Regulation of Translational Effectors by Amino Acid and Mammalian Target of Rapamycin Signaling Pathways

Amino acid deprivation of Chinese hamster ovary cells overexpressing human insulin receptors results in deactivation of p70 S6 kinase (p70) and dephosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), which become unresponsive to insulin; readdition of amino acids restores these responses in a rapamycin-sensitive manner, suggesting that amino acids and mammalian target of rapamycin signal through common effectors. Contrarily, withdrawal of medium amino acids from the hepatoma cell line H4IIE does not abolish the ability of insulin to stimulate p70 and 4E-BP1. The addition of 3-methyladenine (3MA) to H4IIE cells deprived of amino acids inhibited the increment in protein degradation caused by amino acid withdrawal nearly completely at 10 mm and also strongly inhibited the ability of insulin to stimulate p70 and 4E-BP1 at 10 mm. Treatment of H4IIE cells with 3MA did not alter the ability of insulin to activate tyrosine phosphorylation, phosphoinositide 3-kinase, or mitogen-activated protein kinase. In conclusion, the ability of H4IIE cells to maintain the insulin responsiveness of the mammalian target of rapamycin-dependent signaling pathways impinging on p70 and 4E-BP1 without exogenous amino acids reflects the generation of amino acids endogenously through a 3MA-sensitive process, presumably autophagy, a major mechanism of facultative protein degradation in liver.

[1]  J. Avruch,et al.  Amino Acid Sufficiency and mTOR Regulate p70 S6 Kinase and eIF-4E BP1 through a Common Effector Mechanism* , 1998, The Journal of Biological Chemistry.

[2]  C. Kahn,et al.  Bidirectional modulation of insulin action by amino acids. , 1998, The Journal of clinical investigation.

[3]  M. Mcdaniel,et al.  Insulin Mediates Glucose-stimulated Phosphorylation of PHAS-I by Pancreatic Beta Cells , 1998, The Journal of Biological Chemistry.

[4]  A. Gingras,et al.  4E-BP1, a repressor of mRNA translation, is phosphorylated and inactivated by the Akt(PKB) signaling pathway. , 1998, Genes & development.

[5]  Takeshi Noda,et al.  Tor, a Phosphatidylinositol Kinase Homologue, Controls Autophagy in Yeast* , 1998, The Journal of Biological Chemistry.

[6]  M. Andjelkovic,et al.  Phosphorylation and activation of p70s6k by PDK1. , 1998, Science.

[7]  Dario R. Alessi,et al.  3-Phosphoinositide-dependent protein kinase 1 (PDK1) phosphorylates and activates the p70 S6 kinase in vivo and in vitro , 1998, Current Biology.

[8]  G. Thomas,et al.  TOR signalling and control of cell growth. , 1997, Current opinion in cell biology.

[9]  M. Kasuga,et al.  Regulation of eIF-4E BP1 Phosphorylation by mTOR* , 1997, The Journal of Biological Chemistry.

[10]  A. Gingras,et al.  The insulin-induced signalling pathway leading to S6 and initiation factor 4E binding protein 1 phosphorylation bifurcates at a rapamycin-sensitive point immediately upstream of p70s6k , 1997, Molecular and cellular biology.

[11]  R. Abraham,et al.  PHAS/4E-BPs as regulators of mRNA translation and cell proliferation. , 1997, Trends in biochemical sciences.

[12]  Christine C. Hudson,et al.  Phosphorylation of the translational repressor PHAS-I by the mammalian target of rapamycin. , 1997, Science.

[13]  R. Pearson,et al.  Rapamycin suppresses 5′TOP mRNA translation through inhibition of p70s6k , 1997, The EMBO journal.

[14]  A. Meijer,et al.  The phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 inhibit autophagy in isolated rat hepatocytes. , 1997, European journal of biochemistry.

[15]  C. Bauvy,et al.  Guanine Nucleotide Exchange on Heterotrimeric Gi3 Protein Controls Autophagic Sequestration in HT-29 Cells* , 1996, The Journal of Biological Chemistry.

[16]  R. Abraham,et al.  Direct inhibition of the signaling functions of the mammalian target of rapamycin by the phosphoinositide 3‐kinase inhibitors, wortmannin and LY294002. , 1996, The EMBO journal.

[17]  A. Gingras,et al.  Rapamycin blocks the phosphorylation of 4E‐BP1 and inhibits cap‐dependent initiation of translation. , 1996, The EMBO journal.

[18]  R. Abraham,et al.  Immunopharmacology of rapamycin. , 1996, Annual review of immunology.

[19]  N. Sonenberg,et al.  Repression of cap‐dependent translation by 4E‐binding protein 1: competition with p220 for binding to eukaryotic initiation factor‐4E. , 1995, The EMBO journal.

[20]  S. Schreiber,et al.  Control of p70 S6 kinase by kinase activity of FRAP in vivo , 1995, Nature.

[21]  J. Downward A target for Pl(3) kinase , 1995, Nature.

[22]  P. Blackshear,et al.  Control of PHAS-I by Insulin in 3T3-L1 Adipocytes , 1995, The Journal of Biological Chemistry.

[23]  J. Avruch,et al.  Phosphatidylinositol 3-kinase signals activation of p70 S6 kinase in situ through site-specific p70 phosphorylation. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[24]  A. Meijer,et al.  Phosphorylation of Ribosomal Protein S6 Is Inhibitory for Autophagy in Isolated Rat Hepatocytes (*) , 1995, The Journal of Biological Chemistry.

[25]  A. Gingras,et al.  Insulin-dependent stimulation of protein synthesis by phosphorylation of a regulator of 5'-cap function , 1994, Nature.

[26]  Andrius Kazlauskas,et al.  PDGF- and insulin-dependent pp70S6k activation mediated by phosphatidylinositol-3-OH kinase , 1994, Nature.

[27]  R. Roth,et al.  Phosphatidylinositol kinase or an associated protein is a substrate for the insulin receptor tyrosine kinase. , 1990, The Journal of biological chemistry.

[28]  B. Lardeux,et al.  Mechanism and regulation of protein degradation in liver. , 1989, Diabetes/metabolism reviews.

[29]  M. Kadowaki,et al.  Multiphasic control of hepatic protein degradation by regulatory amino acids. General features and hormonal modulation. , 1987, The Journal of biological chemistry.

[30]  J. Avruch,et al.  An insulin-stimulated (ribosomal S6) protein kinase from soluble extracts of H4 hepatoma cells. , 1986, Archives of biochemistry and biophysics.

[31]  P. Seglen,et al.  3-Methyladenine: specific inhibitor of autophagic/lysosomal protein degradation in isolated rat hepatocytes. , 1982, Proceedings of the National Academy of Sciences of the United States of America.

[32]  C. Schworer,et al.  Quantitative relationship between autophagy and proteolysis during graded amino acid deprivation in perfused rat liver. , 1981, The Journal of biological chemistry.

[33]  J. Sommercorn,et al.  Protein degradation in primary monolayer cultures of adult rat hepatocytes. Further evidence for the regulation of protein degradation by amino acids. , 1981, The Journal of biological chemistry.

[34]  C. Schworer,et al.  Induction of autophagy by amino-acid deprivation in perfused rat liver , 1977, Nature.

[35]  B. Trump,et al.  Pathobiology of cell membranes , 1975 .