RSPO2-LGR5 signaling has tumour-suppressive activity in colorectal cancer

SOX17: a new therapeutic target for immune evasion of colorectal cancer

Despite advances in cancer immunotherapies across various cancers, survival outcomes in colorectal cancer (CRC) with these agents remain largely unsatisfactory despite the high tumour burden. Colorectal stem cells (CSCs), especially LGR5+ CSCs, are the significant drivers in CRC initiation, progression and resistance to conventional therapies. Although native immune surveillance is sufficient to combat early tumour formation, CRC evades early immune detection with its well-documented adenoma-to-carcinoma sequence. The exact mechanism underlying this phenomenon still needs to be better understood. SRY-related HMG box gene 17 (SOX17), a transcription factor that specifies embryonic gut formation, is increasingly recognised as a significant factor in CRC tumourigenesis. However, its role as a tumour suppressor or oncogene is still debated. Evidence from a recent study highlighted the critical role of SOX17 in reshaping the tumour immune ecosystem through the simultaneous inhibition of CD8+ T cells and selective suppression of LGR5 expression in CSCs through transcriptional repression, thereby facilitating disease progression. Given its role in immune evasion, SOX17 could be a promising marker in personalised therapy. Additionally, SOX17 could play a role in the diagnostic arena, potentially identifying dysplasia in the gastrointestinal tract. Future clinical, basic and genetic studies focusing on SOX17 are needed to ascertain its mechanistic role in tumour immunomodulation in CRC and diagnosing preneoplastic lesions in the gastrointestinal tract.

Structural insights into the LGR4-RSPO2-ZNRF3 complexes regulating WNT/β-catenin signaling

WNT/β-catenin signaling plays key roles in development and cancer1,2. ZNRF3/RNF43 modulates Frizzleds through ubiquitination, dampening WNT/β-catenin signaling. Conversely, RSPO1-4 binding to LGR4-6 and ZNRF3/RNF43 enhances WNT/β-catenin signaling3-5. Here, we elucidate the overall landscape of architectures in multiple LGR4, RSPO2, and ZNRF3 assemblies, showcasing varying stoichiometries and arrangements. These structures reveal that LGR4 and RSPO2 capture distinct states of ZNRF3. The intrinsic heterogeneity of the LGR4-RSPO2-ZNRF3 assembly is influenced by LGR4 content. Particularly, in the assembly complex with a 2:2:2 ratio, two LGR4 protomers induce and stabilize the inactive state of ZNRF3, characterized by a wide inward-open conformation of two transmembrane helices (TM helices). This specific assembly promotes a stable complex, facilitating LGR4-induced endocytosis of ZNRF3. In contrast, the active dimeric ZNRF3, bound by a single LGR4, adopts a coiled-coil TM helices conformation and dimerization of RING domains. Our findings unveil how LGR4 content mediates diverse assemblies, leading to conformational rearrangements in ZNRF3 to regulate WNT/β-catenin signaling, and provide a structural foundation for drug development targeting Wnt-driven cancers.

E3 ubiquitin ligases and deubiquitinases in colorectal cancer: Emerging molecular insights and therapeutic opportunities

Colorectal cancer (CRC) presents ongoing challenges due to limited treatment effectiveness and a discouraging prognosis, underscoring the need for ground-breaking therapeutic approaches. This review delves into the pivotal role of E3 ubiquitin ligases and deubiquitinases (DUBs), underscoring their role as crucial regulators for tumor suppression and oncogenesis in CRC. We spotlight the diverse impact of E3 ligases and DUBs on CRC's biological processes and their remarkable versatility. We closely examine their specific influence on vital signaling pathways, particularly Wnt/β-catenin and NF-κB. Understanding these regulatory mechanisms is crucial for unravelling the complexities of CRC progression. Importantly, we explore the untapped potential of E3 ligases and DUBs as novel CRC treatment targets, discussing aspects that may guide more effective therapeutic strategies. In conclusion, our concise review illuminates the E3 ubiquitin ligases and deubiquitinases pivotal role in CRC, offering insights to inspire innovative approaches for transforming the treatment landscape in CRC.

Targeting the Wnt/β-catenin signal pathway for the treatment of gastrointestinal cancer: Potential for advancement

Gastrointestinal cancers (GICs) are highly prevalent cancers that threaten human health worldwide. The Wnt/β-catenin signaling pathway has been reported to play a pivotal role in the carcinogenesis of GICs. Numerous interventions targeting the Wnt/β-catenin signaling in GICs are currently being tested in clinical trials with promising results. Unfortunately, there are no clinically approved drugs that effectively target this pathway. This comprehensive review aims to evaluate the impact of clinical therapies targeting the Wnt/β-catenin signaling pathway in GICs. By integrating data from bioinformatics databases and recent literature from the past five years, we examine the heterogeneous expression and regulatory mechanisms of Wnt/β-catenin pathway genes and proteins in GICs. Specifically, we focus on expression patterns, mutation frequencies, and clinical prognoses to understand their implications for treatment strategies. Additionally, we discuss recent clinical trial efforts targeting this pathway. Understanding the inhibitors currently under clinical investigation may help optimize foundational research and clinical strategies. We hope that elucidating the current status of precision therapeutic stratification for patients targeting the Wnt/β-catenin pathway will guide future innovations in precision medicine for GICs.

Exploring LGR5 as a prognostic marker of extrahepatic cholangiocarcinoma: insights from expression analysis and clinical correlations

BACKGROUND

Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) is a cancer stem cell (CSC) marker of colorectal cancer and may be a CSC marker of other cancer types. Few studies have been conducted on LGR5 expression in extrahepatic cholangiocarcinoma (ECC).

METHODS

We analyzed LGR5 expression using RNAscope, a highly sensitive RNA in situ hybridization technique. Fifty-three ECCs were selected from the medical archives at Shinshu University Hospital and analyzed using a tissue microarray. LGR5 expression levels were divided into expression and no expression groups. LGR5 expression and clinicopathological characteristics were analyzed.

RESULTS

Among 25 cases, no LGR5-positive dots were identified. Among 28 cases, some LGR5-positive dots were observed in carcinoma cells, together with a wide range of LGR5-positive cells. LGR5 expression was conspicuous in glandular duct formations. Well- to moderately differentiated types showed significantly higher LGR5 expression than the poorly differentiated type (p = 0.0268). LGR5 expression was associated with good overall survival (p = 0.0219) and good disease-free survival (DFS) (p = 0.0228). High LGR5 expression was associated with well- to moderately-differentiated types, indicating a favorable prognosis. In terms of DFS, multivariate analysis showed that high LGR5 expression was an independent favorable prognostic factor (p = 0.0397).

CONCLUSIONS

These findings suggest that LGR5 is a promising, novel prognostic marker.

RSPO2-associated mitochondrial metabolism defines molecular subtypes with distinct clinical and immune features in esophageal cancer

BACKGROUND

Esophageal cancer is a highly aggressive malignancy with limited treatment options and poor prognosis. The identification of novel molecular subtypes and therapeutic targets is crucial for improving clinical outcomes.

METHOD

In this study, we investigated the role of R-spondin 2 (RSPO2) in esophageal cancer and its association with mitochondrial metabolism. Using bioinformatics analysis of publicly available datasets, we identified a panel of RSPO2-related mitochondrial metabolism genes and their expression patterns in esophageal cancer. Based on these genes, we stratified esophageal cancer patients into distinct molecular subtypes with different survival rates, immune cell infiltration profiles, and drug sensitivities.

RESULTS

Our findings suggest that RSPO2-related mitochondrial metabolism genes may serve as potential therapeutic targets and prognostic markers for esophageal cancer. These genes play an important role in the prognosis, immune cell infiltration and drug sensitivity of esophageal cancer.

CONCLUSION

The identified molecular subtypes provide valuable insights into the underlying molecular mechanisms of esophageal cancer and could guide personalized treatment strategies in the future.

