Rosenberg I L, Smart D A, Gilfillan A M, Rooney S A
Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06510.
Biochim Biophys Acta. 1987 Oct 17;921(3):473-80. doi: 10.1016/0005-2760(87)90074-9.
We previously reported that addition of phosphatidylglycerol to the culture medium stimulates phosphatidylcholine synthesis and cholinephosphate cytidylyltransferase activity in type II pneumocytes. In view of the known biological effects of diacylglycerols and since phosphatidylglycerol could be metabolized to diacylglycerol, we now examined the effects of diacylglycerols on the same parameters. The rate of choline incorporation into phosphatidylcholine was increased 30-60% by 10 microM phosphatidylglycerol, diolein, mixed diacylglycerols and 1-oleoyl-2-acetylglycerol (OAG). The effects of phosphatidylglycerol and OAG were not additive, suggesting a similar mechanism of action. The diacylglycerols and phosphatidylglycerol increased the activity of cholinephosphate cytidylyltransferase in type II cell sonicates by 35-50%, but had no effect on the activities of choline kinase, cholinephosphotransferase or 1-acylglycerophosphocholine acyltransferase. Again, the effects of OAG and phosphatidylglycerol on cytidylyltransferase were not additive. It is known that addition of lipids to the assay mixture increases the activity of cholinephosphate cytidylyltransferase in vitro and inclusion of the above lipids (1.1 mM) in the in vitro assay mixture increased cytidylyltransferase activity in type II cell sonicates. In addition, the stimulatory effects of OAG and of diolein, as well as of phosphatidylglycerol as reported previously, in the culture medium on cytidylyltransferase activity in type II cells were diminished or abolished when the assay was carried out in the presence of sufficient amounts of the same lipids to stimulate maximally the activity in vitro. These data show that lipids in the culture medium stimulate phosphatidylcholine biosynthesis in type II cells by direct activation of cholinephosphate cytidylyltransferase.
我们之前报道过，向培养基中添加磷脂酰甘油可刺激II型肺细胞中磷脂酰胆碱的合成及胆碱磷酸胞苷转移酶的活性。鉴于二酰基甘油已知的生物学效应，且由于磷脂酰甘油可代谢为二酰基甘油，我们现在研究了二酰基甘油对相同参数的影响。10微摩尔的磷脂酰甘油、二油精、混合二酰基甘油和1-油酰基-2-乙酰甘油（OAG）可使胆碱掺入磷脂酰胆碱的速率提高30%-60%。磷脂酰甘油和OAG的作用并非相加，提示作用机制相似。二酰基甘油和磷脂酰甘油可使II型细胞超声裂解物中胆碱磷酸胞苷转移酶的活性提高35%-50%，但对胆碱激酶、胆碱磷酸转移酶或1-酰基甘油磷酸胆碱酰基转移酶的活性无影响。同样，OAG和磷脂酰甘油对胞苷转移酶的作用也不是相加的。已知向测定混合物中添加脂质可在体外提高胆碱磷酸胞苷转移酶的活性，在体外测定混合物中加入上述脂质（1.1毫摩尔）可提高II型细胞超声裂解物中胞苷转移酶的活性。此外，当在存在足够量相同脂质以最大程度刺激体外活性的情况下进行测定时，OAG、二油精以及之前报道的磷脂酰甘油在培养基中对II型细胞中胞苷转移酶活性的刺激作用减弱或消失。这些数据表明，培养基中的脂质通过直接激活胆碱磷酸胞苷转移酶来刺激II型细胞中磷脂酰胆碱的生物合成。
