ß-arrestin2 regulating ß2-adrenergic receptor signaling in hepatic stellate cells contributes to hepatocellular carcinoma progression.

Background: ß-arrestin2 and ß2-adrenergic receptor (ß2-AR) have important roles in malignant tumors, the present study aims to investigate the role of activated ß2-AR in hepatic stellate cells (HSCs) during hepatocellular carcinoma (HCC) progression and the regulatory effect of ß-arrestin2. Methods: Immunofluorescence and Western blot were used to detect the expression of ß-arrestin2 and ß2-AR in HSCs of liver tissues from human HCC samples and diethylnitrosamine (DEN)-induced HCC model mice. We next used ß-arrestin2-/- mice to demonstrate the regulatory role of ß-arrestin2 in DEN mice. The subsets of T cells were quantified by flow cytometry. MTT and wound healing assay were applied to detect the proliferation and migration of cells. Co-immunoprecipitation assay was used to detect the link of ß-arrestin2 and ß2-AR in HSCs. Effect of ß-arrestin2 overexpression on ß2-AR downstream signaling pathway was verified by Western blot. The secretion of CCL2 was detected by ELISA. Results: The expression of ß2-AR was significantly increased, while ß-arrestin2 was decreased in HSCs of HCC tissues. And ß-arrestin2 deficiency exacerbates DEN-induced HCC accompanied with increased ß2-AR expression. The results of flow cytometry showed that the percentage of activated T cells decreased gradually after DEN injection. ß-arrestin2 knockout down-regulated the ratio of activated T cells. In vitro, selective activation of ß2-AR in HSCs promoted the proliferation and migration of HCC cells. ß-arrestin2 overexpression enhanced co-immunoprecipitation of ß-arrestin2 and ß2-AR in activated HSCs, and decreased its downstream Akt phosphorylation. Akt inhibitor decreased secretion of CCL2 in activated HSCs. Conclusion: Our study demonstrated that ß2-AR activation in HSCs induces the proliferation and migration of HCC cells may be through Akt signaling, and this effect appears to be regulated by ß-arrestin2.

ß-Arrestin2 deficiency attenuates oxidative stress in mouse hepatic fibrosis through modulation of NOX4.

Hepatic fibrosis is a disease characterized by excessive deposition of extracellular matrix (ECM) in the liver. Activation of hepatic stellate cells (HSCs) is responsible for most of ECM production. Oxidative stress and reactive oxygen species (ROS) may be important factors leading to liver fibrosis. NADPH oxidase 4 (NOX4) is the main source of ROS in hepatic fibrosis, but the mechanism by which NOX4 regulates oxidative stress is not fully understood. ß-Arrestin2 is a multifunctional scaffold protein that regulates receptor endocytosis, signaling and trafficking. In this study, we investigated whether ß-arrestin2 regulated oxidative stress in hepatic fibrosis. Both ß-arrestin2 knockout (Arrb2 KO) mice and wild-type mice were intraperitoneally injected with carbon tetrachloride (CCl4) to induce hepatic fibrosis. Arrb2 KO mice showed significantly attenuated liver fibrosis, decreased ROS levels and NOX4 expression, and reduced collagen levels in their livers. In vitro, NOX4 knockdown significantly inhibited ROS production, and decreased expression of alpha-smooth muscle actin in angiotensin II-stimulated human HSC cell line LX-2. Through overexpression or depletion of ß-arrestin2 in LX-2 cells, we revealed that decreased ß-arrestin2 inhibited ROS levels and NOX4 expression, and reduced collagen production; it also inhibited activation of ERK and JNK signaling pathways. These results demonstrate that ß-arrestin2 deficiency protects against liver fibrosis by downregulating ROS production through NOX4. This effect appears to be mediated by ERK and JNK signaling pathways. Thus, targeted inhibition of ß-arrestin2 might reduce oxidative stress and inhibit the progression of liver fibrosis.

ß-arrestin2 deficiency protects against hepatic fibrosis in mice and prevents synthesis of extracellular matrix.

Hepatic fibrosis is a disease of the wound-healing response following chronic liver injury, and activated hepatic stellate cells (HSCs) play a crucial role in the progression of hepatic fibrosis. ß-arrestin2 functions as a multiprotein scaffold to coordinate complex signal transduction networks. Although ß-arrestin2 transduces diverse signals in cells, little is known about its involvement in the regulation of liver fibrosis. Our current study utilized a porcine serum-induced liver fibrosis model and found increased expression of ß-arrestin2 in hepatic tissues with the progression of hepatic fibrosis, which was positively correlated with collagen levels. Furthermore, changes in human fibrotic samples were also observed. We next used ß-arrestin2-/- mice to demonstrate that ß-arrestin2 deficiency ameliorates CCl4-induced liver fibrosis and decreases collagen deposition. The in vitro depletion and overexpression experiments showed that decreased ß-arrestin2 inhibited HSCs collagen production and elevated TßRIII expression, thus downregulating the TGF-ß1 pathway components Smad2, Smad3 and Akt. These findings suggest that ß-arrestin2 deficiency ameliorates liver fibrosis in mice, and ß-arrestin2 may be a potential treatment target in hepatic fibrosis.

