Institute of Toxicology, University Medical Center of the Johannes Gutenberg University Mainz, Obere Zahlbacher Str 67, 55131 Mainz, Germany.
Apoptosis. 2013 Aug;18(8):963-79. doi: 10.1007/s10495-013-0842-6.
We investigated the relevance of signaling mechanisms regulated by the Ras-homologous GTPase Rac1 for survival of acute myeloid leukemia (AML) cells harbouring the MLL-AF9 oncogene due to t(9;11)(p21;q23) translocation. Monocytic MLL-AF9 expressing cells (MM6, THP-1) were hypersensitive to both small-molecule inhibitors targeting Rac1 (EHT 1864, NSC 23766) (IC50EHT 12.5 μM) and lipid lowering drugs (lovastatin, atorvastatin) (IC50Lova ~7.5 μM) as compared to acute myelocytic leukemia (NOMO-1, HL60) and T cell leukemia (Jurkat) cells (IC50EHT >30 μM; IC50Lova >25 μM). Hypersensitivity of monocytic cells following Rac1 inhibition resulted from caspase-driven apoptosis as shown by profound activation of caspase-8,-9,-7,-3 and substantial (90 %) decrease in protein expression of pro-survival factors (survivin, XIAP, p-Akt). Apoptotic death was preceded by S139-posphorylation of histone H2AX (γH2AX), a prototypical surrogate marker of DNA double-strand breaks (DSBs). Taken together, abrogation of Rac1 signaling causes DSBs in acute monocytic leukemia cells harbouring the MLL-AF9 oncogene, which, together with downregulation of survivin, XIAP and p-Akt, results in massive induction of caspase-driven apoptotic death. Apparently, Rac1 signaling is required for maintaining genetic stability and maintaining survival in specific subtypes of AML. Hence, targeting of Rac1 is considered a promising novel strategy to induce lethality in MLL-AF9 expressing AML.
我们研究了 Ras 同源 GTP 酶 Rac1 调节的信号转导机制对于携带 MLL-AF9 癌基因的急性髓系白血病（AML）细胞存活的相关性，这些细胞由于 t(9;11)(p21;q23)易位而发生了这种改变。单核细胞 MLL-AF9 表达细胞（MM6、THP-1）对 Rac1 小分子抑制剂（EHT 1864、NSC 23766）（IC50EHT12.5 μM）和降脂药物（洛伐他汀、阿托伐他汀）（IC50Lova7.5 μM）的敏感性均高于急性髓细胞性白血病（NOMO-1、HL60）和 T 细胞白血病（Jurkat）细胞（IC50EHT>30 μM；IC50Lova>25 μM）。 Rac1 抑制后单核细胞的敏感性来自 caspase 驱动的细胞凋亡，这表现为 caspase-8、-9、-7、-3 的强烈激活以及存活因子（survivin、XIAP、p-Akt）的蛋白表达明显下降（~90%）。凋亡死亡之前是组蛋白 H2AX（γH2AX）的 S139 磷酸化，这是 DNA 双链断裂（DSBs）的典型替代标志物。综上所述，Rac1 信号的阻断会导致携带 MLL-AF9 癌基因的急性单核细胞白血病细胞发生 DSBs，与 survivin、XIAP 和 p-Akt 的下调一起，导致 caspase 驱动的凋亡死亡的大量诱导。显然，Rac1 信号对于维持特定 AML 亚型的遗传稳定性和生存是必需的。因此，靶向 Rac1 被认为是诱导表达 MLL-AF9 的 AML 细胞致死的一种有前途的新策略。
