title: Pref-1 (preadipocyte factor 1) activates the MEK/extracellular signal-regulated kinase pathway to inhibit adipocyte differentiation.
abstract: Preadipocyte factor 1 (Pref-1) is found in preadipocytes but is absent in adipocytes. Pref-1 is made as a transmembrane protein but is cleaved to generate a biologically active soluble form. Although Pref-1 inhibition of adipogenesis has been well studied in vitro and in vivo, the signaling pathway for Pref-1 is not known. Here, by using purified soluble Pref-1 in Pref-1 null mouse embryo fibroblasts (MEF), we show that Pref-1 increases MEK/extracellular signal-regulated kinase (ERK) phosphorylation in a time- and dose-dependent manner. Compared to wild-type MEF, differentiation of Pref-1 null MEF into adipocytes is enhanced, as judged by lipid accumulation and adipocyte marker expression. Both wild-type and Pref-1 null MEF show a transient burst of ERK phosphorylation upon addition of adipogenic agents. Wild-type MEF show a significant, albeit lower, second increase in ERK phosphorylation peaking at day 2. This ERK phosphorylation, corresponding to Pref-1 abundance, is absent during differentiation of Pref-1 null MEF. Prevention of this second increase in ERK1/2 phosphorylation in wild-type MEF by the MEK inhibitor PD98059 or by transient depletion of ERK1/2 via small interfering RNA-enhanced adipocyte differentiation. Furthermore, treatment of Pref-1 null MEF with Pref-1 restores this ERK phosphorylation, resulting in inhibition of adipocyte differentiation primarily by preventing peroxisome proliferator-activated receptor gamma2 induction. However, in the presence of PD98059 or depletion of ERK1/2, exogenous Pref-1 cannot inhibit adipocyte differentiation in Pref-1 null MEF. We conclude that Pref-1 activates MEK/ERK signaling, which is required for Pref-1 inhibition of adipogenesis.
authors.affiliation: Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720, USA.
authors.forename: Kyung-Ah
authors.initials: KA
authors.lastname: Kim
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Kim
authors.forename: Yuhui
authors.initials: Y
authors.lastname: Wang
authors.forename: Hei Sook
authors.initials: HS
authors.lastname: Sul
mesh_terms: D017667:Adipocytes / Q000166:cytology* / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins; D002454:Cell Differentiation; D002478:Cells, Cultured; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D018345:Mice, Knockout; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; C512925:Dlk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases