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

Unveiling G-protein coupled receptors as potential targets for ovarian cancer nanomedicines: from RNA sequencing data analysis to in vitro validation

Genetic heterogeneity in ovarian cancer indicates the need for personalised treatment approaches. Currently, very few G-protein coupled receptors (GPCRs) have been investigated for active targeting with nanomedicines such as antibody-conjugated drugs and drug-loaded nanoparticles, highlighting a neglected potential to develop personalised treatment. To address the genetic heterogeneity of ovarian cancer, a future personalised approach could include the identification of unique GPCRs expressed in cancer biopsies, matched with personalised GPCR-targeted nanomedicines, for the delivery of lethal drugs to tumour tissue before, during and after surgery. Here we report on the systematic analysis of public ribonucleic acid-sequencing (RNA-seq) gene expression data, which led to prioritisation of 13 GPCRs as candidates with frequent overexpression in ovarian cancer tissues. Subsequently, primary ovarian cancer cells derived from ascites and ovarian cancer cell lines were used to confirm frequent gene expression for the selected GPCRs. However, the expression levels showed high variability within our selection of samples, therefore, supporting and emphasising the need for the future development of case-to-case personalised targeting approaches.

Transcriptome signatures of host tissue infected with African swine fever virus reveal differential expression of associated oncogenes

African swine fever (ASF) has emerged as a threat to swine production worldwide. Evasion of host immunity by ASF virus (ASFV) is well understood. However, the role of ASFV in triggering oncogenesis is still unclear. In the present study, ASFV-infected kidney tissue samples were subjected to Illumina-based transcriptome analysis. A total of 2463 upregulated and 825 downregulated genes were differentially expressed (p < 0.05). A literature review revealed that the majority of the differentially expressed host genes were key molecules in signaling pathways involved in oncogenesis. Bioinformatic analysis indicated the activation of certain oncogenic KEGG pathways, including basal cell carcinoma, breast cancer, transcriptional deregulation in cancer, and hepatocellular carcinoma. Analysis of host-virus interactions revealed that the upregulated oncogenic RELA (p65 transcription factor) protein of Sus scrofa can interact with the A238L (hypothetical protein of unknown function) of ASFV. Differential expression of oncogenes was confirmed by qRT-PCR, using the H3 histone family 3A gene (H3F3A) as an internal control to confirm the RNA-Seq data. The levels of gene expression indicated by qRT-PCR matched closely to those determined through RNA-Seq. These findings open up new possibilities for investigation of the mechanisms underlying ASFV infection and offer insights into the dynamic interaction between viral infection and oncogenic processes. However, as these investigations were conducted on pigs that died from natural ASFV infection, the role of ASFV in oncogenesis still needs to be investigated in controlled experimental studies.

Computational analysis of G-protein-coupled receptor kinase family members as potential targets for colorectal cancer therapy

Background

G-protein-coupled receptor (GPCR) kinases (GRKs) interact with ligand-activated GPCR, causing intracellular phosphorylation and interfering with the intracellular signal transduction associated with the development of cancer. Colorectal cancer (CRC) is a fast-growing disease, and its molecular mechanism involves various regulatory proteins, including kinases. However, the GRK mechanism in CRC has not been explored.

Methods

We used an integrated computational approach to investigate the potential of GRK family members as targeted proteins in CRC. The GRK expression levels in tumor and normal tissues, colon adenocarcinoma samples, and metastatic colon adenocarcinoma were analyzed using ONCOMINE, GEPIA, and UALCAN, as well as TNM plots. Genetic changes in the GRK family genes were investigated using cBioportal. The prognostic value related to the gene expression of the GRK family was examined using GEPIA and UALCAN. Co-expression analysis of the GRK family was conducted using COXPRESdb. Association analysis of the Gene Ontology, KEGG pathway enrichment, and drug-gene analyses were performed using the over-representation analysis (ORA) in WebGestalt.

