The Ras Inhibitors Caveolin-1 and Docking Protein 1 Activate Peroxisome Proliferator-Activated Receptor γ through Spatial Relocalization at Helix 7 of Its Ligand-Binding Domain
The Ras Inhibitors Caveolin-1 and Docking Protein 1 Activate Peroxisome Proliferator-Activated Receptor γ through Spatial Relocalization at Helix 7 of Its Ligand-Binding Domain
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DOI：
10.1128/mcb.01421-10
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发表时间：
2011-08-01
影响因子：
5.3
通讯作者：
Ebert, Matthias P. A.
中科院分区：
文献类型：
--
作者：
Burgermeister, Elke;Friedrich, Teresa;Ebert, Matthias P. A.
过氧化物酶体增殖物激活受体γ(PPARγ)是一种转录因子，可促进胃内细胞的分化和存活。PPARγ上调小窝蛋白-1(Cav1)，并与其相互作用，小窝1是RAS/丝裂原激活蛋白激酶(MAPKs)的支架蛋白。在胃癌(GC)患者中，PPARγ的胞浆到胞核的定位发生了改变，这表明Cav1在PPAR伽马信号的空间调节中发挥了迄今尚不清楚的作用。我们发现，在体外和体内，Cav1的缺失加速了正常胃和GC细胞的增殖。Cav1的下调增加了PPAR-γ中依赖RAS/MAPK的丝氨酸84的磷酸化，并增强了PPAR-γ靶基因的核转位和配体无关的转录。相反，Cav1过表达通过Cav1支架结构域(CSD)与PPAγ配体结合域螺旋7中保守的疏水基序相互作用，将PPARγ隔离在细胞质中。Cav1与内源性Ras/MAPK抑制因子对接蛋白1(Dok1)协同作用，促进PPAR-γ的配体依赖性转录活性，抑制细胞增殖。配体激活的PPAR伽马还可以减少肿瘤生长，并上调RAS/MAPK抑制剂Cav1和Dok1在小鼠GC模型中的表达。这些结果提示了一种新的PPARγ调节机制，即Ras/MAPK抑制剂作为支架蛋白，隔离PPARγ并使其对配体敏感，从而限制胃上皮细胞的增殖。
Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a transcription factor that promotes differentiation and cell survival in the stomach. PPAR gamma upregulates and interacts with caveolin-1 (Cav1), a scaffold protein of Ras/mitogen-activated protein kinases (MAPKs). The cytoplasmic-to-nuclear localization of PPAR gamma is altered in gastric cancer (GC) patients, suggesting a so-far-unknown role for Cav1 in spatial regulation of PPAR gamma signaling. We show here that loss of Cav1 accelerated proliferation of normal stomach and GC cells in vitro and in vivo. Downregulation of Cav1 increased Ras/MAPK-dependent phosphorylation of serine 84 in PPAR gamma and enhanced nuclear translocation and ligand-independent transcription of PPAR gamma target genes. In contrast, Cav1 overexpression sequestered PPAR gamma in the cytosol through interaction of the Cav1 scaffolding domain (CSD) with a conserved hydrophobic motif in helix 7 of PPA gamma's ligand-binding domain. Cav1 cooperated with the endogenous Ras/MAPK inhibitor docking protein 1 (Dok1) to promote the ligand-dependent transcriptional activity of PPAR gamma and to inhibit cell proliferation. Ligand-activated PPAR gamma also reduced tumor growth and upregulated the Ras/MAPK inhibitors Cav1 and Dok1 in a murine model of GC. These results suggest a novel mechanism of PPAR gamma regulation by which Ras/MAPK inhibitors act as scaffold proteins that sequester and sensitize PPAR gamma to ligands, limiting proliferation of gastric epithelial cells.