A Highly Sensitive Non-Radioactive Activity Assay for AMP-Activated Protein Kinase (AMPK).
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ABSTRACT:
SUBMITTER: Yan Y
PROVIDER: S-EPMC5809138 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:AMPK is a conserved heterotrimeric serine-threonine kinase that regulates anabolic and catabolic pathways in eukaryotes. Its central role in cellular and whole body metabolism makes AMPK a commonly proposed therapeutic target for illnesses characterized by abnormal energy regulation, including cancer and diabetes. Many AMPK modulators, however, produce AMPK-independent effects. To identify drugs that modulate AMPK activity independent of the canonical ATP-binding pocket found throughout the kinome, we designed a robust fluorescence-based high throughput screening assay biased toward the identification of molecules that bind the regulatory region of AMPK through displacement of MANT-ADP, a fluorescent ADP analog. Automated pin tools were used to rapidly transfer small molecules to a low volume assay mixture on 384-well plates. Prior to assay validation, we completed a full assay optimization to maximize the signal-to-background and reduce variability for robust detection of small molecules displacing MANT-ADP. After validation, we screened 13,120 molecules and identified 3 positive hits that dose-dependently inhibited the protein-bound signal of MANT-ADP in the presence of both full-length AMPK and the truncated "regulatory fragment" of AMPK, which is missing the kinase active site. The average Z'-factor for the screen was 0.55 and the compound confirmation rate was 60%. Thus, this fluorescence-based assay may be paired with in vitro kinase assays and cell-based assays to help identify molecules that selectively regulate AMPK with fewer off-target effects on other kinases.
| S-EPMC3854666 | biostudies-literature
Project description:Renal cyst development and expansion in autosomal dominant polycystic kidney disease (ADPKD) involves both fluid secretion and abnormal proliferation of cyst-lining epithelial cells. The chloride channel of the cystic fibrosis transmembrane conductance regulator (CFTR) participates in secretion of cyst fluid, and the mammalian target of rapamycin (mTOR) pathway may drive proliferation of cyst epithelial cells. CFTR and mTOR are both negatively regulated by AMP-activated protein kinase (AMPK). Metformin, a drug in wide clinical use, is a pharmacological activator of AMPK. We find that metformin stimulates AMPK, resulting in inhibition of both CFTR and the mTOR pathways. Metformin induces significant arrest of cystic growth in both in vitro and ex vivo models of renal cystogenesis. In addition, metformin administration produces a significant decrease in the cystic index in two mouse models of ADPKD. Our results suggest a possible role for AMPK activation in slowing renal cystogenesis as well as the potential for therapeutic application of metformin in the context of ADPKD.
| S-EPMC3038735 | biostudies-literature
Project description:AMPK has been termed the fuel sensor of mammalian cells because it directly responds to the depletion of the fuel molecule ATP. In previous work, we found that AMPK is strongly activated by tumor-like hypoxia and glucose deprivation, independently of the oxygen response system associated with HIF-1. We also observed high levels of AMPK activity in tumor cells in vivo, using different model tumors. These findings suggested the hypothesis that modulation of AMPK activity could have therapeutic value for the treatment of solid tumors. To investigate this hypothesis, we have been conducting a SAR study of potential small-molecule modulators of AMPK activity. Here we report that the chemotherapeutic drug SU11248 (sunitinib) is at least as potent an inhibitor of AMPK as compound C, which is a commonly used experimental direct inhibitor of the enzyme. We also provide a computational model of the binding pose of SU11248 to an AMPK? subunit, which suggests a structural basis for the affinity of the drug for the ATP site of the catalytic domain. The ability of SU11248 to inhibit AMPK has potential clinical significance--there may be populations of SU11248-treated patients in which AMPK activity is inhibited in normal as well as in tumor tissue.
| S-EPMC3087946 | biostudies-literature
Project description:BackgroundAlthough numerous non-radioactive methods are in use to measure the catalytic activity of protein kinases, most require specialized equipment and reagents and are not sufficiently sensitive for the detection of endogenous kinase activity in biological samples. Kinases of the DYRK family have important functions in developmental and pathophysiological processes in eukaryotic organisms including mammals. We aimed to develop a highly sensitive, low-tech assay suitable to determine the activity of DYRK family kinases in tissues or cells from diverse sources.ResultsPhosphorylation-site specific antibodies can be used to monitor the accumulation of the phosphorylated product in kinase assays. We present a modified configuration of an enzyme-linked immunosorbent assay (ELISA)-based kinase assay by using the phosphospecific antibody as the capture antibody. This assay format allowed the detection of small amounts of phosphopeptide in mixtures with an excess of the unphosphorylated substrate peptide (10 fmol phosphorylated peptide over a background of 50 pmol unphosphorylated peptide). Consequently, low substrate turnover rates can be determined. We applied this method to the measurement of endogenous DYRK1A activity in mouse heart tissue by immunocomplex kinase assay. Furthermore, we detected DYRK1-like kinase activity in Xenopus laevis oocytes and identified this kinase as a DYRK1 isoform distinct from the Xenopus DYRK1A ortholog.ConclusionWe present a non-radioactive and highly sensitive method for the measurement of endogenous activities of DYRKs in biological samples. Xenopus laevis oocytes contain an active DYRK1-related protein kinase more similar to mammalian DYRK1B than DYRK1A.
