Insulin inhibits leptin receptor signalling in HEK293 cells at the level of janus kinase-2: a potential mechanism for hyperinsulinaemia-associated leptin resistance.
OBJECTIVE
Leptin resistance in obese humans seems to be predominantly caused by signalling abnormalities at the post receptor level. Leptin resistance in obese individuals is frequently associated with insulin resistance and pronounced hyperinsulinaemia indicating a negative crosstalk of the insulin and leptin signalling chain.


METHODS
This hypothesis was tested using a cell model of peripheral leptin signalling, i. e. insulin-secreting cell lines (RINr1046-38). Mechanisms for a crosstalk between the insulin and leptin signalling pathway were also studied in rat-1 and HEK293 cells overexpressing elements of the insulin and leptin signalling chain.


RESULTS
The effects of leptin on insulin secretion are completely cancelled by a 4-h preincubation with 1 nmol/l insulin, supporting the hypothesis of a negative crosstalk of insulin and leptin signalling. We investigated the potential molecular mechanisms in more detail in HEK293 cells and Rat-1 fibroblasts that overexpressed proteins of the insulin and leptin signalling chain. Leptin (60 ng/ml) stimulated autophosphorylation of JAK-2 in HEK 293 cells. This leptin effect could be inhibited by simultaneous treatment of cells with insulin. Furthermore, overexpression of the insulin receptor in HEK 293 cells clearly reduced JAK-2 phosphorylation and led further downstream to a diminished phosphatidylinositol 3-kinase activity. The inhibitory effect of the insulin signal could be partially prevented by transfection of the cells with an inactive mutant of the tyrosine phosphatase SHP-1.


CONCLUSIONS
In summary, our data suggest that the insulin receptor signalling pathway interferes with leptin signalling at the level of JAK-2. Inhibition of JAK-2 phosphorylation might occur through SHP-1-dependent pathways, indicating that hyperinsulinaemia contributes to the pathogenesis of leptin resistance.
Kellerer
M
M
Eberhard-Karls University of Tübingen, Internal Medicine IV, Germany.
Lammers
R
R
Fritsche
A
A
Strack
V
V
Machicao
F
F
Borboni
P
P
Ullrich
A
A
Häring
H U
HU
D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002460:Cell Line; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D004622:Embryo, Mammalian; D015870:Gene Expression; D006801:Humans; D006946:Hyperinsulinism / Q000503:physiopathology*; D007328:Insulin / Q000494:pharmacology*; D007340:Insulinoma; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D007668:Kidney; D020738:Leptin / Q000494:pharmacology*; D010190:Pancreatic Neoplasms; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051381:Rats; D011972:Receptor, Insulin / Q000235:genetics; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D020738:Leptin; D019869:Phosphatidylinositol 3-Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D011972:Receptor, Insulin; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; C515448:LEPR protein, human; C507924:JAK2 protein, human; C507927:Jak2 protein, rat; C516724:PTPN11 protein, human; C509249:PTPN6 protein, human; C516727:Ptpn11 protein, rat; C509250:Ptpn6 protein, rat