Shaker M, Shahabi N A, Sharp B M
Endocrine-Neuroscience and Neuroimmunomodulation Research Laboratory, Minneapolis Medical Research Foundation, MN.
Immunopharmacology. 1994 Nov-Dec;28(3):183-92. doi: 10.1016/0162-3109(94)90053-1.
beta-Endorphin affects mononuclear cell proliferation, cytokine production and calcium uptake in a naloxone-resistant manner. The presence of naloxone-insensitive binding sites for beta-endorphin have been demonstrated on murine EL4-thymoma cells, transformed human mononuclear cells and normal murine splenocytes. Since murine splenic B cells have been shown to express naloxone-resistant receptors for beta-endorphin in response to the mitogen, concanavalin A (Con A), the A20 B-cell lymphoma line was used to further study regulation of this site by Con A and dexamethasone. Analyses showed two sites: a high-affinity site, Kd1 = (8.7 +/- 2.3) x 10(-11) M and binding capacity (Bmax1) of (2.6 +/- 2.0) x 10(3) receptors/cell; and a low-affinity site, Kd2 = (2.2 +/- 0.8) x 10(-8) M with Bmax2 of (1.5 +/- 0.8) x 10(5) receptors/cell. Competition studies showed that N-acetyl-beta-endorphin was approx. 5-fold and beta-endorphin6-31 10-fold less potent than beta-endorphin1-31. Neither beta-endorphin1-27 nor naloxone, morphine or other opioid receptor agonists displaced [125I]beta-endorphin. Con A (20 micrograms/ml) significantly increased the Bmax (3.5-fold; expressed per cell) and resulted in a loss of the higher-affinity site. However, the increased Bmax occurred in proportion to the Con-A-induced increase in protein/cell. Dexamethasone (Dex) also increased Bmax, primarily by increasing (2-3-fold) the number of lower affinity sites. In contrast to Con A, two binding sites persisted after treatment with Dex, which exerted a minimal effect on protein/cell. Therefore, binding/cell and binding/protein/cell were both significantly enhanced by Dex. The combined effects of Dex and Con A on binding failed to show additivity or synergy. When binding was analyzed per protein/cell, the effect of Con A appeared to dominate; the Dex-enhanced binding/protein/cell was no longer evident in the presence of Dex plus Con A. Thus, Dex and Con A may enhance binding by independent mechanisms.
β-内啡肽以一种对纳洛酮耐药的方式影响单核细胞增殖、细胞因子产生和钙摄取。在小鼠EL4胸腺瘤细胞、转化的人单核细胞和正常小鼠脾细胞上已证实存在对β-内啡肽不敏感的结合位点。由于已表明小鼠脾脏B细胞在有丝分裂原刀豆球蛋白A（Con A）作用下表达对β-内啡肽耐药的受体，因此使用A20 B细胞淋巴瘤系进一步研究Con A和地塞米松对该位点的调节。分析显示有两个位点：一个高亲和力位点，Kd1 =（8.7±2.3）×10⁻¹¹ M，结合容量（Bmax1）为（2.6±2.0）×10³个受体/细胞；一个低亲和力位点，Kd2 =（2.2±0.8）×10⁻⁸ M，Bmax2为（1.5±0.8）×10⁵个受体/细胞。竞争研究表明，N-乙酰-β-内啡肽的效力约为β-内啡肽1-31的五分之一，β-内啡肽6-31的效力约为β-内啡肽1-31的十分之一。β-内啡肽1-27、纳洛酮、吗啡或其他阿片受体激动剂均不能取代[¹²⁵I]β-内啡肽。Con A（20微克/毫升）显著增加Bmax（3.5倍；以每个细胞计），并导致高亲和力位点丧失。然而，Bmax的增加与Con A诱导的每个细胞蛋白质增加成比例。地塞米松（Dex）也增加Bmax，主要是通过增加（2-3倍）低亲和力位点的数量。与Con A不同，用Dex处理后两个结合位点仍然存在，Dex对每个细胞的蛋白质影响最小。因此，Dex使每个细胞的结合以及每个细胞蛋白质的结合均显著增强。Dex和Con A对结合的联合作用未显示相加或协同效应。当按每个细胞蛋白质分析结合时，Con A的作用似乎占主导；在存在Dex加Con A的情况下，Dex增强的每个细胞蛋白质结合不再明显。因此，Dex和Con A可能通过独立机制增强结合。
