Mechanisms and inhibition of Porcupine-mediated Wnt acylation

Mechanistic insights into Wnt-β-catenin pathway activation and signal transduction

In multicellular organisms, Wnt proteins govern stem and progenitor cell renewal and differentiation to regulate embryonic development, adult tissue homeostasis and tissue regeneration. Defects in canonical Wnt signalling, which is transduced intracellularly by β-catenin, have been associated with developmental disorders, degenerative diseases and cancers. Although a simple model describing Wnt-β-catenin signalling is widely used to introduce this pathway and has largely remained unchanged over the past 30 years, in this Review we discuss recent studies that have provided important new insights into the mechanisms of Wnt production, receptor activation and intracellular signalling that advance our understanding of the molecular mechanisms that underlie this important cell-cell communication system. In addition, we review the recent development of molecules capable of activating the Wnt-β-catenin pathway with selectivity in vitro and in vivo that is enabling new lines of study to pave the way for the development of Wnt therapies for the treatment of human diseases.

Focal dermal hypoplasia: a probable underrecognized low bone mass disorder secondary to aberrant Wnt signaling

A 29-year-old Spanish Caucasian man, without relevant family history, was attended in our unit due to an undiagnosed skeletal dysplasia associated with low bone mass and several fragility fractures throughout his childhood and adolescence. DXA exams throughout his life showed very low BMD values; currently, his spinal and femoral neck T-scores were - 4.3 and - 3.5, respectively. Blood and urinary tests were normal. Other relevant features included right hand and foot syndactyly, aplasia cutis, right hemibody hypoplasia, vertebral malformations, abnormal-looking humerii, and Asperger's syndrome among others. Whole exome sequencing retrieved a highly probable pathogenic variant in the PORCN gene p.(Arg296Pro) in mosaicism. PORCN mutations cause focal dermal hypoplasia (FDH), an X-linked ultra-rare ecto-mesodermal disorder characterized by several of the findings the patient presented. However, low BMD has not been classically associated with the disease. Noteworthy, PORCN is key for canonical Wnt signaling. Literature scrutiny has yielded other cases of FDH with skeletal fragility during childhood. In addition, preclinical studies with PORCN inhibitors, currently under development as an antitumoral therapy, have shown rapid detrimental effects on bone mass. Collectively, these findings indicate that FDH is probably an underrecognized monogenic cause of low bone mass due to defective Wnt signaling.

The effects of the Wnt/β-catenin signaling pathway on the in vitro differentiation of rat BMSCs into leydig cells

Late-onset hypogonadism (LOH) refers to sexual and non-sexual symptoms in men caused by age-related decreases in circulating testosterone. Leydig cells (LCs) transplantation is considered to be one of a viable approach for LOH therapy, but the limited source of LCs limits the application of this approach. The aim of this study was to induce the directed differentiation of rat bone marrow mesenchymal stem cells (BMSCs) into LCs in vitro, and explore the potential involvement of Wnt/β-catenin signaling pathway in the differentiation process. BMSCs were extracted from rats and characterized by flow cytometry for positive rates of mesenchymal stem cell markers CD29, CD44, CD90, and the hematopoietic marker CD45. BMSCs were divided into three groups: Control, Wnt agonist (CHIR-99021), and Wnt inhibitor (LGK-974), each incubated for 14 days. ELISA and RT-qPCR were used to verify the protein and mRNA expression of β-catenin, LRP5 and TCF, the key factors in Wnt/β-catenin signaling pathway. The average fluorescence intensity of 3β-hydroxysteroid dehydrogenase (3β-HSD) on the surface of LCs was detected by immunofluorescence (IF) assay. The content of testosterone secreted in cell culture medium was detected by ELISA. The results of flow cytometry indicated that we successfully extracted and cultured BMSCs. Moreover, post 14 days of incubation, the changes of β-catenin, LRP5 and TCF, at the protein and mRNA level demonstrate successful intervention in the activation and inhibition of the intracellular Wnt/β-catenin signaling pathway. Compared with the control group, the LCs surface marker 3β-HSD expression intensity in the CHIR-99,021 group was significantly increased by 69% (p < 0.01), while significantly decreased by 59% in LGK-974 group (p < 0.01). The ELISA results indicated a higher testosterone concentration in the CHIR-99,021 group (359.58 ± 17.46 pg/mL) than in the control (225.31 ± 15.42 pg/mL) and LGK-974 groups (183.67 ± 4.47 pg/mL), and the difference was statistically significant (p < 0.05). This study successfully demonstrates the directed differentiation of BMSCs into LCs under the action of inducers. We verified that the Wnt/β-catenin signaling pathway is involved in this differentiation process. The idea proposed in our study for efficiently inducing differentiation of BMSCs into LC in vitro, may provide a safe and sustainable LC source for developing clinically feasible cell transplantation-based LOH therapies.

Carbene-catalyzed chirality-controlled site-selective acylation of saccharides

Acylation stands as a fundamental process in both biological pathways and synthetic chemical reactions, with acylated saccharides and their derivatives holding diverse applications ranging from bioactive agents to synthetic building blocks. A longstanding objective in organic synthesis has been the site-selective acylation of saccharides without extensive pre-protection of alcohol units. In this study, we demonstrate that by simply altering the chirality of N-heterocyclic carbene (NHC) organic catalysts, the site-selectivity of saccharide acylation reactions can be effectively modulated. Our investigation reveals that this intriguing selectivity shift stems from a combination of factors, including chirality match/mismatch and inter- / intramolecular hydrogen bonding between the NHC catalyst and saccharide substrates. These findings provide valuable insights into catalyst design and reaction engineering, highlighting potential applications in glycoside analysis, such as fluorescent labelling, α/β identification, orthogonal reactions, and selective late-stage modifications.

Porcupine expression promotes the progression of oral carcinogenesis

Oral squamous cell carcinoma (OSCC) is the most common type of oral cancer, which is usually preceded by a potentially malignant disorder histologically diagnosed as dysplasia. We and others have provided evidence for the pro-carcinogenic role of the Wnt/β-catenin pathway in this context, in which Wnt ligands stabilize and allow relocalization of β-catenin to the nucleus for transcription of pro-survival and pro-proliferation genes. However, the contribution of Porcupine (PORCN), an O-acyltransferase that catalyzes the palmitoylation of Wnt ligands, to OSCC carcinogenesis is not known. Moreover, the effectiveness of LGK974, a novel PORCN inhibitor remains to be elucidated. By using different ex vivo, in vivo and in vitro OSCC carcinogenesis models, we show that PORCN expression is significantly increased in high-grade dysplasia as well as moderately/poorly- differentiated OSCC. Consistent with these observations, expression of key proteins involved in the Wnt/β-catenin pathway are elevated as well. Importantly, the treatment with LGK974, a chemical PORCN inhibitor, reduced the number and size of oral lesions in mice treated with 4-Nitroquinoline 1-oxide (4NQO), a tobacco smoke surrogate. These results highlight the role of PORCN during OSCC carcinogenesis.

Clues into Wnt cell surface signalosomes and its biogenesis

Wnt morphogens induce signaling via binding their extracellular receptors. Here, we discuss several recent structural studies showing how Wnts engage their receptors frizzled (FZD) and low-density lipoprotein receptor-related protein 5/6 (LRP5/6), how Cachd1 has been shown as an alternative initiator of Wnt signaling, and how lipidated Wnt may be produced and secreted from the cell.