Multiomics data identifies RSPO2 as a prognostic biomarker in human tumors associated with pan-cancer

RSPO2 protein may provide valuable insights into the mechanism underlying various types of tumorigenesis. The role of RSPO2 in pan-cancer has not been reported so far. Therefore, this study aimed to provide a comprehensive analysis of RSPO2 from a pan-cancer perspective employing multiomics data. The expression profile and function of RSPO2 across different tumors were investigated using various web-based tools UALCAN, GEPIA, TIMER, Human Protein Atlas, cBioPortal, TISIDB, STRING, and Metascape to interpret the expression profile, promoter methylation status, genomic alterations, survival analysis, protein-protein interaction, correlation with immune cell subtypes, tumor immune microenvironment and enrichment analysis. Comprehensive pan-cancer analysis indicated that RSPO2 was significantly downregulated in eleven and upregulated in five tumor types compared to normal tissues, validation results further suggest RSPO2 was downregulated in most of the tumors. The protein level expression of RSPO2 was mostly low in malignant tissues. We found that RSPO2 was significantly related to individual pathological stages in BLCA, COAD, LUAD and LUSC. Prognostic analysis indicates that the high RSPO2 expression was significantly correlated with the poor prognosis in BRCA, KICH, KIRP, READ, and UCES. Furthermore, RSPO2 is frequently amplified, exhibits hypermethylated promoter in most cancers, and is associated with immune subtypes, molecular subtypes and immune cell infiltration. Finally, enrichment analysis showed that RSPO2 is involved in the regulation of the canonical Wnt pathway and neuronal development. The overall comprehensive pan-cancer analysis affirms that RSPO2 could be a promising diagnostic and prognostic biomarker and latent therapy target in the future.

R-Spondin 2 governs Xenopus left-right body axis formation by establishing an FGF signaling gradient

Establishment of the left-right (LR, sinistral, dextral) body axis in many vertebrate embryos relies on cilia-driven leftward fluid flow within an LR organizer (LRO). A cardinal question is how leftward flow triggers symmetry breakage. The chemosensation model posits that ciliary flow enriches a signaling molecule on the left side of the LRO that promotes sinistral cell fate. However, the nature of this sinistralizing signal has remained elusive. In the Xenopus LRO, we identified the stem cell growth factor R-Spondin 2 (Rspo2) as a symmetrically expressed, sinistralizing signal. As predicted for a flow-mediated signal, Rspo2 operates downstream of leftward flow but upstream of the asymmetrically expressed gene dand5. Unexpectedly, in LR patterning, Rspo2 acts as an FGF receptor antagonist: Rspo2 via its TSP1 domain binds Fgfr4 and promotes its membrane clearance by Znrf3-mediated endocytosis. Concordantly, we find that at flow-stage, FGF signaling is dextralizing and forms a gradient across the LRO, high on the dextral- and low on the sinistral side. Rspo2 gain- and loss-of function equalize this FGF signaling gradient and sinistralize and dextralize development, respectively. We propose that leftward flow of Rspo2 produces an FGF signaling gradient that governs LR-symmetry breakage.

The biological functions and related signaling pathways of SPON2

Spondin-2 (SPON2), also referred to as M-spondin or DIL-1, is a member of the extracellular matrix protein family known as Mindin-F-spondin (FS). SPON2 can be used as a broad-spectrum tumor marker for more than a dozen tumors, mainly prostate cancer. Meanwhile, SPON2 is also a potential biomarker for the diagnosis of certain non-tumor diseases. Additionally, SPON2 plays a pivotal role in regulating tumor metastasis and progression. In normal tissues, SPON2 has a variety of biological functions represented by promoting growth and development and cell proliferation. This paper presents a comprehensive overview of the regulatory mechanisms, diagnostic potential as a broad-spectrum biomarker, diverse biological functions, involvement in various signaling pathways, and clinical applications of SPON2.

The involvement of E3 ubiquitin ligases in the development and progression of colorectal cancer

To date, colorectal cancer (CRC) still has limited therapeutic efficacy and poor prognosis and there is an urgent need for novel targets to improve the outcome of CRC patients. The highly conserved ubiquitination modification mediated by E3 ubiquitin ligases is an important mechanism to regulate the expression and function of tumor promoters or suppressors in CRC. In this review, we provide an overview of E3 ligases in modulating various biological processes in CRC, including proliferation, migration, stemness, metabolism, cell death, differentiation and immune response of CRC cells, emphasizing the pluripotency of E3 ubiquitin ligases. We further focus on the role of E3 ligases in regulating vital cellular signal pathways in CRC, such as Wnt/β-catenin pathway and NF-κB pathway. Additionally, considering the potential of E3 ligases as novel targets in the treatment of CRC, we discuss what aspects of E3 ligases can be utilized and exploited for efficient therapeutic strategies.

Rspo2 exacerbates rheumatoid arthritis by targeting aggressive phenotype of fibroblast-like synoviocytes and disrupting chondrocyte homeostasis via Wnt/β-catenin pathway

BACKGROUND

The aggressive phenotype of fibroblast-like synoviocytes (FLS) has been identified as a contributing factor to the exacerbation of rheumatoid arthritis (RA) through the promotion of synovitis and cartilage damage. Regrettably, there is currently no effective therapeutic intervention available to address this issue. Recent research has shed light on the crucial regulatory role of R-spondin-2 (Rspo2) in cellular proliferation, cartilage degradation, and tumorigenesis. However, the specific impact of Rspo2 on RA remains poorly understood. We aim to investigate the function and mechanism of Rspo2 in regulating the aggressive phenotype of FLS and maintaining chondrocyte homeostasis in the context of RA.

METHODS

The expression of Rspo2 in knee joint synovium and cartilage were detected in RA mice with antigen-induced arthritis (AIA) and RA patients. Recombinant mouse Rspo2 (rmRspo2), Rspo2 neutralizing antibody (Rspo2-NAb), and recombinant mouse DKK1 (rmDKK1, a potent inhibitor of Wnt signaling pathway) were used to explore the role and mechanism of Rspo2 in the progression of RA, specifically in relation to the aggressive phenotype of FLS and chondrocyte homeostasis, both in vivo and in vitro.

RESULTS

We indicated that Rspo2 expression was upregulated both in synovium and articular cartilage as RA progressed in RA mice and RA patients. Increased Rspo2 upregulated the expression of leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), as the ligand for Rspo2, and β-catenin in FLS and chondrocytes. Subsequent investigations revealed that intra-articular administration of rmRspo2 caused striking progressive synovitis and articular cartilage destruction to exacerbate RA progress in mice. Conversely, neutralization of Rspo2 or inhibition of the Wnt/β-catenin pathway effectively alleviated experimental RA development. Moreover, Rspo2 facilitated FLS aggressive phenotype and disrupted chondrocyte homeostasis primarily through activating Wnt/β-catenin pathway, which were effectively alleviated by Rspo2-NAb or rmDKK1.

CONCLUSIONS

Our data confirmed a critical role of Rspo2 in enhancing the aggressive phenotype of FLS and disrupting chondrocyte homeostasis through the Wnt/β-catenin pathway in the context of RA. Furthermore, the results indicated that intra-articular administration of Rspo2 neutralizing antibody or recombinant DKK1 might represent a promising therapeutic strategy for the treatment of RA.

Genome-Wide Association Study Identifies 4 Novel Risk Loci for Small Intestinal Neuroendocrine Tumors Including a Missense Mutation in LGR5

BACKGROUND & AIMS

Small intestinal neuroendocrine tumor (SI-NET) is a rare disease, but its incidence has increased over the past 4 decades. Understanding the genetic risk factors underlying SI-NETs can help in disease prevention and may provide clinically beneficial markers for diagnosis. Here the results of the largest genome-wide association study of SI-NETs performed to date with 405 cases and 614,666 controls are reported.

METHODS

Samples from 307 patients with SI-NETs and 287,137 controls in the FinnGen study were used for the identification of SI-NET risk-associated genetic variants. The results were also meta-analyzed with summary statistics from the UK Biobank (n = 98 patients with SI-NET and n = 327,529 controls).

RESULTS

We identified 6 genome-wide significant (P < 5 × 10-8) loci associated with SI-NET risk, of which 4 (near SEMA6A, LGR5, CDKAL1, and FERMT2) are novel and 2 (near LTA4H-ELK and in KIF16B) have been reported previously. Interestingly, the top hit (rs200138614; P = 1.80 × 10-19) was a missense variant (p.Cys712Phe) in the LGR5 gene, a bona-fide marker of adult intestinal stem cells and a potentiator of canonical WNT signaling. The association was validated in an independent Finnish collection of 70 patients with SI-NETs, as well as in the UK Biobank exome sequence data (n = 92 cases and n = 392,814 controls). Overexpression of LGR5 p.Cys712Phe in intestinal organoids abolished the ability of R-Spondin1 to support organoid growth, indicating that the mutation perturbed R-Spondin-LGR5 signaling.

