Insulin-like growth factor I synergizes with interleukin 4 for hematopoietic cell proliferation independent of insulin receptor substrate expression.
In the present study, we investigated the potential role of insulin-like growth factor I (IGF-I) receptor (IGF-IR) in cell proliferation by overexpressing it in 32D myeloid progenitor cells. The overexpression of IGF-IR caused the transfectants to proliferate in response to IGF-I in the absence of insulin receptor substrate (IRS) expression. The activation of overexpressed wild-type IGF-IR, but not that of an ATP-binding mutant of IGF-IR, resulted in the increased tyrosine phosphorylation of several intracellular proteins, including SHC, Src homology 2-containing inositol-5-phosphatase, protein kinase C-delta, and Erk2. Grb2 association with SHC and mitogen-activated protein kinase (MAPK) activity was also enhanced in response to IGF-I stimulation. Interestingly, the stimulation of the IGF-IR transfectants with interleukin 4 (IL-4) also resulted in strong mitogenesis independent of IRS expression. Moreover, IGF-I and/or IL-4 induced long-term cell growth of the IGF-IR transfectants. IL-4 was able to synergize with IGF-I for DNA synthesis, even in the parental 32D cells and a pro-B-cell line, Baf3, indicating the physiological importance of the two growth factors in hematopoietic cell proliferation. IL-4 stimulation of the IGF-IR transfectants resulted in enhanced tyrosine phosphorylation of SHC, Erk2, and signal transducer and activator of transcription 6 (STAT6) proteins. Both IL-4 and IGF-I were able to induce c-myc early response gene expression, and this expression was maximal in the presence of both factors. Finally, we demonstrated that a MAPK kinase inhibitor was able to suppress mitogenesis of the IGF-IR transfectants in response to IGF-I and/or IL-4. Together, our results suggest that IL-4 synergizes with IGF-I for hematopoietic cell proliferation, likely through cross talk between SHC/Grb2/MAPK and STAT6 pathways and through c-myc gene up-regulation.
Soon
L
L
Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892, USA.
Flechner
L
L
Gutkind
J S
JS
Wang
L H
LH
Baserga
R
R
Pierce
J H
JH
Li
W
W
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division; D002460:Cell Line; D004789:Enzyme Activation; D051380:GRB2 Adaptor Protein; D005786:Gene Expression Regulation / Q000235:genetics; D016259:Genes, myc / Q000235:genetics; D006410:Hematopoiesis; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D015847:Interleukin-4 / Q000378:metabolism*; D008934:Mitogens / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000235:genetics* / Q000378:metabolism; D050800:STAT6 Transcription Factor; D055765:Shc Signaling Adaptor Proteins; D013234:Stem Cells / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051380:GRB2 Adaptor Protein; D055504:Insulin Receptor Substrate Proteins; D008934:Mitogens; D010750:Phosphoproteins; D011506:Proteins; D050800:STAT6 Transcription Factor; D055765:Shc Signaling Adaptor Proteins; D015534:Trans-Activators; D015847:Interleukin-4; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D020794:Receptor Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D017871:Calcium-Calmodulin-Dependent Protein Kinases