Rao G N, Madamanchi N R, Lele M, Gadiparthi L, Gingras A C, Eling T E, Sonenberg N
Division of Cardiology, University of Texas Medical Branch, Galveston, Texas 77555, USA.
J Biol Chem. 1999 Apr 30;274(18):12925-32. doi: 10.1074/jbc.274.18.12925.
To understand the mechanisms of prostaglandin F2alpha (PGF2alpha)-induced protein synthesis in vascular smooth muscle cells (VSMC), we have studied its effect on two major signal transduction pathways: mitogen-activated protein kinases and phosphatidylinositol 3-kinase (PI3-kinase) and their downstream targets ribosomal protein S6 kinase (p70(S6k)) and eukaryotic initiation factor eIF4E and its regulator 4E-BP1. PGF2alpha induced the activities of extracellular signal-regulated kinase 2 (ERK2) and Jun N-terminal kinase 1 (JNK1) groups of mitogen-activated protein kinases, PI3-kinase, and p70(S6k) in a time-dependent manner in growth-arrested VSMC. PGF2alpha also induced eIF4E and 4E-BP1 phosphorylation, global protein synthesis, and basic fibroblast growth factor-2 (bFGF-2) expression in VSMC. Whereas inhibition of PI3-kinase by wortmannin completely blocked the p70(S6k) activation, it only partially decreased the ERK2 activity, and had no significant effect on global protein synthesis and bFGF-2 expression induced by PGF2alpha. Rapamycin, a potent inhibitor of p70(S6k), also failed to prevent PGF2alpha-induced global protein synthesis and bFGF-2 expression, although it partially decreased ERK2 activity. In contrast, inhibition of ERK2 activity by PD 098059 led to a significant loss of PGF2alpha-induced eIF4E and 4E-BP1 phosphorylation, global protein synthesis, and bFGF-2 expression. PGF2alpha-induced phosphorylation of eIF4E and 4E-BP1 was also found to be sensitive to inhibition by both wortmannin and rapamycin. These findings demonstrate that 1) PI3-kinase-dependent and independent mechanisms appear to be involved in PGF2alpha-induced activation of ERK2; 2) PGF2alpha-induced eIF4E and 4E-BP1 phosphorylation appear to be mediated by both ERK-dependent and PI3-kinase-dependent rapamycin-sensitive mechanisms; and 3) ERK-dependent eIF4E phosphorylation but not PI3-kinase-dependent p70(S6k) activation correlates with PGF2alpha-induced global protein synthesis and bFGF-2 expression in VSMC.
为了解前列腺素F2α（PGF2α）诱导血管平滑肌细胞（VSMC）中蛋白质合成的机制，我们研究了其对两条主要信号转导途径的影响：丝裂原活化蛋白激酶和磷脂酰肌醇3激酶（PI3激酶）及其下游靶点核糖体蛋白S6激酶（p70(S6k)）、真核起始因子eIF4E及其调节因子4E-BP1。PGF2α在生长停滞的VSMC中以时间依赖性方式诱导丝裂原活化蛋白激酶的细胞外信号调节激酶2（ERK2）和Jun N端激酶1（JNK1）组、PI3激酶和p70(S6k)的活性。PGF2α还诱导VSMC中eIF4E和4E-BP1磷酸化、整体蛋白质合成以及碱性成纤维细胞生长因子-2（bFGF-2）表达。渥曼青霉素抑制PI3激酶可完全阻断p70(S6k)的激活，但仅部分降低ERK2活性，对PGF2α诱导的整体蛋白质合成和bFGF-2表达无显著影响。雷帕霉素是p70(S6k)的有效抑制剂，虽然它部分降低了ERK2活性，但也未能阻止PGF2α诱导的整体蛋白质合成和bFGF-2表达。相反，PD 098059抑制ERK2活性导致PGF2α诱导的eIF4E和4E-BP1磷酸化、整体蛋白质合成以及bFGF-2表达显著丧失。还发现PGF2α诱导的eIF4E和4E-BP1磷酸化对渥曼青霉素和雷帕霉素的抑制均敏感。这些发现表明：1）PI3激酶依赖性和非依赖性机制似乎参与了PGF2α诱导的ERK2激活；2）PGF2α诱导的eIF4E和4E-BP1磷酸化似乎由ERK依赖性和PI3激酶依赖性雷帕霉素敏感机制介导；3）ERK依赖性eIF4E磷酸化而非PI3激酶依赖性p70(S6k)激活与PGF2α诱导的VSMC整体蛋白质合成和bFGF-2表达相关。
