Aridor M, Sagi-Eisenberg R
Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
J Cell Biol. 1990 Dec;111(6 Pt 2):2885-91. doi: 10.1083/jcb.111.6.2885.
When loaded alongside GTP-gamma-S into ATP-permeabilized cells, neomycin, at concentrations below 1 mM, inhibits GTP-gamma-S-induced histamine secretion and phosphatidic acid formation (Cockcroft, S., and B. D. Gomperts, 1985. Nature (Lond.). 314: 534-536; Aridor, M., L. M. Traub, and R. Sagi-Eisenberg. 1990. J. Cell Biol. 111:909-917). However, at higher concentrations internally applied neomycin induces histamine secretion in a process that is: (a) dose dependent; (b) dependent on the internal application of GTP; (c) independent of phosphoinositide breakdown; and (d) inhibited by pertussis toxin (PtX) treatment. These results indicate that neomycin can stimulate histamine secretion in a mechanism that bypasses phospholipase C (PLC) activation and yet involves a PtX-sensitive GTP-binding protein (G protein). Unlike its dual effects, when internally applied, neomycin induces histamine secretion from intact mast cells in a dose-dependent manner. Half-maximal and maximal effects are obtained at 0.5 and 1 mM neomycin, respectively. This process is rapid (approximately 30 s), is independent of external Ca2+, and is associated with phosphatidic acid formation, implying that neomycin can activate histamine secretion by a mechanism similar to that utilized by other basic secretagogues of mast cells. Neomycin stimulates fourfold the GTPase activity of cholate-solubilized rat brain membranes in a PtX-inhibitable manner. In addition neomycin, as well as the basic secretagogues of mast cells, compound 48/80, and mastoparan, significantly reduce (by approximately 80%) the ADP ribosylation of PtX substrates present in rat brain membranes. Taken together these data suggest that neomycin can stimulate secretion from mast cells by directly activating G proteins that play a role in stimulus-secretion coupling. When internally applied, neomycin presumably stimulates secretion by activating a G protein that is located downstream to PLC. This G protein serves as a substrate for PtX.
当与GTP-γ-S一起加载到ATP通透的细胞中时，浓度低于1 mM的新霉素会抑制GTP-γ-S诱导的组胺分泌和磷脂酸形成（考克罗夫特，S.，和B. D. 冈珀茨，1985年。《自然》（伦敦）。314: 534 - 536；阿里多尔，M.，L. M. 特劳布，和R. 萨吉-艾森伯格。1990年。《细胞生物学杂志》。111: 909 - 917）。然而，在较高浓度下内部应用新霉素会在以下过程中诱导组胺分泌：（a）剂量依赖性；（b）依赖于GTP的内部应用；（c）独立于磷酸肌醇分解；以及（d）被百日咳毒素（PtX）处理所抑制。这些结果表明，新霉素可以通过一种绕过磷脂酶C（PLC）激活但仍涉及PtX敏感的GTP结合蛋白（G蛋白）的机制来刺激组胺分泌。与其双重作用不同，当内部应用时，新霉素以剂量依赖性方式诱导完整肥大细胞分泌组胺。在新霉素浓度分别为0.5和1 mM时达到半数最大效应和最大效应。这个过程很快（约30秒），独立于细胞外Ca2+，并且与磷脂酸形成相关，这意味着新霉素可以通过与肥大细胞其他碱性促分泌剂类似的机制激活组胺分泌。新霉素以一种可被PtX抑制的方式刺激胆酸盐溶解的大鼠脑膜的GTP酶活性增加四倍。此外，新霉素以及肥大细胞的碱性促分泌剂、化合物48/80和mastoparan，显著降低（约80%）大鼠脑膜中PtX底物的ADP核糖基化。综合这些数据表明，新霉素可以通过直接激活在刺激-分泌偶联中起作用的G蛋白来刺激肥大细胞分泌。当内部应用时，新霉素可能通过激活位于PLC下游的G蛋白来刺激分泌。这种G蛋白是PtX的底物。
