Insulin-like Growth Factor-1/Insulin Bypasses Pref-1/FA1-mediated Inhibition of Adipocyte Differentiation

• Published in: The Journal of biological chemistry 2003-06, Vol.278 (23), p.20906-20914
• Main Authors: Zhang, Hongbin, Nøhr, Jane, Jensen, Charlotte H., Petersen, Rasmus K., Bachmann, Elin, Teisner, Børge, Larsen, Leif K., Mandrup, Susanne, Kristiansen, Karsten
• Format: Article
• Language: English
• Subjects: 1-Methyl-3-isobutylxanthine - pharmacology; 3T3 Cells; Adipocytes - cytology; Adipocytes - metabolism; Animals; Calcium-Binding Proteins; Cell Differentiation - physiology; Dexamethasone - pharmacology; Gene Expression Regulation; Glucocorticoids - pharmacology; Hypoglycemic Agents - pharmacology; Insulin - pharmacology; Insulin-Like Growth Factor I - pharmacology; Intercellular Signaling Peptides and Proteins; MAP Kinase Signaling System - drug effects; MAP Kinase Signaling System - physiology; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases - metabolism; Phosphodiesterase Inhibitors - pharmacology; Repressor Proteins - genetics; Repressor Proteins - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M300022200

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.