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

Targeting the Hippo/YAP1 signaling pathway in hepatocellular carcinoma: From mechanisms to therapeutic drugs (Review)

The Hippo signaling pathway plays a pivotal role in regulating cell growth and organ size. Its regulatory effects on hepatocellular carcinoma (HCC) encompass diverse aspects, including cell proliferation, invasion and metastasis, tumor drug resistance, metabolic reprogramming, immunomodulatory effects and autophagy. Yes‑associated protein 1 (YAP1), a potent transcriptional coactivator and a major downstream target tightly controlled by the Hippo pathway, is influenced by various molecules and pathways. The expression of YAP1 in different cell types within the liver tumor microenvironment exerts varying effects on tumor outcomes, warranting careful consideration. Therefore, research on YAP1‑targeted therapies merits attention. This review discusses the composition and regulation mechanism of the Hippo/YAP1 signaling pathway and its relationship with HCC, offering insights for future research and cancer prevention strategies.

Wnt/β-Catenin signaling pathway in hepatocellular carcinoma: pathogenic role and therapeutic target

Hepatocellular carcinoma (HCC) is the most common primary malignant liver tumor and one of the leading causes of cancer-related deaths worldwide. The Wnt/β-Catenin signaling pathway is a highly conserved pathway involved in several biological processes, including the improper regulation that leads to the tumorigenesis and progression of cancer. New studies have found that abnormal activation of the Wnt/β-Catenin signaling pathway is a major cause of HCC tumorigenesis, progression, and resistance to therapy. New perspectives and approaches to treating HCC will arise from understanding this pathway. This article offers a thorough analysis of the Wnt/β-Catenin signaling pathway's function and its therapeutic implications in HCC.

Rspo2-LGR4 exacerbates hepatocellular carcinoma progression via activation of Wnt/β-catenin signaling pathway

BACKGROUND

The leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4) plays an important role in stem cell differentiation, organ development and cancer. Whether LGR4 affects the progression of hepatocellular carcinoma (HCC) remains unknown. This study aimed to reveal the role of LGR4 in HCC.

METHODS

Clinical samples of HCC were collected to assess the expression of LGR4 and its correlation with patients' clinical characteristics. The expression level of LGR4 in HCC cells was altered by pharmacological and genetic methods, and the role of LGR4 in HCC progression was analyzed by in vivo and in vitro assays. HCC was induced by diethylnitrosamine (DEN) and carbon tetrachloride (CCl4) in wild-type and LGR4 deficient mice, the effect of LGR4 on HCC was examined by histopathological evaluation and biochemical assays.

RESULTS

LGR4 expression was up-regulated in HCC samples, and its expression level was positively correlated with tumor size, microvascular invasion (MVI), TNM stage and pathological differentiation grade of HCC patients. In the mouse HCC model induced by DEN+CCl4, knockdown of LGR4 effectively inhibited the progression of HCC. Silencing of LGR4 inhibited the proliferation, migration, invasion, stem cell-like properties and Warburg effect of HCC cells. These phenotypes were promoted by R-spondin2 (Rspo2), an endogenous ligand for LGR4. Rspo2 markedly increased the nuclear translocation of β-catenin, whereas IWR-1, an inhibitor of Wnt/β-catenin signaling, reversed its effect. Deficiency of LGR4 significantly reduced the nuclear translocation of β-catenin and the expression of its downstream target genes cyclinD1 and c-Myc.

CONCLUSIONS

LGR4 promotes HCC progression via Wnt/β-catenin signaling pathway.

RSPO2 as Wnt signaling enabler: Important roles in cancer development and therapeutic opportunities