In Vitro Models of Cardiovascular Disease: Embryoid Bodies, Organoids and Everything in Between

Cardiovascular disease comprises a group of disorders affecting or originating within tissues and organs of the cardiovascular system; most, if not all, will eventually result in cardiomyocyte dysfunction or death, negatively impacting cardiac function. Effective models of cardiac disease are thus important for understanding crucial aspects of disease progression, while recent advancements in stem cell biology have allowed for the use of stem cell populations to derive such models. These include three-dimensional (3D) models such as stem cell-based models of embryos (SCME) as well as organoids, many of which are frequently derived from embryoid bodies (EB). Not only can they recapitulate 3D form and function, but the developmental programs governing the self-organization of cell populations into more complex tissues as well. Many different organoids and SCME constructs have been generated in recent years to recreate cardiac tissue and the complex developmental programs that give rise to its cellular composition and unique tissue morphology. It is thus the purpose of this narrative literature review to describe and summarize many of the recently derived cardiac organoid models as well as their use for the recapitulation of genetic and acquired disease. Owing to the cellular composition of the models examined, this review will focus on disease and tissue injury associated with embryonic/fetal tissues.

Wnt signaling aberrant activation drives ameloblastoma invasion and recurrence: bioinformatics and in vitro insights

OBJECTIVE

This study aims to explore the regulatory mechanisms of Wnt signaling in the invasion and recurrence of ameloblastoma (AM) to provide a new theoretical basis for its treatment.

METHODS

Bulk RNA sequencing was employed to analyze samples from AM patients, and identify differentially expressed genes. Subsequently, bioinformatics methods such as Weighted Gene Co-Expression Network Analysis (WGCNA), DESeq2, and KEGG enrichment analysis were utilized to construct gene co-expression networks and identify pathways associated with invasion and recurrence. Furthermore, in vitro experiments, including Cell Counting Kit-8 (CCK-8), Wound healing assays, Western blotting, and qPCR were conducted to validate the effects of Wnt signaling on AM biological functions and the expression of related genes and proteins.

RESULTS

Bioinformatics analysis revealed significant activation of the Wnt signaling pathway during AM invasion and recurrence, and differential gene analysis identified specific gene expression patterns associated with the Wnt signaling pathway. In vitro experiments further demonstrated that the standard Wnt/β-catenin pathway activator, Laduviglusib significantly activated Wnt signaling, leading to a marked increase in the mRNA and protein expression levels of TCF7, β-catenin, WNT2B, and LEF1, thereby enhancing the proliferation and migration capabilities of AM cells.

CONCLUSION

This study reveals the critical role of aberrant Wnt signaling activation in AM proliferation and migration, identifying it as a key driver of AM invasion and recurrence. The findings provide new insights into the mechanisms underlying AM invasion and recurrence, laying the foundation for developing novel therapeutic strategies.

Synthesis and Frizzled-receptor binding of a WNT5A hairpin-3 peptide

We synthesized a WNT5A β-hairpin peptide responsible for the protein's binding to its receptor, Frizzled. Full affinity to Frizzled requires all three disulfides but not an invariant tryptophan that significantly contributes to the buried surface area. Our work opens the avenue to target the Wnt-Fzd interface using synthetic peptides.

Nuclear porcupine mediates XRCC6/Ku70 S-palmitoylation in the DNA damage response

BACKGROUND

The activation of the DNA damage response (DDR) heavily relies on post-translational modifications (PTMs) of proteins, which play a crucial role in the prevention of genetic instability and tumorigenesis. Among these PTMs, palmitoylation is a highly conserved process that is dysregulated in numerous cancer types. However, its direct involvement in the DDR and the underlying mechanisms remain unclear.

METHODS

CRISPR-Cas9 technology was used to generate the PORCN KO and PORCN NLS KO cell lines. The effects of PORCN NLS in the DDR were verified by colony formation assays, MTT assays, the DR/EJ5 homologous recombination/non-homologous end-joining reporter system, xenograft tumor growth and immunofluorescence. Mechanisms were explored by mass spectrometry, acyl-biotin exchange (ABE) palmitoylation assay, Click-iT assay, cell subcellular fractionation assay, Western blot analysis, and in vivo and in vitro co-immunoprecipitation.

RESULTS

In this study, we introduce evidence that Porcupine (PORCN) is an integral component of and plays a critical role in the DDR. PORCN deficiency hampers nonhomologous end joining (NHEJ) and highly sensitizes cells to ionizing radiation (IR) both in vitro and in vivo. We also provide evidence that PORCN possesses a nuclear fraction (nPORCN) with S-acyltransferase activity, unlike its membrane-bound O-acyltransferase in the endoplasmic reticulum. Furthermore, we show that nPORCN is necessary for the successful activation of NHEJ. Using mass spectrometry, we reveal the existence of an nPORCN complex and show that nPORCN mediates the S-palmitoylation of XRCC6/Ku70 at five specific cysteine sites in response to IR. Mutation of these sites causes a substantial increase in radiosensitivity and delays NHEJ. Additionally, we present evidence that nPORCN-dependent Ku70 palmitoylation is required for DNA-PKcs/Ku70/Ku80 complex formation.

CONCLUSION

Our findings underscore the crucial role of nPORCN-dependent Ku70 S-palmitoylation in the DDR.

Ehbp1 orchestrates orderly sorting of Wnt/Wingless to the basolateral and apical cell membranes

Wingless (Wg)/Wnt signaling plays a critical role in both development and adult tissue homeostasis. In the Drosophila larval wing disc epithelium, the orderly delivery of Wg/Wnt to the apical and basal cell surfaces is essential for wing development. Here, we identified Ehbp1 as the switch that dictates the direction of Wg/Wnt polarized intracellular transport: the Adaptor Protein complex 1 (AP-1) delivers Wg/Wnt to the basolateral cell surface, and its sequestration by Ehbp1 redirects Wg/Wnt for apical delivery. Genetic analyses showed that Ehbp1 specifically regulates the polarized distribution of Wg/Wnt, a process that depends on the dedicated Wg/Wnt cargo receptor Wntless. Mechanistically, Ehbp1 competes with Wntless for AP-1 binding, thereby preventing the unregulated basolateral Wg/Wnt transport. Reducing Ehbp1 expression, or removing the coiled-coil motifs within its bMERB domain, leads to basolateral Wg/Wnt accumulation. Importantly, the regulation of polarized Wnt delivery by EHBP1 is conserved in vertebrates. The generality of this switch mechanism for regulating intracellular transport remains to be determined in future studies.

Molecular insights into human phosphatidylserine synthase 1 reveal its inhibition promotes LDL uptake

In mammalian cells, two phosphatidylserine (PS) synthases drive PS synthesis. Gain-of-function mutations in the Ptdss1 gene lead to heightened PS production, causing Lenz-Majewski syndrome (LMS). Recently, pharmacological inhibition of PSS1 has been shown to suppress tumorigenesis. Here, we report the cryo-EM structures of wild-type human PSS1 (PSS1WT), the LMS-causing Pro269Ser mutant (PSS1P269S), and PSS1WT in complex with its inhibitor DS55980254. PSS1 contains 10 transmembrane helices (TMs), with TMs 4-8 forming a catalytic core in the luminal leaflet. These structures revealed a working mechanism of PSS1 akin to the postulated mechanisms of the membrane-bound O-acyltransferase family. Additionally, we showed that both PS and DS55980254 can allosterically inhibit PSS1 and that inhibition by DS55980254 activates the SREBP pathways, thus enhancing the expression of LDL receptors and increasing cellular LDL uptake. This work uncovers a mechanism of mammalian PS synthesis and suggests that selective PSS1 inhibitors have the potential to lower blood cholesterol levels.

Structure and mechanism of lysosome transmembrane acetylation by HGSNAT

Lysosomal transmembrane acetylation of heparan sulfates (HS) is catalyzed by HS acetyl-CoA:α-glucosaminide N-acetyltransferase (HGSNAT), whose dysfunction leads to lysosomal storage diseases. The mechanism by which HGSNAT, the sole non-hydrolase enzyme in HS degradation, brings cytosolic acetyl-coenzyme A (Ac-CoA) and lysosomal HS together for N-acyltransferase reactions remains unclear. Here, we present cryogenic-electron microscopy structures of HGSNAT alone, complexed with Ac-CoA and with acetylated products. These structures explain that Ac-CoA binding from the cytosolic side causes dimeric HGSNAT to form a transmembrane tunnel. Within this tunnel, catalytic histidine and asparagine approach the lumen and instigate the transfer of the acetyl group from Ac-CoA to the glucosamine group of HS. Our study unveils a transmembrane acetylation mechanism that may help advance therapeutic strategies targeting lysosomal storage diseases.

Role of circular RNAs in preeclampsia (Review)

Preeclampsia (PE) is a hypertensive disorder of pregnancy characterized by new-onset hypertension and proteinuria after 20 weeks of gestation, which affects 3-8% of pregnant individuals worldwide each year. Prevention, diagnosis and treatment of PE are some of the most important problems faced by obstetrics. There is growing evidence that circular RNAs (circRNAs) are involved in the pathogenesis of PE. The present review summarizes the research progress of circRNAs and then describes the expression patterns of circRNAs in PE and their functional mechanisms affecting PE development. The role of circRNAs as biomarkers for the diagnosis of PE, and the research status of circRNAs in PE are summarized in the hope of finding novel strategies for the prevention and treatment of PE.

Lipid droplets sequester palmitic acid to disrupt endothelial ciliation and exacerbate atherosclerosis in male mice

Disruption of ciliary homeostasis in vascular endothelial cells has been implicated in the development of atherosclerosis. However, the molecular basis for the regulation of endothelial cilia during atherosclerosis remains poorly understood. Herein, we provide evidence in male mice that the accumulation of lipid droplets in vascular endothelial cells induces ciliary loss and contributes to atherosclerosis. Triglyceride accumulation in vascular endothelial cells differentially affects the abundance of free fatty acid species in the cytosol, leading to stimulated lipid droplet formation and suppressed protein S-palmitoylation. Reduced S-palmitoylation of ciliary proteins, including ADP ribosylation factor like GTPase 13B, results in the loss of cilia. Restoring palmitic acid availability, either through pharmacological inhibition of stearoyl-CoA desaturase 1 or a palmitic acid-enriched diet, significantly restores endothelial cilia and mitigates the progression of atherosclerosis. These findings thus uncover a previously unrecognized role of lipid droplets in regulating ciliary homeostasis and provide a feasible intervention strategy for preventing and treating atherosclerosis.

Ultra-large scale virtual screening identifies a small molecule inhibitor of the Wnt transporter Wntless

Wnts are lipid-modified glycoproteins that play key roles in both embryonic development and adult homeostasis. Wnt signaling is dysregulated in many cancers and preclinical data shows that targeting Wnt biosynthesis and secretion can be effective in Wnt-addicted cancers. An integral membrane protein known as Wntless (WLS/Evi) is essential for Wnt secretion. However, WLS remains undrugged thus far. The cryo-EM structure of WLS in complex with WNT8A shows that WLS has a druggable G-protein coupled receptor (GPCR) domain. Using Active Learning/Glide, we performed an ultra-large scale virtual screening from Enamine's REAL 350/3 Lead-Like library containing nearly 500 million compounds. 68 hits were examined after on-demand synthesis in cell-based Wnt reporter and other functional assays. ETC-451 emerged as a potential first-in-class WLS inhibitor. ETC-451 blocked WLS-WNT3A interaction and decreased Wnt-addicted pancreatic cancer cell line proliferation. The current hit provides a starting chemical scaffold for further structure or ligand-based drug discovery targeting WLS.

Drug tolerant persister cell plasticity in cancer: A revolutionary strategy for more effective anticancer therapies

Non-genetic mechanisms have recently emerged as important drivers of anticancer drug resistance. Among these, the drug tolerant persister (DTP) cell phenotype is attracting more and more attention and giving a predominant non-genetic role in cancer therapy resistance. The DTP phenotype is characterized by a quiescent or slow-cell-cycle reversible state of the cancer cell subpopulation and inert specialization to stimuli, which tolerates anticancer drug exposure to some extent through the interaction of multiple underlying mechanisms and recovering growth and proliferation after drug withdrawal, ultimately leading to treatment resistance and cancer recurrence. Therefore, targeting DTP cells is anticipated to provide new treatment opportunities for cancer patients, although our current knowledge of these DTP cells in treatment resistance remains limited. In this review, we provide a comprehensive overview of the formation characteristics and underlying drug tolerant mechanisms of DTP cells, investigate the potential drugs for DTP (including preclinical drugs, novel use for old drugs, and natural products) based on different medicine models, and discuss the necessity and feasibility of anti-DTP therapy, related application forms, and future issues that will need to be addressed to advance this emerging field towards clinical applications. Nonetheless, understanding the novel functions of DTP cells may enable us to develop new more effective anticancer therapy and improve clinical outcomes for cancer patients.

Transcriptome Analysis of Transiently Reversible Cell Vacuolization Caused by Excessive Serum Concentration in Scophthalmus maximus

As an important research tool, cell lines play a vital role in life science research, medical research, and drug development. During the culture of the Scophthalmus maximus head kidney (TK) cell line, we found a phenomenon of cell vacuolization caused by excessive serum concentration. Moreover, the vacuolization of the cells gradually disappeared after passage by trypsin digestion. In clarifying the formation mechanism of this reversible cellular vacuolation, transcriptomics was utilized to explore the mechanism of cell vacuolization caused by excessive serum concentration. Transcriptome analysis indicated that excessive serum concentration could cause the up-regulated expression of PORCN and other genes to promote cell proliferation. Compared with cells whose vacuolization disappeared after trypsin digestion and passage, the expression of mitosis-related genes (BUB1, ttk, Mad2, Cdc20, CDK1, CCNB1), nuclear stability-related genes LMNB1 and tissue stress and repair-related genes HMMR in vacuolated cells caused by excessive serum concentration was significantly up-regulated. There is a regulatory system related to adaptation and stress repair in the cells, which can maintain cell stability to a certain extent. This study provides a theoretical basis for the stable culture of fish cell lines and the solution to the problem of cell vacuolation.

Mapping structural and dynamic divergence across the MBOAT family

Membrane-bound O-acyltransferases (MBOATs) are membrane-embedded enzymes that catalyze acyl chain transfer to a diverse group of substrates, including lipids, small molecules, and proteins. MBOATs share a conserved structural core, despite wide-ranging functional specificity across both prokaryotes and eukaryotes. The structural basis of catalytic specificity, regulation and interactions with the surrounding environment remain uncertain. Here, we combine comparative molecular dynamics (MD) simulations with bioinformatics to assess molecular and interactional divergence across the family. In simulations, MBOATs differentially distort the bilayer depending on their substrate type. Additionally, we identify lipid binding sites surrounding reactant gates in the surrounding membrane. Complementary bioinformatic analyses reveal a conserved role for re-entrant loop-2 in MBOAT fold stabilization and a key hydrogen bond bridging DGAT1 dimerization. Finally, we predict differences in MBOAT solvation and water gating properties. These data are pertinent to the design of MBOAT-specific inhibitors that encompass dynamic information within cellular mimetic environments.

