Amplification and Demultiplexing in Insulin-regulated Akt Protein Kinase Pathway in Adipocytes

• Published in: The Journal of biological chemistry Vol. 287; no. 9; pp. 6128 - 6138
• Main Authors: Tan, Shi-Xiong, Ng, Yvonne, Meoli, Christopher C., Kumar, Ansu, Khoo, Poh-Sim, Fazakerley, Daniel J., Junutula, Jagath R., Vali, Shireen, James, David E., Stöckli, Jacqueline
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 24.02.2012; American Society for Biochemistry and Molecular Biology
• Subjects: 3T3-L1 Cells; Adipocyte; Adipocytes - cytology; Adipocytes - drug effects; Adipocytes - enzymology; Akt PKB; Animals; Antibiotics, Antineoplastic - pharmacology; Computer Simulation; Energy Metabolism - drug effects; Energy Metabolism - physiology; Glucose Transporter Type 4 - metabolism; Hypoglycemic Agents - metabolism; Hypoglycemic Agents - pharmacology; Insulin - metabolism; Insulin - pharmacology; Insulin Receptor Substrate Proteins - metabolism; Insulin Resistance; Insulin Resistance - physiology; IRS1; Mice; mTOR; Nonlinear Dynamics; PDGF; Phosphorylation - drug effects; Phosphorylation - physiology; Platelet-Derived Growth Factor - metabolism; Protein Synthesis; Proto-Oncogene Proteins c-akt - antagonists & inhibitors; Proto-Oncogene Proteins c-akt - genetics; Proto-Oncogene Proteins c-akt - metabolism; Rapamycin; RNA, Small Interfering - pharmacology; Signal Transduction; Signal Transduction - drug effects; Signal Transduction - physiology; Sirolimus - pharmacology; TOR Serine-Threonine Kinases - metabolism; Adipocyte; Protein Synthesis; Signal Transduction; IRS1; PDGF; Insulin Resistance; mTOR; Rapamycin; Akt PKB
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.318238

Akt plays a major role in insulin regulation of metabolism in muscle, fat, and liver. Here, we show that in 3T3-L1 adipocytes, Akt operates optimally over a limited dynamic range. This indicates that Akt is a highly sensitive amplification step in the pathway. With robust insulin stimulation, substantial changes in Akt phosphorylation using either pharmacologic or genetic manipulations had relatively little effect on Akt activity. By integrating these data we observed that half-maximal Akt activity was achieved at a threshold level of Akt phosphorylation corresponding to 5–22% of its full dynamic range. This behavior was also associated with lack of concordance or demultiplexing in the behavior of downstream components. Most notably, FoxO1 phosphorylation was more sensitive to insulin and did not exhibit a change in its rate of phosphorylation between 1 and 100 nm insulin compared with other substrates (AS160, TSC2, GSK3). Similar differences were observed between various insulin-regulated pathways such as GLUT4 translocation and protein synthesis. These data indicate that Akt itself is a major amplification switch in the insulin signaling pathway and that features of the pathway enable the insulin signal to be split or demultiplexed into discrete outputs. This has important implications for the role of this pathway in disease. Akt plays a major role in insulin regulation of metabolism. Akt operates at 5–22% of its dynamic range. This lacks concordance with Akt substrate phosphorylation, GLUT4 translocation, and protein synthesis. Akt is a demultiplexer that splits the insulin signal into discrete outputs. This study provides better understanding of the Akt pathway and has implications for the role of Akt in diseases.