Increased proton-sensing receptor GPR4 signalling promotes colorectal cancer progression by activating the hippo pathway

The Roles of Proton-Sensing G-Protein-Coupled Receptors in Inflammation and Cancer

The precise regulation of pH homeostasis is crucial for normal physiology. However, in tissue microenvironments, it can be impacted by pathological conditions such as inflammation and cancer. Due to the overproduction and accumulation of acids (protons), the extracellular pH is characteristically more acidic in inflamed tissues and tumors in comparison to normal tissues. A family of proton-sensing G-protein-coupled receptors (GPCRs) has been identified as molecular sensors for cells responding to acidic tissue microenvironments. Herein, we review the current research progress pertaining to these proton-sensing GPCRs, including GPR4, GPR65 (TDAG8), and GPR68 (OGR1), in inflammation and cancer. Growing evidence suggests that GPR4 and GPR68 are mainly pro-inflammatory, whereas GPR65 is primarily anti-inflammatory, in various inflammatory disorders. Both anti- and pro-tumorigenic effects have been reported for this family of receptors. Moreover, antagonists and agonists targeting proton-sensing GPCRs have been developed and evaluated in preclinical models. Further research is warranted to better understand the roles of these proton-sensing GPCRs in pathophysiology and is required in order to exploit them as potential therapeutic targets for disease treatment.

Acid-sensing receptor GPR4 plays a crucial role in lymphatic cancer metastasis

Cancer tissues exhibit an acidic microenvironment owing to the accumulation of protons and lactic acid produced by cancer and inflammatory cells. To examine the role of an acidic microenvironment in lymphatic cancer metastasis, gene expression profiling was conducted using human dermal lymphatic endothelial cells (HDLECs) treated with a low pH medium. Microarray and gene set enrichment analysis revealed that acid treatment induced the expression of inflammation-related genes in HDLECs, including genes encoding chemokines and adhesion molecules. Acid treatment-induced chemokines C-X3-C motif chemokine ligand 1 (CX3CL1) and C-X-C motif chemokine ligand 6 (CXCL6) autocrinally promoted the growth and tube formation of HDLECs. The expression of vascular cell adhesion molecule 1 (VCAM-1) increased in HDLECs after acid treatment in a time-dependent manner, which, in turn, enhanced their adhesion to melanoma cells. Among various acid-sensing receptors, HDLECs basally expressed G protein-coupled receptor 4 (GPR4), which was augmented under the acidic microenvironment. The induction of chemokines or VCAM-1 under acidic conditions was attenuated by GPR4 knockdown in HDLECs. In addition, lymph node metastases in a mouse melanoma model were suppressed by administering an anti-VCAM-1 antibody or a GPR4 antagonist. These results suggest that an acidic microenvironment modifies the function of lymphatic endothelial cells via GPR4, thereby promoting lymphatic cancer metastasis. Acid-sensing receptors and their downstream molecules might serve as preventive or therapeutic targets in cancer.

Role of pH-sensing receptors in colitis

Low pH in the gut is associated with severe inflammation, fibrosis, and colorectal cancer (CRC) and is a hallmark of active inflammatory bowel disease (IBD). Subsequently, pH-sensing mechanisms are of interest for the understanding of IBD pathophysiology. Tissue hypoxia and acidosis-two contributing factors to disease pathophysiology-are linked to IBD, and understanding their interplay is highly relevant for the development of new therapeutic options. One member of the proton-sensing G protein-coupled receptor (GPCR) family, GPR65 (T-cell death-associated gene 8, TDAG8), was identified as a susceptibility gene for IBD in a large genome-wide association study. In response to acidic extracellular pH, GPR65 induces an anti-inflammatory response, whereas the two other proton-sensing receptors, GPR4 and GPR68 (ovarian cancer G protein-coupled receptor 1, OGR1), mediate pro-inflammatory responses. Here, we review the current knowledge on the role of these proton-sensing receptors in IBD and IBD-associated fibrosis and cancer, as well as colitis-associated cancer (CAC). We also describe emerging small molecule modulators of these receptors as therapeutic opportunities for the treatment of IBD.

