The Cytotoxicity of Elderberry Ribosome-Inactivating Proteins Is Not Solely Determined by Their Protein Translation Inhibition Activity

Although the protein translation inhibition activity of ribosome inactivating proteins (RIPs) is well documented, little is known about the contribution of the lectin chain to the biological activity of these proteins. In this study, we compared the in vitro and intracellular activity of several S. nigra (elderberry) RIPs and non-RIP lectins. Our data demonstrate that RIPs from elderberry are much more toxic to HeLa cells than to primary fibroblasts. Differences in the cytotoxicity between the elderberry proteins correlated with differences in glycan specificity of their lectin domain, cellular uptake efficiency and intracellular destination. Despite the fact that the bulk of the RIPs accumulated in the lysosomes and partly in the Golgi apparatus, we could demonstrate effective inhibition of protein synthesis in cellula. As we also observed cytotoxicity for non-RIP lectins, it is clear that the lectin chain triggers additional pathways heralding cell death. Our data suggest that one of these pathways involves the induction of autophagy.

尽管核糖体失活蛋白（ribosome inactivating proteins，RIPs）的翻译抑制活性已得到广泛证实，但目前对其凝集素链在该类蛋白生物学活性中的贡献仍知之甚少。本研究对多种接骨木（S. nigra，elderberry）来源的核糖体失活蛋白与非核糖体失活蛋白类凝集素的体外及胞内活性进行了对比分析。我们的实验数据显示，接骨木源核糖体失活蛋白对HeLa细胞的毒性远高于原代成纤维细胞。接骨木源蛋白之间的细胞毒性差异，与其凝集素结构域的聚糖特异性、细胞摄取效率以及细胞内定位差异密切相关。尽管大部分核糖体失活蛋白会富集于溶酶体（lysosomes），部分还可定位于高尔基体（Golgi apparatus），但我们仍可检测到胞内蛋白质合成的有效抑制。由于我们也观察到了非核糖体失活蛋白类凝集素的细胞毒性，由此可见凝集素链可触发额外的细胞死亡通路。我们的实验数据提示，其中一条通路涉及细胞自噬（autophagy）的诱导。