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Dynamin associates with Src-Homology Collagen (Shc) and becomes tyrosine phosphorylated in response to insulin
V Baron1, F Alengrin, E Van Obberghen
1Institut National de la Santé et de la Recherche Médicale U145, Faculté de Médecine, Nice, France.
Abstract:
The activated insulin receptor phosphorylates docking proteins such as Src-Homology Collagen (Shc) and Insulin Receptor Substrate-1 (IRS-1), which then bind several proteins that contain a Src-Homology 2 (SH2) domain. Both Shc and IRS-1 associate with Growth Factor Receptor-Bound protein 2 (Grb2), an adaptor molecule. The hormone-receptor complex is then rapidly internalized through coated-pits. Dynamin, a 100 kDa protein with GTPase activity, is thought to play a crucial role in receptor-mediated endocytosis. In this study, we show that insulin induces tyrosine phosphorylation of dynamin in cells overexpressing human insulin receptors. Phosphorylation is observed rapidly, i.e. within 1 minute of insulin treatment. Moreover, exposure of cells to the hormone leads to co-immunoprecipitation of dynamin with Shc and with insulin receptor. Since dynamin constitutively associates with Grb2, it could be recruited to the insulin signaling complex through binding of Grb2 to tyrosine-phosphorylated Shc.
Insights
Insulin triggers rapid tyrosine phosphorylation of dynamin, a key protein in endocytosis. This phosphorylation links dynamin to the insulin receptor signaling complex via Shc and Grb2, revealing a novel regulatory mechanism.
Area of Science:
- Molecular Cell Biology
- Endocrinology
- Signal Transduction
Background:
- Insulin receptor activation initiates intracellular signaling cascades.
- Docking proteins like Shc and IRS-1 bind to the activated receptor.
- Dynamin is a GTPase crucial for receptor-mediated endocytosis.
Purpose of the Study:
- To investigate the role of dynamin in insulin receptor signaling.
- To determine if insulin induces dynamin phosphorylation.
- To elucidate the mechanism of dynamin recruitment to the insulin signaling complex.
Main Methods:
- Overexpression of human insulin receptors in cultured cells.
- Insulin stimulation followed by tyrosine phosphorylation analysis.
- Co-immunoprecipitation assays to assess protein-protein interactions.
Main Results:
- Insulin rapidly induces tyrosine phosphorylation of dynamin within 1 minute.
- Dynamin co-immunoprecipitates with Shc and the insulin receptor.
- Dynamin's association with Grb2 suggests recruitment via the Shc-Grb2 interaction.
Conclusions:
- Insulin signaling directly regulates dynamin phosphorylation.
- Dynamin is a novel component of the insulin receptor signaling complex.
- This study reveals a new pathway for dynamin's involvement in insulin-mediated endocytosis.