Expression of endogenous epitope-tagged GPR4 in the mouse brain

GPR4 is a proton-sensing G protein-coupled receptor implicated in many peripheral and central physiological processes. GPR4 expression has previously been assessed only via detection of the cognate transcript or indirectly, by use of fluorescent reporters. In this work, CRISPR/Cas9 knock-in technology was used to encode a hemagglutinin (HA) epitope tag within the endogenous locus of Gpr4 and visualize GPR4-HA in the mouse central nervous system using a specific, well characterized HA antibody; GPR4 expression was further verified by complementary Gpr4 mRNA detection. HA immunoreactivity was found in a limited set of brain regions, including in the retrotrapezoid nucleus (RTN), serotonergic raphe nuclei, medial habenula, lateral septum, and several thalamic nuclei. GPR4 expression was not restricted to cells of a specific neurochemical identity as it was observed in excitatory, inhibitory, and aminergic neuronal cell groups. HA immunoreactivity was not detected in brain vascular endothelium, despite clear expression of Gpr4 mRNA in endothelial cells. In the RTN, GPR4 expression was detected at the soma and in proximal dendrites along blood vessels and the ventral surface of the brainstem; HA immunoreactivity was not detected in RTN projections to two known target regions. This localization of GPR4 protein in mouse brain neurons corroborates putative sites of expression where its function has been previously implicated (e.g., CO2-regulated breathing by RTN), and provides a guide for where GPR4 could contribute to other CO2/H+ modulated brain functions. Finally, GPR4-HA animals provide a useful reagent for further study of GPR4 in other physiological processes outside of the brain.Significance Statement GPR4 is a proton-sensing G-protein coupled receptor whose expression is necessary for a number of diverse physiological processes including acid-base sensing in the kidney, immune function, and cancer progression. In the brain, GPR4 has been implicated in the hypercapnic ventilatory response mediated by brainstem neurons. While knockout studies in animals have clearly demonstrated its necessity for normal physiology, descriptions of GPR4 expression have been limited due to a lack of specific antibodies for use in mouse models. In this paper, we implemented a CRISPR/Cas9 knock-in approach to incorporate the coding sequence for a small epitope tag into the locus of GPR4. Using these mice, we were able to describe GPR4 protein expression directly for the first time.

cAMP-PKA/EPAC signaling and cancer: the interplay in tumor microenvironment

Cancer is a complex disease resulting from abnormal cell growth that is induced by a number of genetic and environmental factors. The tumor microenvironment (TME), which involves extracellular matrix, cancer-associated fibroblasts (CAF), tumor-infiltrating immune cells and angiogenesis, plays a critical role in tumor progression. Cyclic adenosine monophosphate (cAMP) is a second messenger that has pleiotropic effects on the TME. The downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), exchange protein activated by cAMP (EPAC) and ion channels. While cAMP can activate PKA or EPAC and promote cancer cell growth, it can also inhibit cell proliferation and survival in context- and cancer type-dependent manner. Tumor-associated stromal cells, such as CAF and immune cells, can release cytokines and growth factors that either stimulate or inhibit cAMP production within the TME. Recent studies have shown that targeting cAMP signaling in the TME has therapeutic benefits in cancer. Small-molecule agents that inhibit adenylate cyclase and PKA have been shown to inhibit tumor growth. In addition, cAMP-elevating agents, such as forskolin, can not only induce cancer cell death, but also directly inhibit cell proliferation in some cancer types. In this review, we summarize current understanding of cAMP signaling in cancer biology and immunology and discuss the basis for its context-dependent dual role in oncogenesis. Understanding the precise mechanisms by which cAMP and the TME interact in cancer will be critical for the development of effective therapies. Future studies aimed at investigating the cAMP-cancer axis and its regulation in the TME may provide new insights into the underlying mechanisms of tumorigenesis and lead to the development of novel therapeutic strategies.

GPR4 Knockout Attenuates Intestinal Inflammation and Forestalls the Development of Colitis-Associated Colorectal Cancer in Murine Models

GPR4 is a proton-sensing G protein-coupled receptor highly expressed in vascular endothelial cells and has been shown to potentiate intestinal inflammation in murine colitis models. Herein, we evaluated the proinflammatory role of GPR4 in the development of colitis-associated colorectal cancer (CAC) using the dextran sulfate sodium (DSS) and azoxymethane (AOM) mouse models in wild-type and GPR4 knockout mice. We found that GPR4 contributed to chronic intestinal inflammation and heightened DSS/AOM-induced intestinal tumor burden. Tumor blood vessel density was markedly reduced in mice deficient in GPR4, which correlated with increased tumor necrosis and reduced tumor cell proliferation. These data demonstrate that GPR4 ablation alleviates intestinal inflammation and reduces tumor angiogenesis, development, and progression in the AOM/DSS mouse model.

Protons taken hostage: Dynamic H-bond networks of the pH-sensing GPR68

Proton-sensing G Protein Coupled Receptors (GPCRs) sense changes in the extracellular pH to effect cell signaling for cellular homeostasis. They tend to be overexpressed in solid tumors associated with acidic extracellular pH, and are of direct interest as drug targets. How proton-sensing GPCRs sense extracellular acidification and activate upon protonation change is important to understand, because it may guide the design of therapeutics. Lack of publicly available experimental structures make it challenging to discriminate between conflicting mechanisms proposed for proton-binding, as main roles have been assigned to either an extracellular histidine cluster or to an internal carboxylic triad. Here we present a protocol to derive and evaluate structural models of the proton-sensing GPR68. This approach integrates state-of-the-art homology modeling with microsecond-timescale atomistic simulations, and with a detailed assessment of the compatibility of the structural models with known structural features of class A GPCRs. To decipher structural elements of potential interest for protonation-coupled conformational changes of GPR68, we used the best-compatible model as a starting point for independent atomistic simulations of GPR68 with different protonation states, and graph computations to characterize the response of GPR68 to changes in protonation. We found that GPR68 hosts an extended hydrogen-bond network that inter-connects the extracellular histidine cluster to the internal carboxylic triad, and which can even reach groups at the cytoplasmic G-protein binding site. Taken together, results suggest that GPR68 relies on dynamic, hydrogen-bond networks to inter-connect extracellular and internal proton-binding sites, and to elicit conformational changes at the cytoplasmic G-protein binding site.

Tumor lactic acid: a potential target for cancer therapy

Tumor development is influenced by circulating metabolites and most tumors are exposed to substantially elevated levels of lactic acid and low levels of nutrients, such as glucose and glutamine. Tumor-derived lactic acid, the major circulating carbon metabolite, regulates energy metabolism and cancer cell signaling pathways, while also acting as an energy source and signaling molecule. Recent studies have yielded new insights into the pro-tumorigenic action of lactic acid and its metabolism. These insights suggest an anti-tumor therapeutic strategy targeting the oncometabolite lactic acid, with the aim of improving the efficacy and clinical safety of tumor metabolism inhibitors. This review describes the current understanding of the multifunctional roles of tumor lactic acid, as well as therapeutic approaches targeting lactic acid metabolism, including lactate dehydrogenase and monocarboxylate transporters, for anti-cancer therapy.

circ_0014736 induces GPR4 to regulate the biological behaviors of human placental trophoblast cells through miR-942-5p in preeclampsia

Previous studies have indicated that the development of preeclampsia (PE) involves the regulation of circular RNA (circRNA). However, the role of hsa_circ_0014736 (circ_0014736) in PE remains unknown. Thus, the study proposes to reveal the function of circ_0014736 in the pathogenesis of PE and the underlying mechanism. The results showed that circ_0014736 and GPR4 expression were significantly upregulated, while miR-942-5p expression was downregulated in PE placenta tissues when compared with normal placenta tissues. circ_0014736 knockdown promoted the proliferation, migration, and invasion of placenta trophoblast cells (HTR-8/SVneo) and inhibited apoptosis; however, circ_0014736 overexpression had the opposite effects. circ_0014736 functioned as a sponge for miR-942-5p and regulated HTR-8/SVneo cell processes by interacting with miR-942-5p. Additionally, GPR4, a target gene of miR-942-5p, was involved in miR-942-5p-mediated actions in HTR-8/SVneo cells. Moreover, circ_0014736 stimulated GPR4 production through miR-942-5p. Collectively, circ_0014736 inhibited HTR-8/SVneo cell proliferation, migration, and invasion and induced cell apoptosis through the miR-942-5p/GPR4 axis, providing a possible target for the treatment of PE.

GPR4 in the pH-dependent migration of melanoma cells in the tumor microenvironment

Due to its high metastatic potential, malignant melanoma is one of the deadliest skin cancers. In melanoma as well as in other cancers, acidification of the tumor microenvironment (=TME, inverse pH-gradient) is a well-known driver of tumor progression and metastasis. Membrane-bound receptors, such as the proton-sensitive GPCR (pH-GPCR) GPR4, are considered as potential initiators of the signalling cascades relevant to malignant transformation. In this study, we investigated the pH-dependent migration of GPR4 wildtype/overexpressing SK-Mel-28 cells using an impedance-based electrical wounding and migration assay and classical Boyden chamber experiments. Migration of GPR4 overexpressing SK-Mel-28 cells was enhanced in a range of pH 6.5-7.5 as compared to controls in the impedance-based electrical wounding and migration assay. In Boyden chamber experiments, GPR4 overexpression only increased migration at pH 7.5 in a Matrigel-free setup, but not at pH 6.5. Results indicate that GPR4 is involved in the migration of melanoma cells, especially in the tumor periphery, and that this process is affected by pH in the TME.

Role of proton-activated G protein-coupled receptors in pathophysiology

Local acidification is a common feature of many disease processes such as inflammation, infarction, or solid tumor growth. Acidic pH is not merely a sequelae of disease but contributes to recruitment and regulation of immune cells, modifies metabolism of parenchymal, immune and tumor cells, modulates fibrosis, vascular permeability, oxygen availability and consumption, invasiveness of tumor cells, and impacts on cell survival. Thus, multiple pH-sensing mechanisms must exist in cells involved in these processes. These pH-sensors play important roles in normal physiology and pathophysiology, and hence might be attractive targets for pharmacological interventions. Among the pH-sensing mechanisms, OGR1 (GPR68), GPR4 (GPR4), and TDAG8 (GPR65) have emerged as important molecules. These G protein-coupled receptors are widely expressed, are upregulated in inflammation and tumors, sense changes in extracellular pH in the range between pH 8 and 6, and are involved in modulating key processes in inflammation, tumor biology, and fibrosis. This review discusses key features of these receptors and highlights important disease states and pathways affected by their activity.

Physiological relevance of proton-activated GPCRs

The detection of H+ concentration variations in the extracellular milieu is accomplished by a series of specialized and non-specialized pH-sensing mechanisms. The proton-activated G protein-coupled receptors (GPCRs) GPR4 (Gpr4), TDAG8 (Gpr65), and OGR1 (Gpr68) form a subfamily of proteins capable of triggering intracellular signaling in response to alterations in extracellular pH around physiological values, i.e., in the range between pH 7.5 and 6.5. Expression of these receptors is widespread for GPR4 and OGR1 with particularly high levels in endothelial cells and vascular smooth muscle cells, respectively, while expression of TDAG8 appears to be more restricted to the immune compartment. These receptors have been linked to several well-studied pH-dependent physiological activities including central control of respiration, renal adaption to changes in acid-base status, secretion of insulin and peripheral responsiveness to insulin, mechanosensation, and cellular chemotaxis. Their role in pathological processes such as the genesis and progression of several inflammatory diseases (asthma, inflammatory bowel disease), and tumor cell metabolism and invasiveness, is increasingly receiving more attention and makes these receptors novel and interesting targets for therapy. In this review, we cover the role of these receptors in physiological processes and will briefly discuss some implications for disease processes.

Alterations in the Ca2+ toolkit in oesophageal adenocarcinoma

Aim:

To investigate alterations in transcription of genes, encoding Ca²⁺ toolkit proteins, in oesophageal adenocarcinoma (OAC) and to assess associations between gene expression, tumor grade, nodal-metastatic stage, and patient survival.

Methods:

The expression of 275 transcripts, encoding components of the Ca²⁺ toolkit, was analyzed in two OAC datasets: the Cancer Genome Atlas [via the University of Alabama Cancer (UALCAN) portal] and the oesophageal-cancer, clinical, and molecular stratification [Oesophageal Cancer Clinical and Molecular Stratification (OCCAMS)] dataset. Effects of differential expression of these genes on patient survival were determined using Kaplan-Meier log-rank tests. OAC grade- and metastatic-stage status was investigated for a subset of genes. Adjustment for the multiplicity of testing was made throughout.

Results:

Of the 275 Ca²⁺-toolkit genes analyzed, 75 displayed consistent changes in expression between OAC and normal tissue in both datasets. The channel-encoding genes, N-methyl-D-aspartate receptor 2D (GRIN2D), transient receptor potential (TRP) ion channel classical or canonical 4 (TRPC4), and TRP ion channel melastatin 2 (TRPM2) demonstrated the greatest increase in expression in OAC in both datasets. Nine genes were consistently upregulated in both datasets and were also associated with improved survival outcomes. The 6 top-ranking genes for the weighted significance of altered expression and survival outcomes were selected for further analysis: voltage-gated Ca²⁺ channel subunit α 1D (CACNA1D), voltage-gated Ca²⁺ channel auxiliary subunit α2 δ4 (CACNA2D4), junctophilin 1 (JPH1), acid-sensing ion channel 4 (ACCN4), TRPM5, and secretory pathway Ca²⁺ ATPase 2 (ATP2C2). CACNA1D, JPH1, and ATP2C2 were also upregulated in advanced OAC tumor grades and nodal-metastatic stages in both datasets.

Conclusions:

This study has unveiled alterations of the Ca²⁺ toolkit in OAC, compared to normal tissue. Such Ca²⁺ signalling findings are consistent with those from studies on other cancers. Genes that were consistently upregulated in both datasets might represent useful markers for patient diagnosis. Genes that were consistently upregulated, and which were associated with improved survival, might be useful markers for patient outcome. These survival-associated genes may also represent targets for the development of novel chemotherapeutic agents.

Proton-Sensing GPCRs in Health and Disease

The group of proton-sensing G-protein coupled receptors (GPCRs) consists of the four receptors GPR4, TDAG8 (GPR65), OGR1 (GPR68), and G2A (GPR132). These receptors are cellular sensors of acidification, a property that has been attributed to the presence of crucial histidine residues. However, the pH detection varies considerably among the group of proton-sensing GPCRs and ranges from pH of 5.5 to 7.8. While the proton-sensing GPCRs were initially considered to detect acidic cellular environments in the context of inflammation, recent observations have expanded our knowledge about their physiological and pathophysiological functions and many additional individual and unique features have been discovered that suggest a more differentiated role of these receptors in health and disease. It is known that all four receptors contribute to different aspects of tumor biology, cardiovascular physiology, and asthma. However, apart from their overlapping functions, they seem to have individual properties, and recent publications identify potential roles of individual GPCRs in mechanosensation, intestinal inflammation, oncoimmunological interactions, hematopoiesis, as well as inflammatory and neuropathic pain. Here, we put together the knowledge about the biological functions and structural features of the four proton-sensing GPCRs and discuss the biological role of each of the four receptors individually. We explore all currently known pharmacological modulators of the four receptors and highlight potential use. Finally, we point out knowledge gaps in the biological and pharmacological context of proton-sensing GPCRs that should be addressed by future studies.

