Gormand Amélie, Berggreen Christine, Amar Lahouari, Henriksson Emma, Lund Ingrid, Albinsson Sebastian, Göransson Olga
Department of Experimental Medical ScienceLund University, BMC C11, 221 84 Lund, SwedenDepartment of BiomedicineKarolinska Institute, Stockholm, Sweden.
Department of Experimental Medical ScienceLund University, BMC C11, 221 84 Lund, SwedenDepartment of BiomedicineKarolinska Institute, Stockholm, Sweden
J Mol Endocrinol. 2014 Aug;53(1):117-30. doi: 10.1530/JME-13-0296. Epub 2014 May 23.
cAMP-response element-binding protein (CREB) is required for the induction of adipogenic transcription factors such as CCAAT/enhancer-binding proteins (C/EBPs). Interestingly, it is known from studies in other tissues that LKB1 and its substrates AMP-activated protein kinase (AMPK) and salt-inducible kinases (SIKs) negatively regulate gene expression by phosphorylating the CREB co-activator CRTC2 and class IIa histone deacetylases (HDACs), which results in their exclusion from the nucleus where they co-activate or inhibit their targets. In this study, we show that AMPK/SIK signalling is acutely attenuated during adipogenic differentiation of 3T3-L1 preadipocytes, which coincides with the dephosphorylation and nuclear translocation of CRTC2 and HDAC4. When subjected to differentiation, 3T3-L1 preadipocytes in which the expression of LKB1 was stably reduced using shRNA (Lkb1-shRNA), as well as Lkb1-knockout mouse embryonic fibroblasts (Lkb1(-/-) MEFs), differentiated more readily into adipocyte-like cells and accumulated more triglycerides compared with scrambled-shRNA-expressing 3T3-L1 cells or Wt MEFs. In addition, the phosphorylation of CRTC2 and HDAC4 was reduced, and the mRNA expression of adipogenic transcription factors Cebpa, peroxisome proliferator-activated receptor γ (Pparg) and adipocyte-specific proteins such as hormone-sensitive lipase (HSL), fatty acid synthase (FAS), aP2, GLUT4 and adiponectin was increased in the absence of LKB1. The mRNA and protein expression of Ddit3/CHOP10, a dominant-negative member of the C/EBP family, was reduced in Lkb1-shRNA-expressing cells, providing a potential mechanism for the up-regulation of Pparg and Cebpa expression. These results support the hypothesis that LKB1 signalling keeps preadipocytes in their non-differentiated form.
环磷酸腺苷反应元件结合蛋白（CREB）是诱导脂肪生成转录因子（如CCAAT/增强子结合蛋白（C/EBP））所必需的。有趣的是，在其他组织的研究中发现，肝脏激酶B1（LKB1）及其底物腺苷酸活化蛋白激酶（AMPK）和盐诱导激酶（SIK）通过磷酸化CREB共激活因子CRTC2和IIa类组蛋白去乙酰化酶（HDAC）来负调控基因表达，这导致它们被排除在细胞核外，而在细胞核中它们可共激活或抑制其靶标。在本研究中，我们发现，在3T3-L1前脂肪细胞的脂肪生成分化过程中，AMPK/SIK信号急剧减弱，这与CRTC2和HDAC4的去磷酸化及核转位相一致。当进行分化时，与表达乱序短发夹RNA（shRNA）的3T3-L1细胞或野生型（Wt）小鼠胚胎成纤维细胞（MEF）相比，使用shRNA稳定降低LKB1表达的3T3-L1前脂肪细胞（Lkb1-shRNA）以及Lkb1基因敲除的小鼠胚胎成纤维细胞（Lkb1(-/-) MEF）更容易分化为脂肪细胞样细胞并积累更多甘油三酯。此外，在缺乏LKB1的情况下，CRTC2和HDAC4的磷酸化减少，脂肪生成转录因子Cebpa、过氧化物酶体增殖物激活受体γ（Pparg）以及激素敏感性脂肪酶（HSL）、脂肪酸合酶（FAS）、aP2、葡萄糖转运蛋白4（GLUT4）和脂联素等脂肪细胞特异性蛋白的mRNA表达增加。在表达Lkb1-shRNA的细胞中，C/EBP家族的显性负性成员Ddit3/CHOP10的mRNA和蛋白表达降低，这为Pparg和Cebpa表达上调提供了一种潜在机制。这些结果支持了LKB1信号使前脂肪细胞保持未分化状态这一假说。
