title: Insulin-like growth factor-1/insulin bypasses Pref-1/FA1-mediated inhibition of adipocyte differentiation.
abstract: Pref-1 is a highly glycosylated Delta-like transmembrane protein containing six epidermal growth factor-like repeats in the extracellular domain. Pref-1 is abundantly expressed in preadipocytes, but expression is down-regulated during adipocyte differentiation. Forced expression of Pref-1 in 3T3-L1 cells was reported to inhibit adipocyte differentiation. Here we show that efficient and regulated processing of Pref-1 occurs in 3T3-L1 preadipocytes releasing most of the extracellular domain as a 50-kDa heterogeneous protein, previously isolated and characterized as FA1. Unexpectedly, we found that forced expression of the soluble form, FA1, or full-length Pref-1 did not inhibit adipocyte differentiation of 3T3-L1 cells when differentiation was induced by standard treatment with methylisobutylxanthine, dexamethasone, and high concentrations of insulin. However, forced expression of either form of Pref-1/FA1 in 3T3-L1 or 3T3-F442A cells inhibited adipocyte differentiation when insulin or insulin-like growth factor-1 (IGF-1) was omitted from the differentiation mixture. We demonstrate that the level of the mature form of the IGF-1 receptor is reduced and that IGF-1-dependent activation of p42/p44 mitogen-activated protein kinases (MAPKs) is compromised in preadipocytes with forced expression of Pref-1. This is accompanied by suppression of clonal expansion and terminal differentiation. Accordingly, supplementation with insulin or IGF-1 rescued p42/p44 MAPK activation, clonal expansion, and adipocyte differentiation in a dose-dependent manner.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M., Denmark.
authors.forename: Hongbin
authors.initials: H
authors.lastname: Zhang
authors.forename: Jane
authors.initials: J
authors.lastname: Nøohr
authors.forename: Charlotte H
authors.initials: CH
authors.lastname: Jensen
authors.forename: Rasmus K
authors.initials: RK
authors.lastname: Petersen
authors.forename: Elin
authors.initials: E
authors.lastname: Bachmann
authors.forename: Borge
authors.initials: B
authors.lastname: Teisner
authors.forename: Leif K
authors.initials: LK
authors.lastname: Larsen
authors.forename: Susanne
authors.initials: S
authors.lastname: Mandrup
authors.forename: Karsten
authors.initials: K
authors.lastname: Kristiansen
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D002135:Calcium-Binding Proteins; D002454:Cell Differentiation / Q000502:physiology; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation; D005938:Glucocorticoids / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; C512925:Dlk1 protein, mouse; D005938:Glucocorticoids; D007004:Hypoglycemic Agents; D007328:Insulin; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D010726:Phosphodiesterase Inhibitors; D012097:Repressor Proteins; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D015056:1-Methyl-3-isobutylxanthine