title: The transcription factors Egr1 and Egr2 have opposing influences on adipocyte differentiation.
abstract: The zinc finger-containing transcription factors Egr1 (Krox24) and Egr2 (Krox20) have been implicated in the proliferation and differentiation of many cell types. Egr2 has earlier been shown to play a positive role in adipocyte differentiation, but the function of Egr1 in this context is unknown. We compared the roles of Egr1 and Egr2 in the differentiation of murine 3T3-L1 adipocytes. Egr1 protein was rapidly induced after addition of differentiation cocktail, whereas Egr2 protein initially remained low before increasing on days 1 and 2, concomitant with the disappearance of Egr1. In marked contrast to the effects of Egr2, differentiation was inhibited by ectopic expression of Egr1 and potentiated by knockdown of Egr1. The pro-adipogenic effects of Egr1 knockdown were particularly notable when isobutylmethylxanthine (IBMX) was omitted from the differentiation medium. However, knockdown of Egr1 did not affect CCAAT/enhancer binding protein (C/EBP)beta protein expression or phosphorylation of CREB Ser133. Further, Egr1 did not directly affect the activity of promoters for the master adipogenic transcription factors, C/EBPalpha or peroxisome proliferator-activated receptor-gamma2, as assessed in luciferase reporter assays. These data indicate that Egr1 and Egr2 exert opposing influences on adipocyte differentiation and that the careful regulation of both is required for maintaining appropriate levels of adipogenesis. Further, the pro-differentiation effects of IBMX involve suppression of the inhibitory influence of Egr1.
authors.affiliation: Department of Clinical Biochemistry, Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK.
authors.forename: K B
authors.initials: KB
authors.lastname: Boyle
authors.forename: D
authors.initials: D
authors.lastname: Hadaschik
authors.forename: S
authors.initials: S
authors.lastname: Virtue
authors.forename: W P
authors.initials: WP
authors.lastname: Cawthorn
authors.forename: S H
authors.initials: SH
authors.lastname: Ridley
authors.forename: S
authors.initials: S
authors.lastname: O'Rahilly
authors.forename: K
authors.initials: K
authors.lastname: Siddle
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D051766:Early Growth Response Protein 1 / Q000378:metabolism* / Q000494:pharmacology; D051767:Early Growth Response Protein 2 / Q000378:metabolism* / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D051379:Mice; D047495:PPAR gamma / Q000378:metabolism; D010766:Phosphorylation; D034622:RNA Interference
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D051766:Early Growth Response Protein 1; D051767:Early Growth Response Protein 2; C486109:Egr1 protein, mouse; C497327:Egr2 protein, mouse; D047495:PPAR gamma; D015056:1-Methyl-3-isobutylxanthine