title: β-Arrestin signal complex plays a critical role in adipose differentiation.
abstract: β-Arrestins were identified as scaffold-proteins that have the capacity to desensitize G protein-coupled receptors. However, it has been found that β-arrestins activate signaling pathways independent of G protein activation. The diversity of these signaling pathways has also been recognized for receptor tyrosine kinase. The aim of the present study was to validate the β-arrestin-dependent signaling mechanism(s) responsible for regulation of adipogenesis. Two signal models were selected, ghrelin and insulin, based on its β-arrestin-associated Akt activity. Herein, we found that β-arrestin 1 and 2 were essential molecules for adipocyte differentiation. More specifically, the role of these scaffolding proteins was demonstrated by depletion of β-arrestin 1 and 2 during ghrelin-induced adipogenesis in 3T3-L1 cells, which decreased the adipocyte differentiation and the expression levels of master regulators of early, the CCAAT/enhancer-binding protein β (C/EBPβ) and the CCAAT/enhancer-binding protein δ (C/EBPδ), and terminal, the peroxisome proliferator-activated receptor (PPARγ) and the CCAAT/enhancer-binding protein α (C/EBPα), adipogenesis. Accordingly ghrelin-induced Akt activity and its downstream targets, the mammalian target of rapamycin complex 1 (mTORC1) and the ribosomal protein S6 kinase beta-1 (S6K1), were inhibited by β-arrestin 1 and 2 siRNAs. By contrast, assays performed during insulin-activated adipogenesis showed an intensifying effect on the adipocyte differentiation as well as on the expression of C/EBPβ, C/EBPδ, PPARγ and C/EBPα. The increase in insulin-induced adipogenesis by β-arrestin knock-down was concomitant to a decrease in the insulin receptor susbtrate-1 (IRS-1) serine phosphorylation, proving the loss of the negative feedback loop on IRS-1/phosphoinositide 3-kinase (PI3K)/Akt. Therefore, β-arrestins control the extent and intensity of the lipogenic and adipogenic factors associated to Akt signaling, although the mechanistic and functional principles that underlie the connection between signaling and β-arrestins are specifically associated to each receptor type.
authors.affiliation: Área de Endocrinología Molecular y Celular, Instituto de Investigación Sanitaria de Santiago, Complejo Hospitalario Universitario de Santiago, Servicio Gallego de Salud, Santiago de Compostela, Spain.
authors.forename: Icía
authors.initials: I
authors.lastname: Santos-Zas
authors.forename: María
authors.initials: M
authors.lastname: Lodeiro
authors.forename: Uxía
authors.initials: U
authors.lastname: Gurriarán-Rodríguez
authors.forename: Mónica
authors.initials: M
authors.lastname: Bouzo-Lorenzo
authors.forename: Carlos S
authors.initials: CS
authors.lastname: Mosteiro
authors.forename: Felipe F
authors.initials: FF
authors.lastname: Casanueva
authors.forename: Xesús
authors.initials: X
authors.lastname: Casabiell
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Pazos
authors.forename: Jesús P
authors.initials: JP
authors.lastname: Camiña
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000096:biosynthesis; D051743:CCAAT-Enhancer-Binding Protein-delta / Q000096:biosynthesis; D022762:CCAAT-Enhancer-Binding Proteins / Q000096:biosynthesis; D002454:Cell Differentiation; D002460:Cell Line; D054439:Ghrelin / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D051379:Mice; D047495:PPAR gamma / Q000096:biosynthesis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D015398:Signal Transduction; D000071559:beta-Arrestin 1; D000071557:beta-Arrestins
chemical_list: C000605255:Arrb1 protein, mouse; D019390:Arrestins; D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; C530718:CEBPA protein, mouse; C545013:Cebpb protein, mouse; C497253:Cebpd protein, mouse; D054439:Ghrelin; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D047495:PPAR gamma; D034741:RNA, Small Interfering; D000071559:beta-Arrestin 1; D000071557:beta-Arrestins; D051743:CCAAT-Enhancer-Binding Protein-delta; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt