Membrane-permeable tastants amplify β2-adrenergic receptor signaling and delay receptor desensitization via intracellular inhibition of GRK2's kinase activity

G protein-coupled receptor kinase 2 regulating β2-adrenergic receptor signaling in M2-polarized macrophages contributes to hepatocellular carcinoma progression

Background: β2-adrenoceptors (β2-ARs) are expressed on the surface of immune cells, including tumor-associated macrophages (TAMs). Previous studies have demonstrated that the expression of β2-ARs in hepatocellular carcinoma (HCC) is significantly increased in vitro. However, the role of β2-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 β2-AR in M2-polarized macrophages by GRK2 can promote HCC.

Purpose: The present study was designed to investigate the role of activated β2-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 β2-AR by terbutaline in M2-polarized macrophages elevated the proliferative, migratory and invasive attributes of HCC cells. Furthermore, GRK2 down-regulation in β2-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 β2-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.

Biomimetic Sensors for the Senses: Towards Better Understanding of Taste and Odor Sensation

Taste and smell are very important chemical senses that provide indispensable information on food quality, potential mates and potential danger. In recent decades, much progress has been achieved regarding the underlying molecular and cellular mechanisms of taste and odor senses. Recently, biosensors have been developed for detecting odorants and tastants as well as for studying ligand-receptor interactions. This review summarizes the currently available biosensing approaches, which can be classified into two main categories: in vitro and in vivo approaches. The former is based on utilizing biological components such as taste and olfactory tissues, cells and receptors, as sensitive elements. The latter is dependent on signals recorded from animals' signaling pathways using implanted microelectrodes into living animals. Advantages and disadvantages of these two approaches, as well as differences in terms of sensing principles and applications are highlighted. The main current challenges, future trends and prospects of research in biomimetic taste and odor sensors are discussed.

The Taste of Caffeine

Many people avidly consume foods and drinks containing caffeine, despite its bitter taste. Here, we review what is known about caffeine as a bitter taste stimulus. Topics include caffeine's action on the canonical bitter taste receptor pathway and caffeine's action on noncanonical receptor-dependent and -independent pathways in taste cells. Two conclusions are that (1) caffeine is a poor prototypical bitter taste stimulus because it acts on bitter taste receptor-independent pathways, and (2) caffeinated products most likely stimulate "taste" receptors in nongustatory cells. This review is relevant for taste researchers, manufacturers of caffeinated products, and caffeine consumers.

New paradigms in GPCR drug discovery

G protein-coupled receptors (GPCRs) remain a major domain of pharmaceutical discovery. The identification of GPCR lead compounds and their optimization are now structure-based, thanks to advances in X-ray crystallography, molecular modeling, protein engineering and biophysical techniques. In silico screening provides useful hit molecules. New pharmacological approaches to tuning the pleotropic action of GPCRs include: allosteric modulators, biased ligands, GPCR heterodimer-targeted compounds, manipulation of polypharmacology, receptor antibodies and tailoring of drug molecules to fit GPCR pharmacogenomics. Measurements of kinetics and drug efficacy are factors influencing clinical success. With the exception of inhibitors of GPCR kinases, targeting of intracellular GPCR signaling or receptor cycling for therapeutic purposes remains a futuristic concept. New assay approaches are more efficient and multidimensional: cell-based, label-free, fluorescence-based assays, and biosensors. Tailoring GPCR drugs to a patient's genetic background is now being considered. Chemoinformatic tools can predict ADME-tox properties. New imaging technology visualizes drug action in vivo. Thus, there is reason to be optimistic that new technology for GPCR ligand discovery will help reverse the current narrowing of the pharmaceutical pipeline.