Depletion of ß-arrestin 2 protects against CCl4-induced liver injury in mice.

Acute liver injury can be caused by oxidative stress within a short period and is a common pathway to many liver diseases. The liver is vulnerable to reactive oxygen species (ROS) and free radical-mediated disorders. ß-arrestin2 was initially discovered to be a negative regulator of G protein-coupled receptor signaling. Recently, ß-arrestin2 has been found to act as a multifunctional adaptor protein and play new roles in regulating intracellular signaling networks. However, the role of ß-arrestin2 in the pathogenesis of acute liver injury is unclear. In this study, we hypothesize that ß-arrestin2 regulates acute liver injury via modulation of oxidative stress. ß-arrestin2 knockout mice were used to investigate the impacts of ß-arrestin2 on carbon tetrachloride (CCl4)-induced acute liver injury and oxidative stress. Results here suggested that ß-arrestin2 deficiency decreased serum activities of aminotransferase and alleviated liver injury induced by CCl4 injection as compared with wildtype mice. ß-arrestin2 knockout mice exhibited stronger tolerance in oxidative stress compared with wild-type mice, which was demonstrated by decreased ROS level and increased superoxide dismutase (SOD) and glutathione (GSH) in the liver. Furthermore, ß-arrestin2 deficiency significantly inhibited NOX4 (a major source of ROS) expression and the activation of the extracellular regulated kinase (ERK) and, c-Jun NH2-terminal kinase (JNK) pathways. These results suggest that ß-arrestin2 deficiency protects against CCl4-induced acute liver injury through attenuating oxidative damage and decreased ERK and JNK phosphorylation.

G protein-coupled receptor kinase 2 regulating ß2-adrenergic receptor signaling in M2-polarized macrophages contributes to hepatocellular carcinoma progression.

Background: ß2-adrenoceptors (ß2-ARs) are expressed on the surface of immune cells, including tumor-associated macrophages (TAMs). Previous studies have demonstrated that the expression of ß2-ARs in hepatocellular carcinoma (HCC) is significantly increased in vitro. However, the role of ß2-AR in M2-polarized macrophages remains unclear. G protein-coupled receptor kinase 2 (GRK2) can regulate G protein-coupled receptor (GPCR). Previous studies showed that down-regulation of GRK2 in HCC contributes the HCC progression, but it still remains unclear whether the regulation of ß2-AR in M2-polarized macrophages by GRK2 can promote HCC. Purpose: The present study was designed to investigate the role of activated ß2-AR in M2-polarized macrophages in the HCC progression and GRK2 regulatory effect, as well as the underlying mechanisms involved. Results: The results demonstrated that the M2-polarized macrophages were increased with HCC progression. In vitro, the activation of ß2-AR by terbutaline in M2-polarized macrophages elevated the proliferative, migratory and invasive attributes of HCC cells. Furthermore, GRK2 down-regulation in ß2-AR activated M2-polarized macrophages activated the downstream cyclic adenosine monophosphate (cAMP)/protein kinase A/cAMP-response element binding protein and cAMP/interleukin-6/signal transducer and the activator of transcription 3 signaling pathways, contributing to the secretion of tumor-associated cytokines, and thus resulting in the promotion of malignant biological behavior in HCC cells. Conclusion: These findings suggest that the regulation of ß2-AR occurs through the silencing of GRK2 in M2-polarized macrophages, which is conducive to HCC development, through its engagement in the activation of downstream signaling.

The role of G protein-coupled receptor kinases in the pathology of malignant tumors.

G protein-coupled receptor kinases (GRKs) constitute seven subtypes of serine/threonine protein kinases that specifically recognize and phosphorylate agonist-activated G protein-coupled receptors (GPCRs), thereby terminating the GPCRs-mediated signal transduction pathway. Recent research shows that GRKs also interact with non-GPCRs and participate in signal transduction in non-phosphorylated manner. Besides, GRKs activity can be regulated by multiple factors. Changes in GRKs expression have featured prominently in various tumor pathologies, and they are associated with angiogenesis, proliferation, migration, and invasion of malignant tumors. As a result, GRKs have been intensively studied as potential therapeutic targets. Herein, we review evolving understanding of the function of GRKs, the regulation of GRKs activity and the role of GRKs in human malignant tumor pathophysiology.

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.