Regulation of D-cyclin translation inhibition in myeloma cells treated with mammalian target of rapamycin inhibitors: rationale for combined treatment with extracellular signal-regulated kinase inhibitors and rapamycin.
Regulation of D-cyclin translation inhibition in myeloma cells treated with mammalian target of rapamycin inhibitors: rationale for combined treatment with extracellular signal-regulated kinase inhibitors and rapamycin.
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DOI：
10.1158/1535-7163.mct-08-0254
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发表时间：
2009-01
影响因子：
5.7
通讯作者：
Lichtenstein A
中科院分区：
文献类型：
--
作者：
Frost P;Shi Y;Hoang B;Gera J;Lichtenstein A
我们已经证明，AKT 活性增强可使多发性骨髓瘤 (MM) 细胞对 mTOR 抑制剂 CCI-779 的抗肿瘤作用敏感。为了测试 AKT 调节作用的机制，我们用激活的 AKT 等位基因或空载体稳定转染 U266 MM 细胞系。转染 AKT 的细胞对雷帕霉素体外诱导的细胞抑制或其类似物 CCI-779 体内诱导的细胞抑制更敏感，而静态 AKT 的细胞则具有抵抗力。在 AKT 转染的 MM 细胞中，mTOR 抑制剂下调 D-cyclin 表达的能力显着增强，部分原因是 AKT 能够抑制 D-cyclin 转录物的帽子独立翻译和内部核糖体进入位点 (IRES) 活性。雷帕霉素反应性的类似 AKT 依赖性调节在第二种骨髓瘤模型中得到了证实：用野生型 PTEN 转染的 PTEN 无效 OPM-2 细胞系。由于 ERK/p38 活性促进 IRES 介导的某些转录本的翻译，因此我们研究了 ERK/p38 作为 AKT 依赖性影响雷帕霉素敏感性的调节剂。 AKT 转染的 U266 细胞显示 ERK 和 p38 活性显着降低。然而，只有 ERK 抑制剂才能阻止耐药“低 AKT”骨髓瘤细胞中的 D-细胞周期蛋白 IRES 活性。此外，ERK 抑制剂通过下调 D-细胞周期蛋白表达和 G1 期阻滞成功地使骨髓瘤细胞对雷帕霉素敏感。然而，激活的 MEK 基因的异位过度表达并不会增加“高 AKT”骨髓瘤细胞中 D-细胞周期蛋白的帽独立翻译，表明 MEK/ERK 活性是 IRES 激活所必需的，但不足以激活。这些数据支持这样一种情况：AKT 活性增强会下调 MM 细胞中的 D 细胞周期蛋白 IRES 功能，而 ERK 会促进活性。
We have shown that heightened AKT activity sensitized multiple myeloma (MM) cells to the anti-tumor effects of the mTOR-inhibitor, CCI-779. To test the mechanism of AKT’s regulatory role, we stably transfected U266 MM cell lines with an activated AKT allele or empty vector. The AKT-transfected cells were more sensitive to cytostasis induced in vitro by rapamycin or in vivo by its analog, CCI-779, whereas cells with quiescent AKT were resistant. The ability of mTOR inhibitors to downregulate D-cyclin expression was significantly greater in AKT-transfected MM cells, due in part, to AKT’s ability to curtail cap-independent translation and internal ribosome entry site (IRES) activity of D-cyclin transcripts. Similar AKT-dependent regulation of rapamycin responsiveness was demonstrated in a second myeloma model: the PTEN-null OPM-2 cell line transfected with wild type PTEN. As ERK/p38 activity facilitates IRES-mediated translation of some transcripts, we investigated ERK/p38 as regulators of AKT-dependent effects on rapamycin sensitivity. AKT-transfected U266 cells demonstrated significantly decreased ERK and p38 activity. However, only an ERK inhibitor prevented D-cyclin IRES activity in resistant “low AKT” myeloma cells. Furthermore, the ERK inhibitor successfully sensitized myeloma cells to rapamycin in terms of down regulated D-cyclin protein expression and G1 arrest. However, ectopic over-expression of an activated MEK gene did not increase cap-independent translation of D-cyclin in “high AKT” myeloma cells indicating that MEK/ERK activity was required but not sufficient for activation of the IRES. These data support a scenario where heightened AKT activity down-regulates D-cyclin IRES function in MM cells and ERK facilitates activity.