Impact of Src homology 2-containing inositol 5'-phosphatase 2 on the regulation of insulin signaling leading to protein synthesis in 3T3-L1 adipocytes cultured with excess amino acids.
Src homology 2-containing inositol 5'-phosphatase 2 (SHIP2) possesses 5'-phosphatase activity to specifically hydrolyze the phosphatidylinositol 3-kinase product PI(3,4,5)P3 in the regulation of insulin signaling. In the present study, we examined the impact of SHIP2 on the regulation of insulin signaling leading to protein synthesis in 3T3-L1 adipocytes cultured with standard and excess concentrations of amino acids. Insulin-induced translocation of PDK1 to the plasma membrane, phosphorylation of Akt and p70S6-kinase and ribosomal protein S6, increase in the amount of 4E-BP1 gamma-form, association of eIF4E with eIF4G, and protein synthesis were decreased by overexpression of wild-type SHIP2 by adenovirus-mediated gene transfer. The effect of SHIP2 overexpression on the regulation of insulin-induced phosphorylation of Akt and p70S6-kinase was somewhat augmented by the incubation with 5-fold excess concentrations of amino acids for 30 min. In contrast, the impact of SHIP2 expression was diminished in insulin-induced phosphorylation of p70S6-kinase and S6, but not of Akt, after the incubation for 16 h. Interestingly, incubation with the excess concentrations of amino acids for 30 min induced activation of phosphatidylinositol 3-kinase and phosphorylation of Akt, whereas phosphorylation of p70S6-kinase and S6 was decreased. Furthermore, although the exposure for longer time periods up to 24 h did not elicit phosphorylation of Akt, it markedly induced phosphorylation of p70S6-kinase and S6. These results indicate that SHIP2 plays an important role in the negative regulation of insulin signaling for the protein synthesis and that the impact of SHIP2 is altered, dependent on the acute or chronic exposure of excess concentrations of amino acids in culture.
Murakami
Shihou
S
Department of Internal Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan.
Sasaoka
Toshiyasu
T
Wada
Tsutomu
T
Fukui
Kazuhito
K
Nagira
Kiyofumi
K
Ishihara
Hajime
H
Usui
Isao
I
Kobayashi
Masashi
M
D041721:3T3-L1 Cells; D048868:Adaptor Proteins, Signal Transducing; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D039642:Eukaryotic Initiation Factors; D015870:Gene Expression; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010750:Phosphoproteins / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000378:metabolism; D038601:Ribosomal Protein S6 / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism; D018909:src Homology Domains / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D039603:Eukaryotic Initiation Factor-4G; D039642:Eukaryotic Initiation Factors; D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D019869:Phosphatidylinositol 3-Kinases; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010750:Phosphoproteins; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D038601:Ribosomal Protein S6; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D014443:Tyrosine; C499527:Eif4ebp1 protein, mouse; C526295:Irs1 protein, mouse; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; C098706:INPPL1 protein, human