AMP活化蛋白激酶信号通路协调细胞生长、自噬和新陈代谢

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The AMP-activated protein kinase (AMPK) signaling pathway coordinates cell growth, autophagy, & metabolism

Maria M. Mihaylova 玛丽亚 · 米哈伊洛娃 and 及Reuben J. Shaw 鲁本 · j · 肖Author information 作者信息Copyright and License information 版权和许可证信息Disclaimer 免责声明The publisher’s final edited version of this article is available at 出版商对本文的最终编辑版本可以在Nat Cell BiolSee other articles in PMC that 参见 PMC 中的其他文章cite 引用 the published article. 发表的文章

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Abstract

摘要

One of the central regulators of cellular and organismal metabolism in eukaryotes is the AMP-activated protein kinase (AMPK), which is activated when intracellular ATP levels lower. AMPK plays critical roles in regulating growth and reprogramming metabolism, and recently has been connected to cellular processes including autophagy and cell polarity. We review here a number of recent breakthroughs in the mechanistic understanding of AMPK function, focusing on a number of new identified downstream effectors of AMPK.

在真核生物中,细胞和生物代谢的中枢调节因子之一是 AMP活化蛋白激酶,它在细胞内 ATP 水平降低时被激活。AMPK 在调节生长和重编程代谢中起着关键作用,最近被认为与包括自噬和细胞极性在内的细胞过程有关。我们在这里回顾了最近在 AMPK 功能的机制理解上的一些突破,重点放在一些新确定的 AMPK 下游效应器上。Go to: 去:

Core AMPK complex Components and Upstream Activators

核心 AMPK 复合组分及上游活化剂

One of the fundamental requirements of all cells is to balance ATP consumption and ATP generation. AMPK is a highly conserved sensor of intracellular adenosine nucleotide levels that is activated when even modest decreases in ATP production result in relative increases in AMP or ADP. In response, AMPK promotes catabolic pathways to generate more ATP, and inhibits anabolic pathways. Genetic analysis of AMPK orthologs in Arabidopsis1Saccharomyces cerevisiae2Dictyostelium3C. elegans4Drosophila5, and even the moss Physcomitrella patens6 has revealed a conserved function of AMPK as a metabolic sensor, allowing for adaptive changes in growth, differentiation, and metabolism under conditions of low energy. In higher eukaryotes like mammals, AMPK plays a general role in coordinating growth and metabolism, and specialized roles in metabolic control in dedicated tissues such as the liver, muscle and fat7.

所有细胞的基本要求之一是平衡三磷酸腺苷的消耗和生成。AMPK 是一种高度保守的细胞内腺苷酸水平的传感器,当 ATP 产量的轻微下降导致 AMP 或 ADP 的相对增加时,这种传感器就会被激活。作为回应,AMPK 促进分解代谢途径产生更多的 ATP,并抑制合成代谢途径。对拟南芥1号、酿酒酵母2号、盘基网柄菌3号、秀丽隐杆菌4号、果蝇5号甚至苔藓小立碗菌6号中 AMPK 同源基因的遗传分析表明,AMPK 作为一种代谢传感器具有保守功能,可以在低能量条件下适应生长、分化和代谢的变化。在像哺乳动物这样的高等真核生物中,AMPK 在协调生长和新陈代谢方面发挥普遍作用,在肝脏、肌肉和脂肪等专门组织中发挥专门的代谢控制作用。

In most species, AMPK exists as an obligate heterotrimer, containing a catalytic subunit (a), and two regulatory subunits (β and γ). AMPK is hypothesized to be activated by a two-pronged mechanism (for a full review, see8). Under lowered intracellular ATP levels, AMP or ADP can directly bind to the γ regulatory subunits, leading to a conformational change that protects the activating phosphorylation of AMPK9,10. Recent studies discovering that ADP can also bind the nucleotide binding pockets in the AMPK γ suggest it may be the physiological nucleotide for AMPK activation under a variety of cellular stresses1811. In addition to nucleotide binding, phosphorylation of Thr172 in the activation loop of AMPK is required for its activation, and several groups have demonstrated that the serine/threonine kinase LKB1 directly mediates this event1214. Interestingly, LKB1 is a tumor suppressor gene mutated in the inherited cancer disorder Peutz-Jeghers syndrome and in a significant fraction of lung and cervical cancers, suggesting that AMPK could play a role in tumor suppression15. Importantly, AMPK can also be phosphorylated on Thr172 in response to calcium flux, independently of LKB1, via CAMKK2 (CAMKKβ) kinase, which is the closest mammalian kinase to LKB1 by sequence homology1619. Additional studies have suggested the MAPKKK family member TAK1/MAP3K7 may also phosphorylate Thr172 but the contexts in which TAK1 might regulate AMPK in vivo, and whether that involves LKB1 still requires further investigation2021.

在大多数物种中,AMPK 作为一种专性异三聚体存在,包含一个催化亚基(a)和两个调节亚基(和)。AMPK 假设可以通过双管齐下的机制来激活(详见第8页)。在细胞内 ATP 水平降低的情况下,AMP 或 ADP 可以直接与调节亚基结合,从而产生一种保护 ampk910磷酸化激活的构象改变。最近的研究发现 ADP 也可以结合 AMPK 中的核苷酸结合口袋,这表明它可能是在各种细胞应力下 AMPK 活化的生理核苷酸。除了核苷酸结合外,活化 AMPK 环路中 Thr172的磷酸化也是激活 AMPK 的必要条件,有几个研究组已经证明,丝氨酸/苏氨酸激酶 LKB1直接介导了这个事件12-14。有趣的是,LKB1是一种肿瘤抑制基因突变,在遗传性癌症疾病珀茨-杰格斯综合征和相当一部分的肺癌和宫颈癌中都有表达,这表明 AMPK 可能在肿瘤抑制中发挥作用。重要的是,AMPK 也可以通过 CAMKK2(camkk)激酶在 Thr172上被磷酸化,以响应钙通量,独立于 LKB1,CAMKK2是哺乳动物中与 LKB1最接近的同源序列16-19的激酶。进一步的研究表明,MAPKKK 家族成员 TAK1/MAP3K7也可能磷酸化 Thr172,但 TAK1在体内可能调节 AMPK 的环境,以及是否涉及 LKB1仍需进一步的研究20、21。

In mammals, there are two genes encoding the AMPK α catalytic subunit (α1 and α2), two β genes (β1 and β2) and three γ subunit genes (γ1, γ2 and γ3)22. The expression of some of these isoforms is tissue restricted, and functional distinctions are reported for the two catalytic α subunits, particularly of AMP- and LKB1-responsiveness and nuclear localization of AMPKα2 compared to the α123. However, the α1 subunit has been shown to localize to the nucleus under some conditions24, and the myristoylation of the (β isoforms has been shown to be required for proper activation of AMPK and its localization to membranes25. Additional control via regulation of the localization of AMPK2628 or LKB12930 remains an critical underexplored area for future research.

