Lee Seung Jin, Yang Eun Kyoung, Kim Sang Geon
College of Pharmacy, Seoul National University, Sillim-dong, Kwanak-gu, Seoul 151-742, Korea.
Mol Pharmacol. 2006 Jul;70(1):415-25. doi: 10.1124/mol.106.022954. Epub 2006 Apr 12.
Peroxisome proliferator-activated receptor (PPAR)-gamma and retinoic acid X receptor (RXR) heterodimer regulates cell growth and differentiation. Zinc finger transcription factor-9 (Zf9), whose phosphorylation promotes target genes, is a transcription factor essential for transactivation of the transforming growth factor (TGF)-beta1 gene. This study investigated whether activation of PPARgamma-RXR heterodimer inhibits TGFbeta1 gene transcription and Zf9 phosphorylation and, if so, what signaling pathway regulates it. Either 15-deoxy-delta(12,14)-prostaglandin J2 (PGJ2) or 9-cis-retinoic acid (RA) treatment decreased the TGFbeta1 mRNA level in L929 fibroblasts. PGJ2 + RA, compared with individual treatment alone, synergistically inhibited the TGFbeta1 gene expression, which was abrogated by PPARgamma antagonists. Likewise, PGJ2 + RA decreased luciferase expression from the TGFbeta1 gene promoter. Promoter deletion analysis of the TGFbeta1 gene revealed that pGL3-323 making up to -323-base pair region, but lacking PPAR-responsive elements, responded to PGJ2 + RA. PGJ2 + RA treatment inhibited the activity of p70 ribosomal S6 kinase-1 (S6K1), abolishing Zf9 phosphorylation at serine as did rapamycin [a mammalian target of rapamycin (mTOR) inhibitor]. Zf9 dephosphorylation by PGJ2 + RA was reversed by transfection of cells with the plasmid encoding constitutively active S6K1 (CA-S6K1). Transfection with dominant negative S6K1 inhibited the TGFbeta1 gene. TGFbeta1 gene repression by PGJ2 + RA was consistently antagonized by CA-S6K1. Ectopic expression of PPARgamma1 and RXRalpha repressed pGL3-323 transactivation with S6K1 inhibition, which was abrogated by CA-S6K1 transfection. PGJ2 + RA induced phosphatase and tensin homolog deleted on chromosome 10 (PTEN), whose overexpression repressed the TGFbeta1 gene through S6K1 inhibition, decreasing extracellular signal-regulated kinase 1/2-90-kDa ribosomal S6 kinase 1 and Akt-mTOR phosphorylations. Data indicate that activation of PPARgamma-RXR heterodimer represses the TGFbeta1 gene and induces Zf9 dephosphorylation via PTEN-mediated S6K1 inhibition, providing insight into pharmacological manipulation of the TGFbeta1 gene regulation.
过氧化物酶体增殖物激活受体（PPAR）-γ与视黄酸X受体（RXR）异二聚体调节细胞生长和分化。锌指转录因子9（Zf9）的磷酸化可促进靶基因表达，它是转化生长因子（TGF）-β1基因反式激活所必需的转录因子。本研究调查了PPARγ-RXR异二聚体的激活是否会抑制TGFβ1基因转录和Zf9磷酸化，若如此，何种信号通路对其进行调控。15-脱氧-δ（12,14）-前列腺素J2（PGJ2）或9-顺式视黄酸（RA）处理均可降低L929成纤维细胞中TGFβ1 mRNA水平。与单独使用PGJ2或RA相比，PGJ2 + RA协同抑制TGFβ1基因表达，而PPARγ拮抗剂可消除这种抑制作用。同样地，PGJ2 + RA可降低TGFβ1基因启动子的荧光素酶表达。对TGFβ1基因进行启动子缺失分析发现，构成至-323碱基对区域但缺乏PPAR反应元件的pGL3-323对PGJ2 + RA有反应。PGJ2 + RA处理可抑制p70核糖体S6激酶-1（S6K1）的活性，使Zf9丝氨酸位点的磷酸化与雷帕霉素（一种哺乳动物雷帕霉素靶蛋白（mTOR）抑制剂）处理的效果相同而被消除。用编码组成型活性S6K1（CA-S6K1）的质粒转染细胞可逆转PGJ2 + RA介导的Zf9去磷酸化。用显性负性S6K1转染可抑制TGFβ1基因。CA-S6K1可持续拮抗PGJ2 + RA对TGFβ1基因的抑制作用。PPARγ1和RXRα的异位表达通过抑制S6K1来抑制pGL3-323的反式激活，而CA-S6K1转染可消除这种抑制作用。PGJ2 + RA可诱导10号染色体上缺失的磷酸酶和张力蛋白同源物（PTEN），其过表达通过抑制S6K1来抑制TGFβ1基因，减少细胞外信号调节激酶1/2-90-kDa核糖体S6激酶1和Akt-mTOR的磷酸化。数据表明，PPARγ-RXR异二聚体的激活通过PTEN介导的S6K1抑制作用来抑制TGFβ1基因并诱导Zf9去磷酸化，这为TGFβ1基因调控的药理操作提供了见解。