| S-EPMC2885986 | biostudies-literature
Project description:Mitochondrial reactive oxygen species (ROS) production is a tightly regulated redox signal that transmits information from the organelle to the cell. Other mitochondrial signals, such as ATP, are sensed by enzymes, including the key metabolic sensor and regulator, AMP-activated protein kinase (AMPK). AMPK responds to the cellular ATP/AMP and ATP/ADP ratios by matching mitochondrial ATP production to demand. Previous reports proposed that AMPK activity also responds to ROS, by ROS acting on redox-sensitive cysteine residues (Cys-299/Cys-304) on the AMPK ? subunit. This suggests an appealing model in which mitochondria fine-tune AMPK activity by both adenine nucleotide-dependent mechanisms and by redox signals. Here we assessed whether physiological levels of ROS directly alter AMPK activity. To this end we added exogenous hydrogen peroxide (H2O2) to cells and utilized the mitochondria-targeted redox cycler MitoParaquat to generate ROS within mitochondria without disrupting oxidative phosphorylation. Mitochondrial and cytosolic thiol oxidation was assessed by measuring peroxiredoxin dimerization and by redox-sensitive fluorescent proteins. Replacing the putative redox-active cysteine residues on AMPK ?1 with alanines did not alter the response of AMPK to H2O2 In parallel with measurements of AMPK activity, we measured the cell ATP/ADP ratio. This allowed us to separate the effects on AMPK activity due to ROS production from those caused by changes in this ratio. We conclude that AMPK activity in response to redox changes is not due to direct action on AMPK itself, but is a secondary consequence of redox effects on other processes, such as mitochondrial ATP production.
| S-EPMC6222118 | biostudies-literature
Project description:AMP-activated-protein-kinase (AMPK) is a key sensor and regulator of cellular and whole-body energy metabolism and plays a key role in regulation of lipid metabolism. Since lipid metabolism has been implicated in neuronal amyloid-beta (Abeta) homeostasis and onset of Alzheimer's disease, we investigated the involvement of AMPK in neuronal lipid metabolism and Abeta production. We observed in cultured rat cortical neurons that Abeta production was significantly reduced when the neurons were stimulated with AMPK activator, 5-aminoimidazole-4-carboxamide-1-d-ribofuranoside (AICAR), but increased when AMPKalpha2 was knocked out, thus indicating the role of AMPK in amyloidogenesis. Although the detailed mechanisms by which AMPK regulates Abeta generation is not well understood, AMPK-mediated alterations in cholesterol and sphingomyelin homeostasis and in turn the altered distribution of Abeta precursor-protein (APP) in cholesterol and sphingomyelin rich membrane lipid rafts participate in Abeta generation. Taken together, this is the first report on the role of AMPK in regulation of neuronal amyloidogenesis.
| S-EPMC2977999 | biostudies-literature
Project description:Nutrient-sensitive pathways regulate both O-GlcNAc transferase (OGT) and AMP-activated protein kinase (AMPK), cooperatively connecting metabolic homeostasis to regulation of numerous intracellular processes essential for life. Similar to phosphorylation, catalyzed by kinases such as AMPK, O-GlcNAcylation is a highly dynamic Ser/Thr-specific post-translational modification of nuclear, cytoplasmic, and mitochondrial proteins catalyzed exclusively by OGT. OGT and AMPK target a multitude of intracellular proteins, with the net effect to protect cells from the damaging effects of metabolic stress. Despite hundreds of studies demonstrating significant overlap in upstream and downstream signaling processes, no study has investigated if OGT and AMPK can directly regulate each other. We show acute activation of AMPK alters the substrate selectivity of OGT in several cell lines and nuclear localization of OGT in C2C12 skeletal muscle myotubes. Nuclear localization of OGT affects O-GlcNAcylation of numerous nuclear proteins and acetylation of Lys-9 on histone 3 in myotubes. AMPK phosphorylates Thr-444 on OGT in vitro; phosphorylation of Thr-444 is tightly associated with AMPK activity and nuclear localization of OGT in myotubes, and phospho-mimetic T444E-OGT exhibits altered substrate selectivity. Conversely, the ?- and ?-subunits of AMPK are O-GlcNAcylated, O-GlcNAcylation of the ?1-subunit increases with AMPK activity, and acute inhibition of O-GlcNAc cycling disrupts activation of AMPK. We have demonstrated significant cross-talk between the O-GlcNAc and AMPK systems, suggesting OGT and AMPK may cooperatively regulate nutrient-sensitive intracellular processes that mediate cellular metabolism, growth, proliferation, and/or tissue function.
