Oncogenic BRAFV600E inhibits BIM expression to promote melanoma cell survival
Oncogenic BRAFV600E inhibits BIM expression to promote melanoma cell survival
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DOI：
10.1111/j.1755-148x.2008.00491.x
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发表时间：
2008-10-01
影响因子：
4.3
通讯作者：
McMahon, Martin
中科院分区：
文献类型：
--
作者：
Cartlidge, Robert A.;Thomas, G. R.;McMahon, Martin
BRAF的体细胞激活突变是在人类黑色素瘤发生中检测到的最早和最常见的遗传异常。然而，激活的BRAF促进黑素瘤细胞周期进展和/或存活的机制仍不清楚。在这里，我们证明了BCL-2家族的促凋亡成员BIM的表达在小鼠和人黑素细胞以及人黑色素瘤细胞中被BRAF -> MEK -> ERK信号转导抑制。黑素细胞的营养因子剥夺导致BIM表达升高。然而，营养因子的再添加或BRAF（V600 E）的条件形式的活化导致BIM表达的快速抑制。在这两种情况下，BIM表达的抑制依赖于MEK 1/2和蛋白酶体的活性。与这些观察结果一致，BRAF（V600 E）或MEK 1/2在人黑素瘤细胞中的药理学抑制（分别使用PLX 4720和CI-1040）导致BIM表达的显著升高。BRAF -> MEK -> ERK信号传导的再激活导致BIM-EL在丝氨酸69上的磷酸化及其随后的降解。有趣的是，黑色素瘤细胞中BIM的内源性表达不足以诱导细胞凋亡，除非与血清剥夺相结合。在这些情况下，通过RNA干扰抑制BIM表达提供了部分保护免于细胞凋亡。这些数据表明，通过BRAF -> MEK -> ERK信号传导调节BIM表达是致癌BRAF（V600 E）可以影响黑色素瘤细胞的异常生理学的一种机制。
Somatic activating mutations of BRAF are the earliest and most common genetic abnormality detected in the genesis of human melanoma. However, the mechanism(s) by which activated BRAF promotes melanoma cell cycle progression and/or survival remain unclear. Here we demonstrate that expression of BIM, a pro-apoptotic member of the BCL-2 family, is inhibited by BRAF -> MEK -> ERK signaling in mouse and human melanocytes and in human melanoma cells. Trophic factor deprivation of melanocytes leads to elevated BIM expression. However, re-addition of trophic factors or activation of a conditional form of BRAF(V600E) leads to rapid inhibition of BIM expression. In both cases, inhibition of BIM expression was dependent on the activity of MEK1/2 and the proteasome. Consistent with these observations, pharmacological inhibition of BRAF(V600E) or MEK1/2 in human melanoma cells (using PLX4720 and CI-1040 respectively) led to a striking elevation of BIM expression. Re-activation of BRAF -> MEK -> ERK signaling led to phosphorylation of BIM-EL on serine 69 and its subsequent degradation. Interestingly, endogenous expression of BIM in melanoma cells was insufficient to induce apoptosis unless combined with serum deprivation. Under these circumstances, inhibition of BIM expression by RNA interference provided partial protection from apoptosis. These data suggest that regulation of BIM expression by BRAF -> MEK -> ERK signaling is one mechanism by which oncogenic BRAF(V600E) can influence the aberrant physiology of melanoma cells.