Whalen M M, Doshi R N, Bader B W, Bankhurst A D
Department of Medicine, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA.
Cell Physiol Biochem. 1999;9(6):297-309. doi: 10.1159/000016324.
Treatment of human natural killer (NK) cells with phospholipase A(2) (PLA(2)) inhibitors, mepacrine and 4-bromophenacyl bromide (BPB), diminished their ability to lyse K562 target cells by as much as 100%. The ability of NK cells to bind to K562 cells was significantly affected by BPB above 2 microM, but not by mepacrine at any concentration tested. This indicates that BPB is having effects on NK cells unrelated to its inhibition of PLA(2) activity at concentrations above 2 microM. The activation of phospholipase C in response to K562 cell binding (as measured by inositol phosphate turnover) was unaffected by inhibition of the PLA(2) activity. The products of PLA(2) catabolism are a fatty acid (often arachidonic acid) and a lysophospholipid. Inhibition of NK cytotoxicity by mepacrine or BPB is reversed significantly when lysophosphatidylcholine, but no other lysolipid, is added back to the NK cells before assaying for cytotoxicity. Arachidonic acid, but not linoleic acid, also significantly reverses inhibition of NK cytotoxicity. Finally, the 15-lipoxygenase product, 15S-hydroperoxyeicosatetraenoic acid (15S-HPETE), is also able to reverse mepacrine-induced inhibition of NK cytotoxicity. The 5-lipoxygenase product 5S-HPETE was not effective. These data indicate that PLA(2) activation is a necessary signal in human NK cytotoxicity and that it is not involved in protein tyrosine kinase and subsequent phospholipase C activation; these latter two enzymes are also required in the cytotoxic response. Thus PLA(2) activation is either a more distal signal, dependent on activation of some earlier signal, or an independent cosignal stimulated by tumor-target binding which generates lysophosphatidylcholine, arachidonic acid, and/or a lipoxygenase product(s).
用磷脂酶A2（PLA2）抑制剂米帕林和4-溴苯甲酰溴（BPB）处理人类自然杀伤（NK）细胞，可使其裂解K562靶细胞的能力降低多达100%。BPB浓度高于2微摩尔/升时，NK细胞与K562细胞结合的能力受到显著影响，但在所测试的任何浓度下米帕林均无此作用。这表明在浓度高于2微摩尔/升时，BPB对NK细胞产生的影响与其对PLA2活性的抑制无关。对K562细胞结合的反应中磷脂酶C的激活（通过肌醇磷酸周转率测定）不受PLA2活性抑制的影响。PLA2分解代谢的产物是一种脂肪酸（通常是花生四烯酸）和一种溶血磷脂。在检测细胞毒性之前，当溶血磷脂酰胆碱而非其他溶血脂质重新添加到NK细胞中时，米帕林或BPB对NK细胞毒性的抑制作用会显著逆转。花生四烯酸而非亚油酸也能显著逆转对NK细胞毒性的抑制。最后，15-脂氧合酶产物15S-氢过氧二十碳四烯酸（15S-HPETE）也能够逆转米帕林诱导的NK细胞毒性抑制。5-脂氧合酶产物5S-HPETE无效。这些数据表明PLA2激活是人类NK细胞毒性中的一个必要信号，且它不参与蛋白酪氨酸激酶及随后的磷脂酶C激活；后两种酶在细胞毒性反应中也是必需的。因此，PLA2激活要么是一个更下游的信号，依赖于某些早期信号的激活，要么是由肿瘤-靶标结合刺激产生溶血磷脂酰胆碱、花生四烯酸和/或一种脂氧合酶产物的独立协同信号。
