森下 英昭 持田製薬(株), バイオサイエンス研, マネージャー(研究職)
AOKI Junken THE TOKYO UNIVERSITY PHARMACEUTICAL SCIENCES, ASSISTANT PROFESSOR, 大学院・薬学系研究科, 助教授 (20250219)
ARAI Hiroyuki THE TOKYO UNIVERSITY PHARMACEUTICAL SCIENCES, PROFESSOR, 大学院・薬学系研究科, 教授 (40167987)
MORISHITA Hideaki MOTIDA PHARMACEUTICAL COMPANY RESEARCH MANAGER
|Budget Amount *help
¥13,300,000 (Direct Cost : ¥13,300,000)
Fiscal Year 2000 : ¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1999 : ¥4,500,000 (Direct Cost : ¥4,500,000)
Fiscal Year 1998 : ¥7,000,000 (Direct Cost : ¥7,000,000)
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
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.