哺乳动物中有两个 AMPK 催化亚基(1和2)基因,两个基因(1和2)和三个亚基(1,2和3)22基因。其中一些亚型的表达受组织限制,并报道了两个催化亚基的功能区别,特别是 ampk 2的 AMP- 和 lkb1-反应性和核定位。然而,在一定条件下,AMPK 的1亚基定位于细胞核内,(异构体的肉豆蔻酰化是 AMPK 正常活化及其定位于细胞膜的必要条件。通过调节 AMPK26-28或 LKB129的本地化进一步控制,30仍然是未来研究的关键领域。

Genetic studies of tissue-specific deletion of LKB1 have revealed that LKB1 mediates the majority of AMPK activation in nearly every tissue type examined to date, though CAMKK2 appears to be particularly involved in AMPK activation in neurons and T cells3132. In addition to regulating AMPKα1 and AMPKα2 phosphorylation, LKB1 phosphorylates and activates another twelve kinases related to AMPK33. This family of kinases includes the MARKs (1-4), SIKs (1-3), BRSK/SADs (1-2) and NUAKs (1-2) sub-families of kinases34. Although only AMPKα1 and AMPKα2 are activated in response to energy stress, there is a significant amount of crosstalk and shared substrates between AMPK and the AMPK related kinases15.

对 LKB1组织特异性缺失的遗传学研究表明,迄今为止,LKB1介导了几乎所有组织类型中 AMPK 的大部分激活,尽管 CAMKK2似乎特别参与了神经元和 t 细胞中 AMPK 的激活。除了调节 ampk 1和 ampk 2的磷酸化外,LKB1还磷酸化并激活另外十二个与 ampk 33相关的激酶。这个激酶家族包括马克斯(1-4)、斯克斯(1-3)、 BRSK/SADs (1-2)和 NUAKs (1-2)激酶亚家族34。虽然只有 AMPK 1和 AMPK 2在能量胁迫下被激活,但在 AMPK 和 AMPK 相关的激酶15之间存在大量的串扰和共享的底物。

Many types of cellular stresses can lead to AMPK activation. In addition to physiological AMP/ADP elevation from stresses such as low nutrients or prolonged exercise, AMPK can be activated in response to several pharmacological agents (see Figure 1). Metformin, the most widely prescribed Type 2 diabetes drug, has been shown to activate AMPK35 and to do so in an LKB1 dependent manner36. Metformin and other biguanides, such as the more potent analog phenformin37, are thought to activate AMPK by acting as mild inhibitors of Complex I of the respiratory chain, which leads to a drop of intracellular ATP levels38,39. Another AMPK agonist, 5-aminoimidazole-4-carboxamide-1-b-d-ribofuranoside (AICAR) is a cell-permeable precursor to ZMP, which mimics AMP, and binds to the AMPKγ subunits40. Interestingly, the chemotherapeutic pemetrexed, which is an inhibitor of thymidylate synthase, also inhibits aminoimidazolecarboxamide ribonucleotide formyltransferase (AICART), the second folate-dependent enzyme of purine biosynthesis, resulting in increased intracellular ZMP and activation of AMPK, similar to AICAR treatment41. Finally, a number of naturally occurring compounds including Resveratrol, a polyphenol found in the skin of red grapes, have been shown to activate AMPK and yield similar beneficial effects on metabolic disease as AICAR and metformin4243. Resveratrol can rapidly activate AMPK via inhibition of the F1F0 mitochondrial ATPase38 and the original studies suggesting that resveratrol directly binds and activates sirtuins have come into question4445. Indeed, the activation of SIRT1 by resveratrol in cells and mice appears to require increased NAD+ levels by AMPK activity4647.

许多类型的细胞应力可以导致 AMPK 活化。除了在低营养或长时间运动等压力下生理性 AMP/ADP 升高外,AMPK 还可以在多种药物作用下被激活(见图1)。二甲双胍,最常用的处方2型糖尿病药物,已被证明能够激活 AMPK35,并且在 LKB1依赖性神经元中起作用。二甲双胍和其他双胍类药物,如更有效的类似物苯福明37,被认为是通过作为呼吸链复合物 i 的温和抑制剂来激活 AMPK,从而导致细胞内 ATP 水平38,39的下降。另一种 AMPK 激动剂5- 氨基咪唑 -4- 甲酰胺 -1-b-d-呋喃核苷(AICAR)是 ZMP 的细胞渗透前体,模拟 AMP,并与 AMPK 亚单位40结合。有趣的是,化疗药物培美曲塞,胸苷酸合成酶的抑制剂,也抑制嘌呤的第二种叶酸依赖性酶氨基咪唑啉甲酰胺核糖核酸转移酶(AICART) ,导致细胞内 ZMP 生物合成增加和 AMPK 的激活,类似于 AICAR 治疗41。最后,一些自然产生的化合物,包括白藜芦醇,一种在红葡萄皮中发现的多酚,已经被证明可以激活 AMPK,并产生类似于 AICAR 和 metformin42,43对代谢疾病的有益作用。白藜芦醇可以通过抑制 F1F0线粒体 ATPase38快速激活 AMPK,最初的研究表明白藜芦醇直接结合和激活 sirtuins 已经成为问题44,45。事实上,白藜芦醇激活 SIRT1的细胞和小鼠似乎需要增加 NAD + 水平的 AMPK 活性46,47。

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Figure 1 图1The AMPK signaling pathway AMPK 信号通路

AMPK is activated when AMP and ADP levels in the cells rise due to variety of physiological stresses, as well as pharmacological inducers. LKB1 is the upstream kinase activating it in response to AMP increase, whereas CAMKK2 activates AMPK in response to calcium increase. Activated AMPK directly phosphorylates a number of subtrates to acutely impact metabolism and growth, as well as phosphorylating a number of transcriptional regulators that mediate long term metabolic reprogramming. Shown are all the best-established substrates to date-those needing further in vivo examination are italicized. Question marks denote candidate substrates whose identified phosphorylation sites diverge from the established optimal substrate motif (which all the others conform to). A full lineup of the identified AMPK phosphorylation sites in these substrates in Supplemental Table 1. Substrates in red have been reported to serve as substrates of other AMPK family members (SIK1, SIK2, MARKs, SADs) in vivo in addition to being substrates of AMPK.

腺苷酸活化蛋白激酶是激活当 AMP 和 ADP 水平在细胞上升,由于各种生理应激,以及药理诱导剂。LKB1是上游激酶,在 AMP 增加时激活它,而 CAMKK2在钙增加时激活 AMPK。激活的 AMPK 直接磷酸化一些亚基,以严重影响代谢和生长,以及磷酸化一些转录调节因子,介导长期代谢重编程。显示是所有最好的建立基板,迄今为止-那些需要进一步的体内检查是斜体。问号表示候选底物,其确定的磷酸化位点偏离既定的最佳底物基序(其他所有符合)。一个完整的阵容确定 AMPK 磷酸化位点在这些补充表1底物。红色底物已经被报道作为 AMPK 家族其他成员(SIK1,SIK2,MARKs,SADs)在体内的底物,除了作为 AMPK 的底物。

The principle therapeutic mode of action of metformin in diabetes is via suppression of hepatic gluconeogenesis74849, though it remains controversial whether AMPK is absolutely required for the glucose lowering effects of metformin50. Since metformin acts as a mitochondrial inhibitor, it should be expected to activate a variety of stress sensing pathways which could redundantly serve to inhibit hepatic gluconeogenesis, of which currently AMPK is just one of the best appreciated. Critical for future studies will be defining the relative contribution of AMPK and other stress-sensing pathways impacted by metformin and the aforementioned energy stress agents in accurate in vivo models of metabolic dysfunction and insulin resistance in which these agents show therapeutic benefit. Nonetheless, metformin, AICAR51, the direct small molecule AMPK activator A76966252, and genetic expression of activated AMPK in liver53 all lower blood glucose levels, leaving AMPK activation a primary goal for future diabetes therapeutics54. As a result of the diverse beneficial effects of this endogenous metabolic checkpoint in other pathological conditions, including several types of human cancer, there is an increasing interest in identifying novel AMPK agonists to be exploited for therapeutic benefits.