| S-EPMC4036179 | biostudies-literature
Project description:AMP-activated protein kinase (AMPK) is a central metabolic regulator that promotes cancer growth and survival under hypoxia and plays a role in the maintenance of cancer stem cells. A major challenge to interrogating the potential of targeting AMPK in cancer is the lack of potent and selective small molecule inhibitors. Compound C has been widely used as an AMPK inhibitor, but it lacks potency and has a poor selectivity profile. The multi-kinase inhibitor, sunitinib, has demonstrated potent nanomolar inhibition of AMPK activity and has scope for modification. Here, we have designed and synthesized several series of oxindoles to determine the structural requirements for AMPK inhibition and to improve selectivity. We identified two potent, novel oxindole-based AMPK inhibitors that were designed to interact with the DFG motif in the ATP-binding site of AMPK, this key feature evades interaction with the common recptor tyrosine kinase targets of sunitinib. Cellular engagement of AMPK by these oxindoles was confirmed by the inhibition of phosphorylation of acetyl-CoA carboxylase (ACC), a known substrate of AMPK, in myeloid leukemia cells. Interestingly, although AMPK is highly expressed and activated in K562 cells these oxindole-based AMPK inhibitors did not impact cell viability or result in significant cytotoxicity. Our studies serve as a platform for the further development of oxindole-based AMPK inhibitors with therapeutic potential.
| S-EPMC7409528 | biostudies-literature
Project description:AMP-activated protein kinase (AMPK) is a central cellular energy sensor that adapts metabolism and growth to the energy state of the cell. AMPK senses the ratio of adenine nucleotides (adenylate energy charge) by competitive binding of AMP, ADP, and ATP to three sites (CBS1, CBS3, and CBS4) in its γ-subunit. Because these three binding sites are functionally interconnected, it remains unclear how nucleotides bind to individual sites, which nucleotides occupy each site under physiological conditions, and how binding to one site affects binding to the other sites. Here, we comprehensively analyze nucleotide binding to wild-type and mutant AMPK protein complexes by quantitative competition assays and by hydrogen-deuterium exchange MS. We also demonstrate that NADPH, in addition to the known AMPK ligand NADH, directly and competitively binds AMPK at the AMP-sensing CBS3 site. Our findings reveal how AMP binding to one site affects the conformation and adenine nucleotide binding at the other two sites and establish CBS3, and not CBS1, as the high affinity exchangeable AMP/ADP/ATP-binding site. We further show that AMP binding at CBS4 increases AMP binding at CBS3 by 2 orders of magnitude and reverses the AMP/ATP preference of CBS3. Together, these results illustrate how the three CBS sites collaborate to enable highly sensitive detection of cellular energy states to maintain the tight ATP homeostastis required for cellular metabolism.
| S-EPMC5535039 | biostudies-literature
Project description:People with Type 2 diabetes mellitus (T2DM) have reduced bone mineral density and an increased risk of fractures due to altered mesenchymal stem cell (MSC) differentiation in the bone marrow. This leads to a shift in the balance of differentiation away from bone formation (osteogenesis) in favour of fat cell development (adipogenesis). The commonly used anti-diabetic drug, metformin, activates the osteogenic transcription factor Runt-related transcription factor 2 (Runx2), which may suppress adipogenesis, leading to improved bone health. Here we investigate the involvement of the metabolic enzyme, AMP-activated protein kinase (AMPK), in these protective actions of metformin. The anti-adipogenic actions of metformin were observed in multipotent C3H10T1/2 MSCs, in which metformin exerted reciprocal control over the activities of Runx2 and the adipogenic transcription factor, PPAR?, leading to suppression of adipogenesis. These effects appeared to be independent of AMPK activation but rather through the suppression of the mTOR/p70S6K signalling pathway. Basal AMPK and mTOR/p70S6K activity did appear to be required for adipogenesis, as demonstrated by the use of the AMPK inhibitor, compound C. This observation was further supported by using AMPK knockout mouse embryo fibroblasts (MEFs) where adipogenesis, as assessed by reduced lipid accumulation and expression of the adipogeneic transcription factor, C/EBP?, was found to display an absolute requirement for AMPK. Further activation of AMPK in wild type MEFS, with either metformin or the AMPK-specific activator, A769662, was also associated with suppression of adipogenesis. It appears, therefore, that basal AMPK activity is required for adipogenesis and that metformin can inhibit adipogenesis through AMPK-dependent or -independent mechanisms, depending on the cellular context.
| S-EPMC5228588 | biostudies-literature