Turner J R, Tartakoff A M, Berger M
Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
J Biol Chem. 1988 Apr 5;263(10):4914-20.
Human neutrophils (PMN) respond to various soluble stimuli by translocating intracellular complement C3b/C4b receptors (CR1) to the cell surface. Ligand-independent internalization of surface CR1 has been demonstrated previously, but the fate of total cellular CR1 during PMN stimulation has not been determined. In order to study the fate of CR1 during neutrophil activation, we have employed a unique approach for the quantitative analysis of intracellular antigens which allows simultaneous measurement of total cellular and surface membrane antigen pools. Stimulation of isolated PMN with N-formyl-Met-Leu-Phe or ionomycin resulted in a mean 7-fold increase in surface CR1 expression within 15 min. Total cellular CR1 decreased by as much as 45% within 15 min, with loss continuing for up to 1 h. Inclusion of NH4Cl during PMN stimulation inhibited the loss of total CR1 without affecting surface CR1 expression. Addition of phenylmethylsulfonyl fluoride inhibited loss of total CR1 and enhanced the stimulus-induced increases in surface CR1. These data suggest that intracellular degradation of CR1 occurs during stimulation of PMN and may involve proteolysis in an acidic intracellular compartment. Since our experiments were done with isolated PMN in the absence of serum and complement components, this degradation occurred in the absence of C3b, the ligand for CR1. To our knowledge, ligand-independent degradation of a cell surface receptor has not been previously detected.
人类中性粒细胞（PMN）通过将细胞内补体C3b/C4b受体（CR1）转运至细胞表面来响应各种可溶性刺激。此前已证实表面CR1存在非配体依赖性内化，但尚未确定PMN刺激期间细胞内总CR1的命运。为了研究中性粒细胞活化过程中CR1的命运，我们采用了一种独特的方法来定量分析细胞内抗原，该方法能够同时测量细胞内总抗原池和表面膜抗原池。用N-甲酰甲硫氨酸-亮氨酸-苯丙氨酸或离子霉素刺激分离的PMN，15分钟内表面CR1表达平均增加7倍。15分钟内细胞内总CR1减少多达45%，且这种减少持续长达1小时。在PMN刺激期间加入氯化铵可抑制总CR1的减少，而不影响表面CR1的表达。加入苯甲基磺酰氟可抑制总CR1的减少，并增强刺激诱导的表面CR1增加。这些数据表明，在PMN刺激过程中发生了CR1的细胞内降解，可能涉及酸性细胞内区室中的蛋白水解。由于我们的实验是在无血清和补体成分的情况下用分离的PMN进行的，这种降解是在缺乏CR1配体C3b的情况下发生的。据我们所知，此前尚未检测到细胞表面受体的非配体依赖性降解。
