Ahmed S, Lee J, Kozma R, Best A, Monfries C, Lim L
Institute of Molecular and Cell Biology, National University of Singapore.
J Biol Chem. 1993 May 25;268(15):10709-12.
Phorbol esters are potent tumor promoters widely used for investigating mechanisms of cell transformation with protein kinase C (PKC) generally considered as being their only protein target. Lysophosphatidic acid (LPA) can act as a mitogen, affecting cell shape and the actin cytoskeleton. There is no identified functional target for LPA. We have isolated a cDNA encoding a protein n-chimaerin that is a high affinity phorbol ester receptor and a p21rac-GTPase activating protein (rac-GAP). p21rac is a member of the ras superfamily of small molecular weight GTP-binding proteins, which stimulates actin microfilament formation in Swiss 3T3 cells and superoxide production by the neutrophil oxidase. We now show that the rac-GAP activity of n-chimaerin is stimulated by phosphatidylserine (PS) and phosphatidic acid (PA) and that phorbol esters can synergize with PS and PA. LPA, in contrast, was found to inhibit n-chimaerin. The phospholipid/phorbol ester modulation of the rac-GAP activity requires the PKC-like cysteine-rich domain of n-chimaerin. Thus, n-chimaerin is a novel functional target (distinct from PKC) for both phorbol esters and LPA. These data suggest that the physiological role of n-chimaerin is to link events initiating at the cell surface/membrane with p21rac effector pathways.
佛波酯是强效肿瘤促进剂，广泛用于研究细胞转化机制，蛋白激酶C（PKC）通常被认为是其唯一的蛋白质靶点。溶血磷脂酸（LPA）可作为有丝分裂原，影响细胞形状和肌动蛋白细胞骨架。目前尚未确定LPA的功能靶点。我们分离出了一个编码n-嵌合蛋白的cDNA，该蛋白是一种高亲和力佛波酯受体和一种p21rac-GTP酶激活蛋白（rac-GAP）。p21rac是小分子量GTP结合蛋白ras超家族的成员，可刺激瑞士3T3细胞中的肌动蛋白微丝形成以及中性粒细胞氧化酶产生超氧化物。我们现在表明，n-嵌合蛋白的rac-GAP活性受到磷脂酰丝氨酸（PS）和磷脂酸（PA）的刺激，并且佛波酯可与PS和PA协同作用。相比之下，发现LPA可抑制n-嵌合蛋白。rac-GAP活性的磷脂/佛波酯调节需要n-嵌合蛋白富含半胱氨酸的PKC样结构域。因此，n-嵌合蛋白是佛波酯和LPA的新型功能靶点（不同于PKC）。这些数据表明，n-嵌合蛋白的生理作用是将细胞表面/膜起始的事件与p21rac效应器途径联系起来。