二甲双胍治疗糖尿病的主要作用方式是通过抑制肝糖原生成7,48,49,但是否绝对需要 AMPK 对二甲双胍50的降糖作用仍有争议。由于二甲双胍作为一种线粒体抑制剂,它应该被期望激活多种应激感知途径,这可以冗余地起到抑制肝脏糖异生的作用,其中目前 AMPK 只是最受重视的一种。未来研究的关键将是在精确的体内代谢紊乱和胰岛素抵抗模型中确定 AMPK 和其他受二甲双胍和上述能量应激因子影响的应激传感通路的相对贡献,这些因子显示了治疗效果。尽管如此,二甲双胍、 AICAR51、 AMPK 激活剂 A76966252和激活 AMPK 在肝脏中的基因表达都降低了血糖水平,使 AMPK 激活成为未来糖尿病治疗的首要目标。由于这种内源性新陈代谢检查点在其他病理状态下,包括几种类型的人类癌症中具有不同的有益作用,人们越来越有兴趣确定新的 AMPK 激动剂,以利用其治疗效果。Go to: 去:

AMPK coordinates Control of Cell Growth and Autophagy

AMPK 协调控制细胞生长和自噬

In conditions where nutrients are scarce, AMPK acts as a metabolic checkpoint inhibiting cellular growth. The most thoroughly described mechanism by which AMPK regulates cell growth is via suppression of the mammalian target of rapamycin complex 1 (mTORC1) pathway. One mechanism by which AMPK controls the mTORC1 is by direct phosphorylation of the tumor suppressor TSC2 on serine 1387 (Ser1345 in rat TSC2). However, in lower eukaryotes, which lack TSC2 and in TSC2-/- mouse embryonic fibroblasts (MEFs) AMPK activation still suppresses mTORC1 5556. This led to the discovery that AMPK also directly phosphorylates Raptor (regulatory associated protein of mTOR), on two conserved serines, which blocks the ability of the mTORC1 kinase complex to phosphorylate its substrates42.

在营养缺乏的条件下,AMPK 作为一个新陈代谢检查点抑制细胞生长。AMPK 通过抑制哺乳动物雷帕霉素靶蛋白复合物1(mTORC1)通路来调节细胞生长,这是目前最为全面的研究机制。AMPK 控制 mTORC1的一个机制是通过直接磷酸化肿瘤抑制因子 TSC2对丝氨酸1387(大鼠 TSC2中的丝氨酸1345)。然而,在缺乏 TSC2和 TSC2-/-小鼠胚胎成纤维细胞(MEFs) AMPK 激活的低等真核生物中,仍然抑制 mtorc155,56。这导致了 AMPK 也直接磷酸化猛禽(mTOR 的调节相关蛋白) ,在两个保守的丝氨酸上,阻止 mTORC1激酶复合体磷酸化其底层的能力。

In addition to regulating cell growth, mTORC1 also controls autophagy, a cellular process of “self engulfment” in which the cell breaks down its own organelles (macroautophagy) and cytosolic components (microautophagy) to ensure sufficient metabolites when nutrients run low. The core components of the autophagy pathway were first defined in genetic screens in budding yeast and the most upstream components of the pathway include the serine/threonine kinase Atg1 and its associated regulatory subunits Atg13 and Atg175758. In budding yeast, the Atg1 complex is inhibited by the Tor-raptor (TORC1) complex5961. The recent cloning of the mammalian orthologs of the Atg1 complex revealed that its activity is also suppressed by mTORC1 through a poorly defined mechanism likely to involve phosphorylation of the Atg1 homologs ULK1 and ULK2, as well as their regulatory subunits (reviewed in62). In contrast to inhibitory phosphorylations from mTORC1, studies from a number of laboratories in the past year have revealed that the ULK1 complex is activated via direct phosphorylation by AMPK, which is critical for its function in autophagy and mitochondrial homeostasis (reviewed in63).

除了调节细胞生长,mTORC1还控制自噬,这是一种细胞“自我吞噬”的过程,在这个过程中,细胞分解自身的细胞器(巨噬细胞自噬)和胞质成分(微噬细胞自噬) ,以确保在营养素不足时有足够的代谢物。自噬途径的核心成分首先定义在芽殖酵母的遗传筛选中,该途径的最上游成分包括丝氨酸/苏氨酸激酶 Atg1及其相关调节亚基 Atg13和 Atg1757,58。在芽殖酵母中,Atg1复合物被 Tor-raptor (TORC1)复合物59-61抑制。最近对 Atg1复合体的哺乳动物同源基因的克隆表明,其活性也受到 mTORC1的抑制,其机制可能涉及 Atg1同源基因 ULK1和 ULK2及其调节亚基的磷酸化(见第62页审查)。与 mTORC1的抑制性磷酸化相反,过去一年来许多实验室的研究表明,ULK1复合体通过 AMPK 的直接磷酸化被激活,这对其在自噬和线粒体稳态中的功能至关重要(见第63页)。

In addition to unbiased mass spectrometry studies discovering endogenous AMPK subunits as ULK1 interactors6465, two recent studies reported AMPK can directly phosphorylate several sites in ULK16667. Our laboratory found that hepatocytes and mouse embryonic fibroblasts devoid of either AMPK or ULK1 had defective mitophagy and elevated levels of p62 (Sequestrosome-1), a protein involved in aggregate turnover which itself is selectively degraded by autophagy66. As observed for other core autophagy proteins, ULK1 was required for cell survival following nutrient deprivation and this also requires the phosphorylation of the AMPK sites in ULK1. Similarly, genetic studies in budding yeast68 and in C. elegans66 demonstrate that Atg1 is needed for the effect of AMPK on autophagy. Interestingly, Kim and colleagues found distinct sites in ULK1 targeted by AMPK, though they also found that AMPK regulation of ULK1 was needed for ULK1 function67. These authors also mapped a direct mTOR phosphorylation site in ULK1 which appears to dictate AMPK binding to ULK1, a finding corroborated by another recent study, though the details differ69. Collectively, these studies show that AMPK can trigger autophagy in a double-pronged mechanism of directly activating ULK1 and inhibiting the suppressive effect of mTORC1 complex1 on ULK1 (see Fig. 2). Many of the temporal and spatial details of the regulation of these three ancient interlocking nutrient-sensitive kinases (AMPK, ULK1, mTOR) remains to be decoded.