Wnt/β-catenin signaling in the development and therapeutic resistance of non-small cell lung cancer

Wnt/β-catenin signaling is a critical pathway that influences development and therapeutic response of non-small cell lung cancer (NSCLC). In recent years, many Wnt regulators, including proteins, miRNAs, lncRNAs, and circRNAs, have been found to promote or inhibit signaling by acting on Wnt proteins, receptors, signal transducers and transcriptional effectors. The identification of these regulators and their underlying molecular mechanisms provides important implications for how to target this pathway therapeutically. In this review, we summarize recent studies of Wnt regulators in the development and therapeutic response of NSCLC.

Accurate structure prediction of biomolecular interactions with AlphaFold 3

The introduction of AlphaFold 21 has spurred a revolution in modelling the structure of proteins and their interactions, enabling a huge range of applications in protein modelling and design2-6. Here we describe our AlphaFold 3 model with a substantially updated diffusion-based architecture that is capable of predicting the joint structure of complexes including proteins, nucleic acids, small molecules, ions and modified residues. The new AlphaFold model demonstrates substantially improved accuracy over many previous specialized tools: far greater accuracy for protein-ligand interactions compared with state-of-the-art docking tools, much higher accuracy for protein-nucleic acid interactions compared with nucleic-acid-specific predictors and substantially higher antibody-antigen prediction accuracy compared with AlphaFold-Multimer v.2.37,8. Together, these results show that high-accuracy modelling across biomolecular space is possible within a single unified deep-learning framework.

Engineering of TurboID-Wingless for the identification of Wingless interactors through in vivo proximity labelling

Wnt signalling coordinates growth and cell fate decisions during development and mis-regulation of Wnt signalling in adults is associated with a range of conditions, including cancer and neurodegenerative diseases. Therefore, means of modulating Wnt proteins and/or cofactors could have significant therapeutic potential. As a first step towards enumerating the Wnt interactome, we devised an in vivo proximity labelling strategy to identify proteins that interact with Wingless (Wg), the main Drosophila Wnt. We engineered the wingless locus to express a functional TurboID-Wg fusion at endogenous levels and identified in vivo interactors by streptavidin pull-down from embryos, followed by mass spectrometry. Further analysis may in future extend the screen coverage and deliver functional validation of the newly identified interactors.

Structure and inhibition of the human lysosomal transporter Sialin

Sialin, a member of the solute carrier 17 (SLC17) transporter family, is unique in its ability to transport not only sialic acid using a pH-driven mechanism, but also transport mono and diacidic neurotransmitters, such as glutamate and N-acetylaspartylglutamate (NAAG), into synaptic vesicles via a membrane potential-driven mechanism. While most transporters utilize one of these mechanisms, the structural basis of how Sialin transports substrates using both remains unclear. Here, we present the cryogenic electron-microscopy structures of human Sialin: apo cytosol-open, apo lumen-open, NAAG-bound, and inhibitor-bound. Our structures show that a positively charged cytosol-open vestibule accommodates either NAAG or the Sialin inhibitor Fmoc-Leu-OH, while its luminal cavity potentially binds sialic acid. Moreover, functional analyses along with molecular dynamics simulations identify key residues in binding sialic acid and NAAG. Thus, our findings uncover the essential conformational states in NAAG and sialic acid transport, demonstrating a working model of SLC17 transporters.

Modulators for palmitoylation of proteins and small molecules

As an essential form of lipid modification for maintaining vital cellular functions, palmitoylation plays an important role in in the regulation of various physiological processes, serving as a promising therapeutic target for diseases like cancer and neurological disorders. Ongoing research has revealed that palmitoylation can be categorized into three distinct types: N-palmitoylation, O-palmitoylation and S-palmitoylation. Herein this paper provides an overview of the regulatory enzymes involved in palmitoylation, including palmitoyltransferases and depalmitoylases, and discusses the currently available broad-spectrum and selective inhibitors for these enzymes.

Wnt pathway inhibition with the porcupine inhibitor LGK974 decreases trabecular bone but not fibrosis in a murine model with fibrotic bone

G protein-coupled receptors (GPCRs) mediate a wide spectrum of physiological functions, including the development, remodeling, and repair of the skeleton. Fibrous dysplasia (FD) of the bone is characterized by fibrotic, expansile bone lesions caused by activating mutations in GNAS. There are no effective therapies for FD. We previously showed that ColI(2.3)+/Rs1+ mice, in which Gs-GPCR signaling was hyper-activated in osteoblastic cell lineages using an engineered receptor strategy, developed a fibrotic bone phenotype with trabecularization that could be reversed by normalizing Gs-GPCR signaling, suggesting that targeting the Gs-GPCR or components of the downstream signaling pathway could serve as a promising therapeutic strategy for FD. The Wnt signaling pathway has been implicated in the pathogenesis of FD-like bone, but the specific Wnts and which cells produce them remain largely unknown. Single-cell RNA sequencing on long-bone stromal cells of 9-wk-old male ColI(2.3)+/Rs1+ mice and littermate controls showed that fibroblastic stromal cells in ColI(2.3)+/Rs1+ mice were expanded. Multiple Wnt ligands were up- or downregulated in different cellular populations, including in non-osteoblastic cells. Treatment with the porcupine inhibitor LGK974, which blocks Wnt signaling broadly, induced partial resorption of the trabecular bone in the femurs of ColI(2.3)+/Rs1+ mice, but no significant changes in the craniofacial skeleton. Bone fibrosis remained evident after treatment. Notably, LGK974 caused significant bone loss in control mice. These results provide new insights into the role of Wnt and Gs-signaling in fibrosis and bone formation in a mouse model of Gs-GPCR pathway overactivation.

Structural insights into the transporting and catalyzing mechanism of DltB in LTA D-alanylation

DltB, a model member of the Membrane-Bound O-AcylTransferase (MBOAT) superfamily, plays a crucial role in D-alanylation of the lipoteichoic acid (LTA), a significant component of the cell wall of gram-positive bacteria. This process stabilizes the cell wall structure, influences bacterial virulence, and modulates the host immune response. Despite its significance, the role of DltB is not well understood. Through biochemical analysis and cryo-EM imaging, we discover that Streptococcus thermophilus DltB forms a homo-tetramer on the cell membrane. We further visualize DltB in an apo form, in complex with DltC, and in complex with its inhibitor amsacrine (m-AMSA). Each tetramer features a central hole. The C-tunnel of each protomer faces the intratetramer interface and provides access to the periphery membrane. Each protomer binds a DltC without changing the tetrameric organization. A phosphatidylglycerol (PG) molecule in the substrate-binding site may serve as an LTA carrier. The inhibitor m-AMSA bound to the L-tunnel of each protomer blocks the active site. The tetrameric organization of DltB provides a scaffold for catalyzing D-alanyl transfer and regulating the channel opening and closing. Our findings unveil DltB's dual function in the D-alanylation pathway, and provide insight for targeting DltB as a anti-virulence antibiotic.

Protein lipidation in cancer: mechanisms, dysregulation and emerging drug targets

Protein lipidation describes a diverse class of post-translational modifications (PTMs) that is regulated by over 40 enzymes, targeting more than 1,000 substrates at over 3,000 sites. Lipidated proteins include more than 150 oncoproteins, including mediators of cancer initiation, progression and immunity, receptor kinases, transcription factors, G protein-coupled receptors and extracellular signalling proteins. Lipidation regulates the physical interactions of its protein substrates with cell membranes, regulating protein signalling and trafficking, and has a key role in metabolism and immunity. Targeting protein lipidation, therefore, offers a unique approach to modulate otherwise undruggable oncoproteins; however, the full spectrum of opportunities to target the dysregulation of these PTMs in cancer remains to be explored. This is attributable in part to the technological challenges of identifying the targets and the roles of protein lipidation. The early stage of drug discovery for many enzymes in the pathway contrasts with efforts for drugging similarly common PTMs such as phosphorylation and acetylation, which are routinely studied and targeted in relevant cancer contexts. Here, we review recent advances in identifying targetable protein lipidation pathways in cancer, the current state-of-the-art in drug discovery, and the status of ongoing clinical trials, which have the potential to deliver novel oncology therapeutics targeting protein lipidation.