Ion Channels, Transporters, and Sensors Interact with the Acidic Tumor Microenvironment to Modify Cancer Progression

Solid tumors, including breast carcinomas, are heterogeneous but typically characterized by elevated cellular turnover and metabolism, diffusion limitations based on the complex tumor architecture, and abnormal intra- and extracellular ion compositions particularly as regards acid-base equivalents. Carcinogenesis-related alterations in expression and function of ion channels and transporters, cellular energy levels, and organellar H⁺ sequestration further modify the acid-base composition within tumors and influence cancer cell functions, including cell proliferation, migration, and survival. Cancer cells defend their cytosolic pH and HCO₃^- concentrations better than normal cells when challenged with the marked deviations in extracellular H⁺, HCO₃^-, and lactate concentrations typical of the tumor microenvironment. Ionic gradients determine the driving forces for ion transporters and channels and influence the membrane potential. Cancer and stromal cells also sense abnormal ion concentrations via intra- and extracellular receptors that modify cancer progression and prognosis. With emphasis on breast cancer, the current review first addresses the altered ion composition and the changes in expression and functional activity of ion channels and transporters in solid cancer tissue. It then discusses how ion channels, transporters, and cellular sensors under influence of the acidic tumor microenvironment shape cancer development and progression and affect the potential of cancer therapies.

GPR4 signaling is essential for the promotion of acid-mediated angiogenic capacity of endothelial progenitor cells by activating STAT3/VEGFA pathway in patients with coronary artery disease

BACKGROUND

Patients with coronary artery disease (CAD) are characterized by a decline in vascular regeneration, which is related to the dysfunction of endothelial progenitor cells (EPCs). G-protein-coupled receptor 4 (GPR4) is a proton-sensing G-protein-coupled receptor (GPCR) that contributes to neovascularization in acidic microenvironments. However, the role of GPR4 in regulating the angiogenic capacity of EPCs from CAD patients in response to acidity generated in ischemic tissue remains completely unclear.

METHODS

The angiogenic capacity of EPCs collected from CAD patients and healthy subjects was evaluated in different pH environments. The GPR4 function of regulating EPC-mediated angiogenesis was analyzed both in vitro and in vivo. The downstream mechanisms were further investigated by genetic overexpression and inhibition.

RESULTS

Acidic environment prestimulation significantly enhanced the angiogenic capacity of EPCs from the non-CAD group both in vivo and in vitro, while the same treatment yielded the opposite result in the CAD group. Among the four canonical proton-sensing GPCRs, GPR4 displays the highest expression in EPCs. The expression of GRP4 was markedly lower in EPCs from CAD patients than in EPCs from non-CAD individuals independent of acid stimulation. The siRNA-mediated knockdown of GPR4 with subsequent decreased phosphorylation of STAT3 mimicked the impaired function of EPCs from CAD patients at pH 6.4 but not at pH 7.4. Elevating GPR4 expression restored the neovessel formation mediated by EPCs from CAD patients in an acidic environment by activating STAT3/VEGFA signaling. Moreover, the beneficial impact of GPR4 upregulation on EPC-mediated angiogenic capacity was abrogated by blockade of the STAT3/VEGFA signaling pathway.

CONCLUSIONS

Our present study demonstrated for the first time that loss of GPR4 is responsible for the decline in proton sensing and angiogenic capacity of EPCs from CAD patients. Augmentation of GPR4 expression promotes the neovessel formation of EPCs by activating STAT3/VEGF signaling. This finding implicates GPR4 as a potential therapeutic target for CAD characterized by impaired neovascularization in ischemic tissues.

Targeting the Hippo Pathway in Prostate Cancer: What's New?

Simple Summary

Prostate cancer is the most commonly diagnosed cancer in men in the UK, accounting for the deaths of over 11,000 men per year. A major problem in this disease are tumours which no longer respond to available treatments. Understanding how this occurs will reveal new ways to treat these patients. In this review, the latest findings regarding a particular group of cellular factors which make up a signalling network called the Hippo pathway will be described. Accumulating evidence suggests that this network contributes to prostate cancer progression and resistance to current treatments. Identifying how this pathway can be targeted with drugs is a promising area of research to improve the treatment of prostate cancer.

Abstract

Identifying novel therapeutic targets for the treatment of prostate cancer (PC) remains a key area of research. With the emergence of resistance to androgen receptor (AR)-targeting therapies, other signalling pathways which crosstalk with AR signalling are important. Over recent years, evidence has accumulated for targeting the Hippo signalling pathway. Discovered in Drosophila melanogasta, the Hippo pathway plays a role in the regulation of organ size, proliferation, migration and invasion. In response to a variety of stimuli, including cell–cell contact, nutrients and stress, a kinase cascade is activated, which includes STK4/3 and LATS1/2 to inhibit the effector proteins YAP and its paralogue TAZ. Transcription by their partner transcription factors is inhibited by modulation of YAP/TAZ cellular localisation and protein turnover. Trnascriptional enhanced associate domain (TEAD) transcription factors are their classical transcriptional partner but other transcription factors, including the AR, have been shown to be modulated by YAP/TAZ. In PC, this pathway can be dysregulated by a number of mechanisms, making it attractive for therapeutic intervention. This review looks at each component of the pathway with a focus on findings from the last year and discusses what knowledge can be applied to the field of PC.

Rho GTPases as Key Molecular Players within Intestinal Mucosa and GI Diseases

Rho proteins operate as key regulators of the cytoskeleton, cell morphology and trafficking. Acting as molecular switches, the function of Rho GTPases is determined by guanosine triphosphate (GTP)/guanosine diphosphate (GDP) exchange and their lipidation via prenylation, allowing their binding to cellular membranes and the interaction with downstream effector proteins in close proximity to the membrane. A plethora of in vitro studies demonstrate the indispensable function of Rho proteins for cytoskeleton dynamics within different cell types. However, only in the last decades we have got access to genetically modified mouse models to decipher the intricate regulation between members of the Rho family within specific cell types in the complex in vivo situation. Translationally, alterations of the expression and/or function of Rho GTPases have been associated with several pathological conditions, such as inflammation and cancer. In the context of the GI tract, the continuous crosstalk between the host and the intestinal microbiota requires a tight regulation of the complex interaction between cellular components within the intestinal tissue. Recent studies demonstrate that Rho GTPases play important roles for the maintenance of tissue homeostasis in the gut. We will summarize the current knowledge on Rho protein function within individual cell types in the intestinal mucosa in vivo, with special focus on intestinal epithelial cells and T cells.

Data mining combined with experiments to validate CEP55 as a prognostic biomarker in colorectal cancer

INTRODUCTION

Colorectal cancer (CRC) is a common tumor with high morbidity and mortality. Current specific diagnosis regarding CRC remains complicated and costly, and specific diagnostic biomarkers are lacking.

METHODS

To find potential diagnostic and prognostic biomarkers for CRC, we screened and analyzed many CRC sequencing data by The Cancer Genome Atlas Program and Gene Expression Omnibus, and validated that CEP55 may be a potential diagnostic biomarker for CRC by molecular cytological experiments and immunohistochemistry, among others.

RESULTS

We found that CEP55 is upregulated in CRC tissues and tumor cells and can promote CRC proliferation and metastasis by activating the p53/p21 axis and that CEP55 mutations in tumor patients result in worse overall survival and disease-free survival time. Besides, we also found that genes, such as CDK1, CCNB1, NEK2, KIF14, CDCA5, and RFC3 were upregulated in tumors, and their mutations would affect the prognosis of CRC patients, but these results await for more experimental evidence.

CONCLUSION

Our study validates CEP55 as a potential diagnostic and prognostic biomarker for CRC, and we also provide multiple genes and potential molecular mechanisms that may serve as diagnostic and prognostic markers for CRC.

Metabolite Sensing GPCRs: Promising Therapeutic Targets for Cancer Treatment?

G-protein-coupled receptors constitute the most diverse and largest receptor family in the human genome, with approximately 800 different members identified. Given the well-known metabolic alterations in cancer development, we will focus specifically in the 19 G-protein-coupled receptors (GPCRs), which can be selectively activated by metabolites. These metabolite sensing GPCRs control crucial processes, such as cell proliferation, differentiation, migration, and survival after their activation. In the present review, we will describe the main functions of these metabolite sensing GPCRs and shed light on the benefits of their potential use as possible pharmacological targets for cancer treatment.

Identification of a 9-gene prognostic signature for breast cancer

Breast cancer (BRCA) is the most common cancer among women and is the second leading cause of cancer death in women. In this study, we developed a 9‐gene prognostic signature to predict the prognosis of patients with BRCA. GSE20685, GSE42568, GSE20711, and GSE88770 were used as training sets. The Kaplan–Meier plot was constructed to assess survival differences and log‐rank test was performed to evaluate the statistical significance. The overall survival (OS) of patients in the low‐risk group was significantly higher than that in the high‐risk group. ROC analysis indicated that this 9‐gene signature shows good diagnostic efficiency both in OS and disease‐free survival (DFS). The 9‐gene signature was further validated through GSE16446, GSE7390, and TCGA‐BRCA datasets. We also established a nomogram that integrates clinicopathological features and 9‐gene signature. The analysis of the calibration plot showed that the nomogram has good prognostic performance. More convincingly, real‐time reverse transcription‐polymerase chain reaction (RT‐PCR) results indicated that the protective prognostic factors in BRCA patients were downregulated, whereas the dangerous prognostic factors were upregulated. The innovation of this article is not only constructing a prognostic gene signature, but also combining with clinical information to further establish a nomogram to better predict the survival probability of patients. It is worth mentioning that this signature also does not depend on other clinical factors or variables.