除了公正的质谱法研究发现内源性 AMPK 亚基为 ULK1,64,65之外,最近的两个研究报道 AMPK 可以直接磷酸化 ULK166,67的几个位点。我们的实验室发现,缺乏 AMPK 或 ULK1的肝细胞和小鼠胚胎成纤维细胞有吞噬功能缺陷,p62(Sequestrosome-1)水平升高,这是一种参与聚集体转化的蛋白质,自噬66可以选择性地降解。正如其他核心自噬蛋白所观察到的,ULK1是细胞在营养缺乏后存活所必需的,这也需要 ULK1中 AMPK 位点的磷酸化。同样,在芽殖的 yeast68和 c. elegans66的基因研究表明,Atg1对于 AMPK 对自噬的影响是必需的。有趣的是,Kim 和他的同事们发现了 AMPK 针对 ULK1的不同位点,尽管他们也发现 ULK1功能67需要 AMPK 调节。这些作者还绘制了 ULK1中一个直接的 mTOR 磷酸化位点,该位点似乎决定了 AMPK 与 ULK1的结合,这一发现得到了另一项最近研究的证实,尽管细节有所不同。总的来说,这些研究表明 AMPK 可以通过直接激活 ULK1和抑制 mTORC1复合物1对 ULK1的抑制作用的双向机制触发自噬(见图2)。这三种古老的营养敏感性连锁激酶(AMPK,ULK1,mTOR)的时间和空间调节的许多细节仍有待破解。

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Figure 2 图2The Ras/ PI3K/ mTOR pathways intersect the LKB1/AMPK pathway at multiple points Ras/PI3K/mTOR 通路与 LKB1/AMPK 通路多点交叉

LKB1, the upstream kinase for AMPK, is the tumor suppressor gene mutated in Peutz–Jeghers syndrome (PJS), as well a significant fraction of sporadic lung cancers and cervical cancers. PJS patients share a number of clinical features with patients inheriting defective PTEN or TSC tumor suppressors, perhaps due to their control of common biochemical pathways, best understood currently being the mammalian target of rapamycin complex 1 (mTORC1) pathway. Extensive cross-regulation of the LKB1/AMPK pathway by the oncogenic Ras and PI3K pathways has been discovered, which may explain how these commonly mutated oncogenes also try to circumvent this endogenous tumor suppressor pathway. The ULK1/hATG1 kinase complex has emerged recently as a central node receiving inputs from both AMPK and mTORC1. A number of kinases that can phosphorylate specific residues in LKB1 or AMPK have been identified (upper inset), though the contexts in which most of these regulatory events occur is poorly defined at present, as is the functional impact of these phosphorylation events on AMPK signaling. The BHD tumor suppressor and its partner FNIP1, as well as the sestrin family of proteins, have also been implicated as being upstream or downstream of AMPK and mTOR depending on the context.

LKB1是 AMPK 的上游激酶,在 Peutz-Jeghers 综合征(PJS)以及相当一部分的散发性肺癌和宫颈癌中发生肿瘤抑制基因突变。PJS 患者与继承有缺陷 PTEN 或 TSC 肿瘤抑制基因的患者有许多共同的临床特征,这可能是由于他们控制了共同的生化通路,目前最好的理解是哺乳动物雷帕霉素复合物1(mTORC1)通路的靶点。已经发现肿瘤基因 Ras 和 PI3K 通路广泛地交叉调控 LKB1/AMPK 信号通路,这可能解释这些常见的突变致癌基因如何也试图规避这种内源性肿瘤抑制通路。ULK1/hATG1激酶复合体是最近出现的一个接受 AMPK 和 mTORC1输入的中心节点。许多激酶可以磷酸化 LKB1或 AMPK 中的特异性残基(上插) ,尽管目前还不清楚这些调控事件发生的背景,以及这些磷酸化事件对 AMPK 信号传导的功能影响。BHD 肿瘤抑制基因及其合作伙伴 FNIP1,以及蛋白质的 sestrin 家族,也被认为是 AMPK 和 mTOR 的上游或下游,这取决于上下文。

Interestingly, AMPK both triggers the acute destruction of defective mitochondria through a ULK1-dependent stimulation of mitophagy, as well as stimulating de novo mitochondrial biogenesis through PGC-1α dependent transcription (see below). Thus AMPK controls mitochondrial homeostasis in a situation resembling “Cash for Clunkers” in which existing defective mitochondria are replaced by new fuel-efficient mitochondria (Fig. 3). One context where AMPK control of mitochondrial homeostasis may be particularly critical is in the context of adult stem cell populations. In a recent study on haematopoetic stem cells, genetic deletion of LKB1 or both of the AMPK catalytic subunits phenocopied fibroblasts lacking ULK1 or the AMPK sites in ULK1 in terms of the marked accumulation of defective mitochondria70.

有趣的是,AMPK 通过 ulk1依赖性的吞噬刺激激发了有缺陷的线粒体的急性破坏,同时通过 pgc-1依赖性的转录刺激了新的线粒体生物发生(见下文)。因此,AMPK 控制线粒体内稳态的情况类似“旧车换现金” ,现有的有缺陷的线粒体被新的燃料效率线粒体取代(图3)。AMPK 对线粒体稳态的控制可能特别关键的一个环境是在成人干细胞群的环境中。在最近的一项关于造血干细胞、 LKB1的删除或缺乏 ULK1或缺乏 ULK1中 AMPK 位点的成纤维细胞中缺陷线粒体70明显聚集的 AMPK 催化亚基的研究中。Figure 3 图3AMPK acts as a mitochondrial “Cash for Clunkers” AMPK 扮演了线粒体“旧车换现金”的角色

Activated AMPK acutely triggers the destruction of existing defective mitochondria via ULK1-dependent mitophagy and simultaneously triggers the biogenesis of new mitochondria via effects on PGC-1a dependent transcription. These dual processes controlled by AMPK have the net effect of replacing existing defective mitochondria with new functional mitochondria. This two-pronged control of mitochondria homeostasis by AMPK will have a number of physiological and pathological conditions where it plays a critical role, and a few are illustrated here.

活化的 AMPK 通过 ulk1依赖的吞噬作用激活现有的有缺陷的线粒体,同时通过影响 PGC-1a 依赖的转录激活新的线粒体的生物发生。这些由 AMPK 控制的双重过程有用新的功能线粒体替换现有的有缺陷的线粒体的净效果。这种双管齐下的控制线粒体内环境稳定的 AMPK 将有一些生理和病理条件,其中它发挥了关键作用,一些是说明在这里。

Beyond effects on mTOR and ULK1, two other reported targets of AMPK in growth control are the tumor suppressor p5371 and the CDK inhibitor p277273, though the reported sites of phosphorylation do not conform well to the AMPK substrate sequence found in other substrates. The recent discovery of AMPK family members controlling phosphatases74 presents another mechanism by which AMPK might control phosphorylation of proteins, without being the kinase to directly phosphorylate the site.

除了对 mTOR 和 ULK1的影响,另外两个已报道的 AMPK 在生长控制中的靶点是肿瘤抑制因子 p5371和 CDK 抑制因子 p2772,73,尽管已报道的磷酸化位点与其他底物中发现的 AMPK 底物序列不完全一致。最近发现的 AMPK 家族成员控制磷酸酶74提出了另一种机制,AMPK 可能控制蛋白的磷酸化,但不是直接磷酸化该位点的激酶。Go to: 去:

Control of Metabolism via Transcription and Direct effects on Metabolic Enzymes

转录调控代谢及其对代谢酶的直接影响

AMPK was originally defined as the upstream kinase for the critical metabolic enzymes Acetyl-CoA carboxylase (ACC1 & ACC2) and HMG-CoA reductase, which serve as the rate-limiting steps for fatty-acid and sterol synthesis in wide-variety of eukaryotes7576. In specialized tissues such as muscle and fat, AMPK regulates glucose uptake via effects on the RabGAP TBC1D1, which along with its homolog TBC1D4 (AS160), play key roles in GLUT4 trafficking following exercise and insulin77. In fat, AMPK also directly phosphorylates lipases, including both hormone sensitive lipase (HSL)78 and adipocyte triglyceride lipase (ATGL)79, an AMPK substrate also functionally conserved in C. elegans4. Interestingly, mammalian ATGL and its liberation of fatty acids has recently been shown to be important in rodent models of cancer-associated cachexia80. Whether AMPK is important in this context remains to be seen.

AMPK 最初被定义为关键代谢酶乙酰辅酶A羧化酶(ACC1 & ACC2)和羟甲基戊二酸单酰辅酶A还原酶的上游激酶,它们在各种真核生物75,76中作为脂肪酸和甾醇合成的限速步骤。AMPK 通过影响 RabGAP TBC1D1和其同源基因 TBC1D4(AS160) ,在运动和胰岛素77后的 GLUT4转运中发挥关键作用。在脂肪中,AMPK 也直接磷酸化脂肪酶,包括激素敏感脂肪酶(HSL)78和脂肪细胞甘油三酯脂肪酶(ATGL)79,AMPK 底物在秀丽隐杆线虫中也是功能保守的。有趣的是,哺乳动物 ATGL 及其脂肪酸的释放最近被证明在啮齿动物癌症相关的喉癌模型中具有重要作用。在这种情况下 AMPK 是否重要还有待观察。

In addition to acutely regulation of these metabolic enzymes, AMPK is also involved in a adaptive reprogramming of metabolism through transcriptional changes. Breakthroughs in this area have come through distinct lines of investigation. AMPK has been reported to phosphorylate and regulate a number of transcription factors, coactivators, the acetyltransferase p300, a subfamily of histone deacetylases, and even histones themselves. In 2010, Bungard et al., reported that AMPK can target transcriptional regulation through phosphorylation of histone H2B on Serine3681. Cells expressing a mutant H2B S36A blunted the induction of stress genes upregulated by AMPK including p21 and cpt1c8182. In addition, AMPK was chromatin immunoprecipitated at the promoters of these genes making this one of the first studies to detect AMPK at specific chromatin loci in mammalian cells81. Notably, Serine36 in H2B does not conform well to the AMPK consensus83; further studies will reveal whether this substrate is an exception or whether this phosphorylation is indirectly controlled.

除了对这些代谢酶的急性调节外,AMPK 还通过转录变化参与代谢的适应性重编程。这一领域的突破是通过不同的调查方式取得的。AMPK 已被报道用于磷酸化和调节许多转录因子、辅活化因子、乙酰转移酶 p300、组蛋白去乙酰化酶亚家族,甚至组蛋白本身。在2010年,Bungard 等人报告说 AMPK 可以通过丝氨酸3681上组蛋白 H2B 的磷酸化作用靶向转录调控。表达突变体 H2B S36A 的细胞对 AMPK 上调的应激基因(包括 p21和 cpt1c81,82)的诱导有抑制作用。此外,AMPK 是在这些基因启动子处的染色质免疫沉淀物,这是首次在哺乳动物细胞81的特定染色质位点检测 AMPK 的研究之一。值得注意的是,H2B 中的 Serine36不符合 AMPK 同意的83; 进一步的研究将揭示这种底物是一个例外还是这种磷酸化是间接控制的。

AMPK activation has also recently been linked to circadian clock regulation, which couples daily light and dark cycles to control of physiology in a wide variety of tissues through tightly coordinated transcriptional programs84. Several master transcription factors are involved in orchestrating this oscillating network. AMPK was shown to regulate the stability of the core clock component Cry1 though phosphorylation of Cry1 Ser71, which stimulates the direct binding of the Fbox protein Fbxl3 to Cry1, targeting it for ubiquitin-mediated degradation24. Importantly, this is the first example of AMPK-dependent phosphorylation inducing protein turnover, although this is a common mechanism utilized by other kinases. One would expect additional substrates in which AMPK-phosphorylation triggers degradation will be discovered. Another study linked AMPK to the circadian clock via effects on Casein kinase85, though the precise mechanism requires further investigation. A recent genetic study in AMPK-deficient mice also indicates that AMPK modulates the circadian clock to different extents in different tissues86.

最近还发现 AMPK 激活与生物钟调节有关,生物钟调节通过紧密协调的转录程序将日光和黑暗周期与各种组织中的生理控制联系起来。几个主转录因子参与编排这个振荡网络。AMPK 通过 Cry1 Ser71的磷酸化调节核心时钟成分 Cry1的稳定性,激活 Fbox 蛋白 Fbxl3与 Cry1的直接结合,靶向泛素介导的降解24。重要的是,这是第一个例子 ampk 依赖的磷酸化诱导蛋白质周转,虽然这是一个共同的机制利用其他激酶。人们会期待在其他底物中发现 ampk 磷酸化触发器降解。另一项研究通过对酪蛋白激酶85的影响将 AMPK 与生物钟联系起来,尽管确切的机制还需要进一步的研究。最近对 AMPK 缺陷小鼠的基因研究也表明,AMPK 在不同的组织中对生物钟有不同程度的调节。

As the role of transcriptional programs in the physiology of metabolic tissues is well-studied, many connections between AMPK and transcriptional control have been found in these systems. Importantly, many of the transcriptional regulators phosphorylated by AMPK in metabolic tissues are expressed more ubiquitously than initially appreciated and may be playing more central roles tying metabolism to growth. One example that was recently discovered is the lipogenic transcriptional factor Srebp187. Srebp1 induces a gene program including targets ACC1 and FASN that stimulate fatty acid synthesis in cells. In addition to being a critical modulator of lipids in liver and other metabolic tissues, Srebp1 mediated control of lipogenesis is needed in all dividing cells as illustrated in a recent study identifying Srebp1 as a major cell growth regulator in Drosophila and mammalian cells88. AMPK was recently found to phosphorylate a conserved serine near the cleavage site within Srebp1, suppressing its activation87. This further illustrates the acute and prolonged nature of AMPK control of biology. AMPK acutely controls lipid metabolism via phosphorylation of ACC1 and ACC2, while mediating long-term adaptive effects via phosphorylation of Srebp1 and loss of expression of lipogenic enzymes. AMPK has also been suggested to phosphorylate the glucose-sensitive transcription factor ChREBP89 which dictates expression of an overlapping lipogenic gene signature with Srebp190. Adding an extra complexity here is the observation that phosphorylation of the histone acetyltransferase p300 by AMPK and its related kinases impacts the acetylation and activity of ChREBP as well91. Interestingly, like Srebp1, ChREBP has also been shown to be broadly expressed and involved in growth control in some tumor cell settings, at least in cell culture92.

