Nikrad Malti, Johnson Thomas, Puthalalath Hamsa, Coultas Leigh, Adams Jerry, Kraft Andrew S
Hollings Cancer Center, Medical University of South Carolina, 86 Jonathan Lucas Street, Charleston, SC 29425, USA.
Mol Cancer Ther. 2005 Mar;4(3):443-9. doi: 10.1158/1535-7163.MCT-04-0260.
Previously, we showed that the proteasome inhibitor bortezomib/Velcade (formerly PS-341) synergizes with the protein tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL), a ligand for certain death receptors, to induce apoptosis in cell lines derived from prostate and colon cancers. Because apoptosis is often triggered by BH3-only proteins of the Bcl-2 family, we have explored the hypothesis that bortezomib contributes to the apoptosis by up-regulating their levels. Indeed, bortezomib induced increases of Bik and/or Bim in multiple cell lines but not notably of two other BH3-only proteins (Puma and Bid) nor other family members (Bax, Bak, Bcl-2, and Bcl-xL). The increase in Bik levels seems to reflect inhibition by bortezomib of its proteasome-mediated degradation. Importantly, both Bik and Bim seem central to the proapoptotic function of bortezomib, because mouse embryo fibroblasts in which the genes for both Bik and Bim had been disrupted were refractory to its cytotoxic action. Similarly, the synergy between bortezomib and TRAIL in killing human prostate cancer cells was impaired in cells in which both Bik and Bim were down-regulated by RNA interference. Further evidence that bortezomib acts through the mitochondrial pathway regulated by the Bcl-2 family is that deficiency for APAF-1, which acts downstream of Bcl-2, also blocked its apoptotic effect. These results implicate BH3-only proteins, in particular both Bik and Bim, as important mediators of the antitumor action of bortezomib and establish their role in its enhancement of TRAIL-induced apoptosis.
此前，我们发现蛋白酶体抑制剂硼替佐米/万珂（原名PS - 341）可与肿瘤坏死因子α相关凋亡诱导配体（TRAIL，一种特定死亡受体的配体）协同作用，诱导前列腺癌和结肠癌来源的细胞系发生凋亡。由于凋亡通常由Bcl - 2家族仅含BH3结构域的蛋白触发，我们探讨了硼替佐米通过上调这些蛋白水平促进凋亡的假说。事实上，硼替佐米在多个细胞系中诱导了Bik和/或Bim水平的升高，但另外两种仅含BH3结构域的蛋白（Puma和Bid）以及其他家族成员（Bax、Bak、Bcl - 2和Bcl - xL）的水平并未显著升高。Bik水平的升高似乎反映了硼替佐米对其蛋白酶体介导降解的抑制作用。重要的是，Bik和Bim似乎都是硼替佐米促凋亡功能的核心，因为Bik和Bim基因均被破坏的小鼠胚胎成纤维细胞对其细胞毒性作用具有抗性。同样，在通过RNA干扰下调Bik和Bim的细胞中，硼替佐米与TRAIL协同杀伤人类前列腺癌细胞的作用也受到损害。进一步证明硼替佐米通过由Bcl - 2家族调节的线粒体途径发挥作用的证据是，在Bcl - 2下游起作用的凋亡蛋白酶激活因子 - 1（APAF - 1）缺陷也会阻断其凋亡效应。这些结果表明，仅含BH3结构域的蛋白，特别是Bik和Bim，是硼替佐米抗肿瘤作用的重要介质，并确立了它们在增强TRAIL诱导凋亡中的作用。
