Down-regulation of G protein-coupled receptor 137 by RNA interference inhibits cell growth of two hepatoma cell lines

GPR137 inactivates Hippo signaling to promote gastric cancer cell malignancy

As the fifth most common cancer in the world, gastric cancer (GC) ranks as the third major cause of cancer-related death globally. Although surgical resection and chemotherapy still remains the mainstay of potentially curative treatment for GC, chemotherapy resistance and adverse side effects limit their clinical applications. Thus, further investigation of the mechanisms of carcinogenesis in GC and discovery of novel biomarkers is of great concern. We herein report that the elevated expression of GPR137 is correlated with GC. Overexpression of GPR137 potentiates human gastric cancer AGS cell malignancy, including proliferation, migration, invasion, colony formation and xenograft growth in nude mice in vivo, whereas knockout of GPR137 by CRISPR/Cas9 gene editing exerts the opposite effects. Mechanistically, GPR137 could bind to MST, the upstream kinases in Hippo pathway, which disrupts the association of MST with LATS, subsequently activating the transcriptional co-activators, YAP and TAZ, and thereby triggering the target transcription and the alterations in GC cell biological actions consequently. Therefore, our findings may provide with the evidence of developing a potentially novel treatment method with specific target for GC.

High expression of GPR50 promotes the proliferation, migration and autophagy of hepatocellular carcinoma cells in vitro

G protein-coupled receptors (GPCRs) play important roles in tumorigenesis and the development of hepatocellular carcinoma (HCC). GPR50 is an orphan GPCR. Previous studies have indicated that GPR50 could protect against breast cancer development and decrease tumor growth in a xenograft mouse model. However, its role in HCC remains indistinct. To detect the role and the regulation mechanism of GPR50 in HCC, GPR50 expression was analyzed in HCC patients (gene expression omnibus database (GEO) (GSE45436)) and detected in HCC cell line CBRH-7919, and the results showed that GPR50 was significantly up-regulated in HCC patients and CBRH-7919 cell line compared to the corresponding normal control. Gpr50 cDNA was transfected into HCC cell line CBRH-7919, and we found that Gpr50 promoted the proliferation, migration, and autophagy of CBRH-7919. The regulation mechanism of GPR50 in HCC was detected by isobaric tags for relative and absolute quantification (iTRAQ) analysis, and we found that GPR50 promoted HCC was closely related to CCT6A and PGK1. Taken together, GPR50 may promote HCC progression via CCT6A-induced proliferation and PGK1-induced migration and autophagy, and GPR50 could be an important target for HCC.

GPR137 Inhibits Cell Proliferation and Promotes Neuronal Differentiation in the Neuro2a Cells

The orphan receptor, G protein-coupled receptor 137 (GPR137), is an integral membrane protein involved in several types of cancer. GPR137 is expressed ubiquitously, including in the central nervous system (CNS). We established a GPR137 knockout (KO) neuro2A cell line to analyze GPR137 function in neuronal cells. KO cells were generated by genome editing using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and cultured as single cells by limited dilution. Rescue cells were then constructed to re-express GPR137 in GPR137 KO neuro2A cells using an expression vector with an EF1-alpha promoter. GPR137 KO cells increased cellular proliferation and decreased neurite outgrowth (i.e., a lower level of neuronal differentiation). Furthermore, GPR137 KO cells exhibited increased expression of a cell cycle regulator, cyclin D1, and decreased expression of a neuronal differentiation marker, NeuroD1. Additionally, GPR137 KO cells exhibited lower expression levels of the neurite outgrowth markers STAT3 and GAP43. These phenotypes were all abrogated in the rescue cells. In conclusion, GPR137 deletion increased cellular proliferation and decreased neuronal differentiation, suggesting that GPR137 promotes cell cycle exit and neuronal differentiation in neuro2A cells. Regulation of neuronal differentiation by GPR137 could be vital to constructing neuronal structure during brain development.

Examining the gut-liver axis in liver cancer using organoid models

The World Health Organization predicts that by 2030 liver cancer will cause 1 million deaths annually, thus becoming the third most lethal cancer worldwide. Hepatocellular carcinoma and cholangiocarcinoma are the two major primary cancer subtypes involving the liver. Both are often diagnosed late, and hence response to treatment and survival are poor. It is therefore of utmost importance to understand the mechanisms by which liver cancers initiate and progress. The causes of primary liver cancer are diverse, resulting primarily from obesity, chronic alcohol abuse or viral hepatitis. Importantly, both alcohol and high fat diet can promote intestinal permeability, enabling microbial translocation from the gut into the liver. As a result, these microbial antigens and metabolites exacerbate hepatic inflammation and fibrosis, increasing the risk of primary liver cancer. Organoids are primary, three-dimensional, stem cell derived liver models that can recapitulate many of the disease phenotypes observed in vivo. This review aims to summarize the advantages of organoid culture to examine the gut-liver axis with respect to cancer initiation and progression. In particular, the use of gut and liver organoid mono- and co-cultures together and with immune cell populations to best recapitulate disease mechanisms and develop therapeutic interventions.

G protein-coupled receptors as potential targets for nonalcoholic fatty liver disease treatment

Nonalcoholic fatty liver disease (NAFLD) is a broad-spectrum disease, ranging from simple hepatic steatosis to nonalcoholic steatohepatitis, which can progress to cirrhosis and liver cancer. Abnormal hepatic lipid accumulation is the major manifestation of this disease, and lipotoxicity promotes NAFLD progression. In addition, intermediate metabolites such as succinate can stimulate the activation of hepatic stellate cells to produce extracellular matrix proteins, resulting in progression of NAFLD to fibrosis and even cirrhosis. G protein-coupled receptors (GPCRs) have been shown to play essential roles in metabolic disorders, such as NAFLD and obesity, through their function as receptors for bile acids and free fatty acids. In addition, GPCRs link gut microbiota-mediated connections in a variety of diseases, such as intestinal diseases, hepatic steatosis, diabetes, and cardiovascular diseases. The latest findings show that gut microbiota-derived acetate contributes to liver lipogenesis by converting dietary fructose into hepatic acetyl-CoA and fatty acids. GPCR agonists, including peptides and natural products like docosahexaenoic acid, have been applied to investigate their role in liver diseases. Therapies such as probiotics and GPCR agonists may be applied to modulate GPCR function to ameliorate liver metabolism syndrome. This review summarizes the current findings regarding the role of GPCRs in the development and progression of NAFLD and describes some preclinical and clinical studies of GPCR-mediated treatment. Overall, understanding GPCR-mediated signaling in liver disease may provide new therapeutic options for NAFLD.

Emerging Roles of G Protein-Coupled Receptors in Hepatocellular Carcinoma

Among a great variety of cell surface receptors, the largest superfamily is G protein-coupled receptors (GPCRs), also known as seven-transmembrane domain receptors. GPCRs can modulate diverse signal-transduction pathways through G protein-dependent or independent pathways which involve β-arrestins, G protein receptor kinases (GRKs), ion channels, or Src kinases under physiological and pathological conditions. Recent studies have revealed the crucial role of GPCRs in the tumorigenesis and the development of cancer metastasis. We will sum up the functions of GPCRs—particularly those coupled to chemokines, prostaglandin, lysophosphatidic acid, endothelin, catecholamine, and angiotensin—in the proliferation, invasion, metastasis, and angiogenesis of hepatoma cells and the development of hepatocellular carcinoma (HCC) in this review. We also highlight the potential avenues of GPCR-based therapeutics for HCC.