Results

GRK2, GRK3, and GRK5 mRNA levels increased significantly in patients with CRC and metastatic CRC. Genetic changes were detected in patients with CRC, including GRK7 (1.1%), GRK2 (1.7%), GRK4 (2.3%), GRK5 (2.5%), GRK6 (2.5%), GRK3 (2.9%), and GRK1 (4%). CRC patients with low mRNA of GRK7 levels had better disease-free and overall survival than those with high GRK7 levels. Hierarchical clustering analysis revealed significant positive correlations between GRK5 and GRK2 and between GRK2 and GRK6. KEGG pathway enrichment analysis showed that the gene network (GN) regulated several cellular pathways, such as the morphine addiction signaling and chemokine signaling pathways in cancer. The drug-gene association analysis indicated that the GN was associated with several drugs, including reboxetine, pindolol, beta-blocking agents, and protein kinase inhibitors.

Conclusion

No research has been conducted on the relation of GRK1 and GRK7 to cancer, particularly CRC. In this work, genes GRK2, GRK3, GRK5, and GRK6 were found to be oncogenes in CRC. Although inhibitors against GRK2, GRK5, and GRK6 have previously been developed, further research, particularly preclinical and clinical studies, is needed before these agents may be used to treat CRC.

G Protein-Coupled Receptor Kinase 4 Is a Novel Prognostic Factor in Hepatocellular Carcinoma

Purpose

We previously reported that G protein-coupled receptor kinase (GRK) 4 halts cell cycle progression and induces cellular senescence in HEK293 cells. The present study was aimed at assessing the prognostic value of GRK4 in hepatocellular carcinoma (HCC).

Methods

GRK4 expression was detected by immunohistochemistry in paired tumoral and peritumoral tissues of 325 HCC patients. One hundred and twenty-six patients from Western China were utilized as a training cohort to develop a nomogram, while 86 patients from Eastern China were used as a validation cohort. The proliferation and migration of lentiviral-GRK4 expressing HepG2 cells were determined by MTT and wound healing assays.

Results

GRK4 was differentially expressed in HCC tissues. Tumoral GRK4 intensity, tumor type, and T stage were independent prognostic factors and used to form a nomogram for predicting overall survival (OS), which obtained a good concordance index of 0.82 and 0.77 in training and validation cohort, respectively. The positive and negative prediction values with nomogram were, respectively, 83% and 75% in training cohort and 100% and 52% in validation cohort. Patients with nomogram scores > 32 and 78 showed high risk for OS. Proliferation and motility capabilities were significantly restrained in GRK4-overexpressing HCC cells. Discussion. Low GRK4 expression in HCC tumor tissues indicates poor clinical outcomes. A prognostic nomogram including tumoral GRK4 expression would improve the predictive accuracy of OS in HCC patients. We also demonstrated that GRK4 overexpression inhibits proliferation and migration of HCC cells. The molecular mechanism underlying is worth further study.

G Protein-Coupled Receptor Kinase 2 as Novel Therapeutic Target in Fibrotic Diseases

G protein-coupled receptor kinase 2 (GRK2), an important subtype of GRKs, specifically phosphorylates agonist-activated G protein-coupled receptors (GPCRs). Besides, current research confirms that it participates in multiple regulation of diverse cells via a non-phosphorylated pathway, including interacting with various non-receptor substrates and binding partners. Fibrosis is a common pathophysiological phenomenon in the repair process of many tissues due to various pathogenic factors such as inflammation, injury, drugs, etc. The characteristics of fibrosis are the activation of fibroblasts leading to myofibroblast proliferation and differentiation, subsequent aggerate excessive deposition of extracellular matrix (ECM). Then, a positive feedback loop is occurred between tissue stiffness caused by ECM and fibroblasts, ultimately resulting in distortion of organ architecture and function. At present, GRK2, which has been described as a multifunctional protein, regulates copious signaling pathways under pathophysiological conditions correlated with fibrotic diseases. Along with GRK2-mediated regulation, there are diverse effects on the growth and apoptosis of different cells, inflammatory response and deposition of ECM, which are essential in organ fibrosis progression. This review is to highlight the relationship between GRK2 and fibrotic diseases based on recent research. It is becoming more convincing that GRK2 could be considered as a potential therapeutic target in many fibrotic diseases.

Role of Calcium Homeostasis in Modulating EMT in Cancer

Calcium is essential for cells to perform numerous physiological processes. In cancer, the augmentation of calcium signaling supports the more proliferative and migratory cells, which is a characteristic of the epithelial-to-mesenchymal transition (EMT). By genetically and epigenetically modifying genes, channels, and entire signaling pathways, cancer cells have adapted to survive with an extreme imbalance of calcium that allows them to grow and metastasize in an abnormal manner. This cellular remodeling also allows for the evasion of immune surveillance and the development of drug resistance, which lead to poor prognosis in patients. Understanding the role calcium flux plays in driving the phenotypes associated with invasion, immune suppression, metastasis, and drug resistance remains critical for determining treatments to optimize clinical outcomes and future drug discovery.

