Boyle K B, Hadaschik D, Virtue S, Cawthorn W P, Ridley S H, O'Rahilly S, Siddle K
Department of Clinical Biochemistry, Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK.
Cell Death Differ. 2009 May;16(5):782-9. doi: 10.1038/cdd.2009.11. Epub 2009 Feb 20.
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.
含锌指结构的转录因子Egr1（Krox24）和Egr2（Krox20）与多种细胞类型的增殖和分化有关。Egr2 earlier已被证明在脂肪细胞分化中起积极作用，但Egr1在此过程中的功能尚不清楚。我们比较了Egr1和Egr2在小鼠3T3-L1脂肪细胞分化中的作用。添加分化诱导剂后，Egr1蛋白迅速被诱导，而Egr2蛋白最初保持低水平，在第1天和第2天增加，同时Egr1消失。与Egr2的作用形成鲜明对比的是，Egr1的异位表达抑制分化，而Egr1的敲低则增强分化。当分化培养基中省略异丁基甲基黄嘌呤（IBMX）时，Egr1敲低的促脂肪生成作用尤为明显。然而，Egr1的敲低并不影响CCAAT/增强子结合蛋白（C/EBP）β蛋白表达或CREB Ser133的磷酸化。此外，在荧光素酶报告基因测定中评估，Egr1并未直接影响主要脂肪生成转录因子C/EBPα或过氧化物酶体增殖物激活受体γ2的启动子活性。这些数据表明，Egr1和Egr2对脂肪细胞分化产生相反的影响，维持适当的脂肪生成水平需要对两者进行精细调节。此外，IBMX的促分化作用涉及抑制Egr1的抑制性影响。