CONCLUSIONS

Our study is the largest genome-wide association study to date on SI-NETs and reported 4 new associated genome-wide association study loci, including a novel missense mutation (rs200138614, p.Cys712Phe) in LGR5, a canonical marker of adult intestinal stem cells.

Advanced Progression for the Heterogeneity and Homeostasis of Intestinal Stem Cells

Current understanding of the leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) in intestinal stem cells (ISCs) is well established, however, the implications of ISC heterogeneity and homeostasis are poorly understood. Prior studies have provided important evidence for the association between heterogeneity of ISC pools with pathogenesis and therapeutic response of malignant disease. Leveraging the advantages of organoids and single cell RNA sequencing (scRNA-seq), glandular development has been simulated and cell heterogeneity has been clarified. Based on this research, several potential ISCs were identified, such as LGR5 + p27 + quiescent ISCs, LGR5 + Mex3a + slowly proliferating stem cells, and CLU + reverse stem cells. We also illustrated major factors responsible for ISC homeostasis including metabolism-related (LKB1, TGR5, HMGCS2), inflammation-related (IFB-b, IFN2, TNF), and Wnt signaling-related (CREPT, Mex3a, MTG16) factors. ISCs play complex roles in intestinal tumorigenesis, chemoresistance and occasional relapse of colon cancer, which bear discussion. In this review, we focus on novel technical challenges in ISCs fate drawing upon recent research with the goals of clarifying our understanding of complex ISCs, elucidating the integrated intestinal crypt niche, and creating new opportunities for therapeutic development.

Expression of Stem Cell Markers in High-LET Space Radiation-Induced Intestinal Tumors in Apc1638N/+ Mouse Intestine

Estimation of cancer risk among astronauts planning to undertake future deep-space missions requires understanding the quantitative and qualitative differences in radiogenic cancers after low- and high-LET radiation exposures. Previously, we reported a multifold higher RBE for high-LET radiation-induced gastrointestinal (GI) tumorigenesis in Apc1638N/+ mice. Using the same model system, i.e., Apc1638N/+ mice, here, we report qualitative differences in the cellular phenotype of low- and high-LET radiation-induced GI tumors. Stem cell (SC) phenotypes were identified using BMI1, ALDH1, CD133, DCLK1, MSI1, and LGR5 markers in low (γ-rays)- and high (56Fe)-LET radiation-induced and spontaneous tumors. We also assessed the expression of these markers in the adjacent normal mucosa. All six of these putative SC markers were shown to be overexpressed in tumors compared to the adjacent normal intestinal tissue. A differential SC phenotype for spontaneous and radiogenic intestinal tumors in Apc1638N/+ mice was observed, where the ALDH1, BMI1, CD133, MSI1, and DCLK1 expressing cells were increased, while LGR5 expressing cells were decreased in 56Fe-induced tumors compared to γ-ray-induced and spontaneous tumors. Furthermore, higher β-catenin activation (marked by nuclear localization) was observed in 56Fe-induced tumors compared to γ and spontaneous tumors. Since differential tumor cell phenotype along with activated β-catenin may very well affect malignant progression, our findings are relevant to understanding the higher carcinogenic risk of high-LET radiation. This study has implications for the assessment of GI-cancer risk among astronauts, as well as for the estimation of secondary cancer risk among patients receiving hadron therapy, considering that our results indicate increased stemness properties after radiation.

CRISPR/dCAS9-mediated DNA demethylation screen identifies functional epigenetic determinants of colorectal cancer

BACKGROUND

Promoter hypermethylation of tumour suppressor genes is frequently observed during the malignant transformation of colorectal cancer (CRC). However, whether this epigenetic mechanism is functional in cancer or is a mere consequence of the carcinogenic process remains to be elucidated.

RESULTS

In this work, we performed an integrative multi-omic approach to identify gene candidates with strong correlations between DNA methylation and gene expression in human CRC samples and a set of 8 colon cancer cell lines. As a proof of concept, we combined recent CRISPR-Cas9 epigenome editing tools (dCas9-TET1, dCas9-TET-IM) with a customized arrayed gRNA library to modulate the DNA methylation status of 56 promoters previously linked with strong epigenetic repression in CRC, and we monitored the potential functional consequences of this DNA methylation loss by means of a high-content cell proliferation screen. Overall, the epigenetic modulation of most of these DNA methylated regions had a mild impact on the reactivation of gene expression and on the viability of cancer cells. Interestingly, we found that epigenetic reactivation of RSPO2 in the tumour context was associated with a significant impairment in cell proliferation in p53-/- cancer cell lines, and further validation with human samples demonstrated that the epigenetic silencing of RSPO2 is a mid-late event in the adenoma to carcinoma sequence.

CONCLUSIONS

These results highlight the potential role of DNA methylation as a driver mechanism of CRC and paves the way for the identification of novel therapeutic windows based on the epigenetic reactivation of certain tumour suppressor genes.

PDE4DIP contributes to colorectal cancer growth and chemoresistance through modulation of the NF1/RAS signaling axis

Phosphodiesterase 4D interacting protein (PDE4DIP) is a centrosome/Golgi protein associated with cyclic nucleotide phosphodiesterases. PDE4DIP is commonly mutated in human cancers, and its alteration in mice leads to a predisposition to intestinal cancer. However, the biological function of PDE4DIP in human cancer remains obscure. Here, we report for the first time the oncogenic role of PDE4DIP in colorectal cancer (CRC) growth and adaptive MEK inhibitor (MEKi) resistance. We show that the expression of PDE4DIP is upregulated in CRC tissues and associated with the clinical characteristics and poor prognosis of CRC patients. Knockdown of PDE4DIP impairs the growth of KRAS-mutant CRC cells by inhibiting the core RAS signaling pathway. PDE4DIP plays an essential role in the full activation of oncogenic RAS/ERK signaling by suppressing the expression of the RAS GTPase-activating protein (RasGAP) neurofibromin (NF1). Mechanistically, PDE4DIP promotes the recruitment of PLCγ/PKCε to the Golgi apparatus, leading to constitutive activation of PKCε, which triggers the degradation of NF1. Upregulation of PDE4DIP results in adaptive MEKi resistance in KRAS-mutant CRC by reactivating the RAS/ERK pathway. Our work reveals a novel functional link between PDE4DIP and NF1/RAS signal transduction and suggests that targeting PDE4DIP is a promising therapeutic strategy for KRAS-mutant CRC.

The Roles of Zinc Finger Proteins in Colorectal Cancer

Despite colorectal cancer remaining a leading worldwide cause of cancer-related death, there remains a paucity of effective treatments for advanced disease. The molecular mechanisms underlying the development of colorectal cancer include altered cell signaling and cell cycle regulation that may result from epigenetic modifications of gene expression and function. Acting as important transcriptional regulators of normal biological processes, zinc finger proteins also play key roles in regulating the cellular mechanisms underlying colorectal neoplasia. These actions impact cell differentiation and proliferation, epithelial-mesenchymal transition, apoptosis, homeostasis, senescence, and maintenance of stemness. With the goal of highlighting promising points of therapeutic intervention, we review the oncogenic and tumor suppressor roles of zinc finger proteins with respect to colorectal cancer tumorigenesis and progression.

NLRC3 deficiency promotes cutaneous wound healing due to the inhibition of p53 signaling

Cutaneous wound healing is a complicated process that is characterized by an initial inflammatory phase followed by a proliferative phase. NLRC3 plays important roles in innate immunity, inflammatory regulation and tumor cell growth. However, the function of NLRC3 in wound healing remains unclear. Here, we investigated the function of NLRC3 in acute cutaneous wound healing using Nlrc3 gene knockout (Nlrc3^-/-) mice. Our results demonstrated that skin wound repair in Nlrc3^-/- mice was significantly accelerated compared with that in wild-type (WT) mice. NLRC3 deficiency promoted the inflammatory and proliferative phases in wounds enhanced the inflammatory response and increased re-epithelialization and granulation tissue formation, and these phenotypes were primarily ascribed to regulatory effects on p53 signaling. Mechanistically, we uncovered novel crosstalk between NLRC3 and p53 signaling and revealed that NLRC3 could mediate the ubiquitination and degradation of p53 in an Hsp90-dependent manner. In conclusion, our study suggests that NLRC3 is a critical negative regulator of the inflammatory response and cell proliferation during wound healing and that blocking NLRC3 may represent a potential approach for accelerating wound healing.

Potential mechanism of oral baicalin treating psoriasis via suppressing Wnt signaling pathway and inhibiting Th17/IL-17 axis by activating PPARγ

Psoriasis (PSO), an immune-mediated chronic inflammatory skin disease, has seriously affected the quality of patients' life. It is urgent to find effective medicines with lower costs and less side effects. Baicalin (HQG) is the main bioactive substance from Scutellaria baicalensis with effects of anti-inflammation and immunoregulation. Herein, we explored the effect of oral HQG treating PSO and its potential mechanism. Firstly, network pharmacology was used to predict that HQG may act on Estrogen, TNF-alpha (tumor necrosis factor, TNF), interleukin-17 (IL-17) signaling pathways and Th17 cell differentiation, especially the key targets including TNF, Proto-oncogene tyrosine-protein kinase Src, Peroxisome proliferator-activated receptor gamma and Matrix metalloproteinase-9. Imiquimod (IMQ)-induced mice were then used to study the effects of HQG treating PSO. HQG could significantly ameliorate the skin lesions, decrease the level of inflammatory factors and inhibit Th1/Th17 cell differentiation in IMQ-induced mice. Finally, transcriptome analysis of skin lesions integrated with the prediction of network pharmacology further demonstrated that the potential mechanism may be associated with suppressing Wnt signaling pathway and inhibiting Th17/IL-17 axis by activating PPARγ. In conclusion, this study suggested that HQG may be a promising agent for further studies in the search for therapeutic strategies to treat PSO in the future.

Unprotected peptide macrocyclization and stapling via a fluorine-thiol displacement reaction

We report the discovery of a facile peptide macrocyclization and stapling strategy based on a fluorine thiol displacement reaction (FTDR), which renders a class of peptide analogues with enhanced stability, affinity, cellular uptake, and inhibition of cancer cells. This approach enabled selective modification of the orthogonal fluoroacetamide side chains in unprotected peptides in the presence of intrinsic cysteines. The identified benzenedimethanethiol linker greatly promoted the alpha helicity of a variety of peptide substrates, as corroborated by molecular dynamics simulations. The cellular uptake of benzenedimethanethiol stapled peptides appeared to be universally enhanced compared to the classic ring-closing metathesis (RCM) stapled peptides. Pilot mechanism studies suggested that the uptake of FTDR-stapled peptides may involve multiple endocytosis pathways in a distinct pattern in comparison to peptides stapled by RCM. Consistent with the improved cell permeability, the FTDR-stapled lead Axin and p53 peptide analogues demonstrated enhanced inhibition of cancer cells over the RCM-stapled analogues and the unstapled peptides.

Strategies capable of stapling unprotected peptides in a straightforward, chemoselective, and clean manner, as well as promoting cellular uptake are of great interest. Here the authors report a peptide macrocyclization and stapling strategy which satisfies those criteria, based on a fluorine thiol displacement reaction.

R-spondin 3 deletion induces Erk phosphorylation to enhance Wnt signaling and promote bone formation in the appendicular skeleton

Activation of Wnt signaling leads to high bone density. The R-spondin family of four secreted glycoproteins (Rspo1-4) amplifies Wnt signaling. In humans, RSPO3 variants are strongly associated with bone density. Here, we investigated the role of Rspo3 in skeletal homeostasis in mice. Using a comprehensive set of mouse genetic and mechanistic studies, we show that in the appendicular skeleton, Rspo3 haplo-insufficiency and Rspo3 targeted deletion in Runx2⁺ osteoprogenitors lead to an increase in trabecular bone mass, with increased number of osteoblasts and bone formation. In contrast and highlighting the complexity of Wnt signaling in the regulation of skeletal homeostasis, we show that Rspo3 deletion in osteoprogenitors results in the opposite phenotype in the axial skeleton, i.e., low vertebral trabecular bone mass. Mechanistically, Rspo3 deficiency impairs the inhibitory effect of Dkk1 on Wnt signaling activation and bone mass. We demonstrate that Rspo3 deficiency leads to activation of Erk signaling which in turn, stabilizes β-catenin and Wnt signaling activation. Our data demonstrate that Rspo3 haplo-insufficiency/deficiency boosts canonical Wnt signaling by activating Erk signaling, to favor osteoblastogenesis, bone formation, and bone mass.

The role of R-spondin proteins in cancer biology

R-spondin (RSPO) proteins constitute a family of four secreted glycoproteins (RSPO1-4) that have appeared as multipotent signaling ligands. The best-known molecular function of RSPOs lie within their capacity to agonize the Wnt/β-catenin signaling pathway. As RSPOs act upon cognate receptors LGR4/5/6 that are typically expressed by stem cells and progenitor cells, RSPO proteins importantly potentiate Wnt/β-catenin signaling especially within these proliferative stem cell compartments. Since multiple organs express LGR4/5/6 receptors and RSPO ligands within their stem cell niches, RSPOs can exert an influential role in stem cell regulation throughout the body. Inherently, over the last decade a multitude of reports implicated the deregulation of RSPOs in cancer development. First, RSPO2 and RSPO3 gene fusions with concomitant enhanced expression have been identified in colon cancer patients, and proposed as an alternative driver of Wnt/β-catenin hyperactivation that earmarks cancer in the colorectal tract. Moreover, the causal oncogenic capacity of RSPO3 overactivation has been demonstrated in the mouse intestine. As a paradigm organ in this field, most of current knowledge about RSPOs in cancer is derived from studies in the intestinal tract. However, RSPO gene fusions as well as enhanced RSPO expression have been reported in multiple additional cancer types, affecting different organs that involve divergent stem cell hierarchies. Importantly, the emerging oncogenic role of RSPO and its potential clinical utility as a therapeutic target have been recognized and investigated in preclinical and clinical settings. This review provides a survey of current knowledge on the role of RSPOs in cancer biology, addressing the different organs implicated, and of efforts made to explore intervention opportunities in cancer cases with RSPO overrepresentation, including the potential utilization of RSPO as novel therapeutic target itself.

Epigenetic induction of lipocalin 2 expression drives acquired resistance to 5-fluorouracil in colorectal cancer through integrin β3/SRC pathway

The therapeutic efficacy of 5-fluorouracil (5-FU) is often reduced by the development of drug resistance. We observed significant upregulation of lipocalin 2 (LCN2) expression in a newly established 5-FU-resistant colorectal cancer (CRC) cell line. In this study, we demonstrated that 5-FU-treated CRC cells developed resistance through LCN2 upregulation caused by LCN2 promoter demethylation and that feedback between LCN2 and NF-κB further amplified LCN2 expression. High LCN2 expression was associated with poor prognosis in CRC patients. LCN2 attenuated the cytotoxicity of 5-FU by activating the SRC/AKT/ERK-mediated antiapoptotic program. Mechanistically, the LCN2-integrin β3 interaction enhanced integrin β3 stability, thus recruiting SRC to the cytomembrane for autoactivation, leading to downstream AKT/ERK cascade activation. Targeting LCN2 or SRC compromised the growth of CRC cells with LCN2-induced 5-FU resistance. Our findings demonstrate a novel mechanism of acquired resistance to 5-FU, suggesting that LCN2 can be used as a biomarker and/or therapeutic target for advanced CRC.

RSPO2 inhibits BMP signaling to promote self-renewal in acute myeloid leukemia

Acute myeloid leukemia (AML) is a rapidly progressing cancer, for which chemotherapy remains standard treatment and additional therapeutic targets are requisite. Here, we show that AML cells secrete the stem cell growth factor R-spondin 2 (RSPO2) to promote their self-renewal and prevent cell differentiation. Although RSPO2 is a well-known WNT agonist, we reveal that it maintains AML self-renewal WNT independently, by inhibiting BMP receptor signaling. Autocrine RSPO2 signaling is also required to prevent differentiation and to promote self-renewal in normal hematopoietic stem cells as well as primary AML cells. Comprehensive datamining reveals that RSPO2 expression is elevated in patients with AML of poor prognosis. Consistently, inhibiting RSPO2 prolongs survival in AML mouse xenograft models. Our study indicates that in AML, RSPO2 acts as an autocrine BMP antagonist to promote cancer cell renewal and may serve as a marker for poor prognosis.

