Insulin growth factor-I and epidermal growth factor receptors recruit distinct upstream signaling molecules to enhance AKT activation in mammary epithelial cells.
IGF-I and epidermal growth factor (EGF) stimulate both normal mammary epithelial cell (MEC) growth and tumorigenesis. Whereas both growth factors increase DNA synthesis in MECs, how they evoke a greater response in combination when they activate similar signaling pathways remains unknown. In the present study, we investigated the signaling pathways by which these mitogens act in concert to increase DNA synthesis. Only EGF activated the MAPK pathway, and no further increase in MAPK activation was observed when both mitogens were added together. Both growth factors activated the phosphatidylinositol-3 kinase pathway, and simultaneous treatment enhanced phosphorylation of both AKT and its downstream target, p70S6K. The enhanced activation of AKT was observed at multiple time points (5 and 15 min) and growth factor concentrations (2.5-100 ng/ml). IGF-I activated AKT via insulin receptor substrate-1 and p85, the regulatory subunit of phosphatidylinositol-3 kinase. Treatment with EGF had no effect on insulin receptor substrate-1; however, it activated the EGF receptor, SHC, and c-Src. EGF treatment caused the association of SHC with Grb2 and Gab2 with phospho-SHC, phospho-Gab1, Grb2, and p85. Interestingly, inhibition of Src activation blocked the ability of EGF, but not IGF-I, to activate AKT. This corresponded with a decrease in phosphorylation of the EGF receptor and its association with phospho-SHC as well as downstream signaling. Unexpectedly, inhibition of Src increased basal MAPK activation. This is the first study to show that EGF and IGF-I use separate upstream components within a given MEC line to enhance AKT phosphorylation, contributing to increased DNA synthesis.
Fleming
Jodie M
JM
Department of Animal Sciences, Rutgers, The State University of New Jersey, 108 Foran Hall, 59 Dudley Road, New Brunswick, New Jersey 08901-8520, USA.
Desury
Gwenaëlle
G
Polanco
Tiffany A
TA
Cohick
Wendie S
WS
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000037:antagonists & inhibitors / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction
D048868:Adaptor Proteins, Signal Transducing; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D021122:Protein Subunits; D055765:Shc Signaling Adaptor Proteins; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D017526:Receptor, IGF Type 1; D016392:Proto-Oncogene Proteins pp60(c-src); D051057:Proto-Oncogene Proteins c-akt