Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA 19104-6030, USA.
Mol Pharmacol. 2011 Jun;79(6):1005-13. doi: 10.1124/mol.111.071472. Epub 2011 Mar 11.
Human mast cells express the G protein coupled receptor (GPCR) for C5a (CD88). Previous studies indicated that C5a could cause mast cell degranulation, at least in part, via a mechanism similar to that proposed for basic neuropeptides such as substance P, possibly involving Mas-related gene 2 (MrgX2). We therefore sought to more clearly define the receptor specificity for C5a-induced mast cell degranulation. We found that LAD2, a human mast cell line, and CD34(+) cell-derived primary mast cells express functional MrgX1 and MrgX2 but the immature human mast cell line HMC-1 does not. A potent CD88 antagonist, PMX-53 (10 nM) inhibited C5a-induced Ca(2+) mobilization in HMC-1 cells, but at higher concentrations (≥30 nM) it caused degranulation in LAD2 mast cells, CD34(+) cell-derived mast cells, and RBL-2H3 cells stably expressing MrgX2. PMX-53 did not, however, activate RBL-2H3 cells expressing MrgX1. Although C5a induced degranulation in LAD2 and CD34(+) cell-derived mast cells, it did not activate RBL-2H3 cells expressing MrgX1 or MrgX2. Replacement of Trp with Ala and Arg with dArg abolished the ability of PMX-53 to inhibit C5a-induced Ca(2+) mobilization in HMC-1 cells and to cause degranulation in RBL-2H3 cells expressing MrgX2. These findings demonstrate that C5a does not use MrgX1 or MrgX2 for mast cell degranulation. Moreover, it reveals the novel finding that PMX-53 functions as a potent CD88 antagonist and a low-affinity agonist for MrgX2. Furthermore, Trp and Arg residues are required for the ability of PMX53 to act as both a CD88 antagonist and a MrgX2 agonist.
人类肥大细胞表达 C5a（CD88）的 G 蛋白偶联受体（GPCR）。先前的研究表明，C5a 可以引起肥大细胞脱颗粒，至少部分是通过类似于基础神经肽（如 P 物质）提出的机制，可能涉及 Mas 相关基因 2（MrgX2）。因此，我们试图更清楚地定义 C5a 诱导的肥大细胞脱颗粒的受体特异性。我们发现，人肥大细胞系 LAD2 和 CD34(+)细胞衍生的原代肥大细胞表达功能性 MrgX1 和 MrgX2，但不成熟的人肥大细胞系 HMC-1 则不表达。一种有效的 CD88 拮抗剂 PMX-53（10 nM）抑制了 HMC-1 细胞中 C5a 诱导的 Ca(2+)动员，但在较高浓度（≥30 nM）下，它会引起 LAD2 肥大细胞、CD34(+)细胞衍生的肥大细胞和稳定表达 MrgX2 的 RBL-2H3 细胞脱颗粒。然而，PMX-53 不会激活表达 MrgX1 的 RBL-2H3 细胞。虽然 C5a 诱导 LAD2 和 CD34(+)细胞衍生的肥大细胞脱颗粒，但它不能激活表达 MrgX1 或 MrgX2 的 RBL-2H3 细胞。用丙氨酸替换色氨酸和用 dArg 替换精氨酸，使 PMX-53 抑制 HMC-1 细胞中 C5a 诱导的 Ca(2+)动员和引起表达 MrgX2 的 RBL-2H3 细胞脱颗粒的能力丧失。这些发现表明 C5a 不用于肥大细胞脱颗粒的 MrgX1 或 MrgX2。此外，它揭示了一个新的发现，即 PMX-53 作为一种有效的 CD88 拮抗剂和 MrgX2 的低亲和力激动剂发挥作用。此外，色氨酸和精氨酸残基是 PMX53 作为 CD88 拮抗剂和 MrgX2 激动剂的能力所必需的。