Rspo2 inhibits TCF3 phosphorylation to antagonize Wnt signaling during vertebrate anteroposterior axis specification

The Wnt pathway activates target genes by controlling the β-catenin-T-cell factor (TCF) transcriptional complex during embryonic development and cancer. This pathway can be potentiated by R-spondins, a family of proteins that bind RNF43/ZNRF3 E3 ubiquitin ligases and LGR4/5 receptors to prevent Frizzled degradation. Here we demonstrate that, during Xenopus anteroposterior axis specification, Rspo2 functions as a Wnt antagonist, both morphologically and at the level of gene targets and pathway mediators. Unexpectedly, the binding to RNF43/ZNRF3 and LGR4/5 was not required for the Wnt inhibitory activity. Moreover, Rspo2 did not influence Dishevelled phosphorylation in response to Wnt ligands, suggesting that Frizzled activity is not affected. Further analysis indicated that the Wnt antagonism is due to the inhibitory effect of Rspo2 on TCF3/TCF7L1 phosphorylation that normally leads to target gene activation. Consistent with this mechanism, Rspo2 anteriorizing activity has been rescued in TCF3-depleted embryos. These observations suggest that Rspo2 is a context-specific regulator of TCF3 phosphorylation and Wnt signaling.

Role of R-spondin 2 in arterial lymphangiogenesis and atherosclerosis

AIMS

Impaired lymphatic drainage of the arterial wall results in intimal lipid accumulation and atherosclerosis. However, the mechanisms regulating lymphangiogenesis in atherosclerotic arteries are not well understood. Our studies identified elevated levels of matrix protein R-spondin 2 (RSPO2) in atherosclerotic arteries. In this study, we investigated the role of RSPO2 in lymphangiogenesis, arterial cholesterol efflux into lesion-draining lymph nodes (LNs) and development of atherosclerosis.

METHODS AND RESULTS

The effect of RSPO2 on lymphangiogenesis was investigated using human lymphatic endothelial cells (LEC) in vitro and implanted Matrigel plugs in vivo. Cellular and molecular approaches, pharmacological agents, and siRNA silencing of RSPO2 receptor LGR4 were used to investigate RSPO2-mediated signalling in LEC. In vivo low-density lipoprotein (LDL) tracking and perivascular blockade of RSPO2-LGR4 signalling using LGR4-extracellular domain (ECD) pluronic gel in hypercholesterolemic mice were utilized to investigate the role of RSPO2 in arterial reverse cholesterol transport and atherosclerosis. Immunoblotting and imaging experiments demonstrated increased RSPO2 expression in human and mouse atherosclerotic arteries compared to non-atherosclerotic controls. RSPO2 treatment inhibited lymphangiogenesis both in vitro and in vivo. LGR4 silencing and inhibition of RSPO2-LGR4 signalling abrogated RSPO2-induced inhibition of lymphangiogenesis. Mechanistically, we found that RSPO2 suppresses PI3K-AKT-endothelial nitric oxide synthase (eNOS) signalling via LGR4 and inhibits activation of the canonical Wnt-β-catenin pathway. ApoE-/- mice treated with LGR4-ECD developed significantly less atherosclerosis compared with control treatment. Finally, increased arterial lymphatic vessel density and improved lymphatic drainage of fluorescently labelled LDL to deep cervical LNs were observed in LGR4-ECD-treated mice.

CONCLUSION

These findings demonstrate that RSPO2 inhibits lymphangiogenesis via LGR4 and downstream impairment of AKT-eNOS-nitric oxide signalling. These results may also inform new therapeutic strategies to promote lymphangiogenesis and improve cholesterol efflux from atherosclerotic arteries.

WNT5a in Colorectal Cancer: Research Progress and Challenges

Despite the clinical development of new adjuvant and neoadjuvant chemotherapy drugs, colorectal cancer is still one of the leading causes of cancer-related death in human beings. WNT5a, an autocrine and paracrine β-catenin independent ligand, has been shown to induce tumor inhibition and carcinogenic signals, depending on the type of cancer. In patients with colorectal cancer, WNT5a triggers a variety of downstream signaling pathways, which mainly affect the migration and invasion of tumor cells. This article reviews the mechanism and therapeutic potential of WNT5a in colorectal cancer. In short, an in-depth understanding of the role of WNT5a in colorectal cancer is very helpful to better deal with this disease.

R-Spondin 2 and WNT/CTNNB1 Signaling Pathways Are Required for Porcine Follicle Development and In Vitro Maturation

The secretion of oocyte-derived paracrine factors, such as R-spondin2, is an essential mechanism for follicle growth by promoting the proliferation and differentiation of cumulus cells around oocytes. In the present study, we aimed to identify the effect of R-spondin2 during follicular development. First, R-spondin2-related factors (R-spondin2, CTNNB1, LGR4, and LGR5) were identified through immunofluorescence in porcine ovarian tissue. CTNNB1 was expressed in ooplasm, and CTNNB1 and LGR4 were expressed in granulosa cells. In addition, R-spondin2, LGR4, and LGR5 were expressed in the theca interna. These results imply that these proteins play a major role in porcine follicular development. In addition, the effects of R-spondin2 on the in vitro maturation process of porcine cumulus oocyte complexes and subsequent embryonic development were confirmed. A treatment of 100 ng/mL R-spondin2 in the in vitro maturation (IVM) process increased nuclear maturation and increased the expression of EGFR mRNA in cumulus cells. The EGFR-ERK signal is essential for oocyte maturation, ovulation, and luteinization. R-spondin2 treatment also increased the expression of CTNNB1 and EGFR in primary cultured cumulus cells. In conclusion, RSPO2 and WNT/CTNNB1 signaling pathways are required for porcine follicle development and are predicted to be involved in the EGFR-ERK signaling pathway.

β-catenin in adrenal zonation and disease

The Wnt signaling pathway is a critical mediator of the development and maintenance of several tissues. The adrenal cortex is highly dependent upon Wnt/β-catenin signaling for proper zonation and endocrine function. Adrenocortical cells emerge in the peripheral capsule and subcapsular cortex of the gland as progenitor cells that centripetally differentiate into steroid hormone-producing cells of three functionally distinct concentric zones that respond robustly to various endocrine stimuli. Wnt/β-catenin signaling mediates adrenocortical progenitor cell fate and tissue renewal to maintain the gland throughout life. Aberrant Wnt/β-catenin signaling contributes to various adrenal disorders of steroid production and growth that range from hypofunction and hypoplasia to hyperfunction, hyperplasia, benign adrenocortical adenomas, and malignant adrenocortical carcinomas. Great strides have been made in defining the molecular underpinnings of adrenocortical homeostasis and disease, including the interplay between the capsule and cortex, critical components involved in maintaining the adrenocortical Wnt/β-catenin signaling gradient, and new targets in adrenal cancer. This review seeks to examine these and other recent advancements in understanding adrenocortical Wnt/β-catenin signaling and how this knowledge can inform therapeutic options for adrenal disease.

MPP7 promotes the migration and invasion of breast cancer cells via EGFR/AKT signaling

Metastasis is a major cause of breast cancer death. MPP7 is a cell polarity controller highly linked to cell migration; however, the function of MPP7 in breast cancer remains unknown. In this study, we reported that MPP7 expression was upregulated in breast cancer tissues and high MPP7 expression predicted poor survival in patients with breast cancer. Ectopic expression of MPP7 markedly enhanced the migration and invasion in breast cancer cells. In contrast, depletion of MPP7 resulted in impaired cell mobility and metastasis. Moreover, we demonstrated that MPP7 exerted its promotional effect via modulation of EMT and activation of the EGFR/AKT cascade. Our study reveals an oncogenic role of MPP7 in breast cancer and suggests that MPP7 may serve as a potential target for exploring novel therapeutic strategies against breast cancer metastasis.

Portrait of Cancer Stem Cells on Colorectal Cancer: Molecular Biomarkers, Signaling Pathways and miRNAome

Colorectal cancer (CRC) is a leading cause of cancer death worldwide, and about 20% is metastatic at diagnosis and untreatable. Increasing evidence suggests that the heterogeneous nature of CRC is related to colorectal cancer stem cells (CCSCs), a small cells population with stemness behaviors and responsible for tumor progression, recurrence, and therapy resistance. Growing knowledge of stem cells (SCs) biology has rapidly improved uncovering the molecular mechanisms and possible crosstalk/feedback loops between signaling pathways that directly influence intestinal homeostasis and tumorigenesis. The generation of CCSCs is probably connected to genetic changes in members of signaling pathways, which control self-renewal and pluripotency in SCs and then establish function and phenotype of CCSCs. Particularly, various deregulated CCSC-related miRNAs have been reported to modulate stemness features, controlling CCSCs functions such as regulation of cell cycle genes expression, epithelial-mesenchymal transition, metastasization, and drug-resistance mechanisms. Primarily, CCSC-related miRNAs work by regulating mainly signal pathways known to be involved in CCSCs biology. This review intends to summarize the epigenetic findings linked to miRNAome in the maintenance and regulation of CCSCs, including their relationships with different signaling pathways, which should help to identify specific diagnostic, prognostic, and predictive biomarkers for CRC, but also develop innovative CCSCs-targeted therapies.

miR-196b-5p Promotes Proliferation, Migration and Invasion of Lung Adenocarcinoma Cells via Targeting RSPO2

Objective

To explore the biological role of miR-196b-5p/RSPO2 in the occurrence and development of lung adenocarcinoma (LUAD) and to provide a basis for finding new therapeutic targets for LUAD.

