Functional coupling of lipid mediator-metabolizing enzymes in mast cell

在本研究中，我们利用小鼠骨髓源性肥大细胞（BMMC）、大鼠肥大细胞瘤RBL和大鼠浆膜肥大细胞（CTMC）研究了参与脂质介质代谢的各种酶之间的功能偶联，如前列腺素（pg）和血小板活化因子（PAF）。花生四烯酸（AA）代谢我们发现，在FcepsilonRI交联与特定细胞因子联合刺激后，肥大细胞会引发双相pgd_2生物合成反应。在几分钟内发生的直接相中，胞质磷脂酶A_2 （cPLA_2）作用下从膜磷脂中释放的AA被组成型环氧合酶COX-1转化为PGD_2。在延迟期，即刺激后5 ~ 10 h，组成型cPLA_2和诱导分泌型PLA_2 （sPLA_2）释放的AA明显优于诱导型COX-2，导致PGD_2持续生成。肥大细胞中表达的sPLA_2同工酶主要为IIA型和V型sPLA_2，它们通过增加COX-2的表达来延缓PGD_2的产生。PAF代谢活化肥大细胞产生PAF，在几分钟内达到峰值，随后迅速下降。PAF的这种快速失活是由PAF乙酰水解酶的分泌形式介导的，该酶在肥大细胞激活后通过胞吐释放。特定的细胞因子组合可上调paf -乙酰水解酶的表达。

In the present study, we have examined the functional coupling between various enzymes involved in the metabolism of lipid mediators, such as prostaglandins (PGs) and platelet-activating factor (PAF), using mouse bone marrow-derived mast cells (BMMC), rat mastocytoma RBL, and rat serosal mast cells (CTMC).1. Arachidonic acid (AA) metabolismWe found that mast cells elicit a biphasic PGD_2-biosynthetic response after stimulation with FcepsilonRI crosslinking in combination with particular cytokines. In the immediate phase, which occurred within several minutes, the AA liberated from membrane phospholipids by the action of cytosolic phospholipase A_2 (cPLA_2) was converted by the constitutive cyclooxygenase (COX) isoform, COX-1, to PGD_2. In the delayed phase, which occurred during 5-10 h after stimulation, the AA released by the constitutive cPLA_2 and inducible secretory PLA_2 (sPLA_2) was presented to inducible COX-2 in marked peference to COX-l, leading to sustained PGD_2 generation. The major sPLA_2 isozymes expressed in mast cells were types IIA and V sPLA_2, which contributed to delayed PGD_2 generation by augmenting COX-2 expression.2. PAF metabolismActivated mast cells produced PAF, which reached a peak within a few minutes and declined rapidly thereafter. This rapid inactivation of PAF was mediated by a secretory form of PAF-acetylhydrolase, which was released by exocytosis following mast cell activation. The expression of PAF-acetylhydrolase was upregulated by particular combination of cytokines.