Early intracellular events induced by in vivo leptin treatment in mouse skeletal muscle.
Experimental evidence suggests that leptin may exert direct effects on peripheral tissues. In this study we investigated some transductional molecules in skeletal muscle, after intraperitoneal leptin injection in wild-type and ob/ob mice. By immunoprecipitation and immunoblotting with anti-phosphotyrosine antibodies, we observed a modified pattern of phosphotyrosine proteins. We then identified an increase in JAK2, IRS1 and IRS2 tyrosine-phosphorylation and in their association with p85, a subunit of PI3K. The increase in PI3K activity in immunoprecipitated p85 did not reach statistical significance, however, both Akt and GSK3 resulted significantly hyper-phosphorylated. Bad, an Akt substrate involved in cell survival, appeared modified in its phosphorylation. ERK1, ERK2 and p38 MAP kinase phosphorylation significantly increased, even if the latter only in wild-type animals. Finally, by EMSA experiments, we documented that leptin increased the DNA binding capacity of Stat3 homodimers and AP-1. Thus, leptin appears to activate, within minutes, some insulin signalling molecules. Stat3 and AP-1 activation by gene expression remodelling could subsequently trigger more leptin-specific effects. Further, leptin might play a still underestimated role in cell survival.
Maroni
P
P
Institute of General Pathology, University of Milano, Via Mangiagalli, 31, Italy.
Bendinelli
P
P
Piccoletti
R
R
D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D007274:Injections, Intraperitoneal; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D020738:Leptin / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D054411:Receptors, Leptin; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D020738:Leptin; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; D018808:Transcription Factor AP-1; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; C515448:LEPR protein, human; C494086:STAT3 protein, human; C494087:Stat3 protein, mouse; C515447:leptin receptor, mouse; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; C494918:AKT1 protein, human