Arachidonic acid release from NIH 3T3 cells by group-I phospholipase A2: involvement of a receptor-mediated mechanism.

Xing M; Miele L; Mukherjee AB

摘要

Group I pancreatic phospholipase A2 (PLA2 I) is primarily a digestive enzyme. Recently, however, in addition to its catalytic activity a receptor-mediated function has been described for this enzyme. PLA2 I binding to its receptor induces cellular chemokinesis, proliferation, and smooth muscle contraction. This enzyme also induces the production of prostaglandin E2 in certain cells and may have a proinflammatory role. However, despite its ability to hydrolyze phospholipids in in vitro assays, PLA2-I does not efficiently catalyze release of AA from intact cells. Here, we demonstrate that while short-term exposure of NIH 3T3 cells to PLA2-I is ineffective, exposure of 6 h or longer significantly increases the basal release of AA. Dose-response curve of PLA2-I-induced AA release was saturable with an EC50 of 14.01 +/- 1.36 nM (n = 3). [3H]-AA was preferentially released over [3H]-oleic acid by PLA2-I. PLA2-I, inactivated with 4-bromophenacyl bromide, was fully capable of mediating AA release. These data suggest that a non-catalytic, receptor-mediated mechanism is involved in PLA2-I-induced AA release in NIH-3T3 cells. This release of AA is not dependent on protein kinase C or Ca2+ concentration. Comparison of the effect of PLA2-I with those of ATP and platelet-derived growth factor indicates that each of these agonists regulates AA release via independent pathways. Neither the basal enzymatic activity of the 85-kDa cytosolic PLA2 nor the protein level of this enzyme was affected by treatment of cells with PLA2-I. However, the increase in basal enzymatic activity of 85 kDa PLA2 due to protein kinase C activation was further enhanced by pretreatment of cells with PLA2-I. We conclude that: (1) short-term exposure of cells to PLA2 I does not cause measurable AA release; (2) release of AA from intact cells by this enzyme requires long-term exposure; (3) AA release is not mediated by a direct catalytic effect of PLA2 I; and (4) AA release by PLA2 I is accomplished via a receptor-mediated process. Taken together, these results raise the possibility that PLA2 I, in addition to its digestive function, may also contribute to aggravate preexisting inflammatory processes and/or to initiate new ones when chronic exposure of cells to this enzyme occurs.

机译：我组胰腺磷脂酶A2 (PLA2)主要消化酶。除了它的催化活性受体介导的功能被描述这种酶。诱发细胞化学运动性、扩散和平滑肌收缩。诱发前列腺素E2的生产某些细胞和促炎的可能的角色。磷脂在体外实验中,PLA2-I没有有效地促进释放AA完好无损细胞。暴露NIH 3 t3细胞PLA2-I无效,暴露6小时或更长显著增加了基底AA的释放。PLA2-I-induced AA版本的剂量反应曲线是饱和的EC50 14.01 + / - 1.36海里吗(n = 3)。[3 h] aa优先被释放[3 h] PLA2-I十八烯酸。与4-bromophenacyl溴化,是完全有能力调解的AA释放。非受体介导机制参与PLA2-I-induced AA在NIH-3T3发布细胞。蛋白激酶C或Ca2 +的浓度。PLA2-I的影响与比较ATP和血小板源生长因子这些受体激动剂调节AA释放通过独立的途径。85 - kda酶活性的胞质PLA2也没有这种酶的蛋白质含量的影响与PLA2-I治疗的细胞。增加基底85 kDa的酶活性PLA2由于蛋白激酶C的激活进一步加强细胞的预处理PLA2-I。细胞PLA2我不会引起明显的AA释放;这种酶需要长期接触;版本不是由直接催化PLA2的我;通过一个受体介导的过程来实现的。综上所述,这些提高的结果可能性,PLA2我,除了它消化功能,也会导致加重先前存在的炎症过程和/或启动新的慢性接触的时候细胞的这种酶发生。

Arachidonic acid release from NIH 3T3 cells by group-I phospholipase A2: involvement of a receptor-mediated mechanism.

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