Thalacker F W, Nilsen-Hamilton M
Department of Biochemistry, Iowa State University, Ames 50011.
Biochem J. 1992 Nov 1;287 ( Pt 3)(Pt 3):855-62. doi: 10.1042/bj2870855.
We have investigated the mechanisms by which type 1 plasminogen activator inhibitor (PAI-1) is regulated by transforming growth factor beta (TGF-beta) and by epidermal growth factor (EGF) in CCL64 mink lung epithelial cells, BSC-1 monkey kidney epithelial cells, mouse embryo fibroblast (AKR-2B 84A) cells and normal rat kidney fibroblasts (NRK). TGF-beta increases PAI-1 expression in all four cell lines, and EGF acts synergistically with TGF-beta to increase PAI-1 expression in CCL64 cells but not in the other three cell lines. Here we show that PAI-1 expression can be regulated independently through two different signal transduction pathways. One pathway involves protein kinase C and is stimulated by the tumour promoter phorbol myristate acetate (PMA). Whereas preincubation with PMA completely eliminated PMA-induced PAI-1 synthesis and secretion in both CCL64 and BSC-1 cells, this treatment had no effect on TGF-beta- and EGF-induced PAI-1 levels. Therefore we conclude that protein kinase C does not mediate the effects of either EGF or TGF-beta on PAI-1 expression. The expression of PAI-1 was decreased by agents increasing intracellular cyclic AMP: (cAMP) cholera toxin, forskolin and dibutyryl cAMP lowered both the basal level and the TGF-beta- and PMA-induced levels of PAI-1 expression. These effects of cAMP-elevating agents and of TGF-beta on PAI-1 protein synthesis were also reflected in changes in TGF-beta-induced PAI-1 gene transcription, as measured by nuclear run-on. These results show that PAI-1 gene expression is sensitive to high levels of intracellular cAMP and that this effect occurs at the transcriptional level. Although increased intracellular cAMP concentrations decrease the absolute level of PAI-1 expression, the ability of TGF-beta and EGF to induce PAI-1 gene expression is unchanged. These results are discussed in relation to the observation that sensitivity to cAMP is a common feature of TGF-beta-regulated genes.
我们研究了1型纤溶酶原激活物抑制剂（PAI-1）在CCL64貂肺上皮细胞、BSC-1猴肾上皮细胞、小鼠胚胎成纤维细胞（AKR-2B 84A）和正常大鼠肾成纤维细胞（NRK）中受转化生长因子β（TGF-β）和表皮生长因子（EGF）调控的机制。TGF-β在所有四种细胞系中均增加PAI-1的表达，而EGF与TGF-β协同作用，在CCL64细胞中增加PAI-1的表达，但在其他三种细胞系中则不然。在此我们表明，PAI-1的表达可通过两种不同的信号转导途径独立调控。一种途径涉及蛋白激酶C，并受到肿瘤启动子佛波酯肉豆蔻酸酯乙酸盐（PMA）的刺激。虽然在CCL64和BSC-1细胞中预先用PMA孵育可完全消除PMA诱导的PAI-1合成和分泌，但该处理对TGF-β和EGF诱导的PAI-1水平没有影响。因此我们得出结论，蛋白激酶C不介导EGF或TGF-β对PAI-1表达的作用。增加细胞内环磷酸腺苷（cAMP）的试剂可降低PAI-1的表达：霍乱毒素、福斯可林和二丁酰cAMP降低了PAI-1表达的基础水平以及TGF-β和PMA诱导的水平。如通过细胞核连续转录测定所示，cAMP升高试剂和TGF-β对PAI-1蛋白合成的这些作用也反映在TGF-β诱导的PAI-1基因转录变化中。这些结果表明，PAI-1基因表达对细胞内高水平的cAMP敏感，且这种作用发生在转录水平。虽然细胞内cAMP浓度的增加会降低PAI-1表达的绝对水平，但TGF-β和EGF诱导PAI-1基因表达的能力并未改变。结合对cAMP敏感性是TGF-β调控基因的共同特征这一观察结果，对这些结果进行了讨论。
