Inhibition of ligand-independent ERK1/2 activity in kidney proximal tubular cells deprived of soluble survival factors up-regulates Akt and prevents apoptosis
Inhibition of ligand-independent ERK1/2 activity in kidney proximal tubular cells deprived of soluble survival factors up-regulates Akt and prevents apoptosis
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DOI：
10.1074/jbc.m312048200
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发表时间：
2004-03-19
影响因子：
4.8
通讯作者：
Levine, JS
中科院分区：
文献类型：
--
作者：
Sinha, D;Bannergee, S;Levine, JS
当剥夺所有存活因子时，小鼠肾近端肾小管上皮细胞（MK-PT）在7-10天内通过凋亡而死亡。我们在这里表明，从MK-PT细胞中撤出所有生存因子与细胞外信号调节激酶-1和-2（ERK 1/2）活性的逐渐增加和磷酸化Akt（一种对细胞生存至关重要的激酶）的逐渐减少有关。药理学抑制ERK 1/2的直接上游激酶MEK 1/2，不仅防止磷酸化Akt的减少，而且延长MK-PT细胞存活。在不存在任何其他已知存活因子的情况下，ERK 1/2本身的抑制在维持MK-PT细胞活力方面与表皮生长因子一样有效。ERK 1/2与Akt在信号分子的多分子组装中共免疫沉淀，所述信号分子至少含有ERK 1/2、Akt、Rsk和3-磷酸肌醇依赖性激酶1（PDK 1）。我们假设激酶Rsk的激活需要ERK 1/2和PDK 1的磷酸化，它作为一个桥梁将ERK 1/2与PDK 1相关的Akt连接起来。尽管已经描述了Raf-MEK-ERK和PI 3 K-Akt信号通路之间的许多相互作用，但我们的结果首次显示了由ERK 1/2起源的信号事件对Akt活性的调节。ERK 1/2的自发激活通过MEK 1/2发生，并且似乎依赖于氧化应激，伴随着默认凋亡途径的诱导。总之，这些数据表明，自发激活的ERK 1/2，在已知的细胞外刺激的情况下，代表了一个以前未被认识到的主要调节途径，决定细胞的命运注定要死的默认途径的细胞凋亡。
Mouse kidney proximal tubular epithelial (MK-PT) cells die by apoptosis over 7-10 days when deprived of all survival factors. We show here that withdrawal of all survival factors from MK-PT cells is associated with a progressive increase in the activity of extracellular signal-regulated kinase-1 and -2 (ERK1/2) and a progressive decrease in phosphorylated Akt, a kinase critical to cell survival. Pharmacological inhibition of MEK1/2, the immediate upstream kinase for ERK1/2, not only prevented the decrease in phosphorylated Akt, but also prolonged MK-PT cell survival. Inhibition of ERK1/2, by itself, in the absence of any other known survival factors, was as potent as epidermal growth factor in maintaining MK-PT cell viability. ERK1/2 co-immunoprecipitated with Akt in a multimolecular assembly of signaling molecules, containing at a minimum ERK1/2, Akt, Rsk, and 3-phosphoinositide dependent kinase 1 (PDK1). We hypothesize that the kinase Rsk, whose activation requires phosphorylation by both ERK1/2 and PDK1, acts as a bridge bringing ERK1/2 into proximity with PDK1-associated Akt. Although a number of interactions between the Raf-MEK-ERK and PI3K-Akt signaling pathways have been described, our results are the first to show modulation of Akt activity by signaling events originating with ERK1/2. Spontaneous activation of ERK1/2 occurs via MEK1/2 and appears to depend on oxidant stress, accompanying induction of the default pathway of apoptosis. Together, these data suggest that the spontaneous activation of ERK1/2, in the absence of known extracellular stimuli, represents a previously unrecognized major regulatory pathway determining the fate of cells destined to die by the default pathway of apoptosis.