The critical role of Shc in insulin-like growth factor-I-mediated mitogenesis and differentiation in 3T3-L1 preadipocytes

Mol Endocrinol. 2000 Jun;14(6):805-13. doi: 10.1210/mend.14.6.0487.

Abstract

Insulin-like growth factor-I (IGF-I) stimulates mitogenesis in proliferating preadipocytes, but when cells reach confluence and become growth arrested, IGF-I stimulates differentiation into adipocytes. IGF-I induces signaling pathways that involve IGF-I receptor-mediated tyrosine phosphorylation of Shc and insulin receptor substrate 1 (IRS-1). Either of these adaptor proteins can lead to activation of the three-kinase cascade ending in activation of the extracellular signal-regulated kinase 1 and -2 (ERK-1 and -2) mitogen-activated protein kinases (MAPKs). Several lines of evidence suggest that activation of MAPK inhibits 3T3-L1 preadipocyte differentiation. We have shown that IGF-I stimulation of MAPK activity is lost as 3T3-L1 preadipocytes begin to differentiate. This change in MAPK signaling coincides with loss of IGF-I-mediated Shc, but not IRS-1, tyrosine phosphorylation. We hypothesized that down-regulation of MAPK via loss of proximal signaling through Shc is an early component in the IGF-I switch from mitogenesis to differentiation in 3T3-L1 preadipocytes. Treatment of subconfluent cells with the MEK inhibitor PD098059 inhibited both IGF-I-activation of MAPK as well as 3H-thymidine incorporation. PD098059, in the presence of differentiation-inducing media, accelerated differentiation in subconfluent cells as measured by expression of adipocyte protein-2 (aP-2), peroxisome proliferator-activated receptor gamma (PPARgamma) and lipoprotein lipase (LPL). Transient transfection of subconfluent cells with Shc-Y317F, a dominant-negative mutant, attenuated IGF-I-mediated MAPK activation, inhibited DNA synthesis, and accelerated expression of differentiation markers aP-2, PPARgamma, and LPL. We conclude that signaling through Shc to MAPK plays a critical role in mediating IGF-I-stimulated 3T3-L1 mitogenesis. Our results suggest that loss of the ability of IGF-I to activate Shc signaling to MAPK may be an early component of adipogenesis in 3T3-L1 cells.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Adaptor Proteins, Signal Transducing*
  • Adaptor Proteins, Vesicular Transport*
  • Adipocytes / cytology*
  • Animals
  • Blotting, Northern
  • Cell Differentiation* / drug effects
  • Cell Division / drug effects
  • Culture Media
  • DNA / biosynthesis
  • Enzyme Inhibitors / pharmacology
  • Flavonoids / pharmacology
  • Insulin-Like Growth Factor I / pharmacology*
  • Mice
  • Mitogen-Activated Protein Kinases / antagonists & inhibitors
  • Mitosis*
  • Mutation
  • Proteins / genetics
  • Proteins / physiology*
  • Recombinant Fusion Proteins / pharmacology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Shc Signaling Adaptor Proteins
  • Src Homology 2 Domain-Containing, Transforming Protein 1
  • Stem Cells / cytology*
  • Transfection

Substances

  • Adaptor Proteins, Signal Transducing
  • Adaptor Proteins, Vesicular Transport
  • Culture Media
  • Enzyme Inhibitors
  • Flavonoids
  • Proteins
  • Recombinant Fusion Proteins
  • Shc Signaling Adaptor Proteins
  • Shc1 protein, mouse
  • Src Homology 2 Domain-Containing, Transforming Protein 1
  • Insulin-Like Growth Factor I
  • DNA
  • Mitogen-Activated Protein Kinases
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one