Epigenetic regulation of mRNA mediates the phenotypic plasticity of cancer cells during metastasis and therapeutic resistance (Review)

Plasticity, the ability of cancer cells to transition between differentiation states without genomic alterations, has been recognized as a major source of intratumoral heterogeneity. It has a crucial role in cancer metastasis and treatment resistance. Thus, targeting plasticity holds tremendous promise. However, the molecular mechanisms of plasticity in cancer cells remain poorly understood. Several studies found that mRNA, which acts as a bridge linking the genetic information of DNA and protein, has an important role in translating genotypes into phenotypes. The present review provided an overview of the regulation of cancer cell plasticity occurring via changes in the transcription and editing of mRNAs. The role of the transcriptional regulation of mRNA in cancer cell plasticity was discussed, including DNA‑binding transcriptional factors, DNA methylation, histone modifications and enhancers. Furthermore, the role of mRNA editing in cancer cell plasticity was debated, including mRNA splicing and mRNA modification. In addition, the role of non‑coding (nc)RNAs in cancer plasticity was expounded, including microRNAs, long intergenic ncRNAs and circular RNAs. Finally, different strategies for targeting cancer cell plasticity to overcome metastasis and therapeutic resistance in cancer were discussed.

LGK974 suppresses the formation of deep vein thrombosis in mice with sepsis

BACKGROUND

Sepsis is a disorder characterized by host inflammation and is caused by systemic infection. The inflammatory cytokine storm results in platelet overactivation, leading to coagulation dysfunction and thrombosis, but the underlying mechanism remains poorly understood. Recent evidence has shown that the Wnt/β-catenin signaling pathway is related to sepsis, but its role and mechanism in sepsis complicated with deep vein thrombosis (DVT) are unclear.

METHODS

In this study, a cecal ligation and puncture (CLP)-induced sepsis model and DVT mouse model were constructed by inferior vena cava ligation. The levels of serum inflammatory factors and adhesion molecules were measured in each group, and the thrombus weight and size, hematoxylin-eosin staining, collagen fiber tissue, and transcriptome of the venous wall were analyzed. The activation of the Wnt/β-catenin signal was evaluated by quantitative real-time polymerase chain reaction, Western blotting, ELISA, and immunohistochemical and immunofluorescence methods.

RESULTS

Sepsis significantly promoted the formation of venous wall collagen fibers and DVT. In addition, Porcn significantly upregulated and activated the Wnt/β-catenin signaling pathway in sepsis mouse models with DVT. In contrast, the Wnt signaling inhibitor LGK974 was found to improve the survival rate, decrease thrombosis, and inhibit the expression of inflammation and adhesion molecules in sepsis mice with DVT. Therefore, activation of the Wnt/β-catenin signal may promote the formation of DVT in sepsis mice.

CONCLUSIONS

LGK974 protects against DVT formation in sepsis mice by inhibiting the activation of the Wnt/β-catenin signal and down-regulating the production of proinflammatory cytokines, PAI-1, and adhesion molecules. LGK974 may be a new candidate for the treatment of sepsis complicated with DVT.

Regeneration of amputated mice digit tips by including Wnt signaling pathway with CHIR99021 and IWP-2 chemicals in limb organ culture system

Objectives

Mammals have limited limb regeneration compared to amphibians. The role of Wnt signaling pathways in limb regeneration has rarely been studied. So, this study aimed to investigate the effect of Wnt-signaling using chemicals CHIR99021 and IWP-2 on amputated mice digit tips regeneration in an in vitro organ culture system.

Materials and Methods

The distal phalanx of paws from C57BL/6J mouse fetuses at E14.5, E16.5, and E18.5 was amputated. Then, the hands were cultured for 7 days. Subsequently, paws were treated with 1-50 µg/ml concentration of CHIR99021 and 5-10 µg/ml concentration of IWP-2. Finally, the new tissue regrowth was assessed by histological analysis, immunohistochemistry for BC, TCF1, CAN, K14, and P63 genes, and beta-catenin and Tcf1 genes were evaluated with RT-qPCR.

Results

The paws of E14.5 and E16.5 days were shrinkaged and compressed after 7 days, so the paws of 18.5E that were alive were selected. As a result, newly-grown masses at digit tips were observed in 25 and 30 µl/ml concentrations of the CHR99021 group but not in the IWP2 treatment (*P<0.05; **P<0.01). qRT-PCR analysis confirmed the significant up-regulation of beta-catenin and Tcf1 genes in CHIR99021 group in comparison to the IWP-2 group (P<0.05). Moreover, Alcian-blue staining demonstrated the presence of cartilage-like tissue at regenerated mass in the CHIR group. In immunohistochemistry analysis beta-catenin, ACN, Keratin-14, and P63 protein expression were observed in digit tips in the CHIR-treated group.

Conclusion

By activating the Wnt signaling pathway, cartilage-like tissue formed in the blastema-like mass in the mouse's amputated digit tips.

Wnt inhibition alleviates resistance to immune checkpoint blockade in glioblastoma

Wnt signaling plays a critical role in the progression and treatment outcome of glioblastoma (GBM). Here, we identified WNT7b as a heretofore unknown mechanism of resistance to immune checkpoint inhibition (αPD1) in GBM patients and murine models. Acquired resistance to αPD1 was found to be associated with the upregulation of Wnt7b and β-catenin protein levels in GBM in patients and in a clinically relevant, stem-rich GBM model. Combining the porcupine inhibitor WNT974 with αPD1 prolonged the survival of GBM-bearing mice. However, this combination had a dichotomous response, with a subset of tumors showing refractoriness. WNT974 and αPD1 expanded a subset of DC3-like dendritic cells (DCs) and decreased the granulocytic myeloid-derived suppressor cells (gMDSCs) in the tumor microenvironment (TME). By contrast, monocytic MDSCs (mMDSCs) increased, while T-cell infiltration remained unchanged, suggesting potential TME-mediated resistance. Our preclinical findings warrant the testing of Wnt7b/β-catenin combined with αPD1 in GBM patients with elevated Wnt7b/β-catenin signaling.

Combined Computational-Biochemical Approach Offers an Accelerated Path to Membrane Protein Solubilization

Membrane proteins are difficult to isolate and purify due to their dependence on the surrounding lipid membrane for structural stability. Detergents are often used to solubilize these proteins, with this approach requiring a careful balance between protein solubilization and denaturation. Determining which detergent is most appropriate for a given protein has largely been done empirically through screening, which requires large amounts of membrane protein and associated resources. Here, we describe an alternative to conventional detergent screening using a computational modeling approach to identify the most likely candidate detergents for solubilizing a protein of interest. We demonstrate our approach using ghrelin O-acyltransferase (GOAT), a member of the membrane-bound O-acyltransferase family of integral membrane enzymes that has not been solubilized or purified in active form. A computationally derived GOAT structural model provides the only structural information required for this approach. Using computational analysis of detergent ability to penetrate phospholipid bilayers and stabilize the GOAT structure, a panel of common detergents were rank-ordered for their proposed ability to solubilize GOAT. The simulations were performed at all-atom resolution for a combined simulation time of 24 μs. Independently, we biologically screened these detergents for their solubilization of fluorescently tagged GOAT constructs. We found computational prediction of protein structural stabilization was the better predictor of detergent solubilization ability, but neither approach was effective for predicting detergents that would support GOAT enzymatic function. The current rapid expansion of membrane protein computational models lacking experimental structural information and our computational detergent screening approach can greatly improve the efficiency of membrane protein detergent solubilization, supporting downstream functional and structural studies.

