Snapper C M, Yamada H, Mond J J, June C H
Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
J Immunol. 1991 Aug 15;147(4):1171-9.
Ly-6A/E is a phosphatidylinositol (PI)-linked membrane protein whose expression is induced or upregulated on normal murine T and B cells by IFN-gamma. Cross-linkage of Ly-6A/E expressed on normal murine T cells stimulates Ca2+ translocation, and in the presence of a protein kinase C (PKC) activator, lymphokine secretion, and cellular proliferation. Utilizing an anti-Ly-6A/E mAb, we studied the effect of cross-linking Ly-6A/E on IFN-gamma-treated resting B cells, for Ca2+ translocation, PI turnover, and cellular proliferation. Since these events are known to be stimulated by cross-linkage of B cell membrane (m)Ig, we compared the changes mediated through these respective membrane proteins. We show that cross-linkage of B cell Ly-6A/E stimulates a large, rapid, and sustained increase in the concentration of intracellular free calcium ([Ca2+]i) comparable in magnitude, though somewhat delayed, relative to that observed after cross-linking of mIg. Cross-linkage of B cell Ly-6A/E does not, however, stimulate detectable PI turnover, in contrast to PI turnover induced by ligation of mIg. Both the Ly-6A/E- and mIg-mediated increase in [Ca2+]i occur through mobilization of internal Ca2+ stores as well as entry of Ca2+ into the cell from the extracellular compartment. Ly-6A/E-mediated Ca2+ translocation appears to be under the regulation of PKC in that short term pretreatment of B cells with the PKC activator, PMA, inhibits the Ly-6A/E- as well as the mIg-mediated increase in [Ca2+]i, whereas prolonged exposure to PMA, under conditions that lead to depletion of PKC, results in an augmentation in Ca2+ translocation after ligation of either Ly-6A/E or mIg. Co-capping studies indicate that Ly-6A/E and mIg cap independently in the B cell membrane, thus suggesting that the Ly-6A/E-induced effects on Ca2+ translocation are not mediated through simultaneous modulation of mIg. Anti-Ly6A/E, by itself, does not stimulate an increase in [3H]thymidine incorporation by IFN-gamma-treated resting B cells, but induces a striking increase in the presence of PMA. By contrast, anti-Ig by itself stimulates significant increases in [3H]thymidine incorporation that is inhibited by PMA. Thus, Ly-6A/E is a potent mediator of B cell activation that may use a signal transduction system in quiescent B cells that is distinct from that of the Ag receptor.
Ly-6A/E是一种磷脂酰肌醇（PI）连接的膜蛋白，其表达可被干扰素-γ在正常小鼠T细胞和B细胞上诱导或上调。正常小鼠T细胞上表达的Ly-6A/E交联可刺激Ca2+转运，并且在蛋白激酶C（PKC）激活剂存在的情况下，刺激淋巴因子分泌和细胞增殖。利用抗Ly-6A/E单克隆抗体，我们研究了Ly-6A/E交联对经干扰素-γ处理的静息B细胞的Ca2+转运、PI转换和细胞增殖的影响。由于已知这些事件可被B细胞膜（m）Ig交联所刺激，我们比较了通过这些各自的膜蛋白介导的变化。我们发现，B细胞Ly-6A/E交联可刺激细胞内游离钙（[Ca2+]i）浓度大幅、快速且持续升高，其幅度与mIg交联后观察到的相当，尽管有所延迟。然而，与mIg连接诱导的PI转换相反，B细胞Ly-6A/E交联不会刺激可检测到的PI转换。Ly-6A/E和mIg介导的[Ca2+]i升高都是通过动员细胞内钙库以及Ca2+从细胞外区室进入细胞而发生的。Ly-6A/E介导的Ca2+转运似乎受PKC调节，因为用PKC激活剂佛波酯（PMA）对B细胞进行短期预处理可抑制Ly-6A/E以及mIg介导的[Ca2+]i升高，而在导致PKC耗竭的条件下长时间暴露于PMA，则会导致Ly-6A/E或mIg连接后Ca2+转运增加。共帽研究表明，Ly-6A/E和mIg在B细胞膜上独立帽化，因此表明Ly-6A/E诱导的对Ca2+转运的影响不是通过同时调节mIg介导的。单独的抗Ly6A/E不会刺激经干扰素-γ处理的静息B细胞的[3H]胸腺嘧啶核苷掺入增加，但在有PMA存在时会诱导显著增加。相比之下，单独的抗Ig会刺激[3H]胸腺嘧啶核苷掺入显著增加，而这会被PMA抑制。因此，Ly-6A/E是B细胞激活的有效介质，它可能在静止B细胞中使用一种与抗原受体不同的信号转导系统。
