Amplification and demultiplexing in insulin-regulated Akt protein kinase pathway in adipocytes.
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.
Diabetes and Obesity Research Program, The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, Sydney, New South Wales 2010, Australia.
Shi-Xiong
SX
Tan
Yvonne
Y
Ng
Christopher C
CC
Meoli
Ansu
A
Kumar
Poh-Sim
PS
Khoo
Daniel J
DJ
Fazakerley
Jagath R
JR
Junutula
Shireen
S
Vali
David E
DE
James
Jacqueline
J
Stöckli
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D003198:Computer Simulation; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000378:metabolism / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D051379:Mice; D017711:Nonlinear Dynamics; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
D000903:Antibiotics, Antineoplastic; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010982:Platelet-Derived Growth Factor; D034741:RNA, Small Interfering; C495693:Slc2a4 protein, mouse; C546843:mTOR protein, mouse; C514862:Akt1 protein, mouse; C494922:Akt2 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus