Department of Cell and Developmental Biology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
Int J Cancer. 2010 Mar 15;126(6):1428-35. doi: 10.1002/ijc.24888.
Mortalin, the mitochondrial hsp70, is a vital constitutively expressed heat shock protein. Its elevated expression has been correlated with malignant transformation and poor cancer prognosis. Cancer cells exhibit increased resistance to complement-dependent cytotoxicity, partly due to their capacity to eliminate the complement membrane attack complex (MAC) from their cell surface. As we have previously reported, mortalin and the complement membrane attack complexes are released in membrane vesicles from complement attacked cells. As shown here, knock down of mortalin with specific siRNA reduces MAC elimination and enhances cell sensitivity to MAC-induced cell death. Similar results were obtained with MKT-077, a cationic rhodacyanine dye that inhibits mortalin. Treatment of human erythroleukemia K562 and colorectal carcinoma HCT116 cells with MKT-077 sensitizes them to cell death mediated by MAC but not by streptolysin O. Pre-treatment of cells with MKT-077 also reduces the extent of MAC-mortalin vesiculation following a sublytic complement attack. In the presence of MKT-077, the direct binding of mortalin to complement C9, the major MAC component, is inhibited. The tumor suppressor protein p53 is a known mortalin client protein. The effect of MKT-077 on complement-mediated lysis of HCT116 p53(+/+) and p53(-/-) cells was found to be independent on the presence of p53. Our results also demonstrate that recombinant human mortain inhibits complement-mediated hemolysis of rabbit erythrocytes as well as zinc-induced C9 polymerization. We conclude that mortalin supports cancer cell resistance to complement-dependent cytotoxicity and propose consideration of mortalin as a novel target for cancer adjuvant immunotherapy.
线粒体热休克蛋白 70（mortalin）是一种重要的组成型热休克蛋白。其表达水平的升高与恶性转化和不良的癌症预后相关。癌细胞对补体依赖性细胞毒性具有更高的抵抗力，部分原因是它们能够从细胞表面清除补体膜攻击复合物（MAC）。正如我们之前报道的， mortalin 和补体膜攻击复合物会从被补体攻击的细胞中释放到膜囊泡中。如图所示，用特异性 siRNA 敲低 mortalin 会减少 MAC 的清除，并增强细胞对 MAC 诱导的细胞死亡的敏感性。使用阳离子罗丹明染料 MKT-077 抑制 mortalin 也会得到类似的结果。用 MKT-077 处理人红白血病 K562 和结直肠癌细胞 HCT116 可使其对 MAC 介导的细胞死亡敏感，但对链球菌溶血素 O 不敏感。在用 MKT-077 预处理细胞后，补体亚致死攻击后 MAC-mortalin 囊泡化的程度也会降低。在 MKT-077 存在的情况下， mortalin 与补体 C9（主要的 MAC 成分）的直接结合被抑制。肿瘤抑制蛋白 p53 是已知的 mortalin 客户蛋白。发现 MKT-077 对 HCT116 p53(+/+)和 p53(-/-)细胞补体介导的裂解的影响与 p53 的存在无关。我们的研究结果还表明，重组人 mortain 抑制补体介导的兔红细胞溶血以及锌诱导的 C9 聚合。我们得出结论， mortalin 支持癌细胞对补体依赖性细胞毒性的抵抗力，并提出将 mortalin 作为癌症辅助免疫治疗的新靶标进行考虑。
