Theoharides T C, Wang L, Pang X, Letourneau R, Culm K E, Basu S, Wang Y, Correia I
Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, MA, USA.
J Pharmacol Exp Ther. 2000 Sep;294(3):810-21.
Disodium cromoglycate (cromolyn) inhibits mast cell secretion, but its mechanism has not been elucidated. One possibility is the phosphorylation of a 78-kDa mast cell protein, two fragments of which are homologous to moesin, a member of the ezrin, radixin, moesin family. These proteins appear to be involved in signal transduction by regulating functional associations between the cell surface and the cytoskeleton. Moesin cDNA was cloned from rat basophil leukemia cells, which are similar to mucosal mast cells, and polyclonal antiserum was prepared against recombinant moesin expressed in Escherichia coli. Moesin phosphorylated in mast cells treated with cromolyn shifted from the soluble to the precipitable fraction and associated with Sepharose-linked beta-actin. Recombinant moesin also associated with Sepharose-linked beta-actin, and so did purified RBL moesin, but only if the latter was first denatured. Moesin thus appears to have actin binding sites that are not exposed under normal conditions but may become available by in vivo phosphorylation or by denaturation. Immunocytochemistry using confocal microscopy showed moesin to be primarily localized on the inner aspect of the plasma membrane and around secretory granules. Double immunocytochemistry for moesin and actin colocalized them in most areas. Ultracryoimmunoelectron microscopy to preserve the antigenicity of moesin identified the protein close to the plasma and secretory granule membranes. Cromolyn appeared to induce clustering of moesin around secretory granules. It is hypothesized that conformational changes of moesin, regulated by phosphorylation/dephosphorylation, may lead to positional rearrangements with respect to the membrane/cytoskeleton that could possibly regulate mast cell secretion.
色甘酸钠（色甘酸）可抑制肥大细胞分泌，但其作用机制尚未阐明。一种可能性是一种78 kDa肥大细胞蛋白发生磷酸化，该蛋白的两个片段与埃兹蛋白、根蛋白、埃莫蛋白家族成员埃莫蛋白同源。这些蛋白似乎通过调节细胞表面与细胞骨架之间的功能关联参与信号转导。从与黏膜肥大细胞相似的大鼠嗜碱性粒细胞白血病细胞中克隆出埃莫蛋白cDNA，并制备了针对在大肠杆菌中表达的重组埃莫蛋白的多克隆抗血清。用色甘酸处理的肥大细胞中磷酸化的埃莫蛋白从可溶部分转移至可沉淀部分，并与琼脂糖偶联的β -肌动蛋白结合。重组埃莫蛋白也与琼脂糖偶联的β -肌动蛋白结合，纯化的大鼠嗜碱性粒细胞白血病细胞埃莫蛋白也如此，但前提是后者首先变性。因此，埃莫蛋白似乎具有在正常条件下未暴露但可通过体内磷酸化或变性而暴露的肌动蛋白结合位点。使用共聚焦显微镜的免疫细胞化学显示埃莫蛋白主要定位于质膜内侧和分泌颗粒周围。埃莫蛋白和肌动蛋白的双重免疫细胞化学在大多数区域将它们共定位。用于保留埃莫蛋白抗原性的超低温免疫电子显微镜在靠近质膜和分泌颗粒膜处鉴定出该蛋白。色甘酸似乎诱导埃莫蛋白在分泌颗粒周围聚集。据推测，由磷酸化/去磷酸化调节的埃莫蛋白构象变化可能导致其相对于膜/细胞骨架的位置重排，这可能调节肥大细胞分泌。