R-spondins are secretory proteins localized in the endoplasmic reticulum and Golgi bodies and are processed through the secretory pathway. Among the R-spondin family, RSPO2 has emanated as a novel regulator of Wnt signaling, which has now been acknowledged in numerous in vitro and in vivo studies. Cancer is an abnormal growth of cells that proliferates and spreads uncontrollably due to the accumulation of genetic and epigenetic factors that constitutively activate Wnt signaling in various types of cancer. Colorectal cancer (CRC) begins when cells in the colon and rectum follow an indefinite pattern of division due to aberrant Wnt activation as one of the key hallmarks. Decades-long progress in research on R-spondins has demonstrated their oncogenic function in distinct cancer types, particularly CRC. As a critical regulator of the Wnt pathway, it modulates several phenotypes of cells, such as cell proliferation, invasion, migration, and cancer stem cell properties. Recently, RSPO mutations, gene rearrangements, fusions, copy number alterations, and altered gene expression have also been identified in a variety of cancers, including CRC. In this review, we addressed the recent updates regarding the recurrently altered R-spondins with special emphasis on the RSPO2 gene and its involvement in potentiating Wnt signaling in CRC. In addition to the compelling physiological and biological roles in cellular fate and regulation, we propose that RSPO2 would be valuable as a potential biomarker for prognostic, diagnostic, and therapeutic use in CRC.

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.

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.

R-spondin family biology and emerging linkages to cancer

The R-spondin protein family comprises four members (RSPO1-4), which are agonists of the canonical Wnt/β-catenin pathway. Emerging evidence revealed that RSPOs should not only be viewed as agonists of the Wnt/β-catenin pathway but also as regulators for tumor development and progression. Aberrant expression of RSPOs is related to tumorigenesis and tumor development in multiple cancers and their expression of RSPOs has also been correlated with anticancer immune cell signatures. More importantly, the role of RSPOs as potential target therapies and their implication in cancer progressions has been studied in the preclinical and clinical settings. These findings highlight the possible therapeutic value of RSPOs in cancer medicine. However, the expression pattern, effects, and mechanisms of RSPO proteins in cancer remain elusive. Investigating the many roles of RSPOs is likely to expand and improve our understanding of the oncogenic mechanisms mediated by RSPOs. Here, we reviewed the recent advances in the functions and underlying molecular mechanisms of RSPOs in tumor development, cancer microenvironment regulation, and immunity, and discussed the therapeutic potential of targeting RSPOs for cancer treatment. In addition, we also explored the biological feature and clinical relevance of RSPOs in cancer mutagenesis, transcriptional regulation, and immune correlation by bioinformatics analysis.KEY MESSAGESAberrant expressions of RSPOs are detected in various human malignancies and are always correlated with oncogenesis.Although extensive studies of RSPOs have been conducted, their precise molecular mechanism remains poorly understood.Bioinformatic analysis revealed that RSPOs may play a part in the development of the immune composition of the tumor microenvironment.

Targeting ligand-dependent wnt pathway dysregulation in gastrointestinal cancers through porcupine inhibition

Gastrointestinal cancers are responsible for more cancer deaths than any other system of the body. This review summarises how Wnt pathway dysregulation contributes to the development of the most common gastrointestinal cancers, with a particular focus on the nature and frequency of upstream pathway aberrations. Tumors with upstream aberrations maintain a dependency on the presence of functional Wnt ligand, and are predicted to be tractable to inhibitors of Porcupine, an enzyme that plays a key role in Wnt secretion. We summarise available pre-clinical efficacy data from Porcupine inhibitors in vitro and in vivo, as well as potential toxicities and the data from early phase clinical trials. We appraise the rationale for biomarker-defined targeted approaches, as well as outlining future opportunities for combination with other therapeutics.

The RSPO-LGR4/5-ZNRF3/RNF43 module in liver homeostasis, regeneration, and disease

WNT/β-catenin signaling plays pivotal roles during liver development, homeostasis, and regeneration. Likewise, its deregulation disturbs metabolic liver zonation and is responsible for the development of a large number of hepatic tumors. Liver fibrosis, which has become a major health burden for society and a hallmark of NASH, can also be promoted by WNT/β-catenin signaling. Upstream regulatory mechanisms controlling hepatic WNT/β-catenin activity may constitute targets for the development of novel therapies addressing these life-threatening conditions. The R-spondin (RSPO)-leucine-rich repeat-containing G protein-coupled receptor (LGR) 4/5-zinc and ring finger (ZNRF) 3/ring finger 43 (RNF43) module is fine-tuning WNT/β-catenin signaling in several tissues and is essential for hepatic WNT/β-catenin activity. In this review article, we recapitulate the role of the RSPO-LGR4/5-ZNRF3/RNF43 module during liver development, homeostasis, metabolic zonation, regeneration, and disease. We further discuss the controversy around LGR5 as a liver stem cell marker.

Advances in prognostic and therapeutic targets for hepatocellular carcinoma and intrahepatic cholangiocarcinoma: The hippo signaling pathway

Primary liver cancer is the sixth most frequently diagnosed cancer worldwide and the third leading cause of cancer-related death. The majority of the primary liver cancer cases are hepatocellular carcinoma and intrahepatic cholangiocarcinoma. Worldwide, there is an increasing incidence of primary liver cancer cases due to multiple risk factors ranging from parasites and viruses to metabolic diseases and lifestyles. Often, patients are diagnosed at advanced stages, depriving them of surgical curability benefits. Moreover, the efficacy of the available chemotherapeutics is limited in advanced stages. Furthermore, tumor metastases and recurrence make primary liver cancer management exceptionally challenging. Thus, exploring the molecular mechanisms for the development and progression of primary liver cancer is critical in improving diagnostic, treatment, prognostication, and surveillance modalities. These mechanisms facilitate the discovery of specific targets that are critical for novel and more efficient treatments. Consequently, the Hippo signaling pathway executing a pivotal role in organogenesis, hemostasis, and regeneration of tissues, regulates liver cells proliferation, and apoptosis. Cell polarity or adhesion molecules and cellular metabolic status are some of the biological activators of the pathway. Thus, understanding the mechanisms exhibited by the Hippo pathway is critical to the development of novel targeted therapies. This study reviews the advances in identifying therapeutic targets and prognostic markers of the Hippo pathway for primary liver cancer in the past six years.

Interplay Between Fatty Acids, Stearoyl-Co-A Desaturase, Mechanistic Target of Rapamycin, and Yes-Associated Protein/Transcriptional Coactivator With PDZ-Binding Motif in Promoting Hepatocellular Carcinoma

Nonalcoholic fatty liver disease has reached pandemic proportions with one of its most consequential complications being hepatocellular carcinoma (HCC). Nonalcoholic fatty liver disease-related HCC is becoming the leading indication for liver transplantation in the United States. Given the scarcity of available organs, early detection and prevention remain key in prevention and management of the disease. Over the years, the yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) pathway emerged as a key signal transduction pathway in the pathogenesis of HCC. In this review, we explore the interplay between the YAP/TAZ pathway as a point of convergence in HCC pathogenesis. We review the evidence of how lipid reprogramming and key lipid pathways, saturated and monounsaturated fatty acids (through the rate-limiting enzyme stearoyl Co-A desaturase), the mevalonic acid pathway (the role of statins), and mechanistic target of rapamycin all play critical roles in intricate and complex networks that tightly regulate the YAP/TAZ pro-oncogenic pathway.

The role of YAP1 in liver cancer stem cells: proven and potential mechanisms

YAP1 (Yes-associated protein 1) is one of the principal factors that mediates oncogenesis by acting as a driver of gene expression. It has been confirmed to play an important role in organ volume control, stem cell function, tissue regeneration, tumorigenesis and tumor metastasis. Recent research findings show that YAP1 is correlated with the stemness of liver cancer stem cells, and liver cancer stem cells are closely associated with YAP1-induced tumor initiation and progression. This article reviews the advancements made in research on the mechanisms by which YAP1 promotes liver cancer stem cells and discusses some potential mechanisms that require further study.

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.

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.

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.

The Matrix Revolution: Matricellular Proteins and Restructuring of the Cancer Microenvironment

The extracellular matrix (ECM) surrounding cells is indispensable for regulating their behavior. The dynamics of ECM signaling are tightly controlled throughout growth and development. During tissue remodeling, matricellular proteins (MCP) are secreted into the ECM. These factors do not serve classical structural roles, but rather regulate matrix proteins and cell-matrix interactions to influence normal cellular functions. In the tumor microenvironment, it is becoming increasingly clear that aberrantly expressed MCPs can support multiple hallmarks of carcinogenesis by interacting with various cellular components that are coupled to an array of downstream signals. Moreover, MCPs also reorganize the biomechanical properties of the ECM to accommodate metastasis and tumor colonization. This realization is stimulating new research on MCPs as reliable and accessible biomarkers in cancer, as well as effective and selective therapeutic targets.