Kimoto M, Javors M A, Ekholm J, Siafaka-Kapadai A, Hanahan D J
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
Arch Biochem Biophys. 1992 Nov 1;298(2):471-9. doi: 10.1016/0003-9861(92)90437-2.
This laboratory demonstrated earlier that oleic acid inhibited platelet activating factor (PAF)-induced aggregation and serotonin release of rabbit platelets (M. Miwa, C. Hill, R. Kumar, J. Sugatani, M. S. Olson, and D. J. Hanahan, 1987, J. Biol. Chem. 262, 527-530). More recently, we reported that oleic acid caused a decrease in phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2), but did not affect the level of inositol-1,4,5-trisphosphate (IP3), in rabbit platelets (D. Nunez, J. Randon, C. Gandhi, A. Siafaka-Kapadai, M. S. Olson, and D. J. Hanahan, 1990, J. Biol. Chem. 265, 18330-18838). These results suggested that oleic acid did not stimulate phospholipase C. In contrast, PAF induced a decrease in PIP2 and an increase in PIP level and IP3. These effects were shown to be attenuated by oleic acid. In this current study, our experiments show that (a) oleic acid blocked PAF-induced rise in intracellular [Ca2+] (to provide a mechanism in agreement with our previous experiments which showed that oleic acid inhibited PAF-induced IP3 rise in platelets) and (b) oleic acid itself induced a gradual rise in [Ca2+]i, which would provide a mechanism for oleic acid-induced aggregation despite the fact that oleic acid did not cause the production of IP3 (Nunez et al., 1990). Oleic acid, in a dose-dependent manner, was shown to inhibit PAF-induced Ca2+ mobilization from intra- and extracellular sources. The inhibition was closely related to the suppressive effect of oleic acid on PAF-induced aggregation. Furthermore, oleic acid inhibited the PAF-stimulated phosphorylation of the 20- and 40-kDa proteins. At concentrations above 20 microM, oleic acid itself could induce platelet aggregation and Ca2+ mobilization, but the time sequence of these two responses in human platelets was significantly different from those obtained with PAF. Oleic acid alone, at 20 microM, caused a 1.4-fold increase in the cAMP level in platelets which was followed by a decline to a basal value at higher concentrations of this fatty acid. It seemed clear that elevation of adenylate cyclase activity was not associated with free fatty acid inhibition of platelet activation. Interestingly, both PAF and oleic acid added separately to human platelets induced protein-tyrosine phosphorylation, but oleic acid did not cause any inhibition of PAF-induced protein-tyrosine phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)
该实验室早些时候证明，油酸可抑制血小板活化因子（PAF）诱导的兔血小板聚集和5-羟色胺释放（M. 三泽、C. 希尔、R. 库马尔、J. 菅谷、M. S. 奥尔森和D. J. 哈纳汉，1987年，《生物化学杂志》262卷，527 - 530页）。最近，我们报道油酸可使兔血小板中的磷脂酰肌醇 - 4 - 磷酸（PIP）和磷脂酰肌醇 - 4,5 - 二磷酸（PIP2）水平降低，但不影响肌醇 - 1,4,5 - 三磷酸（IP3）的水平（D. 努涅斯、J. 兰东、C. 甘地、A. 西亚法卡 - 卡帕代、M. S. 奥尔森和D. J. 哈纳汉，1990年，《生物化学杂志》265卷，18330 - 18838页）。这些结果表明油酸不会刺激磷脂酶C。相反，PAF可使PIP2水平降低，PIP水平和IP3升高。这些效应被证明可被油酸减弱。在本研究中，我们的实验表明：（a）油酸可阻断PAF诱导的细胞内[Ca2 +]升高（以提供一种与我们之前实验一致的机制，之前的实验表明油酸可抑制PAF诱导的血小板中IP3升高）；（b）油酸本身可诱导[Ca2 +]i逐渐升高，这将为油酸诱导的聚集提供一种机制，尽管油酸不会导致IP3的产生（努涅斯等人，1990年）。油酸以剂量依赖的方式被证明可抑制PAF诱导的细胞内和细胞外钙动员。这种抑制与油酸对PAF诱导的聚集的抑制作用密切相关。此外，油酸可抑制PAF刺激的20 kDa和40 kDa蛋白的磷酸化。在浓度高于20 microM时，油酸本身可诱导血小板聚集和钙动员，但人血小板中这两种反应的时间顺序与PAF诱导的显著不同。单独的20 microM油酸可使血小板中的cAMP水平升高1.4倍，在该脂肪酸浓度更高时随后降至基础值。很明显，腺苷酸环化酶活性的升高与游离脂肪酸对血小板活化的抑制无关。有趣的是，分别添加到人类血小板中的PAF和油酸均可诱导蛋白酪氨酸磷酸化，但油酸不会抑制PAF诱导的蛋白酪氨酸磷酸化。（摘要截选至400字）
