Modulation of insulin-like growth factor I mitogenic signaling in 3T3-L1 preadipocyte differentiation.
Insulin-like growth factor I (IGF-I) stimulates mitogenesis in proliferating 3T3-L1 preadipocytes. However, IGF-I functions to stimulate differentiation once growth arrest occurs at confluence. Epidermal growth factor (EGF) is also a potent mitogen in these cells, but inhibits differentiation of preadipocytes. We compared mitogenic signaling via the mitogen-activated protein kinase (MAPK) pathway in response to IGF-I or EGF in proliferating, growth-arrested, and differentiating 3T3-L1 cells. IGF-I stimulation of MAPK was rapid and maximal in proliferating 3T3-L1 preadipocytes, but decreased greatly in differentiating cells. EGF was more potent than IGF-I in stimulating MAPK activity in 3T3-L1 cells, and activation of MAPK was maintained in differentiating cells. These results suggest an uncoupling of MAPK activation specific to IGF-I-mediated 3T3-L1 preadipocyte differentiation. Studies of proximal signaling revealed Shc phosphorylation and Shc/Grb2 complex formation in IGF-I-treated proliferating, but not differentiating, cells. Insulin receptor substrate-1 phosphorylation after IGF-I treatment was present in proliferating, quiescent, and differentiating preadipocytes. Shc phosphorylation and Grb2 association after EGF treatment were present throughout all phases of growth. The change in IGF-I signaling via Shc phosphorylation and MAPK activity during 3T3-L1 differentiation indicates that loss of IGF-I mitogenic signaling via the MAPK pathway is part of the differentiation process.
Boney
C M
CM
Department of Pediatrics, Rhode Island Hospital and Brown University, Providence 02903, USA. charlotte_boney@brown.edu
Smith
R M
RM
Gruppuso
P A
PA
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D051380:GRB2 Adaptor Protein; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D008934:Mitogens / Q000494:pharmacology*; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D007328:Insulin; D008934:Mitogens; D011506:Proteins; D055765:Shc Signaling Adaptor Proteins; C528034:Shc1 protein, mouse; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D017871:Calcium-Calmodulin-Dependent Protein Kinases