Laboratory of Biochemistry and Molecular Biology, Department of Biological and Environmental Sciences and Technologies, University of Salento, Via Prov.le Lecce-Monteroni, Lecce, Italy.
J Cell Physiol. 2012 Jun;227(6):2388-97. doi: 10.1002/jcp.22974.
Liver is an important target for thyroid hormone actions. T(3) exerts its effects by two mechanisms: (i) Genomic actions consisting of T(3) link to nuclear receptors that bind responsive elements in the promoter of target genes, (ii) non-genomic actions including integrin αvb3 receptor-mediated MAPK/ERK and PI3K/Akt/mTOR-C1 activation. SREBP-1a, SREBP-1c, and SREBP-2 are transcription factors involved in the regulation of lipogenic genes. We show in Hep G2 cells that T(3) determined a dose- and time-dependent increase in the level of the precursor form of SREBP-1 without affecting SREBP-1 mRNA abundance. T(3) also induced phosphorylation of ERK1/2, Akt and of mTOR-C1 target S6K-P70, and the cytosol-to-membrane translocation of PKC-α. Modulation of SREBP-1 protein level by T(3) was dependent on MAPK/ERK, PI3K/Akt/mTOR-C1 pathway activation since the MEK inhibitor PD98059 or the PI3K inhibitor LY294002 abolished the stimulatory effect of T(3) . Conversely, the effect of T(3) on SREBP-1 level was enhanced by using rapamycin, mTOR-C1 inhibitor. These data suggest a negative control of mTOR-C1 target S6K-P70 on PI3K/Akt pathway. The effect of T(3) on SREBP-1 content increased also by using PKC inhibitors. These inhibitors increased the action of T(3) on Akt phosphorylation suggesting that conventional PKCs may work as negative regulators of the T(3) -dependent SREBP-1 increase. T(3) effects were partially abrogated by tetrac, an inhibitor of the T(3) -αvβ3 receptor interaction and partially evoked by T(3) analog T(3) -agarose. These findings support a model in which T(3) activates intracellular signaling pathways which may be involved in the increment of SREBP-1 level through an IRES-mediated translation mechanism.
肝脏是甲状腺激素作用的重要靶器官。T(3) 通过两种机制发挥作用：(i) 基因组作用，包括 T(3) 与核受体结合，核受体结合靶基因启动子中的反应元件，(ii) 非基因组作用，包括整合素 αvb3 受体介导的 MAPK/ERK 和 PI3K/Akt/mTOR-C1 激活。SREBP-1a、SREBP-1c 和 SREBP-2 是参与调节脂肪生成基因的转录因子。我们在 Hep G2 细胞中表明，T(3) 确定了剂量和时间依赖性增加 SREBP-1 的前体形式的水平，而不影响 SREBP-1 mRNA 丰度。T(3) 还诱导 ERK1/2、Akt 和 mTOR-C1 靶标 S6K-P70 的磷酸化，以及 PKC-α 的细胞质到膜的易位。T(3) 对 SREBP-1 蛋白水平的调节依赖于 MAPK/ERK、PI3K/Akt/mTOR-C1 途径的激活，因为 MEK 抑制剂 PD98059 或 PI3K 抑制剂 LY294002 消除了 T(3) 的刺激作用。相反，使用雷帕霉素，mTOR-C1 抑制剂，增强了 T(3) 对 SREBP-1 水平的影响。这些数据表明 mTOR-C1 靶标 S6K-P70 对 PI3K/Akt 途径的负调控。使用 PKC 抑制剂也增加了 T(3)对 SREBP-1 含量的作用。这些抑制剂增加了 T(3)对 Akt 磷酸化的作用，表明传统 PKC 可能作为 T(3)依赖性 SREBP-1 增加的负调节剂。T(3) 效应部分被 T(3) -αvβ3 受体相互作用的抑制剂 tetrac 阻断，部分被 T(3) 类似物 T(3) -agarose 诱发。这些发现支持了一种模型，即 T(3) 激活细胞内信号通路，这些信号通路可能通过 IRES 介导的翻译机制参与 SREBP-1 水平的增加。
