Studies on mammalian Ca^<2+>-dependent phospholipase A_2s

磷脂酶A2(PLA2)是催化sn-2位磷脂水解酶家族中的一员，可释放产生花生四烯酸(AA)的游离脂肪酸，花生四烯酸(AA)是生物活性二十烷酸的前体，也是溶血磷脂的前体。磷脂酶A_2参与多种细胞反应，如信号转导、宿主防御、凝血、吞噬和膜重塑等。根据最新的分类，PLA2_2可根据其结构和酶特性分为几个亚类，包括胞浆(CPLA_2)和分泌型(SLA_2)磷脂酶A_2同工酶以及钙离子非依赖性磷脂酶A_2(IPLA_2)。在本研究中，我们研究了几种典型的磷脂酶A_2和两种环氧合酶(COX)亚型在PG生物合成即刻和延迟反应中的功能偶联。CPIA_2、SPLA2-IIA和SPLA2-V是促进离子载体或缓激肽刺激后细胞释放AA的“信号PLA2”，…更多的是引起即时反应，而IL-1则引起延迟反应。由这些信号释放的AA在即刻反应中被两个COX转化为PGE_2，在延迟反应中被COX-2短暂地转化为PGE_2。在“磷脂重塑”中起关键作用的ipla在延迟反应中不能与COX-2偶联，而通过COX-L而不是COX-2与离子载体诱导的特异性PGE_2的产生有关。SPLA2-X诱导脂肪酸释放的方式类似于IPIA2，而不是其他sPLA2。胞外SPLA2S-IIA和-V，但胞内CPLA2和iPLA2都不能促进邻近COX表达细胞合成PGE2，这意味着这些SPLA2作为PG生物合成反应信号的旁分泌放大器从一个细胞到另一个细胞发挥着特殊的作用。细胞激活后，信号PLA2定位于胞核周围，COX同工酶均存在。Cpla_2以钙依赖的方式与核周微丝蛋白Vimentin结合，并从胞浆转运到核周膜。SPLA2-IIA结合GPI锚定的硫酸乙酰肝素蛋白多糖葡聚糖，使SPLA2-IIA进入小窝和核周，促进SPLA2-IIA诱导的A.A释放和PGE_2生成。较少

Phospholipase A_2 (PLA_2) represents a growing family of enzymes that catalyze the hydrolysis of phospholipids at the sn-2 position, liberating free fatty acids inducing arachidonic acid (AA), a precursor of bioactive eicosanoids, and lysophospholipids. PLA_2 has been implicated in diverse cellular responses, such as signal transduction, host defense, blood coagulation, cigestion, and membrane remodeling. Accorcing to an updated classification, PLA2_2 can be subdivided into several groups based upon their stnictures and enzymatic characteristics, inducing Ca^2-dependent cytosolic (cPLA_2) and secretory (sPLA_2) PLA_2 isozymes and Ca^<2+>-independent PLA_2 (iPLA_2). In the present study, the functional coupling of several clstinct PLA_2s and two cyclooxygenase (COX) isoforms during immediate and delayed PG-biosynthetic responses was examined cPIA_2, sPLA_2-IIA and sPLA_2-V were " signaling PLA-_2s" that promoted AA release from cells after stimulation with ionophore or bradykinin, which … More evoked the immediate response, and IL-1, which induced the delayed response. AA released by these signaling PLA_2s was converted to PGE_2 by both COXs during the immediate response and pretbminantly by COX-2 during the dulayed response. iPLA,, which plays a crucial role in "phospholipid remodeling', failed to couple with COX-2 during the delayed response, whereas it was linked to ionophore-induced immeciate PGE_2 generation via COX-l in preference to COX-2. sPLA_2-X induced fatty acid release in a manner similar to iPIA_2 rather than other sPLA2s. Extracellular sPLA_2s-IIA and -V.but neither intracellular cPLA_2 nor iPLA_2, augmented PGE_2 synthesis by neighboring COX-expressing cells, implying that these sPLA_2s play a particular role as paracrine amplifiers of the PG-biosynthetic response signal from one cell to another. After cell activation, signaling PLA_2s were localized around the nucleus where both COX isozymes were present. cPLA_2 bound to vimentin, a perinuclear intermeiziate filament protein, in Ca^<2+>-dependent manner and translocated from the cytosol to perinuclear membrane. sPLA_2-IIA bound a GPI-anchored heparan sulfate proteoglycan glypican, which &livered sPLA_2-IIA into caveolae and perinuclear sites and augmented sPLA_2-IIA-meciated A.A release and PGE_2 generation. Less