Molecular basis of Wnt biogenesis, secretion, and Wnt7-specific signaling

Wnt proteins are enzymatically lipidated by Porcupine (PORCN) in the ER and bind to Wntless (WLS) for intracellular transport and secretion. Mechanisms governing the transfer of these low-solubility Wnts from the ER to the extracellular space remain unclear. Through structural and functional analyses of Wnt7a, a crucial Wnt involved in central nervous system angiogenesis and blood-brain barrier maintenance, we have elucidated the principles of Wnt biogenesis and Wnt7-specific signaling. The Wnt7a-WLS complex binds to calreticulin (CALR), revealing that CALR functions as a chaperone to facilitate Wnt transfer from PORCN to WLS during Wnt biogenesis. Our structures, functional analyses, and molecular dynamics simulations demonstrate that a phospholipid in the core of Wnt-bound WLS regulates the association and dissociation between Wnt and WLS, suggesting a lipid-mediated Wnt secretion mechanism. Finally, the structure of Wnt7a bound to RECK, a cell-surface Wnt7 co-receptor, reveals how RECKCC4 engages the N-terminal domain of Wnt7a to activate Wnt7-specific signaling.

Cryo-EM structures of Myomaker reveal a molecular basis for myoblast fusion

The fusion of mononucleated myoblasts produces multinucleated muscle fibers leading to the formation of skeletal muscle. Myomaker, a skeletal muscle-specific membrane protein, is essential for myoblast fusion. Here we report the cryo-EM structures of mouse Myomaker (mMymk) and Ciona robusta Myomaker (cMymk). Myomaker contains seven transmembrane helices (TMs) that adopt a G-protein-coupled receptor-like fold. TMs 2-4 form a dimeric interface, while TMs 3 and 5-7 create a lipid-binding site that holds the polar head of a phospholipid and allows the alkyl tails to insert into Myomaker. The similarity of cMymk and mMymk suggests a conserved Myomaker-mediated cell fusion mechanism across evolutionarily distant species. Functional analyses demonstrate the essentiality of the dimeric interface and the lipid-binding site for fusogenic activity, and heterologous cell-cell fusion assays show the importance of transcellular interactions of Myomaker protomers for myoblast fusion. Together, our findings provide structural and functional insights into the process of myoblast fusion.

Beyond energy and growth: the role of metabolism in developmental signaling, cell behavior and diapause

Metabolism is crucial for development through supporting cell growth, energy production, establishing cell identity, developmental signaling and pattern formation. In many model systems, development occurs alongside metabolic transitions as cells differentiate and specialize in metabolism that supports new functions. Some cells exhibit metabolic flexibility to circumvent mutations or aberrant signaling, whereas other cell types require specific nutrients for developmental progress. Metabolic gradients and protein modifications enable pattern formation and cell communication. On an organism level, inadequate nutrients or stress can limit germ cell maturation, implantation and maturity through diapause, which slows metabolic activities until embryonic activation under improved environmental conditions.

Tumor microenvironment-induced tumor cell plasticity: relationship with hypoxic stress and impact on tumor resistance

The role of tumor interaction with stromal components during carcinogenesis is crucial for the design of efficient cancer treatment approaches. It is widely admitted that tumor hypoxic stress is associated with tumor aggressiveness and thus impacts susceptibility and resistance to different types of treatments. Notable biological processes that hypoxia functions in include its regulation of tumor heterogeneity and plasticity. While hypoxia has been reported as a major player in tumor survival and dissemination regulation, the significance of hypoxia inducible factors in cancer stem cell development remains poorly understood. Several reports indicate that the emergence of cancer stem cells in addition to their phenotype and function within a hypoxic tumor microenvironment impacts cancer progression. In this respect, evidence showed that cancer stem cells are key elements of intratumoral heterogeneity and more importantly are responsible for tumor relapse and escape to treatments. This paper briefly reviews our current knowledge of the interaction between tumor hypoxic stress and its role in stemness acquisition and maintenance. Our review extensively covers the influence of hypoxia on the formation and maintenance of cancer stem cells and discusses the potential of targeting hypoxia-induced alterations in the expression and function of the so far known stem cell markers in cancer therapy approaches. We believe that a better and integrated understanding of the effect of hypoxia on stemness during carcinogenesis might lead to new strategies for exploiting hypoxia-associated pathways and their targeting in the clinical setting in order to overcome resistance mechanisms. More importantly, at the present time, efforts are oriented towards the design of innovative therapeutical approaches that specifically target cancer stem cells.

Cellular and Molecular Mechanisms of the Tumor Stroma in Colorectal Cancer: Insights into Disease Progression and Therapeutic Targets

Colorectal cancer (CRC) is a major health burden worldwide and is the third most common type of cancer. The early detection and diagnosis of CRC is critical to improve patient outcomes. This review explores the intricate interplay between the tumor microenvironment, stromal interactions, and the progression and metastasis of colorectal cancer. The review begins by assessing the gut microbiome's influence on CRC development, emphasizing its association with gut-associated lymphoid tissue (GALT). The role of the Wnt signaling pathway in CRC tumor stroma is scrutinized, elucidating its impact on disease progression. Tumor budding, its effect on tumor stroma, and the implications for patient prognosis are investigated. The review also identifies conserved oncogenic signatures (COS) within CRC stroma and explores their potential as therapeutic targets. Lastly, the seed and soil hypothesis is employed to contextualize metastasis, accentuating the significance of both tumor cells and the surrounding stroma in metastatic propensity. This review highlights the intricate interdependence between CRC cells and their microenvironment, providing valuable insights into prospective therapeutic approaches targeting tumor-stroma interactions.

Molecular mechanism of palmitic acid and its derivatives in tumor progression

Palmitic acid (PA) is a saturated fatty acid commonly found in coconut oil and palm oil. It serves as an energy source for the body and plays a role in the structure and function of cell membranes. Beyond its industrial applications, PA has gained attention for its potential therapeutic properties. Modern pharmacological studies have demonstrated that PA exhibits anti-inflammatory, antioxidant, and immune-enhancing effects. In recent years, PA has emerged as a promising anti-tumor agent with demonstrated efficacy against various malignancies including gastric cancer, liver cancer, cervical cancer, breast cancer, and colorectal cancer. Its anti-tumor effects encompass inducing apoptosis in tumor cells, inhibiting tumor cell proliferation, suppressing metastasis and invasion, enhancing sensitivity to chemotherapy, and improving immune function. The main anticancer mechanism of palmitic acid (PA) involves the induction of cell apoptosis through the mitochondrial pathway, facilitated by the promotion of intracellular reactive oxygen species (ROS) generation. PA also exhibits interference with the cancer cell cycle, leading to cell cycle arrest predominantly in the G1 phase. Moreover, PA induces programmed cell autophagy death, inhibits cell migration, invasion, and angiogenesis, and synergistically enhances the efficacy of chemotherapy drugs while reducing adverse reactions. PA acts on various intracellular and extracellular targets, modulating tumor cell signaling pathways, including the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), endoplasmic reticulum (ER), B Cell Lymphoma-2 (Bcl-2), P53, and other signaling pathways. Furthermore, derivatives of PA play a significant regulatory role in tumor resistance processes. This paper provides a comprehensive review of recent studies investigating the anti-tumor effects of PA. It summarizes the underlying mechanisms through which PA exerts its anti-tumor effects, aiming to inspire new perspectives for the treatment of malignant tumors in clinical settings and the development of novel anti-cancer drugs.

