Differential and competitive regulation of human melanocortin 1 receptor signaling by β-arrestin isoforms

Abstract

SummaryThe melanocortin 1 receptor (MC1R) is a G-protein-coupled receptor (GPCR) crucial for the regulation of melanocyte proliferation and differentiation. MC1R activation by melanocortin hormones triggers the cAMP pathway and stimulates the extracellular-signalregulated protein kinases ERK1 and ERK2 to promote synthesis of photoprotective eumelanin pigments, among other effects. Signaling from most GPCRs is regulated by the b-arrestin (ARRB) family of cytosolic multifunctional adaptor proteins, which mediate signal termination and endocytosis of GPCR-agonist complexes. The ubiquitously expressed non-visual b-arrestin1 (ARRB1) and b-arrestin2 (ARRB2) are highly similar but not functionally equivalent. Their role in the regulation of MC1R is unknown. Using a combination of co-immunoprecipitation, gel filtration chromatography, confocal microscopy, siRNA-mediated knockdown and functional assays, we demonstrated agonist-independent competitive interactions of ARRB1 and ARRB2 with MC1R, which might also be independent of phosphorylation of Ser/Thr residues in the C-terminus of the MC1R. The effects of ARRBs were isoform specific; ARRB2 inhibited MC1R agonist-dependent cAMP production but not ERK activation, stimulated internalization and showed prolonged co-localization with the receptor in endocytic vesicles. By contrast, ARRB1 had no effect on internalization or functional coupling, but competed with ARRB2 for binding MC1R, which might increase signaling by displacement of inhibitory ARRB2. These data suggest a new mechanism of MC1R functional regulation based on the relative expression of ARRB isoforms, with possible activatory ARRB1-dependent effects arising from partial relief of inhibitory ARRB2-MC1R interactions. Thus, competitive displacement of inhibitory ARRBs by functionally neutral ARRB isoforms might exert a paradigm-shifting signal-promoting effect to fine-tune signaling downstream of certain GPCRs.

Skin phototype: a new perspective

“…In non-melanoma skin cancer, PTEN acts as an essential genomic gatekeeper through the regulation of the UV-induced DNA repair (Ming et al, 2011). Moreover, the interaction between MC1R and the b-arrestin (ARRB) family of cytosolic multifunctional adaptor proteins has been recently described (Abrisqueta et al, 2013), and b-arrestins are implicated in modulation of DNA damage signalling pathways (Hara et al, 2011). In association with melanin, the antioxidant defence system has to act in an integrated manner in order to minimize the damage caused by UV-generated free radicals within the cell (Briganti and Picardo, 2003).…”

Pyrimidinyl Biphenylureas Act as Allosteric Modulators to Activate Cannabinoid Receptor 1 and Initiateβ-Arrestin–Dependent Responses

“…3) for compounds PSNCBAM1, LDK1283, LDK1288, and LDK1305. GPCR signaling and internalization are dependent on different b-arrestin isoforms, which has been viewed previously for other GPCRs (Vibhuti et al, 2011;Abrisqueta et al, 2013;Srivastava et al, 2015). Thus, these allosteric modulators are not orthosteric agonists (e.g., they enhance CP55940 binding) but rather can function as PAMs (e.g., binding analysis) or ago-allosteric modulators (i.e., they can function in signaling without the orthosteric compound being present).…”

Conjugation with Dihydrolipoic Acid Imparts Caffeic Acid Ester Potent Inhibitory Effect on Dopa Oxidase Activity of Human Tyrosinase

“…To this end, we used HBL human melanoma cells as a convenient cellular model. HBL cells are wild type for the MC1R , NRAS and BRAF genes, which allows them to respond to αMSH by activating the cAMP and ERK pathways responsible for the regulation of MITF expression and stability, much like normal human melanocytes [46] Accordingly, they have been widely used to study the molecular mechanisms accounting for the physiological responses to αMSH [47,48,49]. Moreover, their high basal pigmentation and tyrosinase activity make them well-suited for the analysis of potential depigmenting agents.…”