Francis M L, Okazaki I, Moss J, Kurosky A, Pecanha L M, Mond J J
Section on Rheumatology, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC 27157, USA.
J Immunol. 1995 May 15;154(10):4956-64.
To investigate whether ADP-ribosylation of proteins by cholera toxin could influence B cell activation, B cells were incubated with the A subunit of cholera toxin. Ionomycin acted synergistically to induce B cell proliferation with the A subunit of cholera toxin but not with cAMP-enhancing agents or with the B subunit of cholera toxin, suggesting that the synergistic effect of the A subunit was mediated via ADP-ribosylation and not via cAMP elevations or ganglioside GM1 binding. Indeed, inhibitors of ADP-ribosylation blocked the synergistic effect. Unlike anti-Ig, B cell proliferation stimulated by LPS or by the combination of the A subunit and ionomycin was observed in protein kinase C (PKC)-depleted B cells. However, neither the A subunit nor ionomycin enhanced B cell proliferation stimulated by low dose LPS, suggesting that the A subunit plus ionomycin stimulated an activation pathway distinct from the LPS-stimulated pathway. Additionally, unlike LPS, the A subunit plus ionomycin did not stimulate B cells in vitro to secrete Ig. IL-4 acted synergistically with the A subunit to induce B cell proliferation to the same extent as it did with anti-Ig; unlike the anti-Ig plus IL-4 synergy, however, the A subunit plus IL-4-mediated synergy persisted in PKC-depleted B cells. Taken together, our data suggest that cholera toxin A subunit-catalyzed ADP-ribosylation modifies a non-Gs protein involved in the activation of B cells, either through a novel pathway or at a point distal to the activation of PKC along the anti-Ig-stimulated pathway.
为了研究霍乱毒素对蛋白质的 ADP 核糖基化是否会影响 B 细胞活化，将 B 细胞与霍乱毒素的 A 亚基一起孵育。离子霉素与霍乱毒素的 A 亚基协同作用诱导 B 细胞增殖，但与 cAMP 增强剂或霍乱毒素的 B 亚基无协同作用，这表明 A 亚基的协同作用是通过 ADP 核糖基化介导的，而不是通过 cAMP 升高或神经节苷脂 GM1 结合介导的。事实上，ADP 核糖基化抑制剂可阻断这种协同作用。与抗 Ig 不同，在蛋白激酶 C（PKC）缺失的 B 细胞中观察到了 LPS 或 A 亚基与离子霉素组合刺激的 B 细胞增殖。然而，A 亚基和离子霉素均未增强低剂量 LPS 刺激的 B 细胞增殖，这表明 A 亚基加离子霉素刺激了一条不同于 LPS 刺激途径的活化途径。此外，与 LPS 不同，A 亚基加离子霉素在体外不刺激 B 细胞分泌 Ig。IL-4 与 A 亚基协同作用诱导 B 细胞增殖，其程度与它与抗 Ig 协同作用时相同；然而，与抗 Ig 加 IL-4 的协同作用不同，A 亚基加 IL-4 介导的协同作用在 PKC 缺失的 B 细胞中持续存在。综上所述，我们的数据表明，霍乱毒素 A 亚基催化的 ADP 核糖基化通过一条新途径或在沿着抗 Ig 刺激途径 PKC 活化的远端位点修饰参与 B 细胞活化的非 Gs 蛋白。
