Browsing by Subject "AMPK"

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  • Rajakylä, Eeva Kaisa; Lehtimäki, Jaakko I.; Acheva, Anna; Schaible, Niccole; Lappalainen, Pekka; Krishnan, Ramaswamy; Tojkander, Sari (2020)
    Summary Defects in the maintenance of intercellular junctions are associated with loss of epithelial barrier function and consequent pathological conditions, including invasive cancers. Epithelial integrity is dependent on actomyosin bundles at adherens junctions, but the origin of these junctional bundles is incompletely understood. Here we show that peripheral actomyosin bundles can be generated from a specific actin stress fiber subtype, transverse arcs, through their lateral fusion at cell-cell contacts. Importantly, we find that assembly and maintenance of peripheral actomyosin bundles are dependent on the mechanosensitive CaMKK2/AMPK signaling pathway and that inhibition of this route leads to disruption of tension-maintaining actomyosin bundles and re-growth of stress fiber precursors. This results in redistribution of cellular forces, defects in monolayer integrity, and loss of epithelial identity. These data provide evidence that the mechanosensitive CaMKK2/AMPK pathway is critical for the maintenance of peripheral actomyosin bundles and thus dictates cell-cell junctions through cellular force distribution.
  • Tojkander, Sari; Ciuba, Katarzyna; Lappalainen, Pekka (2018)
    Stress fibers are contractile actomyosin bundles that guide cell adhesion, migration, and morphogenesis. Their assembly and alignment are under precise mechanosensitive control. Thus, stress fiber networks undergo rapid modification in response to changes in biophysical properties of the cell's surroundings. Stress fiber maturation requires mechanosensitive activation of 5 0 AMP-activated protein kinase (AMPK), which phosphorylates vasodilator- stimulated phosphoprotein (VASP) to inhibit actin polymerization at focal adhesions. Here, we identify Ca2+-calmodulin-dependent kinase kinase 2 (CaMKK2) as a critical upstream factor controlling mechanosensitive AMPK activation. CaMKK2 and Ca2+ influxes were enriched around focal adhesions at the ends of contractile stress fibers. Inhibition of either CaMKK2 or mechanosensitive Ca2+ channels led to defects in phosphorylation of AMPK and VASP, resulting in a loss of contractile bundles and a decrease in cell-exerted forces. These data provide evidence that Ca2+, CaMKK2, AMPK, and VASP form a mechanosensitive signaling cascade at focal adhesions that is critical for stress fiber assembly.
  • Latorre, Jèssica; Ortega, Francisco J.; Liñares-Pose, Laura; Moreno-Navarrete, José M.; Lluch, Aina; Comas, Ferran; Oliveras-Cañellas, Núria; Ricart, Wifredo; Höring, Marcus; Zhou, You; Liebisch, Gerhard; Nidhina Haridas, P.A.; Olkkonen, Vesa M.; López, Miguel; Fernández-Real, José M. (2020)
    Background: While the impact of metformin in hepatocytes leads to fatty acid (FA) oxidation and decreased lipogenesis, hepatic microRNAs (miRNAs) have been associated with fat overload and impaired metabolism, contributing to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Methods: We investigated the expression of hundreds of miRNAs in primary hepatocytes challenged by compounds modulating steatosis, palmitic acid and compound C (as inducers), and metformin (as an inhibitor). Then, additional hepatocyte and rodent models were evaluated, together with transient mimic miRNAs transfection, lipid droplet staining, thin-layer chromatography, quantitative lipidomes, and mitochondrial activity, while human samples outlined the translational significance of this work. Findings: Our results show that treatments triggering fat accumulation and AMPK disruption may compromise the biosynthesis of hepatic miRNAs, while the knockdown of the miRNA-processing enzyme DICER in human hepatocytes exhibited increased lipid deposition. In this context, the ectopic recovery of miR-30b and miR-30c led to significant changes in genes related to FA metabolism, consistent reduction of ceramides, higher mitochondrial activity, and enabled b-oxidation, redirecting FA metabolism fromenergy storage to expenditure. Interpretation: Current findings unravel the biosynthesis of hepatic miR-30b and miR-30c in tackling inadequate FA accumulation, offering a potential avenue for the treatment of NAFLD. Funding: Instituto de Salud Carlos III (ISCIII), Govern de la Generalitat (PERIS2016), Associacio Catalana de Diabetis (ACD), Sociedad Espanola de Diabetes (SED), Fondo Europeo de Desarrollo Regional (FEDER), Xunta de Galicia, Ministerio de Economia y Competitividad (MINECO), "La Caixa" Foundation, and CIBER de la Fisiopatologia de la Obesidad y Nutricion (CIBEROBN). (c) 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)