随着转录程序在代谢组织生理学中的作用被广泛研究,AMPK 和转录控制之间的许多联系已经在这些系统中被发现。重要的是,许多由 AMPK 磷酸化的转录调节因子在代谢组织中的表达比最初认为的更加普遍,可能在新陈代谢和生长中起着更加重要的作用。最近发现的一个例子是脂肪生成转录因子 Srebp187。1诱导一个基因程序,包括针对 ACC1和 FASN 的基因程序,这些基因程序能够刺激细胞中的脂肪酸合成。除了作为肝脏和其他代谢组织中脂质的重要调节剂,Srebp1介导的脂质形成控制在所有分裂细胞中都是必需的,最近的一项研究证实 Srebp1是果蝇和哺乳动物细胞中主要的细胞生长调节剂88。最近发现 AMPK 可以磷酸化 Srebp1蛋白裂解位点附近的保守丝氨酸,从而抑制其活化87。这进一步说明了 AMPK 控制生物学的急性和长期性。AMPK 通过 ACC1和 ACC2的磷酸化来控制脂质代谢,同时通过 Srebp1的磷酸化和脂肪生成酶表达的丢失来介导长期的适应效应。AMPK 也被认为可以磷酸化葡萄糖敏感的转录因子 ChREBP89,该基因表达与 Srebp190重叠的脂肪基因标记。更为复杂的是,AMPK 磷酸化组蛋白乙酰转移酶 p300及其相关激酶,影响 ChREBP 的乙酰化和活性。有趣的是,和 Srebp1一样,ChREBP 也被证明在一些肿瘤细胞中广泛表达并参与生长控制,至少在细胞培养中是这样。

Similarly, while best appreciated for roles in metabolic tissues, the CRTC family of transcriptional co-activators for CREB and its related family members may also play roles in epithelial cells and cancer93. Recent studies in C. elegans revealed that phosphorylation of the CRTC ortholog by AMPK is needed for AMPK to promote lifespan extension94, reinforcing the potentially broad biological functions of these coactivators. In addition to these highly conserved targets of AMPK and its related kinases, AMPK has also been reported to phosphorylate the nuclear receptors HNF4α (NR2A1)95 and TR4 (NR2C2)96, the coactivator PGC-1α97 and the zinc-finger protein AREBP (ZNF692)98, though development of phospho-specific antibodies and additional functional studies are needed to further define the functional roles of these events.

同样,虽然 CRTC 家族的转录共激活因子在代谢组织中的作用得到了最好的评价,但 CREB 及其相关家族成员的转录共激活因子也可能在上皮细胞和癌细胞中发挥作用。最近对秀丽隐杆线虫的研究表明,AMPK 通过磷酸化 CRTC 同源序列来促进 AMPK 延长寿命94,强化了这些辅活化子潜在的广泛生物学功能。除了 AMPK 及其相关激酶的这些高度保守的靶点外,AMPK 还被报道磷酸化了核受体 hnf4(NR2A1)95和 TR4(NR2C2)96、辅激活因子 pgc-197和锌指蛋白 AREBP (ZNF692)98,尽管磷酸化特异性抗体的开发和其他功能研究需要进一步确定这些事件的功能作用。

Another recently described set of transcriptional regulators targeted by AMPK and its related family members across a range of eukaryotes are the class IIa family of histone deacetylases (HDACs)99105. In mammals the class IIa HDACs comprise a family of four functionally overlapping members: HDAC4, HDAC5, HDAC7, and HDAC9106 Like CRTCs, class IIa HDACs are inhibited by phosphorylation by AMPK and its family members, resulting in 14-3-3 binding and cytoplasmic sequestration. Recently, we discovered that similar to CRTCs, in liver the class IIa HDACs are dephosphorylated in response to the fasting hormone glucagon, resulting in transcriptional increases that are normally opposed by AMPK. Once nuclear, class IIa HDACs bind FOXO family transcription factors, stimulating their de-acetylation and activation,104 increasing expression of gluconeogenesis genes including G6Pase and PEPCK. Collectively, these findings suggest AMPK suppresses glucose production through two transcriptional effects: reduced expression of CREB targets via CRTC inactivation and reduced expression of FOXO target genes via class IIa HDAC inactivation (Figure 4). It is worth noting that while AMPK activation inhibits expression of FOXO gluconeogenic targets in the liver, in other cell types AMPK is reported to stimulate a set of FOXO-dependent target genes in stress resistance via direct phosphorylation of novel sites in FOXO3 and FOXO4 (though not FOXO1)107, an effect which appears conserved in C. elegans108. Ultimately, defining the tissues, isoforms, and conditions where the AMPK pathway controls FOXO via phosphorylation or acetylation is an important goal for understanding how these two ancient metabolic regulators are coordinated.

另一个最近描述的一套转录调节因子 AMPK 及其相关家族成员跨越一系列的真核生物是 IIa 类组蛋白去乙酰化酶(HDACs)99-105。在哺乳动物中 IIa HDACs 类由4个功能重叠的成员组成: HDAC4,HDAC5,HDAC7,和 HDAC9106类似 CRTCs,IIa HDACs 被 AMPK 及其家族成员的磷酸化抑制,导致14-3-3结合和细胞质隔离。最近,我们发现类似于 CRTCs,IIa HDACs 类肝脏对空腹胰高血糖素的反应是去磷酸化,导致转录增加,这通常是 AMPK 所反对的。IIa 类 HDACs 一旦与 FOXO 家族转录因子结合,刺激其去乙酰化和活化,104个糖异生基因包括 G6Pase 和 PEPCK 的表达增加。总的来说,这些发现表明 AMPK 通过两种转录效应抑制葡萄糖的产生: 通过 CRTC 失活减少 CREB 靶基因的表达和通过 IIa HDAC 失活减少 FOXO 靶基因的表达(图4)。值得注意的是,虽然 AMPK 活化抑制 FOXO 葡萄糖异生靶基因在肝脏的表达,但在其他细胞类型 AMPK 通过直接磷酸化 FOXO3和 FOXO4(虽然不是 FOXO1)107中的新位点来刺激一组 FOXO 依赖的抗应激靶基因,这种效应在秀丽隐杆线虫中是保守的。最终,定义 AMPK 通过磷酸化或乙酰化控制 FOXO 的组织、异构体和条件是了解这两种古老的代谢调节因子如何协调的一个重要目标。

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Figure 4 图4AMPK control of transcription AMPK 对转录的调控

AMPK regulates several physiological processes through phosphorylation of transcription factors and co-activators. It shares substrates with its AMPK family related kinases to negatively regulate gluconeogenesis in the liver by phosphorylation and inhibition of the CRCT2 and Class IIa HDACs. These phosphorylation events induce binding to 14-3-3 scaffold proteins and sequestration of these transcription regulators into the cytoplasm. AMPK also regulates transcription factors via inducing their degradation (Cry1), preventing their proteolytic activation and translocation to nucleus (Srebp1), and by disrupting protein-protein (p300) or protein-DNA interactions (Arebp, HNF4a). AMPK has also been shown to directly control phosphorylation of Histone 2B on Serine 36 as well as indirectly controlling SIRT1 activity via increasing NAD+ levels.

