Akt signaling and freezing survival in the wood frog, Rana sylvatica.

BACKGROUND The wood frog (Rana sylvatica) exhibits well-developed natural freeze tolerance supported by multiple mechanisms of biochemical adaptation. The present study investigated the role and regulation of the Akt signaling pathway in wood frog tissues (with a focus on liver) responding to freezing stress. METHODS Immunoblotting was used to assess total and phospho-Akt levels, total and phospho-PDK1, PTEN protein level, as well as total and phospho-FOXO1 levels. RT-PCR was used to investigate transcript levels of PTEN and microRNAs. RESULTS Akt was inhibited in skeletal muscle, kidney and heart after 24h freezing exposure with a reversal after thawing. The responses of the main kinase (PDK-1) and phosphatase (PTEN) that regulate Akt were consistent with freeze activation of Akt in liver; freezing exposure activated PDK-1 via enhanced Ser-241 phosphorylation whereas PTEN protein levels were reduced. Levels of three microRNAs (miR-26a, miR-126 and miR-217) that regulate pten expression were elevated in liver during freezing. One well-known role of Akt is in anti-apoptosis, mediated in part by Akt phosphorylation of Ser-256 on FOXO1. Freezing triggered an increase in liver phospho-FOXO1 Ser-256 content, suggesting that an important action of Akt may be apoptosis inhibition. CONCLUSIONS Akt activation in wood frog is stress and tissue specific, with multi-facet regulations (posttranslational and posttranscriptional) involved in supporting this specific signal transduction response. GENERAL SIGNIFICANCE This study implicates the Akt pathway in the metabolic reorganization of cellular metabolism in support of freezing survival.

[1]  P. Cohen,et al.  Characterization of a 3-phosphoinositide-dependent protein kinase which phosphorylates and activates protein kinase Bα , 1997, Current Biology.

[2]  K. Storey,et al.  Effects of temperature and freezing on hepatocytes isolated from a freeze-tolerant frog. , 1994, The American journal of physiology.

[3]  R. Khandelwal,et al.  Reciprocal regulation of glycogen phosphorylase and glycogen synthase by insulin involving phosphatidylinositol-3 kinase and protein phosphatase-1 in HepG2 cells , 2000, Molecular and Cellular Biochemistry.

[4]  D. Barford,et al.  Molecular mechanism for the regulation of protein kinase B/Akt by hydrophobic motif phosphorylation. , 2002, Molecular cell.

[5]  B. Rubinsky,et al.  Cryomicroscopic analysis of freezing in liver of the freeze-tolerant wood frog. , 1992, American Journal of Physiology.

[6]  D R Alessi,et al.  Phosphorylation of Ser-241 is essential for the activity of 3-phosphoinositide-dependent protein kinase-1: identification of five sites of phosphorylation in vivo. , 1999, The Biochemical journal.

[7]  J. Rossi,et al.  TGF-β activates Akt kinase via a microRNA-dependent amplifying circuit targeting PTEN , 2009, Nature Cell Biology.

[8]  H. Vaudry,et al.  Freeze tolerance in the wood frog Rana sylvatica is associated with unusual structural features in insulin but not in glucagon. , 1998, Journal of molecular endocrinology.

[9]  P. Cohen,et al.  Role of Translocation in the Activation and Function of Protein Kinase B* , 1997, The Journal of Biological Chemistry.

[10]  Reuven Agami,et al.  The PTEN-regulating microRNA miR-26a is amplified in high-grade glioma and facilitates gliomagenesis in vivo. , 2009, Genes & development.

[11]  Kyle K. Biggar,et al.  Amplification and sequencing of mature microRNAs in uncharacterized animal models using stem-loop reverse transcription-polymerase chain reaction. , 2011, Analytical biochemistry.

[12]  K. Storey,et al.  β-Adrenergic, Hormonal, and Nervous Influences on Cryoprotectant Synthesis by Liver of the Freeze-Tolerant Wood FrogRana sylvatica , 1996 .

[13]  P. Vogt,et al.  Phosphorylation of AKT: a Mutational Analysis , 2011, Oncotarget.

[14]  K. Storey,et al.  Physiology, Biochemistry, and Molecular Biology of Vertebrate Freeze Tolerance: The Wood Frog , 2004 .

[15]  Shannon N. Tessier,et al.  PI 3 K-Akt regulation as a molecular mechanism of the stress response during aerobic dormancy , 2012 .

[16]  B. Hemmings,et al.  Molecular cloning and identification of a serine/threonine protein kinase of the second-messenger subfamily. , 1991, Proceedings of the National Academy of Sciences of the United States of America.

[17]  Jing Zhang,et al.  Regulation of p53 by reversible post-transcriptional and post-translational mechanisms in liver and skeletal muscle of an anoxia tolerant turtle, Trachemys scripta elegans. , 2013, Gene.

[18]  K. Storey,et al.  Cell cycle regulation in the freeze tolerant wood frog, Rana sylvatica , 2012, Cell cycle.

[19]  T. Kita,et al.  Oxidative stress induces GLUT4 translocation by activation of PI3‐K/Akt and dual AMPK kinase in cardiac myocytes , 2008, Journal of cellular physiology.

[20]  D. James,et al.  Akt activation is required at a late stage of insulin-induced GLUT4 translocation to the plasma membrane. , 2005, Molecular endocrinology.