  • Siskovs, Klims (Helsingin yliopisto, 2021)
    STK11/LKB1 is a tumor suppressor gene and mutated in 18% of lung adenocarcinomas. Tumor suppressor liver kinase B1 (LKB1) is known to activate adenosine monophosphate-activated protein kinase (AMPK) and 12 AMPK-related kinases (ARKs) by phosphorylating a conserved threonine residue in their T-loop region. A number of studies focused on investigating the influence of LKB1-AMPK signaling on cancer cell proliferation. However, there is no systematic study for identifying the critical LKB1 kinase substrates in suppressing lung cancer cell growth. In this project, the LKB1-deficient lung adenocarcinoma cell line A549 cells were sequentially overexpressed with constitutively active mutants of AMPKα1, AMPKα2, MARK1, MARK2, MARK3, MARK4, NUAK1, NUAK2, SIK1, SIK2, SIK3. The overexpression status was confirmed at both genetic and protein levels by qPCR and Western blotting, correspondingly. In vitro growth assays demonstrated up to 33% reduced growth rate of A549 cells overexpressing AMPKα1, AMPKα2 and NUAK1. Furthermore, siRNA knockdown of the selected substrates in LKB1-overexpressing A549 cells significantly rescued the cell growth defect. These findings suggest, that AMPKα1, AMPKα2 and NUAK1 kinases are critical for LKB1-mediated cell growth defect in lung adenocarcinoma.
  • Savelius, Mariel (Helsingin yliopisto, 2020)
    Breast cancer remains as the leading cause of cancer deaths among women. Triple-negative breast cancer (TNBC) is one of the most aggressive breast cancer subtypes and lacks targetable receptors, consequently, cannot be treated with current hormone of anti-HER2 targeting therapies. Thus, there is a need for discovering novel and well-tolerated therapies. MYC is a proto-oncogene and a transcription factor, that is frequently amplified and overexpressed in breast cancers. MYC is involved in many cellular processes promoting cell proliferation, however, overexpression of MYC can also sensitize cells to replicative stress and apoptotic cell death. In our previous studies we have shown that pharmacological activation of AMPK, a cellular energy sensor, synergises with Bcl-2 family inhibitors, such as navitoclax and venetoclax, and activates MYC-dependent apoptosis in breast cancer cell lines, transgenic mouse models of MYC-dependent mammary tumorigenesis and in MYC-high patient-derived explant cultures (PDECs). In subsequent study we observed, that indirect AMPK activator metformin alone inhibited tumor growth in vivo, but did not induce apoptosis in mouse tumors or in PDECs. Metformin, a type II diabetes mellitus drug, has shown anti-cancer effects in some population studies and is under investigation for a cancer therapies, however the whole mechanism of action in cancer is still not well-known. To elucidate metformin’s effects on MYC overexpressing triple-negative breast cancer cells, I will present, that metformin has anti-proliferative effects and show that long term metformin treatment induces senescence biomarkers in MYC-high TNBC breast cancer cell lines. To study metformin's short and long-term anti-proliferative activity, cell proliferation during and after drug treatment was investigated, which showed, that metformin’s effects do not seem to persist long after drug withdrawal. In conclusion, the key observation of this thesis was, that metformin does inhibit the proliferation of MYC overexpressing cancer cells and presents a senescence phenotype that possibly can be exploited to find new targeted therapies for triple-negative breast cancer patients.