AMPK 通过转录因子和共激活因子的磷酸化调节多种生理过程。它与 AMPK 家族相关的激酶共享一个底物,通过磷酸化和抑制 CRCT2和 IIa HDACs 类来负向调节肝脏中的糖异生。这些磷酸化事件诱导结合14-3-3支架蛋白和固存这些转录调节因子进入细胞质。AMPK 还通过诱导转录因子降解(Cry1)、阻止其蛋白水解激活和转移到细胞核(Srebp1) ,以及通过干扰蛋白质-蛋白质(p300)或蛋白质-dna 相互作用(Arebp、 HNF4a)来调节转录因子。AMPK 也被证明可以直接控制丝氨酸36上组蛋白2B 的磷酸化,以及通过提高 NAD + 水平间接控制 SIRT1的活性。

In addition to phosphorylating transcription regulators, AMPK has also been shown to regulate the activity of the deacetylase SIRT1 in some tissues via effects on NAD+ levels109110. As SIRT1 targets a number of transcriptional regulators for deacetylation, this adds yet another layer of temporal and tissue specific control of metabolic transcription by AMPK. This has been studied best in the context of exercise and skeletal muscle physiology, where depletion of ATP activates AMPK and through SIRT1 promotes fatty acid oxidation and mitochondrial gene expression. Interestingly, AMPK was also implicated in skeletal muscle reprogramming in a study where sedentary mice were treated with AICAR for 4 weeks and able to perform 44% better than control vehicle receiving counterparts111. This metabolic reprogramming was shown to require PPARβ/δ111 and likely involves PGC-1α as well97, though the AMPK substrates critical in this process have not yet been rigorously defined. Interestingly, the only other single agent ever reported to have such endurance reprogramming properties besides AICAR is Resveratrol112, whose action in regulating metabolism is now known to be critical dependent on AMPK47.

除了磷酸化转录调节因子外,AMPK 还通过影响 NAD + 水平109,110来调节某些组织中去乙酰化酶 SIRT1的活性。由于 SIRT1作用于许多脱乙酰基的转录调节因子,这又增加了一层 AMPK 对代谢转录的时间和组织特异性控制。这已经在运动和骨骼肌生理学的背景下得到了最好的研究,ATP 的损耗激活 AMPK 和通过 SIRT1促进脂肪酸氧化和线粒体基因表达。有趣的是,在一项研究中,AMPK 也牵涉到骨骼肌重编程,在这项研究中,久坐不动的老鼠接受 AICAR 治疗4周,能够比接受对照组的老鼠表现好44% 。这种新陈代谢重编程被证明需要 ppar/111和可能涉及 pgc-1以及97,虽然在这个过程中关键的 AMPK 底物还没有被严格定义。有趣的是,除 AICAR 外,唯一报道具有这种耐力重编程特性的单一制剂是白藜芦醇112,现已知其调节代谢的作用严重依赖于 AMPK47。Go to: 去:

Control of Cell Polarity, Migration, & Cytoskeletal Dynamics

细胞极性、迁移和细胞骨架动力学的控制

In addition to the ample data for AMPK in cell growth and metabolism, recent studies suggest that AMPK may control cell polarity and cytoskeletal dynamics in some settings113. It has been known for some time that LKB1 plays a critical role in cell polarity from simpler to complex eukaryotes. In C. elegans114 and Drosophila115, LKB1 orthologs establish cellular polarity during critical asymmetric cell divisions and in mammalian cell culture, activation of LKB1 was sufficient to promote polarization of certain epithelial cell lines116. Initially, it was assumed that the AMPK-related MARKs (Microtubule Affinity Regulating Kinases), which are homologs of C. elegans par-1 and play well-established roles in polarity, were the principal targets of LKB1 in polarity117. However, recent studies also support a role for AMPK in cell polarity.

除了 AMPK 在细胞生长和代谢方面的大量数据外,最近的研究表明 AMPK 可能在某种程度上控制细胞极性和细胞骨架动力学。LKB1在从简单到复杂的真核生物的细胞极性中发挥着重要作用。在线虫114和果蝇115中,LKB1直系亲缘关系在细胞不对称分裂和哺乳动物细胞培养中建立细胞极性,LKB1的激活足以促进某些上皮细胞线粒体116的极化。起初,人们认为与线虫 par-1同源并在极性中发挥重要作用的 ampk 相关标记(Microtubule Affinity Regulating Kinases,ampk)是 LKB1在极性117中的主要靶标。然而,最近的研究也支持 AMPK 在细胞极性中的作用。

In Drosophila, loss of AMPK results in altered polarity118119 and in mammalian MDCK cells, AMPK was activated and needed for proper re-polarization and tight junction formation following calcium switch120121. Moreover, LKB1 was shown to localize to adherens junctions in MDCK cells and E-cadherin RNAi led to specific loss of this localization and AMPK activation at these sites30. The adherens junctions protein Afadin122 and a Golgi-specific nucleotide exchange factor for Arf5 (GBF1)123 have been reported to be regulated by AMPK and may be involved in this polarity122, though more studies are needed to define these events and their functional consequences. In Drosophila AMPK deficiency altered multiple polarity markers, including loss of myosin light chain (MLC) phosphorylation118. While it was suggested in this paper that MLC may be a direct substrate of AMPK, this seems unlikely as the sites do not conform to the optimal AMPK substrate motif. However, AMPK and its related family members have been reported to modulate the activity of kinases and phosphatases that regulate MLC (MLCK, MYPT1), so MLC phosphorylation may be indirectly controlled via one of these potential mechanisms.