The structure of phosphatidylinositol remodeling MBOAT7 reveals its catalytic mechanism and enables inhibitor identification

Cells remodel glycerophospholipid acyl chains via the Lands cycle to adjust membrane properties. Membrane-bound O-acyltransferase (MBOAT) 7 acylates lyso-phosphatidylinositol (lyso-PI) with arachidonyl-CoA. MBOAT7 mutations cause brain developmental disorders, and reduced expression is linked to fatty liver disease. In contrast, increased MBOAT7 expression is linked to hepatocellular and renal cancers. The mechanistic basis of MBOAT7 catalysis and substrate selectivity are unknown. Here, we report the structure and a model for the catalytic mechanism of human MBOAT7. Arachidonyl-CoA and lyso-PI access the catalytic center through a twisted tunnel from the cytosol and lumenal sides, respectively. N-terminal residues on the ER lumenal side determine phospholipid headgroup selectivity: swapping them between MBOATs 1, 5, and 7 converts enzyme specificity for different lyso-phospholipids. Finally, the MBOAT7 structure and virtual screening enabled identification of small-molecule inhibitors that may serve as lead compounds for pharmacologic development.

Rocking the MBOAT: Structural insights into the membrane bound O-acyltransferase family

The membrane-bound O-acyltransferase (MBOAT) superfamily catalyses the transfer of acyl chains to substrates implicated in essential cellular functions. Aberrant function of MBOATs is associated with various diseases and MBOATs are promising drug targets. There has been recent progress in structural characterisation of MBOATs, advancing our understanding of their functional mechanism. Integrating information across the MBOAT family, we characterise a common MBOAT fold and provide a blueprint for substrate and inhibitor engagement. This work provides context for the diverse substrates, mechanisms, and evolutionary relationships of protein and small-molecule MBOATs. Further work should aim to characterise MBOATs, as inherently lipid-associated proteins, within their membrane environment.

Mechanism of action for small-molecule inhibitors of triacylglycerol synthesis

Inhibitors of triacylglycerol (TG) synthesis have been developed to treat metabolism-related diseases, but we know little about their mechanisms of action. Here, we report cryo-EM structures of the TG-synthesis enzyme acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a membrane bound O-acyltransferase (MBOAT), in complex with two different inhibitors, T863 and DGAT1IN1. Each inhibitor binds DGAT1's fatty acyl-CoA substrate binding tunnel that opens to the cytoplasmic side of the ER. T863 blocks access to the tunnel entrance, whereas DGAT1IN1 extends further into the enzyme, with an amide group interacting with more deeply buried catalytic residues. A survey of DGAT1 inhibitors revealed that this amide group may serve as a common pharmacophore for inhibition of MBOATs. The inhibitors were minimally active against the related MBOAT acyl-CoA:cholesterol acyltransferase 1 (ACAT1), yet a single-residue mutation sensitized ACAT1 for inhibition. Collectively, our studies provide a structural foundation for developing DGAT1 and other MBOAT inhibitors.

Profiling and targeting cancer stem cell signaling pathways for cancer therapeutics

Tumorigenic cancer stem cells (CSCs) represent a subpopulation of cells within the tumor that express genetic and phenotypic profiles and signaling pathways distinct from the other tumor cells. CSCs have eluded many conventional anti-oncogenic treatments, resulting in metastases and relapses of cancers. Effectively targeting CSCs' unique self-renewal and differentiation properties would be a breakthrough in cancer therapy. A better characterization of the CSCs' unique signaling mechanisms will improve our understanding of the pathology and treatment of cancer. In this paper, we will discuss CSC origin, followed by an in-depth review of CSC-associated signaling pathways. Particular emphasis is given on CSC signaling pathways' ligand-receptor engagement, upstream and downstream mechanisms, and associated genes, and molecules. Signaling pathways associated with regulation of CSC development stand as potential targets of CSC therapy, which include Wnt, TGFβ (transforming growth factor-β)/SMAD, Notch, JAK-STAT (Janus kinase-signal transducers and activators of transcription), Hedgehog (Hh), and vascular endothelial growth factor (VEGF). Lastly, we will also discuss milestone discoveries in CSC-based therapies, including pre-clinical and clinical studies featuring novel CSC signaling pathway cancer therapeutics. This review aims at generating innovative views on CSCs toward a better understanding of cancer pathology and treatment.

A rising tide lifts all MBOATs: recent progress in structural and functional understanding of membrane bound O-acyltransferases

Acylation modifications play a central role in biological and physiological processes. Across a range of biomolecules from phospholipids to triglycerides to proteins, introduction of a hydrophobic acyl chain can dramatically alter the biological function and cellular localization of these substrates. Amongst the enzymes catalyzing these modifications, the membrane bound O-acyltransferase (MBOAT) family occupies an intriguing position as the combined substrate selectivities of the various family members span all three classes of these biomolecules. MBOAT-dependent substrates are linked to a wide range of health conditions including metabolic disease, cancer, and neurodegenerative disease. Like many integral membrane proteins, these enzymes have presented challenges to investigation due to their intractability to solubilization and purification. However, over the last several years new solubilization approaches coupled with computational modeling, crystallography, and cryoelectron microscopy have brought an explosion of structural information for multiple MBOAT family members. These studies enable comparison of MBOAT structure and function across members catalyzing modifications of all three substrate classes, revealing both conserved features amongst all MBOATs and distinct architectural features that correlate with different acylation substrates ranging from lipids to proteins. We discuss the methods that led to this renaissance of MBOAT structural investigations, our new understanding of MBOAT structure and implications for catalytic function, and the potential impact of these studies for development of new therapeutics targeting MBOAT-dependent physiological processes.

Novel PORCN inhibitor WHN-88 targets Wnt/β-catenin pathway and prevents the growth of Wnt-driven cancers

Wnt/β-catenin signaling pathway is a classical and crucial oncogenic pathway in many carcinomas, and Porcupine (PORCN) is an O-acyltransferase, which is indispensable and highly specific for catalyzing palmitoylation of Wnt ligands and facilitating their secretion and biofunction. Targeting PORCN provides a promising approach to specifically cure Wnt-driven cancers from the root. In this study, we designed series of pyridonyl acetamide compounds, and discovered a novel PORCN inhibitor WHN-88 with a unique di-iodinated pyridone structural fragment, which is significantly different from the reported inhibitors. We demonstrated that WHN-88 effectively abolished palmitoylation of Wnt ligands and prevented their secretion and the subsequent Wnt/β-catenin signaling transduction. Further experiments showed that, at well-tolerated doses, WHN-88 remarkably suppressed the spontaneous occurrence and growth of MMTV-Wnt1 murine breast tumors. Consistently, WHN-88 also notably restrained the progress of xenografted Wnt-driven human tumors, including PA-1 teratocarcinoma with high autocrine Wnt signaling and Aspc-1 pancreatic carcinoma with Wnt-sensitizing RNF43 mutation. Additionally, we disclosed that WHN-88 inhibited cancer cell stemness obviously. Together, we verified WHN-88 is a novel PORCN inhibitor with potent efficacy against the Wnt-driven cancers. Our findings enriched the structural types of PORCN inhibitors, and facilitated the development and application of PORCN inhibiting therapy in clinic.