Differential Regulation of GPCRs-Are GRK Expression Levels the Key?

G protein-coupled receptors (GPCRs) comprise the largest family of transmembrane receptors and their signal transduction is tightly regulated by GPCR kinases (GRKs) and β-arrestins. In this review, we discuss novel aspects of the regulatory GRK/β-arrestin system. Therefore, we briefly revise the origin of the "barcode" hypothesis for GPCR/β-arrestin interactions, which states that β-arrestins recognize different receptor phosphorylation states to induce specific functions. We emphasize two important parameters which may influence resulting GPCR phosphorylation patterns: (A) direct GPCR-GRK interactions and (B) tissue-specific expression and availability of GRKs and β-arrestins. In most studies that focus on the molecular mechanisms of GPCR regulation, these expression profiles are underappreciated. Hence we analyzed expression data for GRKs and β-arrestins in 61 tissues annotated in the Human Protein Atlas. We present our analysis in the context of pathophysiological dysregulation of the GPCR/GRK/β-arrestin system. This tissue-specific point of view might be the key to unraveling the individual impact of different GRK isoforms on GPCR regulation.

Involvement of the Catecholamine Pathway in Glioblastoma Development

Glioblastoma (GBM) is the most aggressive tumor of the central nervous system (CNS). The standard of care improves the overall survival of patients only by a few months. Explorations of new therapeutic targets related to molecular properties of the tumor are under way. Even though neurotransmitters and their receptors normally function as mediators of interneuronal communication, growing data suggest that these molecules are also involved in modulating the development and growth of GBM by acting on neuronal and glioblastoma stem cells. In our previous DNA CpG methylation studies, gene ontology analyses revealed the involvement of the monoamine pathway in sequential GBM. In this follow-up study, we quantitated the expression levels of four selected catecholamine pathway markers (alpha 1D adrenergic receptor-ADRA1D; adrenergic beta receptor kinase 1 or G protein-coupled receptor kinase 2-ADRBK1/GRK2; dopamine receptor D2-DRD2; and synaptic vesicle monoamine transporter-SLC18A2) by immunohistochemistry, and compared the histological scores with the methylation levels within the promoters + genes of these markers in 21 pairs of sequential GBM and in controls. Subsequently, we also determined the promoter and gene methylation levels of the same markers in an independent database cohort of sequential GBM pairs. These analyses revealed partial inverse correlations between the catecholamine protein expression and promoter + gene methylation levels, when the tumor and control samples were compared. However, we found no differences in the promoter + gene methylation levels of these markers in either our own or in the database primary-recurrent GBM pairs, despite the higher protein expression of all markers in the primary samples. This observation suggests that regulation of catecholamine expression is only partially related to CpG methylation within the promoter + gene regions, and additional mechanisms may also influence the expression of these markers in progressive GBM. These analyses underscore the involvement of certain catecholamine pathway markers in GBM development and suggest that these molecules mediating or modulating tumor growth merit further exploration.

G protein-coupled receptor kinase 2 modifies the cellular reaction to cisplatin through interactions with NADPH oxidase 4

G protein-coupled receptor kinases (GRKs), in addition to their role in modulating signal transduction mechanisms associated with activated G protein-coupled receptors (GPCRs), can also interact with many non-GPCR proteins to mediate cellular responses to chemotherapeutics. The rationale for this study is based on the presumption that GRK2 modulates the responses of cancer cells to the chemotherapeutic cisplatin. In this report, we show that GRK2 modulates the responses of cancer cells to cisplatin. Cervical cancer HeLa cells stably transfected with GRK2 shRNA, to decrease GRK2 protein expression, show increased sensitivity to cisplatin. Of interest, these cells also show increased accumulation of NADPH, associating with decreased NADP buildup, at low concentrations of cisplatin tested. These changes in NADPH and NADP levels are also observed in the breast cancer MDA MB 231 cells, which has lower endogenous GRK2 protein expression levels, but not BT549, a breast cancer cell line with higher GRK2 protein expression. This effect of NADPH accumulation may be associated with a decrease in NADPH oxidase 4 (NOX4) protein expression, which is found to correlate with GRK2 protein expression in cancer cells-a relationship which mimics that observed in cardiomyocytes. Furthermore, like in cardiomyocytes, GRK2 and NOX4 interact to form complexes in cancer cells. Collectively, these results suggest that GRK2 interacts with NOX4 to modify cisplatin sensitivity in cancer cells and may also factor into the success of cisplatin-based regimens.

