Fagan-Solis Katerina D, Reaves Denise K, Rangel M Cristina, Popoff Michel R, Stiles Bradley G, Fleming Jodie M
Department of Biology, North Carolina Central University, Durham, NC, USA.
Mol Cancer. 2014 Jul 2;13:163. doi: 10.1186/1476-4598-13-163.
Translational exploration of bacterial toxins has come to the forefront of research given their potential as a chemotherapeutic tool. Studies in select tissues have demonstrated that Clostridium perfringens iota toxin binds to CD44 and lipolysis stimulated lipoprotein receptor (LSR) cell-surface proteins. We recently demonstrated that LSR expression correlates with estrogen receptor positive breast cancers and that LSR signaling directs aggressive, tumor-initiating cell behaviors. Herein, we identify the mechanisms of iota toxin cytotoxicity in a tissue-specific, breast cancer model with the ultimate goal of laying the foundation for using iota toxin as a targeted breast cancer therapy.
In vitro model systems were used to determine the cytotoxic effect of iota toxin on breast cancer intrinsic subtypes. The use of overexpression and knockdown technologies confirmed the roles of LSR and CD44 in regulating iota toxin endocytosis and induction of cell death. Lastly, cytotoxicity assays were used to demonstrate the effect of iota toxin on a validated set of tamoxifen resistant breast cancer cell lines.
Treatment of 14 breast cancer cell lines revealed that LSR+/CD44- lines were highly sensitive, LSR+/CD44+ lines were slightly sensitive, and LSR-/CD44+ lines were resistant to iota cytotoxicity. Reduction in LSR expression resulted in a significant decrease in toxin sensitivity; however, overexpression of CD44 conveyed toxin resistance. CD44 overexpression was correlated with decreased toxin-stimulated lysosome formation and decreased cytosolic levels of iota toxin. These findings indicated that expression of CD44 drives iota toxin resistance through inhibition of endocytosis in breast cancer cells, a role not previously defined for CD44. Moreover, tamoxifen-resistant breast cancer cells exhibited robust expression of LSR and were highly sensitive to iota-induced cytotoxicity.
Collectively, these data are the first to show that iota toxin has the potential to be an effective, targeted therapy for breast cancer.
鉴于细菌毒素作为一种化疗工具的潜力，其转化研究已成为研究的前沿领域。在特定组织中的研究表明，产气荚膜梭菌iota毒素与CD44和脂肪分解刺激脂蛋白受体（LSR）细胞表面蛋白结合。我们最近证明，LSR表达与雌激素受体阳性乳腺癌相关，并且LSR信号传导指导侵袭性、肿瘤起始细胞行为。在此，我们在组织特异性乳腺癌模型中确定iota毒素细胞毒性的机制，最终目标是为将iota毒素用作靶向乳腺癌治疗奠定基础。
使用体外模型系统确定iota毒素对乳腺癌内在亚型的细胞毒性作用。使用过表达和敲低技术证实了LSR和CD44在调节iota毒素内吞作用和诱导细胞死亡中的作用。最后，使用细胞毒性测定来证明iota毒素对一组经过验证的耐他莫昔芬乳腺癌细胞系的作用。
对14种乳腺癌细胞系的处理表明，LSR+/CD44-细胞系高度敏感，LSR+/CD44+细胞系稍敏感，而LSR-/CD44+细胞系对iota细胞毒性具有抗性。LSR表达的降低导致毒素敏感性显著降低；然而，CD44的过表达赋予毒素抗性。CD44过表达与毒素刺激的溶酶体形成减少和iota毒素的胞质水平降低相关。这些发现表明，CD44的表达通过抑制乳腺癌细胞的内吞作用来驱动iota毒素抗性，这是CD44以前未定义的作用。此外，耐他莫昔芬的乳腺癌细胞表现出LSR的强烈表达，并且对iota诱导的细胞毒性高度敏感。
总体而言，这些数据首次表明iota毒素有可能成为一种有效的乳腺癌靶向治疗方法。
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