Kolesnick R N, Paley A E
J Biol Chem. 1987 Jul 5;262(19):9204-10.
Phorbol esters have been shown to cause degradation and synthesis of phosphatidylcholine. The present studies measure effects of another class of protein kinase C activators, the 1,2-diacylglycerols, on phosphatidylcholine metabolism using GH3 rat pituitary cells. 1,2-Dioctanoylglycerol (diC8, 200 micrograms/ml) reduced phosphatidylcholine levels to 95 and 70% of control by 5 min and 1 h, respectively, in cells labeled to equilibrium with [3H]choline. Concomitantly, lysophosphatidylcholine increased 3.5-fold by 15 min and remained elevated for 1 h. Glycerol 3-phosphocholine, the product of sequential deacylation of phosphatidylcholine, increased 5-fold in the medium over 1 h. DiC8 also increased the levels of unesterified arachidonic and stearic acids. Arachidonic acid was preferentially released from the 2-position of phosphatidylcholine to form lysophosphatidylcholine. These results suggest that diC8 stimulates a phospholipase A2. 1-Oleoyl-2-acetylglycerol produced similar effects. In contrast, phorbol esters failed to enhance degradation in these cells. 1,2-Diacylglycerols and phorbol esters, however, stimulated phosphatidylcholine synthesis via the CDP-choline pathway. This was measured as concentration-dependent incorporation of 32Pi and [3H]choline into phosphatidylcholine in short-term labeling studies. The effects of maximal concentrations of diC8 and the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, were additive. Furthermore, in cells down-modulated for phorbol ester action, diC8-induced degradation and synthesis were unchanged. These studies demonstrate that phorbol esters and 1,2-diacylglycerols have different effects on phosphatidylcholine metabolism and suggest that 1,2-diacylglycerols may stimulate phosphatidylcholine metabolism via a pathway independent of the protein kinase C which mediates phorbol ester action. This represents the first description of a biochemical pathway activated by 1,2-diacylglycerols and not by phorbol esters.
佛波酯已被证明可引起磷脂酰胆碱的降解和合成。本研究使用GH3大鼠垂体细胞，检测另一类蛋白激酶C激活剂——1,2 - 二酰基甘油对磷脂酰胆碱代谢的影响。在与[3H]胆碱达到平衡标记的细胞中，1,2 - 二辛酰甘油（二C8，200微克/毫升）在5分钟和1小时时分别将磷脂酰胆碱水平降至对照的95%和70%。同时，溶血磷脂酰胆碱在15分钟时增加3.5倍，并在1小时内保持升高。磷脂酰胆碱依次脱酰基的产物甘油3 - 磷酸胆碱在1小时内培养基中增加了5倍。二C8还增加了未酯化花生四烯酸和硬脂酸的水平。花生四烯酸优先从磷脂酰胆碱的2位释放形成溶血磷脂酰胆碱。这些结果表明二C8刺激了磷脂酶A2。1 - 油酰基 - 2 - 乙酰甘油产生了类似的效果。相比之下，佛波酯未能增强这些细胞中的降解。然而，1,2 - 二酰基甘油和佛波酯通过CDP - 胆碱途径刺激磷脂酰胆碱合成。这在短期标记研究中通过32Pi和[3H]胆碱向磷脂酰胆碱的浓度依赖性掺入来测定。二C8和佛波酯12 - O - 十四酰佛波醇 - 13 - 乙酸酯的最大浓度的作用是相加的。此外，在对佛波酯作用进行下调的细胞中，二C8诱导的降解和合成没有变化。这些研究表明佛波酯和1,2 - 二酰基甘油对磷脂酰胆碱代谢有不同的影响，并表明1,2 - 二酰基甘油可能通过独立于介导佛波酯作用的蛋白激酶C的途径刺激磷脂酰胆碱代谢。这是对由1,2 - 二酰基甘油而非佛波酯激活的生化途径的首次描述。