Methods

Differentially expressed genes were analyzed based on LUAD microarray, and the target gene of the target miRNA was predicted. qRT-PCR was used to detect the expression levels of miR-196b-5p and RSPO2 mRNA in normal human bronchial epithelial cell line BEAS-2B and LUAD cell lines A549, NCI-H1792 and NCI-H226. Western blot was used to evaluate protein expression. Cell proliferative, migratory and invasive abilities were detected by CCK-8 and transwell assays. Dual-luciferase assay was conducted to verify the targeting relationship between miR-196b-5p and RSPO2.

Results

The results of qRT-PCR showed that miR-196b-5p was significantly highly expressed in LUAD cells, and the expression level of its downstream target gene RSPO2 was significantly decreased. The results of CCK-8 and transwell assays exhibited that miR-196b-5p promoted proliferation, migration and invasion of LUAD cells, while RSPO2 inhibited the malignant progression of LUAD cells. Dual-luciferase assay confirmed the targeted binding relationship between miR-196b-5p and RSPO2. Overexpression of RSPO2 partially reversed the promotion of miR-196b-5p on proliferation, migration and invasion of LUAD cells.

Conclusion

miR-196b-5p promoted proliferation, migration and invasion of LUAD cells by targeting and down-regulating RSPO2, which provided ideas for searching new targets for the diagnosis and treatment of LUAD.

R-Spondins 2 and 3 Are Overexpressed in a Subset of Human Colon and Breast Cancers

Wnt signaling is activated in many cancer types, yet targeting the canonical Wnt pathway has been challenging for cancer therapy. The pathway might be effectively targeted at many levels depending on the mechanism by which it has become hyperactive. Recently, mouse genetic screens have found that R-spondins (RSPOs) act as oncogenes. Evidence includes recurrent genomic rearrangements that led to increased RSPO2 or RSPO3 expression in human colorectal adenocarcinomas, exclusive of APC mutations. RSPOs modulate Wnt signaling to promote epithelial cell proliferation and survival. These secreted proteins modulate Wnt signaling by binding to G-coupled receptors LGR4/5/6, ultimately inhibiting frizzled membrane clearance by RNF43 and ZNRF3. They also exert their function independent of leucine-rich repeat-containing, G protein-coupled receptors (LGRs) by binding to ZNRF3 and RNF43. This results in increased β-catenin concentration that, after translocation to the nucleus, acts as a transcriptional coactivator of genes necessary for proliferation and cell survival. In this article, we aimed to identify the role of RSPOs in colon and breast cancers by using in silico and in vitro studies. We found that expression of RSPO2 and RSPO3 at high levels characterized a subset of colorectal cancers (CRCs). RSPO2 expression was found to characterize a subset of triple-negative breast cancers. In both instances, increased expression of RSPOs was associated with an activated Wnt signaling gene expression profile. Furthermore, knockdown of RSPO2 decreased Wnt signaling and proliferation in human breast cancer cells. Our findings show and confirm that RSPO2 and RSPO3 expression is upregulated in a subset of colorectal adenocarcinomas and breast cancers and that both are attractive druggable oncoprotein targets against such cancers. We also describe novel fusion transcripts that occur in CRC.

Expression of R-Spondin 1 in ApcMin/+ Mice Suppresses Growth of Intestinal Adenomas by Altering Wnt and Transforming Growth Factor Beta Signaling

BACKGROUND & AIMS

Mutations in the APC gene and other genes in the Wnt signaling pathway contribute to development of colorectal carcinomas. R-spondins (RSPOs) are secreted proteins that amplify Wnt signaling in intestinal stem cells. Alterations in RSPO genes have been identified in human colorectal tumors. We studied the effects of RSPO1 overexpression in ApcMin/+ mutant mice.

METHODS

An adeno associated viral vector encoding RSPO1-Fc fusion protein, or control vector, was injected into ApcMin/+mice. Their intestinal crypts were isolated and cultured as organoids. which were incubated with or without RSPO1-Fc and an inhibitor of transforming growth factor beta receptor (TGFBR). Livers were collected from mice and analyzed by immunohistochemistry. Organoids and adenomas were analyzed by quantitative reverse-transcription PCR, single cell RNA sequencing, and immunohistochemistry.

RESULTS

Intestines from Apc+/+ mice injected with the vector encoding RSPO1-Fc had significantly deeper crypts, longer villi, with increased EdU labeling, indicating increased proliferation of epithelial cells, in comparison to mice given control vector. AAV-RSPO1-Fc-transduced ApcMin/+ mice also developed fewer and smaller intestinal tumors and had significantly longer survival times. Adenomas of ApcMin/+ mice injected with the RSPO1-Fc vector showed a rapid increase in apoptosis and in the expression of Wnt target genes, followed by reduced expression of messenger RNAs and proteins regulated by the Wnt pathway, reduced cell proliferation, and less crypt branching than adenomas of mice given the control vector. Addition of RSPO1 reduced the number of adenoma organoids derived from ApcMin/+ mice and suppressed expression of Wnt target genes but increased phosphorylation of SMAD2 and transcription of genes regulated by SMAD. Inhibition of TGFBR signaling in organoids stimulated with RSPO1-Fc restored organoid formation and expression of genes regulated by Wnt. The TGFBR inhibitor restored apoptosis in adenomas from ApcMin/+ mice expressing RSPO1-Fc back to the same level as in the adenomas from mice given the control vector.

CONCLUSIONS

Expression of RSPO1 in ApcMin/+ mice increases apoptosis and reduces proliferation and Wnt signaling in adenoma cells, resulting in development of fewer and smaller intestinal tumors and longer mouse survival. Addition of RSPO1 to organoids derived from adenomas inhibits their growth and promotes proliferation of intestinal stem cells that retain the APC protein; these effects are reversed by TGFB inhibitor. Strategies to increase the expression of RSPO1 might be developed for the treatment of intestinal adenomas.

Unlike LGR4, LGR5 potentiates Wnt-β-catenin signaling without sequestering E3 ligases

LGR4 and LGR5 encode two homologous receptors with critical, yet distinct, roles in organ development and adult stem cell survival. Both receptors are coexpressed in intestinal crypt stem cells, bind to R-spondins (RSPOs) with high affinity, and potentiate Wnt-β-catenin signaling, presumably by the same mechanism: forming RSPO-bridged complexes with the E3 ligases RNF43 and ZNRF3 to inhibit ubiquitylation of Wnt receptors. However, direct evidence for RSPO-bound, full-length LGR5 interacting with these E3 ligases in whole cells has not been reported, and only LGR4 is essential for the self-renewal of intestinal stem cells. Here, we examined the mechanisms of action of LGR4 and LGR5 in parallel using coimmunoprecipitation, proximity ligation, competition binding, and time-resolved FRET assays in whole cells. Full-length LGR4 formed a tight complex with ZNRF3 and RNF43 even without RSPO, whereas LGR5 did not interact with either E3 ligase with or without RSPO. Domain-swapping experiments with LGR4 and LGR5 revealed that the seven-transmembrane domain of LGR4 conferred interaction with the E3 ligases. Native LGR4 and LGR5 existed as dimers on the cell surface, and LGR5 interacted with both FZD and LRP6 of the Wnt signalosome to enhance LRP6 phosphorylation and potentiate Wnt-β-catenin signaling. These findings provide a molecular basis for the weaker activity of LGR5 in the potentiation of Wnt signaling that may underlie the distinct roles of LGR4 and LGR5 in organ development, as well as the self-renewal and fitness of adult stem cells.

