Mono- or dual-phosphorylation of akt kinase is regulated by distinct receptors that involve the common insulin receptor substrate.
We have previously shown that the interleukin (IL)-4 signal transduction involves the Insulin Receptor Substrate (IRS) in human colorectal carcinoma cells LS513. In the present study it was tested whether IL-4 counters Insulin-like Growth Factor (IGF)-1 through competition at the IRS signal transduction pathway and, thus, induces a molecular "insulin resistance" or whether IL-4 invokes an alternative signal transduction. The activated receptors of IL-4 and IGF-I both docked to IRS-1 and IRS-2 and invoked IRS complex formation with phosphatidylinositol (PI) 3-kinase, as assessed by immunoprecipitation and detection of the precipitated compounds by immunoblot analysis. Both, IL-4 and IGF-1, signaling pathways induced phosphorylation of Akt kinase in a PI 3-kinase-dependent manner, as assessed by addition of the PI 3-kinase inhibitor Ly294002. Interleukin-4 stimulation induced mono-phosphorylation at serine residue S473 of Akt kinase but failed to activate the kinase. Insulin-like growth factor-1 stimulation invoked dual-phosphorylation at S473 and T308 of Akt kinase and subsequent activation of the kinase. When LS513 cells were treated with IL-4 to induce mono-phosphorylation of Akt, dual- phosphorylation and activation of Akt kinase in response to IGF-1 were still intact. Interleukin-4 yet reduced cell growth by at least 50% both, in the absence and presence of growth factor IGF-1. In the LS513 cells, IL-4 stimulated phosphorylation of Jak2, an adapter molecule at the IL-4 receptor, and phosphorylation of transcription factor Stat6 both, in the absence and presence of IGF-1. We found a similar IL-4 signal transduction and growth suppression in multiple human cell cultures, including primary cells. Our findings indicate that the molecular mechanism underlying growth suppression by IL-4 may depend on gene-expression but not on "insulin/growth factor resistance" at IRS.
Schnyder
Bruno
B
University of Fribourg, Department of Medicine, Fribourg, Switzerland. bruno.schnyder@unifr.ch
Lahm
Harald
H
Pittet
Martine
M
Schnyder-Candrian
Silvia
S
D002455:Cell Division / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D015847:Interleukin-4 / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D050800:STAT6 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D002867:Chromones; D004791:Enzyme Inhibitors; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D015847:Interleukin-4; D047908:Intracellular Signaling Peptides and Proteins; D053614:Janus Kinase 2; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D050800:STAT6 Transcription Factor; D015534:Trans-Activators; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C494101:STAT6 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C507924:JAK2 protein, human; C494918:AKT1 protein, human