title: Signaling by vitamin A and retinol-binding protein in regulation of insulin responses and lipid homeostasis.
abstract: Vitamin A, retinol, circulates in blood bound to serum retinol binding protein (RBP) and is transported into cells by a membrane protein termed stimulated by retinoic acid 6 (STRA6). It was reported that serum levels of RBP are elevated in obese rodents and humans, and that increased level of RBP in blood causes insulin resistance. A molecular mechanism by which RBP can exert such an effect is suggested by the recent discovery that STRA6 is not only a vitamin A transporter but also functions as a surface signaling receptor. Binding of RBP-ROH to STRA6 induces the phosphorylation of a tyrosine residue in the receptor C-terminus, thereby activating a JAK/STAT signaling cascade. Consequently, in STRA6-expressing cells such as adipocytes, RBP-ROH induces the expression of STAT target genes, including SOCS3, which suppresses insulin signaling, and PPARγ, which enhances lipid accumulation. RBP-retinol thus joins the myriad of cytokines, growth factors and hormones which regulate gene transcription by activating cell surface receptors that signal through activation of Janus kinases and their associated transcription factors STATs. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.
authors.affiliation: Department of Pharmacology and Nutrition, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4695, USA.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Berry
authors.forename: Noa
authors.initials: N
authors.lastname: Noy
mesh_terms: D000818:Animals; D006706:Homeostasis; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D053612:Janus Kinases / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids; D008565:Membrane Proteins / Q000378:metabolism*; D047495:PPAR gamma / Q000096:biosynthesis / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D050791:STAT Transcription Factors / Q000096:biosynthesis / Q000378:metabolism; D015398:Signal Transduction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000096:biosynthesis / Q000378:metabolism; D014801:Vitamin A / Q000097:blood / Q000378:metabolism*
chemical_list: D007328:Insulin; D008055:Lipids; D008565:Membrane Proteins; D047495:PPAR gamma; D012177:Retinol-Binding Proteins; C106644:SOCS3 protein, human; D050791:STAT Transcription Factors; C519685:STRA6 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014801:Vitamin A; D053612:Janus Kinases