pH sensing in skin tumors: Methods to study the involvement of GPCRs, acid-sensing ion channels and transient receptor potential vanilloid channels

Solid tumors exhibit an inversed pH gradient with increased intracellular pH (pH_i ) and decreased extracellular pH (pH_e ). This inside-out pH gradient is generated via sodium/hydrogen antiporter 1, vacuolar-type H + ATPases, monocarboxylate transporters, (bi)carbonate (co)transporters and carboanhydrases. Our knowledge on how pH_e -signals are sensed and what the respective receptors induce inside cells is scarce. Some pH-sensitive receptors (GPR4, GPR65/TDAG8, GPR68/OGR1, GPR132/G2A, possibly GPR31 and GPR151) and ion channels (acid-sensing ion channels ASICs, transient receptor potential vanilloid receptors TRPVs) transduce signals inside cells. As little is known on the expression and function of these pH sensors, we used immunostainings to study tissue samples from common and rare skin cancers. Our current and future work is directed towards investigating the impact of all the pH-sensing receptors in different skin tumors using cell culture techniques with selective knockdown/knockout (siRNA/CRISPR-Cas9). To study cell migration and proliferation, novel impedance-based wound healing assays have been developed and are used. The field of pH sensing in tumors and wounds holds great promise for the development of pH-targeting therapies, either against pH regulators or sensors to inhibit cell proliferation and migration.

Involvement of the G-Protein-Coupled Receptor 4 in the Increased Expression of RANK/RANKL/OPG System and Neurotrophins by Nucleus Pulposus Cells under the Degenerated Intervertebral Disc-Like Acidic Microenvironment

Intervertebral disc (IVD) degeneration is associated with local inflammation and increased expression of neurotrophins. Acidic microenvironment is believed to cause the progression of IVD degeneration. However, there is a paucity of information regarding the relationship between acidic microenvironment and the inflammation and expression of neurotrophins in IVD. G-protein-coupled receptor 4 (GPR4) is a pH-sensing receptor, which can activate the inflammation and increase the expression levels of nerve growth factor in acidic microenvironment. In this study, culture media with pH 7.2 (representing the normal IVD-like acidic condition) and pH 6.5 (degenerated IVD-like acidic condition) were prepared. The gene and protein expression levels of GPR4 in SD rat nucleus pulposus cells were determined under the acidic conditions. And cyclic AMP (cAMP), the second messenger of GPR4, was assayed. Furthermore, the expression levels of receptor activator of nuclear factor κ B (RANK), RANKL ligand (RANKL), osteoprotegerin (OPG), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) were also determined. To clarify the involvement of GPR4 in the upregulation of the expression of RANK/RANKL/OPG system and neurotrophins, gene knockdown and forced expression of GPR4 and inhibiting its downstream cAMP accumulation and Ca²⁺ mobilization were performed. The alternation of the expression levels of matrix metalloproteinase-3 (MMP-3), MMP-13, and aggrecanase-2 (ADAMTS-5) were evaluated by RT-PCR and western blot. The results showed that GPR4 was expressed in rat nucleus pulposus cells, and the expression was upregulated under the degenerated IVD-like acidic microenvironment. cAMP accumulation levels were increased under the degenerated IVD-like acidic culture conditions. The expression levels of RANK, RANKL, OPG, NGF, and BNDF were significantly upregulated under the degenerated IVD-like acidic microenvironment. GPR4 knockdown and reduction of cAMP by the inhibitor SQ22536 abolished the upregulation of the expression of RANK, RANKL, OPG, NGF, and BNDF under the degenerated IVD-like acidic microenvironment. On the opposite, acidosis-induced cAMP accumulation and upregulation of RANK, RANKL, OPG, NGF, and BNDF were further promoted by GPR4 overexpression. The expression levels of MMP-3, MMP-13, and ADAMTS-5 were upregulated under the degenerated IVD-like acidic condition, which can be promoted or attenuated by GPR4 overexpression or knockdown, respectively. We concluded that GPR4-mediated cAMP accumulation was involved in the increased expression of RANK/RANKL/OPG system and neurotrophins by nucleus pulposus cells under the degenerated IVD-like acidic microenvironment.

[Emerging roles of Hippo signaling pathway in gastrointestinal cancers and its molecular mechanisms]

