Conditional mutagenesis of G-protein coupled receptors and G-proteins

Deciphering the specific role of Gαi/o isoforms: functional selective oxytocin ligands and somatostatin SST5 receptor mutants

Receptor coupling to different G-proteins and β-arrestins has been described for a number of GPCRs (G-protein-coupled receptors), suggesting a multi-state model of receptor activation in which each receptor can assume a number of different active conformations, each capable of promoting the coupling to a specific effector. Consistently, functional-selective ligands and biased agonists have been described to be able to induce and/or stabilize only a subset of specific active conformations. Furthermore, GPCR mutants deficient in selective coupling have been reported. Functional selective ligands and receptor mutants thus constitute unique tools to dissect the specific roles of different effectors, in particular among the Gi/o family. In the present mini-review, we focus on (i) the identification of functional selective OXT (oxytocin)-derived peptides capable of activating single Gi/o isoforms, namely Gi1 or Gi3; and (ii) the characterization of an SS (somatostatin) receptor SST5 mutant selectively impaired in its GoA coupling. These analogues and receptor mutants represent unique tools for examining the contribution of Gi/o isoforms in complex biological responses and open the way for the development of drugs with peculiar selectivity profiles.

Heterotrimeric G proteins, focal adhesion kinase, and endothelial barrier function

Ligands by binding to G protein coupled receptors (GPCRs) stimulate dissociation of heterotrimeric G proteins into Gα and Gβγ subunits. Released Gα and Gβγ subunits induce discrete signaling cues that differentially regulate focal adhesion kinase (FAK) activity and endothelial barrier function. Activation of G proteins downstream of receptors such as protease activated receptor 1 (PAR1) and histamine receptors rapidly increases endothelial permeability which reverses naturally within the following 1-2 h. However, activation of G proteins coupled to the sphingosine-1-phosphate receptor 1 (S1P1) signal cues that enhance basal barrier endothelial function and restore endothelial barrier function following the increase in endothelial permeability by edemagenic agents. Intriguingly, both PAR1 and S1P1 activation stimulates FAK activity, which associates with alteration in endothelial barrier function by these agonists. In this review, we focus on the role of the G protein subunits downstream of PAR1 and S1P1 in regulating FAK activity and endothelial barrier function.

Diagnostic approach to platelet function disorders

Platelet disorders are common bleeding disorders, with a variety of congenital and acquired causes. The diagnostic evaluation of platelet disorders challenges both clinicians and clinical laboratories, as testing for these conditions is complex, not well standardized and time consuming. An understanding of normal platelet function has provided insights on the pathogenesis of many platelet function disorders. Knowledge of the key features of platelet disorders aids their diagnostic assessment. Tests for aggregation, secretion and dense granule defects continue to be the most helpful for the evaluation of suspected platelet function disorders.