三阴性乳腺癌 (TNBC) 占所有乳腺癌的 10-20%，具有侵袭性，具有高转移潜力，并且由于治疗选择有限，预后较差。 LT-IIc 是 ADP（核糖基化不耐热肠毒素）II 型亚家族的成员，与一组独特的细胞表面神经节苷脂受体结合，对 TNBC 细胞系具有细胞毒性，但对非转化乳腺没有细胞毒性活性上皮细胞。在这里，从切除的人类肿瘤中分离出的原代 TNBC 细胞显示出对 LT-IIc 的特异性增强的细胞毒性反应，与测试的其他肠毒素相反。 MDA-MB-231 细胞（TNBC 模型）用于评估 LT-IIc 细胞毒性的潜在机制，LT-IIc 诱导细胞内 cAMP 升高并刺激 cAMP 反应元件结合蛋白 (CREB) 信号通路。为了剖析 ADP-核糖基化、cAMP 诱导和神经节苷脂连接在细胞毒性反应中的作用，将 MDA-MB-231 细胞暴露于野生型 LT-IIc，即缺乏 ADP-IIc 的重组 B-五聚体。核糖基化 A 多肽，或具有酶失活 A1 结构域的 LT-IIc 突变体。这些实验表明，LT-IIc 的 ADP-核糖基转移酶活性对于诱导 MDA-MB-231 细胞的致死性不是必需的。相比之下，具有改变的神经节苷脂结合活性的突变体LT-IIc未能在MDA-MB-231细胞中触发细胞毒性反应。此外，神经节苷脂表达的药理抑制可保护 MDA-MB-231 细胞免受 LT-IIc 的细胞毒性作用。这些数据表明，神经节苷脂连接，而不是 cAMP 产生或 ADP-核糖基转移酶活性的诱导，对于启动 MDA-MB-231 细胞的 LT-IIc 依赖性细胞死亡至关重要。这些实验揭示了 LT-IIc 和神经节苷脂在信号转导中以前未知的特性，为 TNBC 的靶向治疗提供了潜力，这是一种迫切需要的选择。

Triple-negative breast cancer (TNBC), which constitutes 10-20 percent of all breast cancers, is aggressive, has high metastatic potential, and carries a poor prognosis due to limited treatment options. LT-IIc, a member of the type II subfamily of ADP-ribosylating-heat-labile enterotoxins that bind to a distinctive set of cell-surface ganglioside receptors-is cytotoxic toward TNBC cell lines, but has no cytotoxic activity for non-transformed breast epithelial cells. Here, primary TNBC cells, isolated from resected human tumors, showed an enhanced cytotoxic response specifically toward LT-IIc, in contrast to other enterotoxins that were tested. MDA-MB-231 cells, a model for TNBC, were used to evaluate potential mechanisms of cytotoxicity by LT-IIc, which induced elevated intracellular cAMP and stimulated the cAMP response element-binding protein (CREB) signaling pathway. To dissect the role of ADP-ribosylation, cAMP induction, and ganglioside ligation in the cytotoxic response, MDA-MB-231 cells were exposed to wild-type LT-IIc, the recombinant B-pentamer of LT-IIc that lacks the ADP-ribosylating A polypeptide, or mutants of LT-IIc with an enzymatically inactivated A1-domain. These experiments revealed that the ADP-ribosyltransferase activity of LT-IIc was nonessential for inducing the lethality of MDA-MB-231 cells. In contrast, a mutant LT-IIc with an altered ganglioside binding activity failed to trigger a cytotoxic response in MDA-MB-231 cells. Furthermore, the pharmacological inhibition of ganglioside expression protected MDA-MB-231 cells from the cytotoxic effects of LT-IIc. These data establish that ganglioside ligation, but not the induction of cAMP production nor ADP-ribosyltransferase activity, is essential to initiating the LT-IIc-dependent cell death of MDA-MB-231 cells. These experiments unveiled previously unknown properties of LT-IIc and gangliosides in signal transduction, offering the potential for the targeted treatment of TNBC, an option that is desperately needed.