Leptin activates PI-3 kinase in C2C12 myotubes via janus kinase-2 (JAK-2) and insulin receptor substrate-2 (IRS-2) dependent pathways.
We have recently shown that leptin mimicks insulin effects on glucose transport and glycogen synthesis through a phosphatidylinositol-3 (PI) kinase dependent pathway in C2C12 myotubes. The aim of the present study was to identify the signalling path from the leptin receptor to the PI-3 kinase. We stimulated C2C12 myotubes with insulin (100 nmol/l, 5 min) or leptin (0.62 nmol/l, 10 min) and determined PI-3 kinase activity in immunoprecipitates with specific non-crossreacting antibodies against insulin-receptor substrate (IRS 1/IRS 2) and against janus kinase (JAK 1 and JAK 2). While insulin-stimulated PI-3 kinase activity is detected in IRS-1 and IRS-2 immunoprecipitates, leptin-stimulated PI-3 kinase activity is found only in IRS-2 immunoprecipitates, suggesting that the leptin signal to PI-3 kinase occurs via IRS-2 and not IRS-1. Leptin-, but not insulin-stimulated PI-3 kinase activity is also detected in immunoprecipitates with antibodies against JAK-2, but not JAK-1. The data suggest that JAK-2 and IRS-2 couple the leptin signalling pathway to the insulin signalling chain. Since we have also detected leptin-stimulated tyrosine phosphorylation of JAK-2 and IRS-2 in C2C12 myotubes it can be assumed that leptin activates JAK-2 which induces tyrosine phosphorylation of IRS-2 leading to activation of PI-3 kinase. As we could not detect the long leptin receptor isoform in C2C12 myotubes we conclude that this signalling pathway is activated by a short leptin receptor isoform.
Kellerer
M
M
Eberhard-Karls-Universität Tübingen, IV. Med. Abteilung, Germany.
Koch
M
M
Metzinger
E
E
Mushack
J
J
Capp
E
E
Häring
H U
HU
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D020738:Leptin; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism*; D010750:Phosphoproteins / Q000276:immunology / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D015398:Signal Transduction
D000906:Antibodies; D002352:Carrier Proteins; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526298:Irs2 protein, mouse; D020738:Leptin; D010750:Phosphoproteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; C515447:leptin receptor, mouse; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2