A role for C/EBPβ in regulating peroxisome proliferator-activated receptor γ activity during adipogenesis in 3T3-L1 preadipocytes
A role for C/EBPβ in regulating peroxisome proliferator-activated receptor γ activity during adipogenesis in 3T3-L1 preadipocytes
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DOI：
10.1074/jbc.m100797200
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发表时间：
2001-05-25
影响因子：
4.8
通讯作者：
Farmer, SR
中科院分区：
文献类型：
--
作者：
Hamm, JK;Park, BH;Farmer, SR
3 T3-L1前脂肪细胞的分化部分地由涉及地塞米松（DEX）、3-异丁基-1-甲基黄嘌呤（MIX）和胰岛素激活CCAAT/增强子结合蛋白（C/EBP）和过氧化物酶体增殖物激活受体γ（PPAR γ）的级联转录事件调节。在这项研究中，我们证明，3 T3-L1前脂肪细胞暴露于DEX和胰岛素不能诱导脂肪形成，如缺乏C/EBP α，PPAR γ 2和脂肪蛋白2/脂肪酸结合蛋白表达所示;然而，PPAR γ 1表达。用PPAR γ配体曲格列酮处理这些MM缺陷细胞，诱导C/EBP α表达并挽救脂肪形成中的阻断。在这方面，我们还表明，在不存在进行中的蛋白质合成的情况下，在异位表达PPAR γ的C3 H10 T1/2细胞中，曲格列酮诱导C/EBP α基因表达，这表明C/EBP α基因被PPAR γ直接反式激活。C/EBP β显性阴性亚型异位表达（肝脏富集的转录抑制蛋白（LIP））抑制3 T3-L1细胞中DEX、MM和胰岛素对C/EBP α、PPAR γ 2和脂肪蛋白2/脂肪酸结合蛋白的诱导，而不影响DEX对PPAR γ 1的诱导，将表达LIP的前脂肪细胞与DEX、MM沿着暴露于曲格列酮，胰岛素诱导分化成脂肪细胞。此外，我们表明，在这些脂蛋白表达脂肪细胞中C/EBP α的持续表达需要持续暴露于曲格列酮。综上所述，这些观察结果表明，抑制C/EBP β活性不仅阻断C/EBP α和PPAR γ 2表达，而且还使前脂肪细胞依赖于外源性PPAR γ配体分化为脂肪细胞。因此，我们提出C/EBP β在脂肪形成过程中调节PPAR γ活性的额外作用，我们提出了一种诱导前脂肪细胞分化的替代方法，该方法依赖于地塞米松相关的PPAR γ 1表达诱导。
The differentiation of 3T3-L1 preadipocytes is regulated in part by a cascade of transcriptional events involving activation of the CCAAT/enhancer-binding proteins (C/EBPs) and peroxisome proliferator-activated receptor gamma (PPAR gamma) by dexamethasone (DEX), 3-isobutyl-1-methylxanthine (MIX), and insulin. In this study, we demonstrate that exposure of 3T3-L1 preadipocytes to DEX and insulin fails to induce adipogenesis as indicated by a lack of C/EBP alpha, PPAR gamma2, and adipose protein 2/fatty acid-binding protein expression; however, PPAR gamma1 is expressed. Treatment of these MM-deficient cells with a PPAR gamma ligand, troglitazone, induces C/EBP alpha expression and rescues the block in adipogenesis, In this regard, we also show that induction of C/EBP alpha gene expression by troglitazone in C3H10T1/2 cells ectopically expressing PPAR gamma occurs in the absence of ongoing protein synthesis, suggesting a direct transactivation of the C/EBP alpha gene by PPAR gamma, Furthermore, ectopic expression of a dominant negative isoform of C/EBP beta (liver-enriched transcriptional inhibitory protein (LIP)) inhibits the induction of C/EBP alpha, PPAR gamma2, and adipose protein 2/fatty acid-binding protein by DEX, MM, and insulin in 3T3-L1 cells without affecting the induction of PPAR gamma1 by DEX, Exposure of LIP-expressing preadipocytes to troglitazone along with DEX, MM, and insulin induces differentiation into adipocytes. Additionally, we show that sustained expression of C/EBP alpha in these LIP-expressing adipocytes requires constant exposure to troglitazone. Taken together, these observations suggest that inhibition of C/EBP beta activity not only blocks C/EBP alpha and PPAR gamma2 expression, but it also renders the preadipocytes dependent on an exogenous PPAR gamma ligand for their differentiation into adipocytes, We propose, therefore, an additional role for C/EBP beta in regulating PPAR gamma activity during adipogenesis, and we suggest an alternative means of inducing preadipocyte differentiation that relies on the dexamethasone-associated induction of PPAR gamma1 expression.