Hippo signaling pathway is highly conservative in evolution. MST1/2, LATS1/2, and the effector protein YAP/TAZ are the core members of this signaling pathway in mammalian cells. There have been many studies on YAP/TAZ and its downstream, however, the upstream regulatory factors of the Hippo signaling pathway remain unclear, and become one of the hot research directions of this pathway at present. In addition, Hippo signaling pathway can cross-talk with other signaling pathways such as Wnt and Notch signaling pathways, and plays an important role in controlling organ size, maintaining tissue homeostasis, and promoting tissue repair and regeneration. Abnormal Hippo signaling pathway may lead to the occurrence of a variety of tumors, especially gastrointestinal cancers such as liver cancer, colorectal cancer and gastric cancer. The abnormal expression of its members in gastrointestinal cancers is related to cancer cell proliferation, apoptosis, invasion and migration. Hippo signaling pathway is vital for liver repair and regeneration. Its inactivation will lead to the occurrence of primary liver cancer. The mechanism of YAP in liver cancer mainly depends on TEAD-mediated gene transcription. Hippo signaling pathway is also important for maintaining intestinal homeostasis, and its imbalance can lead to the occurrence and recurrence of colorectal cancer. In primary and metastatic gastric cancer, the expression of YAP/TAZ is significantly up-regulated, but the specific molecular mechanism is unclear. This article summarizes the recent progress on Hippo signaling pathway and its upstream regulatory factors, its roles in the development of gastrointestinal cancers and related molecular mechanisms; and also discusses the future research directions of Hippo signaling pathway.

lncRNA and mRNA signature for prognosis prediction of glioblastoma

Aims: We aimed to find out potential novel biomarkers for prognosis of glioblastoma (GBM). Materials & methods: We downloaded mRNA and lncRNA expression profiles of 169 GBM and five normal samples from The Cancer Genome Atlas and 129 normal brain samples from genotype-tissue expression. We use R language to perform the following analyses: differential RNA expression analysis of GBM samples using 'edgeR' package, survival analysis taking count of single or multiple gene expression level using 'survival' package, univariate and multivariate Cox regression analysis using Cox function plugged in 'survival' package. Gene ontology and Kyoto encyclopedia of genes and genomes pathway analysis were performed using FunRich tool online. Results and conclusion: We obtained differentially DEmRNAs and DElncRNAs in GBM samples. Most prognostically relevant mRNAs and lncRNAs were filtered out. 'GPCR ligand binding' and 'Class A/1' are found to be of great significance. In short, our study provides novel biomarkers for prognosis of GBM.

Proton-sensing G protein-coupled receptors: detectors of tumor acidosis and candidate drug targets

Cells in tumor microenvironments (TMEs) use several mechanisms to sense their low pH (<7.0), including via proton-sensing G protein-coupled receptors (psGPCRs): GPR4, GPR65/TDAG8, GPR68/OGR1 and GPR132/G2A. Numerous cancers have increased expression of psGPCRs. The psGPCRs may contribute to features of the malignant phenotype via actions on specific cell-types in the TME and thereby promote tumor survival and growth. Here, we review data regarding psGPCR expression in tumors and cancer cells, impact of psGPCRs on survival in solid tumors and a bioinformatics approach to infer psGPCR expression in cell types in the TME. New tools are needed to help define contributions of psGPCRs in tumor biology and to identify potentially novel therapeutic agents for a variety of cancers.

SH3BGRL2 inhibits growth and metastasis in clear cell renal cell carcinoma via activating hippo/TEAD1-Twist1 pathway

Background

Clear cell renal cell carcinoma (ccRCC) is one of the most prevalent malignancies in the world, and tumor metastasis is still the main reason for disease progression. Accumulating evidence shows that SH3BGRL2 may play a key role in tumor progression and metastasis. However, the role of SH3BGRL2 in ccRCC has not been systematically investigated and remains elusive.

Methods

The clinical significance of SH3BGRL2 was evaluated by bioinformatic analysis and tissue microarray (TMA) samples. SH3BGRL2 expression was determined by RT-PCR, western blot and immunohistochemistry staining. Tumor suppressive effect of SH3BGRL2 was determined by both in vitro and in vivo studies. Western blot, chromatin immunoprecipitation assay and luciferase report assay were applied for mechanism dissection.

Findings

SH3BGRL2 was crucial for epithelial-mesenchymal transition (EMT) progression and metastasis in ccRCC. Clinically, SH3BGRL2 was identified as an independent prognostic factor for ccRCC patients. Gain- and loss-of-function results suggested that SH3BGRL2 played a critical role in cell proliferation, migration and invasion. Mechanistically, we found that SH3BGRL2 acted as a tumor suppressor through Hippo/TEAD1 signaling, then TEAD1 altered Twist1 expression at the transcriptional level via directly binding to its promoter region.

Interpretation

Our findings established that SH3BGRL2 performed as a tumor suppressor and modulator via Hippo/TEAD1-Twist1 signaling in ccRCC, and the alteration of SH3BGRL2 could serve as a functional response biomarker of tumor progression and metastasis in ccRCC.

Role of Sphingosylphosphorylcholine in Tumor and Tumor Microenvironment

Sphingosylphosphorylcholine (SPC) is a unique type of lysosphingolipid found in some diseases, and has been studied in cardiovascular, neurological, and inflammatory phenomena. In particular, SPC’s studies on cancer have been conducted mainly in terms of effects on cancer cells, and relatively little consideration has been given to aspects of tumor microenvironment. This review summarizes the effects of SPC on cancer and tumor microenvironment, and presents the results and prospects of modulators that regulate the various actions of SPC.