Kam Yoonseok, Exton John H
Howard Hughes Medical Institute and the Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
FASEB J. 2004 Feb;18(2):311-9. doi: 10.1096/fj.03-0731com.
Mitogens activate protein translation through phosphorylation of p7S6 kinase (p70(S6K)) and eIF4E binding protein 1 (4E-BP1) mediated by the mammalian target of rapamycin (mTOR) or phosphoinositide 3-kinase (PI3K). A recent report (Science 294, 1942, 2001) has implicated phospholipase D (PLD) in mTOR signaling. We studied the role of PLD in the phosphorylation of p70(S6K) and 4E-BP1 induced by lysophosphatidic acid (LPA) and platelet-derived growth factor (PDGF) using fibroblasts deficient in PLD activity and also 1-butanol, which inhibits phosphatidic acid production by PLD. The reduction in PLD activity in both situations impaired the effect of LPA on mTOR signaling but did not inhibit the effect of PDGF. PDGF induced marked phosphorylation of Akt (a PI3K target) but this was not affected by PLD deficiency. LPA caused much less phosphorylation of Akt and this was dependent on PLD activity. Toxin B, which inactivates Rho GTPases, markedly impaired PLD1 activation and phosphorylation of Akt, p70(S6K), and 4E-BP1 induced by LPA but had a minimal or no effect on the actions of PDGF. These results support the hypothesis that LPA activates protein translation through the action of PLD1-generated PA on mTOR and the PI3K/Akt pathway whereas PDGF acts through P13K/Akt independent of PLD1.
有丝分裂原通过雷帕霉素哺乳动物靶蛋白（mTOR）或磷酸肌醇3激酶（PI3K）介导的p7S6激酶（p70(S6K)）和真核翻译起始因子4E结合蛋白1（4E-BP1）的磷酸化来激活蛋白质翻译。最近一份报告（《科学》294, 1942, 2001）表明磷脂酶D（PLD）参与mTOR信号传导。我们使用PLD活性缺陷的成纤维细胞以及抑制PLD产生磷脂酸的1-丁醇，研究了PLD在溶血磷脂酸（LPA）和血小板衍生生长因子（PDGF）诱导的p70(S6K)和4E-BP1磷酸化中的作用。在这两种情况下PLD活性的降低损害了LPA对mTOR信号传导的作用，但并未抑制PDGF的作用。PDGF诱导Akt（一种PI3K靶点）发生显著磷酸化，但这不受PLD缺陷的影响。LPA引起的Akt磷酸化要少得多，且这依赖于PLD活性。使Rho GTP酶失活的毒素B显著损害了LPA诱导的PLD1激活以及Akt、p70(S6K)和4E-BP1的磷酸化，但对PDGF的作用影响极小或无影响。这些结果支持了以下假说：LPA通过PLD1产生的磷脂酸作用于mTOR和PI3K/Akt途径来激活蛋白质翻译，而PDGF通过PI3K/Akt起作用，且不依赖于PLD1。
