Patho-Physiological function of Phosphatidylserine-specific Phospholipase A1-Specific role of PS-PLA 1 in mast cell activation-

磷脂酰丝氨酸特异性磷脂酶a1的病理生理功能- PS-PLA1在肥大细胞活化中的特异性作用。细胞膜中的磷脂酰丝氨酸（PS）被认为是激活蛋白激酶C和血液凝固的必要辅助因子。最近，PS已被证明可以调节多种酶的活性，如c-Raf-1蛋白激酶、一氧化氮合酶、Na+/K+- atp酶、动力蛋白GTPase和二酰基甘油激酶。在各种类型的细胞中，PS主要位于质膜的内小叶上，但在细胞因子、炎症反应和血小板活化等多种因素的刺激下，也会出现在外小叶上。表面暴露的PS也被证明是网状内皮系统去除受损或老化细胞的信号，并在细胞凋亡中观察到。因此，必须严格调节PS在细胞表面的暴露。另一种含丝氨酸的磷脂，溶酶ops，在病理生理条件下作为脂质介质的作用更为复杂。例如，lysoPS被证明与局部肥大细胞相互作用，产生特异性和立体选择性激活。它还能诱导卵巢癌和乳腺癌细胞内胞质游离Ca2+ ([Ca2+]i)和溶酶蛋白的短暂增加，尤其是带不饱和脂肪酸的2-酰基-1-溶酶蛋白，抑制丝裂原诱导的T细胞活化。溶血蛋白存在于人血清、房水和泪腺液中。它很可能是由PS通过磷脂酶A1或A2产生的，但体内裂解ops产生和消除的确切机制仍有待阐明。在本研究中，我们发现磷脂酰丝氨酸特异性磷脂酶A1， PS-PLA1，在FCERI交联剂存在的情况下，通过产生2-酰基-1- lysops，刺激RPMC释放组胺。2-酰基-1- lysops的效力与1-酰基-2- lysops几乎相等。催化失活性的PS-PLA1，其活性丝氨酸残基（Ser166）被丙氨酸残基取代，没有表现出这种活性。sPLA2-IIA是另一种在体外能够产生溶酶ops的分泌性PLA2，对RPMC也是一种较差的组胺诱导剂。ps - pla1显著刺激粗RPMC释放组胺，表明溶酶ops主要来源于肥大细胞以外的细胞。与此现象一致，当RPMC与凋亡的Jurkat细胞混合时，酶更有效地刺激组胺释放。在这些条件下，PS-PLA1处理的凋亡细胞释放出含有不饱和脂肪酸的溶酶蛋白。最后，与PS-PLA1具有亲和力的肝素完全阻断了该酶的刺激作用。综上所述，PS- pla1可能与硫酸肝素蛋白聚糖结合，有效水解出现在凋亡细胞细胞膜上的PS，并刺激2-酰基-1- lysops介导的肥大细胞活化。少

Patho-physiological function of Phosphatidylserine-specific Phospholipase A1-Specific role of PS-PLA1 in mast cell activation.Phosphatidylserine (PS) in cell membranes is known to be an essential cofactor for the activation of protein kinase C and for blood coagulation. More recently, PS has been shown to regulate the activity of various enzymes, such as c-Raf-1 protein kinase, nitric oxide synthase, Na+/K+-ATPase, dynamin GTPase, and diacylglycerol kinase. PS is predominantly located on the inner leatlet of plasma membranes in various types of cell, but appears on the outer leaflet after stimulation by various factors such as cytokines, inflammatory reactions and platelet activation. Surface-exposed PS has also been shown to act as a signal for the removal of damaged or aged cells by the reticuloendothelial system, and is observed in cells undergoing apoptosis. Thus, the exposure of PS on the cell surface must be tightly regulated. Another serine-containing phospholipid, lysoPS, is im … More plicated to act as a lipid mediator under patho-physiological conditions. For example, lysoPS is demonstrated to interact with local mast cells, producing specific and stereo-selective activation. It also induces transient increases in cytosolic free Ca2+ ([Ca2+]i) in ovarian and breast cancer cells and lysoPS, especially 2-acyl-1-lysoPS with unsaturated fatty acid, inhibits mitogen-induced T cell activation. LysoPS is present in human serum, the aqueous humor and the lachrymal gland fluid of the eye. It is likely to be produced from PS by phospholipase A1 or A2, but the precise mechanisms of lysoPS production and elimination in vivo remain to be clarified. In the present study we show that phosphatidylserine-specific phospholipase A1, PS-PLA1, stimulates histamine release from RPMC though a production of 2-acyl-1-lysoPS in the presence of FCERI cross-linker. The potency of 2-acyl-1-lysoPS is almost equal to that of 1-acyl-2-lysoPS.A catalytically inactive PS-PLA1, in which an active serine residue (Ser166) was replaced with an alanine residue did not show such activity. sPLA2-IIA, another secretory PLA2 that is capable of producing lysoPS in vitro, was also a poor histamine inducer against RPMC.PS-PLA1 significantly stimulated histamine release from crude RPMC, indicating that lysoPS is mainly derived from cells other than mast cells. In agreement with this phenomenon, the enzyme stimulated the histamine release more efficiently when RPMC was mixed with apoptotic Jurkat cells. Under these conditions, lysoPS with unsaturated fatty acid was released from the apoptotic cells treated with PS-PLA1. Finally, heparin, which has affinity for PS-PLA1, completely blocked the stimulatory effect of the enzyme. In conclusion, PS-PLA1 may bind to heparan sulfate proteoglycan, efficiently hydrolyze PS appearing on plasma membranes of apoptotic cells and stimulate mast cell activation mediated by 2-acyl-1-lysoPS. Less