by selective loss of motor neurons due to poorly understood mechanisms. Evidence indicates that Shh might play an important role in ALS, and that Shh signaling might be also adversely affected in ALS. Since little is known about the functional status of Shh pathway in patients with ALS, we therefore sought to determine whether Shh protein levels or biological activity in cerebrospinal fluid (CSF) was less in ALS patients than controls, and whether these measures could be correlated with ALS disease severity and disease progression, and with other CSF analytes of biological interest in ALS. Comparing Shh levels in the CSF of normal controls (n = 13), neurological controls (n = 12), and ALS patients (n = 9) measured by ELISA, we found that CSF Shh levels were not different between controls and ALS patients. However, when assessing Shh biological activity in CSF using in vitro cell-based assays, which measure Shh activity as inducible Gli-driven luminescence, we found that in the presence of exogenous recombinant Shh or the Shh agonist, purmorphamine, the inducible activity of CSF was significantly augmented in the control groups as expected, but not in the ALS group, suggesting the presence of an inhibitor of Shh signaling in ALS CSF samples. Since purmorphamine acts on Smoothened, downstream of Shh and its receptor Patched, the inhibitory action is downstream of Smoothened. Our results also demonstrated that while the inhibitory effect of ALS CSF on Shh signaling did not correlate significantly with ALS disease characteristics, the levels of IL-1β and TNF-α did. In addition to being significantly elevated in ALS CSF, these cytokines negatively correlated with the disease duration, whereas GDF11 was a favorable predictor of ALS clinical score. We also found that TNF-α significantly inhibited Shh biological activity in vitro, potentially suggesting a novel role of TNF-α in ALS pathogenesis. Collectively, this is the first report demonstrating that Shh signaling in CSF of ALS patients is compromised.

GLI1, a master regulator of the hallmark of pancreatic cancer

Hedgehog signaling is highly conserved across species and governs proper embryonic development. Germline gene mutations that reduce this signaling activity cause a variety of developmental abnormalities such as holoprosencephaly, while those that enhance Hedgehog signaling activity induce a tumor-predisposition condition Nevoid basal cell carcinoma syndrome. Furthermore, dysregulated activation of Hedgehog signaling has been recognized in various sporadic malignancies, including pancreatic adenocarcinoma. Pancreatic adenocarcinoma develops through a multistep carcinogenesis starting with oncogenic mutation of the KRAS gene. During this process, precancerous or cancer cells secrete Hedgehog ligand proteins to promote characteristic desmoplastic stroma around the cells, which in turn activates the expression of the downstream transcription factor GLI1 inside the cells. The quantitative and spatiotemporal dysregulation of GLI1 subsequently leads to the expression of transcriptional target genes of GLI1 that govern the hallmark of malignant properties. Here, after a brief introductory outline, a perspective is offered of Hedgehog signaling with a special focus on the role of GLI1 in pancreatic carcinogenesis.

SCF (Fbxl17) ubiquitylation of Sufu regulates Hedgehog signaling and medulloblastoma development

Skp1-Cul1-F-box protein (SCF) ubiquitin ligases direct cell survival decisions by controlling protein ubiquitylation and degradation. Sufu (Suppressor of fused) is a central regulator of Hh (Hedgehog) signaling and acts as a tumor suppressor by maintaining the Gli (Glioma-associated oncogene homolog) transcription factors inactive. Although Sufu has a pivotal role in Hh signaling, the players involved in controlling Sufu levels and their role in tumor growth are unknown. Here, we show that Fbxl17 (F-box and leucine-rich repeat protein 17) targets Sufu for proteolysis in the nucleus. The ubiquitylation of Sufu, mediated by Fbxl17, allows the release of Gli1 from Sufu for proper Hh signal transduction. Depletion of Fbxl17 leads to defective Hh signaling associated with an impaired cancer cell proliferation and medulloblastoma tumor growth. Furthermore, we identify a mutation in Sufu, occurring in medulloblastoma of patients with Gorlin syndrome, which increases Sufu turnover through Fbxl17-mediated polyubiquitylation and leads to a sustained Hh signaling activation. In summary, our findings reveal Fbxl17 as a novel regulator of Hh pathway and highlight the perturbation of the Fbxl17-Sufu axis in the pathogenesis of medulloblastoma.