Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298, USA.
J Biol Chem. 2010 Nov 26;285(48):37531-41. doi: 10.1074/jbc.M110.141556. Epub 2010 Sep 28.
The low affinity receptor for IgE, CD23, is the natural regulator of IgE synthesis, and understanding both the synthesis and the catabolism of CD23 are, thus, important issues. Membrane CD23 is cleaved by a disintegrin and metalloproteinase 10 (ADAM10) and this cleavage influences the ability of CD23 to regulate IgE. In contrast to the belief that cleavage is a cell surface event, endosomal neutralization with NH(4)Cl was found to dramatically reduce CD23 cleavage, suggesting that the majority of CD23 cleavage occurred subsequent to internalization in the endosomal pathway and not at the cell surface. In line with this, full-length CD23 was shown to be sorted in an ADAM10-dependent manner into exosomes. Greatly increased ADAM10-mediated CD23 cleavage was seen at endosomal pH. Additionally, the stalk region of CD23 was found to interact with ADAM10 and ADAM10 binding of CD23 was found to be protease independent. SPR analysis of the interaction indicated about a 10-fold increase in the R(max) at endosomal pH (pH 5.8) compared with pH 7.4, whereas the affinity of the interaction was not significantly changed. The R(max) change, combined with the increased cleavage at endosomal pH, indicates greater accessibility of the CD23 stalk region for ADAM10 at the lower pH. These results indicate a model where CD23 internalization results in ADAM10-dependent incorporation into exosomes, followed by partial cleavage of CD23 by ADAM10 prior to being released from the cell. The increased cleavage at endosomal pH also has implications for other ADAM10 substrates.
IgE 的低亲和力受体 CD23 是 IgE 合成的天然调节剂，因此，了解 CD23 的合成和分解代谢都是重要的问题。膜结合型 CD23 通过金属蛋白酶 10（ADAM10）进行切割，这种切割影响 CD23 调节 IgE 的能力。与认为切割是细胞表面事件的观点相反，用氯化铵进行内体中和发现，CD23 的切割显著减少，这表明大多数 CD23 的切割发生在细胞内吞进入内体途径之后，而不是在细胞表面。与此一致的是，全长 CD23 以 ADAM10 依赖的方式被分选到外体中。在内体 pH 下，观察到 ADAM10 介导的 CD23 切割大大增加。此外，发现 CD23 的茎区与 ADAM10 相互作用，并且发现 CD23 与 ADAM10 的结合是蛋白酶非依赖性的。SPR 分析表明，与 pH 7.4 相比，内体 pH（pH 5.8）下 ADAM10 与 CD23 的相互作用的 R(max)增加了约 10 倍，而相互作用的亲和力没有明显变化。这种 R(max)的变化，加上内体 pH 下 CD23 切割的增加，表明 CD23 茎区在较低 pH 下对 ADAM10 的可及性更高。这些结果表明了一个模型，其中 CD23 的内吞作用导致 ADAM10 依赖的内体纳入，然后在从细胞中释放之前，ADAM10 对 CD23 进行部分切割。内体 pH 下切割的增加也对其他 ADAM10 底物具有影响。