Lgr5 Marks Adult Progenitor Cells Contributing to Skeletal Muscle Regeneration and Sarcoma Formation

Regeneration of adult skeletal muscle is driven largely by resident satellite cells, a stem cell population increasingly considered to display a high degree of molecular heterogeneity. In this study, we find that Lgr5, a receptor for Rspo and a potent mediator of Wnt/β-catenin signaling, marks a subset of activated satellite cells that contribute to muscle regeneration. Lgr5 is found to be rapidly upregulated in purified myogenic progenitors following acute cardiotoxin-induced injury. In vivo lineage tracing using our Lgr5-2ACre^ERT2R26tdTomato^LSL reporter mouse model shows that Lgr5⁺ cells can reconstitute damaged muscle fibers following muscle injury, as well as replenish the quiescent satellite cell pool. Moreover, conditional mutation in Lgr52ACre^ERT2;Kras^G12D;Trp53^flox/flox mice drives undifferentiated pleomorphic sarcoma formation in adult mice, thereby substantiating Lgr5⁺ cells as a cell of origin of sarcomas. Our findings provide the groundwork for developing Rspo/Wnt-signaling-based therapeutics to potentially enhance regenerative outcomes of skeletal muscles in degenerative muscle diseases.

Wnt Pathway: An Integral Hub for Developmental and Oncogenic Signaling Networks

The Wnt pathway is an integral cell-to-cell signaling hub which regulates crucial development processes and maintenance of tissue homeostasis by coordinating cell proliferation, differentiation, cell polarity, cell movement, and stem cell renewal. When dysregulated, it is associated with various developmental diseases, fibrosis, and tumorigenesis. We now better appreciate the complexity and crosstalk of the Wnt pathway with other signaling cascades. Emerging roles of the Wnt signaling in the cancer stem cell niche and drug resistance have led to development of therapeutics specifically targeting various Wnt components, with some agents currently in clinical trials. This review highlights historical and recent findings on key mediators of Wnt signaling and how they impact antitumor immunity and maintenance of cancer stem cells. This review also examines current therapeutics being developed that modulate Wnt signaling in cancer and discusses potential shortcomings associated with available therapeutics.

LGR5 constitutively activates NF-κB signaling to regulate the growth of intestinal crypts

Mammalian LGR5 and LGR4, markers of adult stem cells, are involved in many physiological functions by enhancing WNT signaling. However, whether LGR5 and LGR4 are coupled to other intracellular signaling pathways to regulate stem cell function remains unknown. Here, we show that LGR5 and LGR4 can constitutively activate NF-κB signaling in a ligand-independent manner, which is dependent on their C-termini, but independent of receptor endocytosis. Moreover, the C-termini of LGR5/4 interact with TROY, which is required for activating NF-κB signaling. In small intestinal crypt organoids, overexpression of a C-terminal deletion mutant of LGR5 inhibits the growth and bud formation of organoids, whereas overexpression of the R-spondin-binding mutant of LGR5 that is defective for WNT signaling can still promote organoid growth. Our study reveals that NF-κB signaling, regulated by LGR5 and LGR4, plays an important role in the survival of colon cancer cells and the growth of intestinal crypts. Our findings also suggest that LGR5/4-induced NF-κB signaling and WNT signaling may co-regulate the growth of LGR5⁺ adult stem cells and intestinal crypts.

R-spondin2 Suppresses the Progression of Hepatocellular Carcinoma via MAPK Signaling Pathway

The R-spondin family plays important roles in embryonic development, including in humans. However, information on the relationship between R-spondin2 and hepatocellular carcinoma (HCC) is lacking. This study aimed was to explore the mechanisms of R-spondin2 action in the progression of HCC. By analyzing R-spondin2 expression levels in HCC tissues by IHC and database, we identified that HCC tissues had lower expression levels of R-spondin2, correlated with a poor prognosis. We also established R-spondin2-overexpressing and knockdown cell lines and measured their viabilities and invasion abilities in vitro and their oncogenic capacity in vivo. Human mRNA microarray analysis was performed to screen for mRNAs that were differentially expressed between R-spondin2-overexpressing and control HCC cells. Microarray and Western blot analyses showed significant changes in the MAPK signaling pathway after transfection. Furthermore, in vivo experiments indicated that R-spondin2 knockdown increased the tumorigenicity of HCC cells after subcutaneous implantation in mice. Altogether, our results indicate that the R-spondin2, which might be a novel tumor suppressor gene, were responsible for inhibiting the proliferation and invasion of HCC via the MAPK signaling pathway. IMPLICATIONS: R-spondin2 gene might be a novel tumor suppressor gene providing new clues to clarify the biological behavior of HCC and thus reduce patient mortality and prolong survival.

LGR5 controls extracellular matrix production by stem cells in the developing intestine

The Lgr5 receptor is a marker of intestinal stem cells (ISCs) that regulates Wnt/b-catenin signaling. In this study, phenotype analysis of knockin/knockout Lgr5-eGFP-IRES-Cre and Lgr5-DTReGFP embryos reveals that Lgr5 deficiency during Wnt-mediated cytodifferentiation results in amplification of ISCs and early differentiation into Paneth cells, which can be counteracted by in utero treatment with the Wnt inhibitor LGK974. Conditional ablation of Lgr5 postnatally, but not in adults, alters stem cell fate toward the Paneth lineage. Together, these in vivo studies suggest that Lgr5 is part of a feedback loop to adjust the Wnt tone in ISCs. Moreover, transcriptome analyses reveal that Lgr5 controls fetal ISC maturation associated with acquisition of a definitive stable epithelial phenotype, as well as the capacity of ISCs to generate their own extracellular matrix. Finally, using the ex vivo culture system, evidences are provided that Lgr5 antagonizes the Rspondin 2-Wnt-mediated response in ISCs in organoids, revealing a sophisticated regulatory process for Wnt signaling in ISCs.

TYRO3 facilitates cell growth and metastasis via activation of the Wnt/β-catenin signaling pathway in human gastric cancer cells

It has become increasingly important to identify valuable therapeutic targets to improve the prognosis of cancer patients. Although emerging evidence has suggested TYRO3 as a potential therapeutic target in various types of cancers, less is known about its role in gastric cancer (GC) development. Herein, we investigated the functional and molecular mechanisms by which TYRO3 influenced GC. TYRO3 mRNA and protein were evaluated by quantitative real-time PCR (qRT-PCR), western blotting, and immunohistochemistry. Other methods including stable transfection of TYRO3 into GC cells, wound healing, Transwell assays, CCK-8 assays, colony formation assays, immunocytochemistry in vitro, and tumorigenesis in vivo were also conducted. Our results indicated that high levels of TYRO3 significantly correlated with clinical metastasis and poor prognoses in patients with GC. In addition, TYRO3 silencing distinctively suppressed GC cell growth, invasion, and metastasis both in vitro and in vivo. Conversely, TYRO3 overexpression led to the opposite effects. Mechanistic analyses revealed that the Wnt/β-catenin signaling pathway might be involved in TYRO3-facilitated GC cell behavior. Collectively, we demonstrated that elevated TYRO3 expression contributed to GC cell growth and metastasis via the Wnt/β-catenin pathway, suggesting a novel therapeutic target for GC.

Gastric squamous-columnar junction contains a large pool of cancer-prone immature osteopontin responsive Lgr5-CD44+ cells

Areas of a junction between two types of epithelia are known to be cancer-prone in many organ systems. However, mechanisms for preferential malignant transformation at the junction areas remain insufficiently elucidated. Here we report that inactivation of tumor suppressor genes Trp53 and Rb1 in the gastric squamous-columnar junction (SCJ) epithelium results in preferential formation of metastatic poorly differentiated neoplasms, which are similar to human gastroesophageal carcinoma. Unlike transformation-resistant antral cells, SCJ cells contain a highly proliferative pool of immature Lgr5⁻CD44⁺ cells, which are prone to transformation in organoid assays, comprise early dysplastic lesions, and constitute up to 30% of all neoplastic cells. CD44 ligand osteopontin (OPN) is preferentially expressed in and promotes organoid formation ability and transformation of the SCJ glandular epithelium. OPN and CD44 overexpression correlate with the worst prognosis of human gastroesophageal carcinoma. Thus, detection and selective targeting of the active OPN-CD44 pathway may have direct clinical relevance.

Cancers arising from the gastric squamous-columnar junction have high incidence and are characterized by a poor prognosis. Here, the authors use genetic mouse models to show that loss of p53 and Rb1 expression results in preferential tumour development at the gastric squamous-columnar junction that contains a large pool of osteopontin responsive Lgr5-CD44+ cells.

