Department of Clinical and Molecular Bio-Medicine, University of Catania, Catania, Italy.
Mol Cancer Ther. 2013 Jun;12(6):1085-98. doi: 10.1158/1535-7163.MCT-12-0550. Epub 2013 Mar 27.
The BCR-ABL oncoprotein of chronic myelogenous leukemia (CML) displays exclusive cytoplasmic localization and constitutive tyrosine kinase activity leading to the activation of different pathways that favor cell proliferation and survival. BCR-ABL induces survivin expression at both the mRNA and protein level, thus inhibiting the apoptotic machinery of CML cells and contributing to the expansion of the leukemic clone. We report that, in human CML cell lines, BCR-ABL-mediated upregulation of survivin involves the JAK2/STAT3 pathway since silencing of either protein caused a consistent reduction in survivin expression. Cell lines unresponsive to imatinib mesylate (IM) because of BCR-ABL gene amplification were not resensitized to the drug after survivin downregulation. However, cells insensitive to IM because of point mutations in the BCR-ABL kinase domain were highly responsive to hydroxyurea (HU) after survivin silencing. To address the possible clinical applications of our results, we used shepherdin, a cell-permeable peptidomimetic compound that downregulates survivin expression by preventing its interaction with Hsp90. Incubation with shepherdin of immortalized cell lines both sensitive and resistant to IM enhanced cell death induced by HU and doxorubicin. Similarly, the combination of shepherdin with first- and second-generation tyrosine kinase inhibitors reduced the colony-forming potential of human progenitors derived from both patients with IM-sensitive and IM-resistant CML. These results suggest that strategies aimed at reducing survivin levels may represent a potential therapeutic option for patients with CML unresponsive to IM.
慢性髓性白血病（CML）的 BCR-ABL 癌蛋白显示出独特的细胞质定位和组成性酪氨酸激酶活性，导致不同途径的激活，有利于细胞增殖和存活。BCR-ABL 在 mRNA 和蛋白质水平上诱导生存素的表达，从而抑制 CML 细胞的凋亡机制，并有助于白血病克隆的扩增。我们报告说，在人类 CML 细胞系中，BCR-ABL 介导的生存素上调涉及 JAK2/STAT3 途径，因为这两种蛋白质的沉默都会导致生存素表达的一致减少。由于 BCR-ABL 基因扩增而对甲磺酸伊马替尼（IM）无反应的细胞系在生存素下调后不能重新对药物敏感。然而，由于 BCR-ABL 激酶结构域中的点突变而对 IM 不敏感的细胞在用生存素沉默后对羟基脲（HU）非常敏感。为了探讨我们研究结果的可能临床应用，我们使用了一种穿透细胞的肽模拟化合物 shepherdin，它通过防止生存素与 Hsp90 相互作用来下调生存素的表达。用 shepherdin 孵育对 IM 敏感和耐药的永生化细胞系均可增强 HU 和阿霉素诱导的细胞死亡。同样，shepherdin 与第一代和第二代酪氨酸激酶抑制剂联合使用可降低源自对 IM 敏感和耐药 CML 的患者的人类祖细胞的集落形成潜力。这些结果表明，降低生存素水平的策略可能代表对 IM 无反应的 CML 患者的一种潜在治疗选择。