GRK2 Suppresses Hepatocellular Carcinoma Metastasis and Invasion Through Down-Regulation of Prostaglandin E Receptor 2

Background

Hepatocellular carcinoma (HCC) is an aggressive form of human liver cancer and the fifth most common malignancy worldwide. Novel effective treatment strategies for HCC are urgently in clinical because of its poor response to conventional therapies. G protein-coupled receptor kinases (GRKs), including GRK2 and GRK3, are known that involves in various essential cellular processes and regulates numerous signaling pathways. However, the role of GRK2/3 in invasion and metastasis of HCC still remains unclear.

Materials and Methods

Immunohistochemistry, Western blot, laser confocal microscopy and qRT-PCR were used to detect the expression of GRK2/3 and EP2 in liver tissues of HCC patients and DEN-induced HCC mice. Wound healing and transwell assay were applied to measure the migration and invasion of HCC cells after transfected with GRK2 siRNA. The downstream pathway of Akt and ERK was verified by Western blot.

Results

The expression of GRK2 was significantly decreased, while GRK3 was not significantly changed in HCC tissues compared with noncancerous tissues of HCC patients. Moreover, GRK2 expression was reduced during liver tumorigenesis in diethylnitrosamine-induced liver tumor model. In addition, our in vitro study showed that GRK2 expression was gradually decreased with increasing HCC cell line metastatic potential, and GRK2 knockdown significantly promoted the migration and invasion of HCC cells. Furthermore, low GRK2 expression was associated with increased expression of EP2 receptor translocation to HCC cell membrane, and the activation of Akt pathway.

Conclusion

These data suggest that GRK2 inhibits HCC metastasis and invasion may be through regulating EP2 receptor translocation, and this effect appears to be mediated by Akt pathway.

G protein coupled receptor kinases modulate Caenorhabditis elegans reactions to heat stresses

In this report, we explored if G protein coupled receptor kinases (GRKs) can help modulate the heat stress responses of Caenorhabditis (C.) elegans. Loss of function grk-2 C. elegans mutants were more tolerant to increases in heat and display an ability for heat stress-associated hormesis at a longer exposure time unlike the wild type N2 animals and the loss of function grk-1 C. elegans mutants. The loss of function grk-1 mutants recovered more from acute heat stress compared to the wild type N2 animals. Animals with low Ce-GRK2 protein expression showed increased DAF-16 nuclear localization during the early stages of heat stress exposure compared to the other RNAi-treated animals, demonstrating altered insulin/insulin-like growth factor signaling (IIS) pathway activity in response to the stress. pdk-1 and akt-1 may play key roles in conjunction with Ce-GRK2 in the heat stress response. Collectively, these findings demonstrate that GRKs influence C. elegans heat stress behaviors.

Angiotensin Receptors Heterodimerization and Trafficking: How Much Do They Influence Their Biological Function?

G-protein–coupled receptors (GPCRs) are targets for around one third of currently approved and clinical prescribed drugs and represent the largest and most structurally diverse family of transmembrane signaling proteins, with almost 1000 members identified in the human genome. Upon agonist stimulation, GPCRs are internalized and trafficked inside the cell: they may be targeted to different organelles, recycled back to the plasma membrane or be degraded. Once inside the cell, the receptors may initiate other signaling pathways leading to different biological responses. GPCRs’ biological function may also be influenced by interaction with other receptors. Thus, the ultimate cellular response may depend not only on the activation of the receptor from the cell membrane, but also from receptor trafficking and/or the interaction with other receptors. This review is focused on angiotensin receptors and how their biological function is influenced by trafficking and interaction with others receptors.