[21]  D. Tindall,et al.  Skp2 inhibits FOXO1 in tumor suppression through ubiquitin-mediated degradation. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[22]  M. Pruschy,et al.  Temperature sensitivity of phospho-Ser(473)-PKB/AKT. , 2008, Biochemical and biophysical research communications.

[23]  D. Guertin,et al.  Phosphorylation and Regulation of Akt/PKB by the Rictor-mTOR Complex , 2005, Science.

[24]  K. Storey,et al.  Triggering of cryoprotectant synthesis by the initiation of ice nucleation in the freeze tolerant frog,Rana sylvatica , 1985, Journal of Comparative Physiology B.

[25]  J. Testa,et al.  A retroviral oncogene, akt, encoding a serine-threonine kinase containing an SH2-like region. , 1991, Science.

[26]  J. Woodgett,et al.  Molecular cloning and characterisation of a novel putative protein-serine kinase related to the cAMP-dependent and protein kinase C families. , 1991, European journal of biochemistry.

[27]  K. Storey,et al.  Glycogen synthase kinase-3: cryoprotection and glycogen metabolism in the freeze-tolerant wood frog , 2012, Journal of Experimental Biology.

[28]  M. Greenberg,et al.  Akt Promotes Cell Survival by Phosphorylating and Inhibiting a Forkhead Transcription Factor , 1999, Cell.

[29]  J. P. Costanzo,et al.  Post-freeze recovery of peripheral nerve function in the freeze-tolerant wood frog, Rana sylvatica , 2004, Journal of Comparative Physiology B.

[30]  P. Cohen,et al.  Glycogen synthase kinase-3 from rabbit skeletal muscle. Separation from cyclic-AMP-dependent protein kinase and phosphorylase kinase. , 1980, European journal of biochemistry.

[31]  K. Storey,et al.  Stress-induced activation of the AMP-activated protein kinase in the freeze-tolerant frog Rana sylvatica. , 2006, Cryobiology.

[32]  K. Storey,et al.  Metabolic responses to dehydration by liver of the wood frog, Rana sylvatica , 1994 .

[33]  D. Bartel MicroRNAs: Target Recognition and Regulatory Functions , 2009, Cell.

[34]  J. Penninger,et al.  Cardiac regulation by phosphoinositide 3-kinases and PTEN. , 2008, Cardiovascular research.

[35]  Huan Yang,et al.  The Akt/PKB pathway: molecular target for cancer drug discovery , 2005, Oncogene.

[36]  Michael Majeski,et al.  Multiple elements regulate nuclear/cytoplasmic shuttling of FOXO1: characterization of phosphorylation- and 14-3-3-dependent and -independent mechanisms. , 2004, The Biochemical journal.

[37]  K. Storey,et al.  Biochemical adaption for freezing tolerance in the wood frog,Rana sylvatica , 2004, Journal of Comparative Physiology B.

[38]  K. Storey,et al.  Purification and characterization of protein kinase A from liver of the freeze-tolerant wood frog: role in glycogenolysis during freezing. , 2000, Cryobiology.

[39]  K. Storey Strategies for exploration of freeze responsive gene expression: advances in vertebrate freeze tolerance. , 2004, Cryobiology.

[40]  K. Storey Organ-specific metabolism during freezing and thawing in a freeze-tolerant frog. , 1987, The American journal of physiology.

[41]  Tomohiko Maehama,et al.  The Tumor Suppressor, PTEN/MMAC1, Dephosphorylates the Lipid Second Messenger, Phosphatidylinositol 3,4,5-Trisphosphate* , 1998, The Journal of Biological Chemistry.

[42]  D. Gillespie,et al.  Akt/PKB suppresses DNA damage processing and checkpoint activation in late G2 , 2010, The Journal of cell biology.

[43]  R. Jope,et al.  The multifaceted roles of glycogen synthase kinase 3β in cellular signaling , 2001, Progress in Neurobiology.

[44]  A. Krivoruchko,et al.  Molecular mechanisms of turtle anoxia tolerance: A role for NF-kappaB. , 2010, Gene.

[45]  R. Hresko,et al.  mTOR·RICTOR Is the Ser473 Kinase for Akt/Protein Kinase B in 3T3-L1 Adipocytes* , 2005, Journal of Biological Chemistry.

[46]  P. Sen,et al.  Involvement of the Akt/PKB signaling pathway with disease processes , 2003, Molecular and Cellular Biochemistry.

[47]  J. R. Layne,et al.  Resumption of physiological functions in the wood frog (Rana sylvatica) after freezing. , 1991, The American journal of physiology.

[48]  Kyle K Biggar,et al.  MicroRNA regulation below zero: differential expression of miRNA-21 and miRNA-16 during freezing in wood frogs. , 2009, Cryobiology.

[49]  Ru-Fang Yeh,et al.  miR-126 regulates angiogenic signaling and vascular integrity. , 2008, Developmental cell.

[50]  K. Storey,et al.  Mitogen-activated protein kinases: new signaling pathways functioning in cellular responses to environmental stress , 2003, Journal of Experimental Biology.

[51]  W. Snodgrass Physiology , 1897, Nature.

[52]  P. Cohen,et al.  Glycogen synthase kinase-3 from rabbit skeletal muscle. , 2005, Methods in enzymology.

[53]  Bill X. Huang,et al.  Phosphatidylserine is a critical modulator for Akt activation , 2011, The Journal of cell biology.