Role of Phosphorylation in the Control of Clathrin-Mediated Internalization of GPCR

The process by which G protein-coupled receptors (GPCRs) are internalized through the clathrin-coated vesicles involves interactions of multifunctional adaptor proteins. These interactions are tightly controlled by phosphorylation and dephosphorylation mechanisms resulting in the regulation of receptor endocytosis. However, the identities of the kinases involved in this process remained largely unknown until recently. This paper discusses advances in our knowledge of the important role played by protein phosphorylation in the regulation of the endocytic machinery and how phosphorylation controls the coated vesicle cycle

Angiotensin type 1A receptor regulates β-arrestin binding of the β2-adrenergic receptor via heterodimerization

Heterodimerization between angiotensin type 1A receptor (AT1R) and β2-adrenergic receptor (β2AR) has been shown to modulate G protein-mediated effects of these receptors. Activation of G protein-coupled receptors (GPCRs) leads to β-arrestin binding, desensitization, internalization and G protein-independent signaling of GPCRs. Our aim was to study the effect of heterodimerization on β-arrestin coupling. We found that β-arrestin binding of β2AR is affected by activation of AT1Rs. Costimulation with angiotensin II and isoproterenol markedly enhanced the interaction between β2AR and β-arrestins, by prolonging the lifespan of β2AR-induced β-arrestin2 clusters at the plasma membrane. While candesartan, a conventional AT1R antagonist, had no effect on the β-arrestin2 binding to β2AR, TRV120023, a β-arrestin biased agonist, enhanced the interaction. These findings reveal a new crosstalk mechanism between AT1R and β2AR, and suggest that enhanced β-arrestin2 binding to β2AR can contribute to the pharmacological effects of biased AT1R agonists. © 201

Control of anterior GRadient 2 (AGR2) dimerization links endoplasmic reticulum proteostasis to inflammation

International audienceAnterior gradient 2 (AGR2) is a dimeric protein disulfide isomerase family member involved in the regulation of protein quality control in the endoplasmic reticulum (ER). Mouse AGR2 deletion increases intestinal inflammation and promotes the development of inflammatory bowel disease (IBD). Although these biological effects are well established, the underlying molecular mechanisms of AGR2 function toward inflammation remain poorly defined. Here, using a protein-protein interaction screen to identify cellular regulators of AGR2 dimerization, we unveiled specific enhancers, including TMED2, and inhibitors of AGR2 dimerization, that control AGR2 functions. We demonstrate that modulation of AGR2 dimer formation, whether enhancing or inhibiting the process, yields pro-inflammatory phenotypes, through either autophagy-dependent processes or secretion of AGR2, respectively. We also demonstrate that in IBD and specifically in Crohn's disease, the levels of AGR2 dimerization modulators are selectively deregulated, and this correlates with severity of disease. Our study demonstrates that AGR2 dimers act as sensors of ER homeostasis which are disrupted upon ER stress and promote the secretion of AGR2 monomers. The latter might represent systemic alarm signals for pro-inflammatory responses

Regulation of the endocytic adaptor proteins [beta] arrestin and AP-2 during clathrin-mediated internalization of Angiotensin II type 1 receptor

G protein-coupled receptors (GPCRs) are the largest family of cell-surface receptors. They transduce the signals mediated by a diverse range of signalling molecules, including ions, amines, and peptides, as well as photons, to mediate intracellular functions. These receptors play a fundamental role in many physiological responses such as cardiovascular functions. To remain responsive to their environment, cells must find a way to rapidly desensitize and resensitize their activated GPCRs. Desensitization of receptors, for instance, involves the phosphorylation of receptors by G protein-coupled receptor kinase (GRKs) followed by the recruitment of betaarrestin. This interferes with the binding of the G protein (the signalling effector). betaarrestin then targets the receptors to the clathrin endocytosis pathway, and serves as an adaptor linking receptors to other signalling pathways. Internalization of receptors serves not only to remove desensitized receptors from the plasma membrane, but also to engage receptors in the resensitization pathway.The internalization of Angiotensin II (Ang II) type 1 receptor (AT1R) is controversial and poorly described. Therefore, our laboratory studies the mechanisms behind AT1R internalization. The agonist-induced internalization of AT1R begins with the formation of a complex including betaarrestin, the clathrin adaptor AP-2, and the tyrosine protein kinase, c-Src. In turn, this c-Src recruitment regulates the clathrin-mediated internalization of AT1R by controlling the formation of endocytic complexes during endocytosis. Indeed, the recruitment of c-Src is involved in the dissociation of AP-2 during receptor internalization. Based on our evidence that AP-2 and c-Src can be found in the same complex, we suggested that AP-2 could be phosphorylated by c-Src. Indeed, we found that Ang II induced the c-Src-mediated tyrosine phosphorylation of the beta-subunit of AP-2 (beta2-adaptin). We were able to map one of the tyrosines in beta2-adaptin and assess its role in regulating the binding of its principal partner: betaarrestin. The phosphorylation state of beta2-adaptin dictates its association profile with betaarrestin: when phosphorylated it reduces its binding to betaarrestin. Finally, we proposed a model for AT1R internalization. Overall, these studies are significant because they allow a better understanding of the underlying mechanism that regulates the initial steps of clathrin-coated vesicle endocytosis of AT1R

Vade-mecum de l'orfévre et du bijoutier, contenant le compte fait de plus de 50,000 opérations relatives à l'orfèvrerie et à la bijouterie... (7e édition) / par E. Fessart,...

Contient une table des matièresAvec mode text