Differential Role of Serines and Threonines in Intracellular Loop 3 and C-Terminal Tail of the Histamine H4 Receptor in β-Arrestin and G Protein-Coupled Receptor Kinase Interaction, Internalization, and Signaling

The histamine H₄ receptor (H₄R) activates Gα_i-mediated signaling and recruits β-arrestin2 upon stimulation with histamine. β-Arrestins play a regulatory role in G protein-coupled receptor (GPCR) signaling by interacting with phosphorylated serine and threonine residues in the GPCR C-terminal tail and intracellular loop 3, resulting in receptor desensitization and internalization. Using bioluminescence resonance energy transfer (BRET)-based biosensors, we show that G protein-coupled receptor kinases (GRK) 2 and 3 are more quickly recruited to the H₄R than β-arrestin1 and 2 upon agonist stimulation, whereas receptor internalization dynamics toward early endosomes was slower. Alanine-substitution revealed that a serine cluster at the distal end of the H₄R C-terminal tail is essential for the recruitment of β-arrestin1/2, and consequently, receptor internalization and desensitization of G protein-driven extracellular-signal-regulated kinase (ERK)1/2 phosphorylation and label-free cellular impedance. In contrast, alanine substitution of serines and threonines in the intracellular loop 3 of the H₄R did not affect β-arrestin2 recruitment and receptor desensitization, but reduced β-arrestin1 recruitment and internalization. Hence, β-arrestin recruitment to H₄R requires the putative phosphorylated serine cluster in the H₄R C-terminal tail, whereas putative phosphosites in the intracellular loop 3 have different effects on β-arrestin1 versus β-arrestin2. Mutation of these putative phosphosites in either intracellular loop 3 or the C-terminal tail did not affect the histamine-induced recruitment of GRK2 and GRK3 but does change the interaction of H₄R with GRK5 and GRK6, respectively. Identification of H₄R interactions with these proteins is a first step in the understanding how this receptor might be dysregulated in pathophysiological conditions.

CP-25 exerts anti-angiogenic effects on a rat model of adjuvant-induced arthritis by promoting GRK2-induced downregulation of CXCR4-ERK1/2 signaling in endothelial cells

Angiogenesis can produce an invasive and destructive front, also named a pannus, comprised of inflammatory vascular tissue that covers and erodes articular cartilage, subchondral bone and peri‑articular soft tissues in rheumatoid arthritis (RA). Paeoniflorin‑6'‑O‑benzene sulfonate (CP‑25) is a novel ester derivative of paeoniflorin. We previously demonstrated that CP‑25 exerts anti‑inflammatory and immunoregulatory effects. CP‑25 also exhibits a marked therapeutic effect on adjuvant‑induced arthritis (AA), and is able to inhibit synovial and immune cell function, according to our previous study. However, the effect of CP‑25 on angiogenesis remains unclear. In the present study, AA was initiated in Sprague‑Dawley rats via intradermal immunization in the right hind metatarsal footpad with heat‑killed Mycobacterium butyricum in liquid paraffin, and rats were divided into four groups: Normal, AA rat model, CP‑25 (50 mg/kg) and methotrexate (0.5 mg/kg) groups (n=10 rats/group). Subsequently, joint synovium in AA rats was pathologically evaluated by hematoxylin and eosin staining, synovial vascular proliferation was evaluated by immunofluorescence, the synovial expression levels of C‑X‑C motif chemokine ligand 12 (CXCL12) were detected by immunohistochemistry and ELISA, and synovial C‑X‑C chemokine receptor type 4 (CXCR4) was detected by western blotting. The results demonstrated that CP‑25 ameliorated clinical signs and pannus formation in the ankle joint in rats with AA. Furthermore, there was a positive correlation between pannus score and CXCL12 and CXCR4 expression. In addition, the effects of CP‑25 on endothelial cell function and CXCL12/CXCR4 signaling were studied in vitro using human umbilical vein endothelial cells (HUVECs). The results demonstrated that CXCL12 significantly promoted HUVEC proliferation, migration and tube formation, and that CP‑25 could reverse these abnormalities by inhibiting plasma membrane localization of G protein‑coupled receptor kinase 2 (GRK2) in HUVECs. These findings suggested that CP‑25 may markedly inhibit pannus formation in AA. This effect may be associated with a reduction in the plasma membrane localization of GRK2 in endothelial cells, an enhancement of the inhibitory effect of GRK2 on ERK1/2 in the cytoplasm, a reduction in the phosphorylation of ERK1/2 and in the function of HUVECs.