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在肥大细胞激活中的特定作用。细胞膜上的磷脂酰丝氨酸(PS)被认为是激活蛋白激酶C和凝血的重要辅助因子。最近，PS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+-ATPase、动力蛋白GTP酶和二酰甘油激酶。PS主要分布在各种类型细胞的质膜内层，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出现在外叶。表面暴露的PS也被证明是网状内皮系统清除受损或老化细胞的信号，并在正在发生凋亡的细胞中观察到。因此，必须严格控制PS在细胞表面的暴露。另一种含丝氨酸的磷脂，Llysops是im…更多的是在病理生理条件下起到脂质介质的作用。例如，溶菌素被证明可以与局部肥大细胞相互作用，产生特异性和立体选择性的激活。它还诱导卵巢癌细胞和乳腺癌细胞胞浆内游离钙离子([Ca2+]i)的一过性增加，并抑制丝裂原诱导的T细胞活化，特别是含有不饱和脂肪酸的2-酰基-1-溶酶多糖。LysoPS存在于人的血清、房水和眼睛的泪腺液中。它很可能是由磷脂酶A1或A2从PS中产生的，但体内产生和消除溶菌素的确切机制仍有待阐明。在本研究中，我们证明了磷脂酰丝氨酸专一性磷脂酶A1，PS-PLA1，在FCERI交联剂存在的情况下，通过产生2-酰基-1-溶菌素来刺激RPMC释放组胺。2-酰基-1-溶菌素的活性几乎与1-酰基-2-溶菌素相同，而用丙氨酸取代活性丝氨酸残基(Ser166)的PS-PLA1则不具有这种活性。另一种能在体外产生溶菌素的分泌型磷脂酶A2对RPMC的组胺诱导剂也很差。PS-PLA1能显著刺激RPMC释放组胺，表明溶菌素主要来源于肥大细胞以外的其他细胞。与这一现象相一致的是，当RPMC与凋亡的Jurkat细胞混合时，该酶更有效地刺激组胺释放。在此条件下，PS-PLA1处理的凋亡细胞释放出含有不饱和脂肪酸的溶菌素。最后，与PS-PLA1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可与硫酸乙酰肝素蛋白多糖结合，有效地降解出现在凋亡细胞质膜上的PS，并通过2-酰基-1-溶菌素介导的肥大细胞活化。较少

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