Genome-wide methylation and expression profiling identify methylation-associated genes in colorectal cancer

Aim: To identify methylation-associated genes in the carcinogenesis of colorectal cancer (CRC). Materials & methods: Genome-wide patterns of DNA methylation and gene expression in CRC tissues and adjacent normal tissues were determined and further validated in The Cancer Genome Atlas data and Chinese CRC patients, respectively. Gene overexpression and knockdown cells were constructed to investigate their biological roles in CRC. Results: After validations, hypermethylation of eight genes were found to be correlated with their reduced transcription, and hypomethyaltion of three genes were associated with their upregulation. CADM3, CNRIP1, GRHL2, GRIA4, GSTM2 and NRXN1 were associated with the overall survival of CRC patients. CNRIP1 and GSTM2 were mainly responsible for the proliferation in CRC cells. Conclusion: A total of 11 genes may be promising biomarkers for CRC.

Clinicopathologic and prognostic significance of LGR5, a cancer stem cell marker in patients with colorectal cancer

Aim:

To analyze the clinicopathologic and prognostic significance of Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), a cancer stem cell marker expression in a cohort of colorectal cancer patients (CRC).

Patients & methods:

A total of 76 formalin-fixed paraffin-embedded tissue blocks of primary or metastatic tumors from 49 CRC patients were collected for duration 2009–2015. LGR5 expression was assessed through immunohistochemical staining of a tissue microarray.

Results:

LGR5 was significantly over expressed in CRC tissue samples and found to be a statistically significant independent prognostic marker for an improved overall survival.

Conclusion:

LGR5 expression was higher in colorectal cancer than in normal tissue. LGR5 was an independent prognostic marker for better clinical outcomes and might be used as a potential therapeutic target in CRCs.

Silencing LGR6 Attenuates Stemness and Chemoresistance via Inhibiting Wnt/β-Catenin Signaling in Ovarian Cancer

Leucine-rich-repeat-containing G protein-coupled receptors (LGRs) have been widely found to be implicated with development and progression in multiple cancer types. However, the clinical significance and biological functions of LGR6 in ovarian cancer remains unclear. In this study, LGR6 expression was mainly examined by immunohistochemistry. Functional assays in vitro and animal experiments in vivo were carried out to explore the effect of LGR6 on cancer stem cell (CSC) characteristics and chemotherapeutic responses in ovarian cancer cells. Luciferase assays and GSEA were used to discern the underlying mechanisms contributing to the roles of LGR6 in ovarian cancer. Here, we reported that LGR6 was upregulated in ovarian cancer, which positively correlated with poor chemotherapeutic response and progression survival in ovarian cancer patients. Loss-of-function assays showed that downregulating LGR6 abrogated the CSC-like phenotype and chemoresistance in vitro. More importantly, silencing LGR6 improved the chemoresistance of ovarian cancer cells to cisplatin in vivo. Mechanistic investigation further revealed that silencing LGR6 inhibited stemness and chemoresistance by repressing Wnt/β-catenin signaling. Collectively, our results uncover a novel mechanism contributing to LGR6-induced chemotherapeutic resistance in ovarian cancer, providing the evidence for LGR6 as a potential therapeutic target in ovarian cancer.

R-spondin 2 Drives Liver Tumor Development in a Yes-Associated Protein-Dependent Manner

Each year, more than 25,000 people succumb to liver cancer in the United States, and this neoplasm represents the second cause of cancer-related death globally. R-spondins (RSPOs) are secreted regulators of Wnt signaling that function in development and promote tissue stem cell renewal. In cancer, RSPOs 2 and 3 are oncogenes first identified by insertional mutagenesis screens in tumors induced by mouse mammary tumor virus and by transposon mutagenesis in the colonic epithelium of rodents. RSPO2 has been reported to be activated by chromosomal rearrangements in colorectal cancer and overexpressed in a subset of hepatocellular carcinoma. Using human liver tumor gene expression data, we first discovered that a subset of liver cancers were characterized by high levels of RSPO2 in contrast to low levels in adjacent nontumor tissue. To determine if RSPOs are capable of inducing liver tumors, we used an in vivo model from which we found that overexpression of RSPO2 in the liver promoted Wnt signaling, hepatomegaly, and enhanced liver tumor formation when combined with loss of transformation-related protein 53 (Trp53). Moreover, the Hippo/yes-associated protein (Yap) pathway has been implicated in many human cancers, influencing cell survival. Histologic and gene expression studies showed activation of Wnt/β-catenin and Hippo/Yap pathways following RSPO2 overexpression. We demonstrate that knockdown of Yap1 leads to reduced tumor penetrance following RSPO2 overexpression in the context of loss of Trp53. Conclusion: RSPO2 overexpression leads to tumor formation in the mouse liver in a Hippo/Yap-dependent manner. Overall, our results suggest a role for Yap in the initiation and progression of liver tumors and uncover a novel pathway activated in RSPO2-induced malignancies. We show that RSPO2 promotes liver tumor formation in vivo and in vitro and that RSPO2's oncogenic activity requires Hippo/Yap activation in hepatocytes. Both RSPO2 and YAP1 are suggested to represent novel druggable targets in Wnt-driven tumors of the liver.

GPR56 Drives Colorectal Tumor Growth and Promotes Drug Resistance through Upregulation of MDR1 Expression via a RhoA-Mediated Mechanism

Drug resistance continues to be a major obstacle of effective therapy for colorectal cancer, leading to tumor relapse or treatment failure. Cancer stem cells (CSC) or tumor-initiating cells are a subpopulation of tumor cells which retain the capacity for self-renewal and are suggested to be implicated in drug resistance. LGR5 is highly expressed in colorectal cancer and marks CSCs that drive tumor growth and metastasis. LGR5(⁺) CSCs cells were shown to interconvert with more drug-resistant LGR5(^-) cancer cells, and treatment with LGR5-targeted antibody-drug conjugates (ADC) eliminated LGR5(⁺) tumors, yet a fraction of LGR5(^-) tumors eventually recurred. Therefore, it is important to identify mechanisms associated with CSC plasticity and drug resistance in order to develop curative therapies. Here, we show that loss of LGR5 in colon cancer cells enhanced resistance to irinotecan and 5-fluorouracil and increased expression of adhesion G-protein-coupled receptor, GPR56. GPR56 expression was significantly higher in primary colon tumors versus matched normal tissues and correlated with poor survival outcome. GPR56 enhanced drug resistance through upregulation of MDR1 levels via a RhoA-mediated signaling mechanism. Loss of GPR56 led to suppression of tumor growth and increased sensitivity of cancer cells to chemotherapy and monomethyl auristatin E-linked anti-LGR5 ADCs, by reducing MDR1 levels. These findings suggest that upregulation of GPR56 may be a mechanism associated with CSC plasticity by which LGR5(^-) cancer cells acquire a more drug-resistant phenotype. IMPLICATIONS: Our findings suggest that targeting GPR56 may provide a new strategy for the treatment of colorectal cancer and combatting drug resistance.

Lgr5 in cancer biology: functional identification of Lgr5 in cancer progression and potential opportunities for novel therapy

Cancer remains one of the leading lethal diseases worldwide. Identifying biomarkers of cancers might provide insights into the strategies for the development of novel targeted anti-cancer therapies. Leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) has been recently discovered as a candidate marker of cancer stem cell populations. Aberrant increased expression of Lgr5 may represent one of the most common molecular alterations in some human cancers, leading to long-term potentiation of canonical Wnt/β-catenin signaling. On the other hand, however, Lgr5-mediated suppression in canonical Wnt/β-catenin signaling has also been reported in certain cancers, such as B cell malignancies. Until now, therapeutic approaches targeting Lgr5-associated signaling axis are not yet clinically available. Increasing evidence have indicated that endogenous Lgr5+ cell population is implicated in tumor initiation, progression, and metastasis. This review is to summarize our current knowledge about the importance of Lgr5 in cancer biology and the underlying molecular mechanisms of Lgr5-mediated tumor-promoting/suppressive activities, as well as potentially useful preventive strategies in treating tumor. Therefore, targeted therapeutic modulation of Lgr5+ cancer cell population by targeting Wnt/β-catenin signaling through targeted drug delivery system or targeted genome editing might be promising for potential novel anti-cancer treatments. Simultaneously, combination of therapeutics targeting both Lgr5+ and Lgr5- cancer cells may deserve further consideration considering the plasticity of cancer cells. Also, a more specific targeting of cancer cells using double biomarkers may be much safer and more effective for anti-cancer therapy.