Design of substrates and inhibitors of G protein-coupled receptor kinase 2 (GRK2) based on its phosphorylation reaction

ZBTB16 eases lipopolysaccharide‑elicited inflammation, apoptosis and degradation of extracellular matrix in chondrocytes during osteoarthritis by suppressing GRK2 transcription

Osteoarthritis (OA) is a chronic degenerative disease of the bone that is a major contributor of disability in the elderly population. Zinc finger and BTB domain-containing 16 (ZBTB16) is a transcription factor that has been previously revealed to be impaired in human OA tissues. The present study was designed to elaborate the potential impact of ZBTB16 on OA and to possibly assess any latent regulatory mechanism. ZBTB16 expression in human OA tissues was examined using the Gene Expression Series (GSE) database (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE169077) whereas ZBTB16 expression in chondrocytes was examined using reverse transcription-quantitative PCR (RT-qPCR) and western blotting. Cell viability was examined using a Cell Counting Kit-8 assay. A TUNEL assay and western blotting were used to assess cell apoptosis and apoptosis-related markers, including Bcl-2, Bax and cleaved caspase-3. The levels and expression of inflammatory factors, including TNF-α, IL-1β and IL-6, were determined by ELISA and western blotting. RT-qPCR and western blotting were also used to analyze the expression levels of extracellular matrix (ECM)-degrading enzymes, including MMP-13, a disintegrin-like and metalloproteinase with thrombospondin type-1 motifs-5, aggrecan and collagen type II α1. After the potential binding of ZBTB16 with the G protein coupled receptor kinase type 2 (GRK2) promoter was predicted using the Cistrome DB database, GRK2 expression was confirmed by RT-qPCR and western blotting. Chromatin immunoprecipitation and luciferase reporter assays were then used to determine the potential interaction between ZBTB16 and the GRK2 promoter. Following GRK2 overexpression in ZBTB16-overexpressing chondrocytes by co-transfection of GRK2 and ZBTB16 overexpression plasmids, the aforementioned functional experiments were performed again. ZBTB16 expression was found to be reduced in human OA tissues compared with in normal cartilage tissues and lipopolysaccharide (LPS)-stimulated chondrocytes. ZBTB16 overexpression increased cell viability whilst decreasing apoptosis, inflammation and ECM degradation by LPS-treated chondrocytes. In addition, GRK2 expression was found to be increased in LPS-stimulated chondrocytes. ZBTB16 successfully bound to the GRK2 promoter, which negatively modulated GRK2 expression. GRK2 upregulation reversed the effects of ZBTB16 overexpression on the viability, apoptosis, inflammation and ECM degradation by LPS-challenged chondrocytes. In conclusion, these data suggest that ZBTB16 may inhibit the development of OA through the transcriptional inactivation of GRK2.

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 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.

Leonurine hydrochloride-a new drug for the treatment of menopausal syndrome: Synthesis, estrogen-like effects and pharmacokinetics

This research aimed to investigate the estrogen-like effects of Leonurine hydrochloride (Leo). First, we developed a total synthesis of Leo from 3,4,5-trimethoxy-benzoic acid and the structure was confirmed through 1H NMR and mass spectrometry (MS). Then the estrogenic activity of Leo in vitro and in vivo was studied. The proliferation and proliferation inhibitory effects of Leo on MCF-7 cells and MDA-MB-231 cells indicate that Leo exerts estrogen-like effects through estrogen receptor α (ERα) and estrogen receptor β((ERβ) in vitro. Uterotrophic assay in juvenile mice showed that Leo has an estrogen-like effect in vivo, as it can promote the development of the uterus of juvenile mice, increase its uterine coefficient and the size of the uterine cavity, as well as the increased number of uterine glands and the thickened uterine wall. For further research, cyclophosphamide (CTX) was used to establish a mouse model of ovarian function decline. Through this model, we found that Leo can restore the estrous cycle of mice, increase the number of primordial and primary follicles in the ovaries of mice, and regulate the disordered hypothalamic-pituitary-ovarian (HPOA) axis of mice. Finally, the pharmacokinetics of Leo was studied and oral bioavailability of Leo was calculated to be 2.21%. Leo was synthesized and the estrogen-like effect in vitro and in vivo was confirmed as well as its pharmacokinetics.

The RAF Kinase Inhibitor Protein (RKIP): Good as Tumour Suppressor, Bad for the Heart

The RAF kinase inhibitor protein, RKIP, is a dual inhibitor of the RAF1 kinase and the G protein-coupled receptor kinase 2, GRK2. By inhibition of the RAF1-MAPK (mitogen-activated protein kinase) pathway, RKIP acts as a beneficial tumour suppressor. By inhibition of GRK2, RKIP counteracts GRK2-mediated desensitisation of G protein-coupled receptor (GPCR) signalling. GRK2 inhibition is considered to be cardioprotective under conditions of exaggerated GRK2 activity such as heart failure. However, cardioprotective GRK2 inhibition and pro-survival RAF1-MAPK pathway inhibition counteract each other, because inhibition of the pro-survival RAF1-MAPK cascade is detrimental for the heart. Therefore, the question arises, what is the net effect of these apparently divergent functions of RKIP in vivo? The available data show that, on one hand, GRK2 inhibition promotes cardioprotective signalling in isolated cardiomyocytes. On the other hand, inhibition of the pro-survival RAF1-MAPK pathway by RKIP deteriorates cardiomyocyte viability. In agreement with cardiotoxic effects, endogenous RKIP promotes cardiac fibrosis under conditions of cardiac stress, and transgenic RKIP induces heart dysfunction. Supported by next-generation sequencing (NGS) data of the RKIP-induced cardiac transcriptome, this review provides an overview of different RKIP functions and explains how beneficial GRK2 inhibition can go awry by RAF1-MAPK pathway inhibition. Based on RKIP studies, requirements for the development of a cardioprotective GRK2 inhibitor are deduced.

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.