Weiss R H, Yabes A P
Department of Internal Medicine, University of California, Davis 95616, USA.
Am J Physiol. 1996 Feb;270(2 Pt 1):C619-27. doi: 10.1152/ajpcell.1996.270.2.C619.
In contrast to their role as potent tumor promoters, phorbol esters can cause inhibition of cell growth. Because the effect of phorbol esters occurs through activation of protein kinase C (PKC) and because activated PKC is translocated to the membrane placing it in a position to act on the intracellular portion of the growth factor receptor, we asked whether this inhibitory effect is mediated through the action of phorbol 12-myristate 13-acetate (PMA) on receptor association with the signal transfer proteins. When added to rat vascular smooth muscle (VSM) cells concurrently with basic fibroblast growth factor (bFGF), PMA at 100 ng/ml completely inhibits bFGF-stimulated DNA synthesis. Under the same growth-inhibitory conditions of PMA addition, aggregation of phosphatidylinositol 3-kinase (PI3K) to the fibroblast growth factor receptor and tyrosine phosphorylation of the 85-kDa regulatory component of the signal transfer protein PI3K are reduced by 94 and 79%, respectively. PI3K catalytic activity, as measured by conversion of phosphatidylinositol to phosphatidylinositol 3-phosphate, is decreased 88% by PMA addition. This effect is not specific to PI3K, since aggregation of phospholipase C-gamma 1 to the activated bFGF receptor is also decreased by PMA treatment. In addition, the PI3K inhibitor wortmannin markedly attenuates bFGF-stimulated VSM cell growth in a dose-dependent manner. These data suggest that the site of growth inhibition by PMA in VSM cells lies upstream of signal transfer particle aggregation and that such growth arrest may be mediated through inhibition of activation of PI3K.
与佛波酯作为强效肿瘤促进剂的作用相反，佛波酯可导致细胞生长抑制。由于佛波酯的作用是通过激活蛋白激酶C（PKC）发生的，并且由于活化的PKC易位至细胞膜，使其能够作用于生长因子受体的细胞内部分，因此我们研究了这种抑制作用是否是通过佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）对受体与信号转导蛋白的结合作用来介导的。当与碱性成纤维细胞生长因子（bFGF）同时添加到大鼠血管平滑肌（VSM）细胞中时，100 ng/ml的PMA可完全抑制bFGF刺激的DNA合成。在添加PMA的相同生长抑制条件下，磷脂酰肌醇3激酶（PI3K）与成纤维细胞生长因子受体的聚集以及信号转导蛋白PI3K的85 kDa调节亚基的酪氨酸磷酸化分别减少了94%和79%。通过磷脂酰肌醇转化为磷脂酰肌醇3 - 磷酸来测量的PI3K催化活性，在添加PMA后降低了88%。这种作用并非PI3K所特有，因为磷脂酶C - γ1与活化的bFGF受体的聚集在PMA处理后也减少了。此外，PI3K抑制剂渥曼青霉素以剂量依赖的方式显著减弱bFGF刺激的VSM细胞生长。这些数据表明，PMA在VSM细胞中抑制生长的位点位于信号转导颗粒聚集的上游，并且这种生长停滞可能是通过抑制PI3K的激活来介导的。