在果蝇中,AMPK 的缺失导致了极性的改变118,119,在哺乳动物 MDCK 细胞中,AMPK 被激活,并需要适当的复极化和紧密连接的形成,随后钙切换120,121。此外,LKB1定位于 MDCK 细胞的粘附连接处,E-cadherin rna 干扰导致这一定位丢失,AMPK 活化在这些位点30。粘附连接蛋白 Afadin122和针对 Arf5(GBF1)123的高尔基特异性核苷酸交换因子蛋白已被 AMPK 调控,可能参与了这一极性122,尽管这些事件及其功能后果需要更多的研究来确定。在果蝇中,AMPK 缺乏改变了多种极性标记,包括肌球蛋白轻链磷酸化损失118。尽管本文提出 MLC 可能是 AMPK 的直接底物,但这似乎不太可能,因为这些位点不符合 AMPK 的最佳底物基序。然而,AMPK 及其相关家族成员已被报道调控 MLCK (MLCK,MYPT1)的激酶和磷酸酶活性,因此 MLC 磷酸化可能通过这些潜在机制之一间接受到控制。

Another recent study discovered the microtubule plus end protein CLIP-170 (CLIP1) as a direct AMPK substrate124. Mutation of the AMPK site in CLIP-170 caused slower microtubule assembly, suggesting a role in the dynamic of CLIP-170 dissociation from the growing end of microtubules. It is noteworthy that mTORC1 was also previously suggested as a kinase for CLIP-170125, introducing the possibility that like ULK1, CLIP-170 may be a convergence point in the cell for AMPK and mTOR signaling. Consistent with this, besides effects on cell growth, LKB1/AMPK control of mTOR was recently reported to control cilia126 and neuronal polarization under conditions of energy stress127. In addition, the regulation of CLIP-170 by AMPK is reminiscent of the regulation of MAPs (microtubule associated proteins) by the AMPK related MARK kinases, which are critical in Tau hyperphosphorylation in Alzheimer’s models128129. Indeed AMPK itself has been shown to target the same sites in Tau under some conditions as well130.

另一项最近的研究发现微管加端蛋白 CLIP-170(CLIP-170)是一个直接的 AMPK 亚基。CLIP-170的 AMPK 位点突变导致微管组装速度减慢,提示 CLIP-170在微管生长末端解离的动力学过程中发挥作用。值得注意的是,mTORC1之前也被认为是 CLIP-170125的激酶,这可能引入了与 ULK1一样,CLIP-170可能是 AMPK 和 mTOR 信号转导的汇合点。与此相一致的是,除了对细胞生长的影响外,最近报道 LKB1/AMPK 对 mTOR 的调控可以在能量应力条件下控制纤毛虫126和神经元极化。此外,AMPK 对 CLIP-170的调节使人联想到 AMPK 相关的 MARK 激酶对 map (微管相关蛋白)的调节,这在阿尔茨海默病模型128,129的 Tau 过度磷酸化中是至关重要的。事实上,AMPK 本身已被证明在某些条件下以 Tau 的相同地点为目标。

Finally, an independent study suggested a role for AMPK in polarizing neurons via control of PI3K localization131. Here, AMPK was shown to directly phosphorylate Kinesin Light Chain 2 (KLC2) and inhibit axonal growth via preventing PI3K localization to the axonal tip. Interestingly, a previous study examined the related protein KLC1 as a target of AMPK and determined it was not a real substrate in vivo132. Further experiments are needed to clarify whether AMPK is a bona fide kinase for KLC1 or KLC2 in vivo and in which tissues.

最后,一项独立的研究提出 AMPK 通过控制 PI3K 定位131在偏振神经元中的作用。AMPK 可以直接磷酸化 Kinesin Light Chain 2(KLC2) ,并通过阻止 PI3K 定位于轴突顶端来抑制轴突生长。有趣的是,先前的一项研究检测了相关蛋白 KLC1作为 AMPK 的靶标,并确定它在 vivo132中不是一个真正的底物。还需要进一步的实验来澄清 AMPK 在体内是否是 KLC1或 KLC2的真正激酶,以及在哪些组织中。Go to: 去:

Emerging themes and future directions

新兴主题和未来方向

An explosion of studies in the past 5 years has begun decoding substrates of AMPK playing roles in a variety of growth, metabolism, autophagy, and cell polarity processes. An emergent theme in the field is that AMPK and its related family members often redundantly phosphorylate a common set of substrates on the same residues, though the tissue expression and condition under which AMPK or its related family members are active vary. For example, CRTCs, Class IIa HDACs, p300, Srebp1, IRS1, and tau are reported to be regulated by AMPK and/or its SIK and MARK family members depending on the cell type or conditions. As a example of the complexity to be expected, SIK1 itself is transcriptionally regulated and its kinase activity is modulated by Akt and PKA so the conditions under which it is expressed and active will be a narrow range in specific cell types only, and usually distinct from conditions where AMPK is active. Delineating the tissues and conditions in which the 12 AMPK related kinases are active remains a critical goal for dissecting the growth and metabolic roles of their shared downstream substrates. A much more comprehensive analysis of AMPK and its family members using genetic loss of function and RNAi is needed to decode the relative importance of each AMPK family kinase on a given substrate for each cell type.

在过去的5年里,大量的研究已经开始解码 AMPK 在生长、新陈代谢、自噬和细胞极性过程中起作用的底物。这一领域的一个新兴主题是 AMPK 及其相关家族成员通常在相同的残基上多余地磷酸化一组共同的底物,尽管 AMPK 及其相关家族成员活跃的组织表达和条件各不相同。例如,CRTCs、 IIa HDACs 类、 p300、 Srebp1、 IRS1和 tau 据报道由 AMPK 和/或其 SIK 和 MARK 家族成员根据细胞类型或条件进行调节。例如,SIK1本身是转录调控的,其激酶活性受 Akt 和 PKA 调控,因此它表达和活化的条件仅限于特定细胞类型,通常不同于 AMPK 活化的条件。描述12个 AMPK 相关激酶活性的组织和条件仍然是解剖它们共享的下游底物的生长和代谢作用的关键目标。使用功能的遗传损失和 rna 干扰对 AMPK 及其家族成员进行更全面的分析,需要解码每个 AMPK 家族激酶在给定底物上对每个细胞类型的相对重要性。

Now with a more complete list of AMPK substrates, it is also becoming clear that there is a convergence of AMPK signaling with PI3K and Erk signaling in growth control pathways, and with insulin and cAMP-dependent pathways in metabolic control. The convergence of these pathways reinforces the concept that there is a small core of rate-limiting regulators that control distinct aspects of biology and act as master coordinators of cell growth, metabolism, and ultimately cell fate. As more targets of AMPK are decoded, the challenge will be in defining more precisely which targets are essential and relevant for the beneficial effects of AMPK activation seen in pathological states ranging from diabetes to cancer to neurological disorders. The identification of these downstream effectors will provide new targets for therapeutically treating these diseases by unlocking this endogenous mechanism that evolution has developed to restore cellular and organismal homeostasis.

现在,随着 AMPK 底物清单的完整,我们也越来越清楚地看到,AMPK 信号与生长控制通路中的 PI3K 和 Erk 信号,以及与代谢控制中的胰岛素和 camp 依赖通路有一定的汇合作用。这些途径的融合强化了这样一个概念,即有一小部分限速调节器核心控制生物学的不同方面,并充当细胞生长、新陈代谢以及最终细胞命运的主要协调者。随着 AMPK 的更多靶点被解码,挑战将是更精确地定义哪些靶点对于 AMPK 激活的有益影响至关重要和相关,这些有益影响可见于糖尿病、癌症和神经系统疾病等病理状态。这些下游效应因子的识别将为治疗这些疾病提供新的靶点,通过解锁这种进化发展出来的恢复细胞和生物体内环境稳定的内在机制。Go to: 去:

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