  • Wjuga, Anna (Helsingfors universitet, 2009)
    2,3,7,8-Tetrachlorodibentso-p-dioksin (TCDD) is the most potent congener of the group of dioxins. It forms as a byproduct or impurity in many chemical processes. TCDD is enriched in the food chain and people are exposed to it in small portions chronically mainly by nutrition. TCDD has many toxic impacts on humans and animals which are mediated by the cellular aryl hydrocarbon -receptor. In spite of decades of research the toxic mechanisms of TCDD are poorly known. By investigating the toxicity of TCDD with large doses in experimental animals we will gain more insight into its toxic mechanisms and into its risks to humans. An important form of acute toxicity of TCDD is the wasting syndrome in which rats eat less, lose weight and finally die or after a sublethal dose stay thinner than littermates. The mechanism by which TCDD causes the wasting syndrome is unclear. Two central enzymes that take part in the regulation of the body's energy balance are the adenosine monophosphate activated protein kinase (AMPK) and stearoyl-CoA-desaturase 1 (Scd1). Changes in the expression or the regulation of their action could well be related to the wasting syndrome. The goal of this experiment was to compare in liver the mRNA expression of AMPK, Scd1 and control genes which are widely used in quantitative PCR in dioxin-sensitive Long-Evans (L-E) and resistant Han/Wistar (H/W) rat strains after a large (lethal to the sensitive strain) TCDD dose at early phases of intoxication (days 1, 4 and 10). There was also a L-E rat group whose feed was restricted to mimic the wasting caused by TCDD. The goal of the feed restriction was to separate the possible primary effect of TCDD from a secondary effect, depletion of energy. RNA was isolated from liver samples and the cDNA was made from isolated RNA with M-MLV-derived reverse transcriptase enzyme using oligo dT and random hexamer primers. The mRNAs of Scd1-enzyme and the control genes in the liver samples were measured using real-time quantitative PCR and specific primers. At 10 days feed restriction lowered significantly the expression of AMPK mRNA in L-E-rats. At 4 and 10 days feed restriction lowered significantly also the expression of Scd1 mRNA; on day 10 the mRNA level of control rats was about 10,000-fold higher. At day 1 TCDD elevated the expression of Scd1-enzyme. TCDD did not cause a significant decrease in the expression of Scd1-enzyme on day 4 and on day 10 the decrease was significantly less, about 1/10 of the level in control rats. These findings suggest that either TCDD inhibits the strong decrease of AMPK and Scd1 caused by energy deficiency or it causes an induction of AMPK and Scd1 which in turn is countered by the weight loss caused by the wasting syndrome. Overall it seems that rats exposed to TCDD do not recognize the energy depletion and their hepatocytes do not turn on the energy sparing mode of metabolism. Feed restriction and TCDD affected clearly also the expression of the control genes GAPDH, Pgk1 and Bact which were believed to be stable. The use of control genes which are linked to the regulation of cellular energy balance is risky in long-term feed restriction experiments.
  • Saikkala, Minea (Helsingin yliopisto, 2021)
    Lung cancer is one of the most common and deadliest cancers worldwide, but the mechanisms behind different types of lung cancer are still poorly understood. Non-small cell lung cancer makes up 80% of lung cancers, and some epigenetic mechanisms have been proposed for it. Epigenetic modifications are a way of influencing the expression of genes by inhibition or activation. PRC2 is an epigenetic modulator that catalyses the formation of methyl groups on histone 3 lysine 27, which is an epigenetic mark with repressive nature. PRC2 has been proposed to be downstream of AMPK, an energy sensor of the cell, which is phosphorylated by LKB1 under energy stress conditions. Inactivating mutations in LKB1 are known to cause and worsen non-small cell lung cancer, and the overexpression of EZH2, the catalytic subunit of PRC2, has similar effects. Therefore, establishing a novel downstream mechanism linking LKB1, AMPK, and PRC2 together could explain one mechanism for NSCLC tumorigenesis. Changes in metabolism are a feature of cancer cells, and this pathway could also link energy stress and cancer together. Mouse embryonic fibroblast and H358 cell lines overexpressing wild type EZH2, mutant EZH2 and GFP were generated and treated with the glycolysis inhibitor 2-deoxyglucose to study the effects of energy stress. Levels of histone methylation and phosphorylation statuses of AMPK and its downstream target ACC were assessed with Western blotting, and expression levels of potential PRC2 target genes with RT-qPCR. The study setting proved to be functional for the response of AMPK to energy stress conditions, as both AMPK and ACC were phosphorylated in the presence of 2-DG. In mouse embryonic fibroblasts, PIM1 showed different gene expression with wild type and mutant EZH2, suggesting that its activation would be regulated through the phosphorylation of the T311 site of EZH2 during energy stress. The results from histone methylation statuses did not follow the hypothesis, possibly because of the lack of specificity of detecting global H3K27me3. Other target genes besides PIM1 in MEFs did not show significant changes in expression level. Considering that the incorporation of the mutant EZH2 into PRC2 complexes was not validated, additional research would be needed to confirm or deny the explained mechanism between PRC2 and AMPK.