The role of Evi/Wntless in exporting Wnt proteins

Intercellular communication by Wnt proteins governs many essential processes during development, tissue homeostasis and disease in all metazoans. Many context-dependent effects are initiated in the Wnt-producing cells and depend on the export of lipidated Wnt proteins. Although much focus has been on understanding intracellular Wnt signal transduction, the cellular machinery responsible for Wnt secretion became better understood only recently. After lipid modification by the acyl-transferase Porcupine, Wnt proteins bind their dedicated cargo protein Evi/Wntless for transport and secretion. Evi/Wntless and Porcupine are conserved transmembrane proteins, and their 3D structures were recently determined. In this Review, we summarise studies and structural data highlighting how Wnts are transported from the ER to the plasma membrane, and the role of SNX3-retromer during the recycling of its cargo receptor Evi/Wntless. We also describe the regulation of Wnt export through a post-translational mechanism and review the importance of Wnt secretion for organ development and cancer, and as a future biomarker.

Wnt/β-Catenin Signaling and Resistance to Immune Checkpoint Inhibitors: From Non-Small-Cell Lung Cancer to Other Cancers

Lung cancer is the leading cause of cancer-related deaths worldwide. The standard of care for advanced non-small-cell lung cancer (NSCLC) without driver-gene mutations is a combination of an anti-PD-1/PD-L1 antibody and chemotherapy, or an anti-PD-1/PD-L1 antibody and an anti-CTLA-4 antibody with or without chemotherapy. Although there were fewer cases of disease progression in the early stages of combination treatment than with anti-PD-1/PD-L1 antibodies alone, only approximately half of the patients had a long-term response. Therefore, it is necessary to elucidate the mechanisms of resistance to immune checkpoint inhibitors. Recent reports of such mechanisms include reduced cancer-cell immunogenicity, loss of major histocompatibility complex, dysfunctional tumor-intrinsic interferon-γ signaling, and oncogenic signaling leading to immunoediting. Among these, the Wnt/β-catenin pathway is a notable potential mechanism of immune escape and resistance to immune checkpoint inhibitors. In this review, we will summarize findings on these resistance mechanisms in NSCLC and other cancers, focusing on Wnt/β-catenin signaling. First, we will review the molecular biology of Wnt/β-catenin signaling, then discuss how it can induce immunoediting and resistance to immune checkpoint inhibitors. We will also describe other various mechanisms of immune-checkpoint-inhibitor resistance. Finally, we will propose therapeutic approaches to overcome these mechanisms.

Molecular Alterations and Putative Therapeutic Targeting of Planar Cell Polarity Proteins in Breast Cancer

BACKGROUND

Treatment and outcomes of breast cancer, one of the most prevalent female cancers, have improved in recent decades. However, metastatic breast cancer remains incurable in most cases, and new therapies are needed to ameliorate prognosis. Planar cell polarity (PCP) is a characteristic of epithelial cells that form layers and is integral to the communication of these cells with neighboring cells. Dysfunction of PCP is observed in cancers and may confer a targetable vulnerability.

METHODS

The breast cancer cohorts from The Cancer Genome Atlas (TCGA) and the METABRIC study were interrogated for molecular alterations in genes of the PCP pathway. The groups with the most prevalent alterations were characterized, and survival was compared with counterparts not possessing PCP alterations. Breast cancer cell lines with PCP alterations from the Cancer Cell Line Encyclopedia (CCLE) were interrogated for sensitivity to drugs affecting PCP.

RESULTS

Among genes of the PCP pathway, VANGL2, NOS1AP and SCRIB display amplifications in a sizable minority of breast cancers. Concomitant up-regulation at the mRNA level can be observed mostly in basal cancers, but it does not correlate well with the amplification status of the genes, as it can also be observed in non-amplified cases. In an exploration of cell line models, two of the four breast cancer cell line models with amplifications in VANGL2, NOS1AP and SCRIB display sensitivity to drugs inhibiting acyl-transferase porcupine interfering with the WNT pathway. This sensitivity suggests a possible therapeutic role of these inhibitors in cancers bearing the amplifications.

CONCLUSION

Molecular alterations in PCP genes can be observed in breast cancers with a predilection for the basal sub-type. An imperfect correlation of copy number alterations with mRNA expression suggests that post-translational modifications are important in PCP regulation. Inhibitors of acyl-transferase porcupine may be rational candidates for combination therapy development in PCP-altered breast cancers.

The logistics of Wnt production and delivery

Wnts are secreted proteins that control stem cell maintenance, cell fate decisions, and growth during development and adult homeostasis. Wnts carry a post-translational modification not seen in any other secreted protein: during biosynthesis, they are appended with a palmitoleoyl moiety that is required for signaling but also impairs solubility and hence diffusion in the extracellular space. In some contexts, Wnts act only in a juxtacrine manner but there are also instances of long range action. Several proteins and processes ensure that active Wnts reach the appropriate target cells. Some, like Porcupine, Wntless, and Notum are dedicated to Wnt function; we describe their activities in molecular detail. We also outline how the cell infrastructure (secretory, endocytic, and retromer pathways) contribute to the progression of Wnts from production to delivery. We then address how Wnts spread in the extracellular space and form a signaling gradient despite carrying a hydrophobic moiety. We highlight particularly the role of lipid-binding Wnt interactors and heparan sulfate proteoglycans. Finally, we briefly discuss how evolution might have led to the emergence of this unusual signaling pathway.

Visualizing WNT signaling in mammalian systems

WNT/CTNNB1 signaling plays a critical role in the development of all multicellular animals. Here, we include both the embryonic stages, during which tissue morphogenesis takes place, and the postnatal stages of development, during which tissue homeostasis occurs. Thus, embryonic development concerns lineage development and cell fate specification, while postnatal development involves tissue maintenance and regeneration. Multiple tools are available to researchers who want to investigate, and ideally visualize, the dynamic and pleiotropic involvement of WNT/CTNNB1 signaling in these processes. Here, we discuss and evaluate the decisions that researchers need to make in identifying the experimental system and appropriate tools for the specific question they want to address, covering different types of WNT/CTNNB1 reporters in cells and mice. At a molecular level, advanced quantitative imaging techniques can provide spatio-temporal information that cannot be provided by traditional biochemical assays. We therefore also highlight some recent studies to show their potential in deciphering the complex and dynamic mechanisms that drive WNT/CTNNB1 signaling.

Gone with the Wnt(less): a mechanistic perspective on the journey of Wnt

Wnts are short-range signaling proteins, expressed in all metazoans from sponges to humans, critical for cell development and fate. There are 19 different Wnts in the human genome with varying expression levels and patterns, and post-translational modifications. Common to essentially all Wnts is the palmitoleation of a conserved serine by the O-acyltransferase PORCN in the endoplasmic reticulum (ER). All lipidated Wnts then bind a dedicated carrier Wntless (WLS), endowed with the task of transporting them from the ER to the plasma membrane, and ultimately facilitating their release to receptors on the Wnt-receiving cell to initiate signaling. Here, we will focus on the WLS-mediated transport step. There are currently two published structures, both obtained by single-particle cryo-electron microscopy of the Wnt/WLS complex: human Wnt8A-bound and human Wnt3A-bound WLS. We analyze the two Wnt/WLS structures - remarkably similar despite the sequence similarity between Wnt8A and Wnt3A being only ∼39% - to begin to understand the conserved nature of this binding mechanism, and ultimately how one carrier can accommodate a family of 19 different Wnts. By comparing how Wnt associates with WLS with how it binds to PORCN and FZD receptors, we can begin to speculate on mechanisms of Wnt transfer from PORCN to WLS, and from WLS to FZD, thus providing molecular-level insight into these essential steps of the Wnt signaling pathway.