Phosphorylation by Akt within the ST loop of AMPK-α1 down-regulates its activation in tumour cells.
Phosphorylation by Akt within the ST loop of AMPK-α1 down-regulates its activation in tumour cells.
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DOI：
10.1042/bj20131344
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发表时间：
2014-04-15
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影响因子：
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通讯作者：
Hardie DG
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文献类型：
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作者：
Hawley SA;Ross FA;Gowans GJ;Tibarewal P;Leslie NR;Hardie DG
胰岛素/IGF-1（胰岛素样生长因子1）激活的蛋白激酶Akt（也称为蛋白激酶B）磷酸化AMPK-α1（AMP激活的蛋白激酶-α1）C端结构域内“ST环”（富含丝氨酸/苏氨酸的环）中的Ser 487，导致上游激酶在激活位点Thr 172处抑制磷酸化。令人惊讶的是，AMPK-α2上的等效位点Ser 491不是Akt靶点，而是通过自磷酸化修饰。用IGF-1刺激HEK（人胚肾）-293细胞后，可降低随后的Thr 172磷酸化和AMPK-α1对激活剂A769662和Ca 2+离子载体A23187的激活，我们发现这种效应依赖于Akt激活和Ser 487磷酸化。与此一致，在三种PTEN（10号染色体上缺失的磷酸酶和张力蛋白同源物）-无效肿瘤细胞系（其中通常抑制Akt途径的脂质磷酸酶PTEN不存在，因此Akt被过度激活）中，AMPK对A769662的激活具有抗性。然而，通过药理学抑制Akt或通过活性PTEN的再表达可以恢复AMPK的完全激活。我们还表明，Thr 172磷酸化的抑制是由于磷酸化的ST环与激酶结构域的α C-螺旋内的碱性侧链的相互作用。我们的研究结果表明，Akt在肿瘤细胞中过度激活的一个先前未被认识的作用是抑制LKB 1（肝激酶B1）-AMPK通路的激活，否则这将抑制细胞生长和增殖。Akt磷酸化AMPK的α1亚基Ser 487，导致Thr 172磷酸化和LKB 1激活减少。我们建立了这种效应的分子机制，并表明它会导致AMPK在几个PTEN无效的肿瘤细胞系下调。
The insulin/IGF-1 (insulin-like growth factor 1)-activated protein kinase Akt (also known as protein kinase B) phosphorylates Ser487 in the ‘ST loop’ (serine/threonine-rich loop) within the C-terminal domain of AMPK-α1 (AMP-activated protein kinase-α1), leading to inhibition of phosphorylation by upstream kinases at the activating site, Thr172. Surprisingly, the equivalent site on AMPK-α2, Ser491, is not an Akt target and is modified instead by autophosphorylation. Stimulation of HEK (human embryonic kidney)-293 cells with IGF-1 caused reduced subsequent Thr172 phosphorylation and activation of AMPK-α1 in response to the activator A769662 and the Ca2+ ionophore A23187, effects we show to be dependent on Akt activation and Ser487 phosphorylation. Consistent with this, in three PTEN (phosphatase and tensin homologue deleted on chromosome 10)-null tumour cell lines (in which the lipid phosphatase PTEN that normally restrains the Akt pathway is absent and Akt is thus hyperactivated), AMPK was resistant to activation by A769662. However, full AMPK activation could be restored by pharmacological inhibition of Akt, or by re-expression of active PTEN. We also show that inhibition of Thr172 phosphorylation is due to interaction of the phosphorylated ST loop with basic side chains within the αC-helix of the kinase domain. Our findings reveal that a previously unrecognized effect of hyperactivation of Akt in tumour cells is to restrain activation of the LKB1 (liver kinase B1)–AMPK pathway, which would otherwise inhibit cell growth and proliferation. Akt phosphorylates the α1 subunit of AMPK at Ser487, leading to reduced Thr172 phosphorylation and activation by LKB1. We establish a molecular mechanism for this effect and show that it causes down-regulation of AMPK in several PTEN-null tumour cell lines.