Related Experiment Videos
Caveolin is an activator of insulin receptor signaling
M Yamamoto1, Y Toya, C Schwencke
1Cardiovascular and Pulmonary Research Institute, Allegheny University of the Health Sciences, Pittsburgh, Pennsylvania 15212, USA.
Abstract:
Recent data have demonstrated that caveolin, a major structural protein of caveolae, negatively regulates signaling molecules localized to caveolae. The interaction of caveolin with several caveolae-associated signaling proteins is mediated by the binding of the scaffolding region of caveolin to a hydrophobic amino acid-containing region within the regulated proteins. The presence of a similar motif within the insulin receptor kinase prompted us to investigate the caveolar localization and regulation of the insulin receptor by caveolin. We found that overexpression of caveolin-3 augmented insulin-stimulated phosphorylation of insulin receptor substrate-1 in 293T cells but not the phosphorylation of insulin receptor. Peptides corresponding to the scaffolding domain of caveolin potently stimulated insulin receptor kinase activity toward insulin receptor substrate-1 or a Src-derived peptide in vitro and in a caveolin subtype-dependent fashion. Peptides from caveolin-2 exhibited no effect, whereas caveolin-1 and -3 stimulated activity 10- and 17-fold, respectively. Peptides which increased insulin receptor kinase activity did so without affecting insulin receptor auto-phosphorylation. Furthermore, the insulin receptor bound to immobilized caveolin peptides, and this binding was inhibited in the presence of free caveolin-3 peptides. Thus, we have identified a novel mechanism by which the insulin receptor is bound and activated by specific caveolin subtypes. Furthermore, these data define a new role for caveolin as an activator of signaling.
Insights
Caveolin proteins bind and activate the insulin receptor kinase, a novel signaling mechanism. This discovery reveals a new role for caveolin as a positive regulator of cellular signaling pathways.
Area of Science:
- Cellular Biology
- Molecular Signaling
- Protein Interactions
Background:
- Caveolins are structural proteins of caveolae, known to negatively regulate signaling molecules.
- Caveolin interacts with signaling proteins via its scaffolding domain, binding to hydrophobic regions.
Purpose of the Study:
- To investigate the role of caveolin in the localization and regulation of the insulin receptor.
- To determine if caveolin subtypes can modulate insulin receptor kinase activity.
Main Methods:
- Overexpression of caveolin-3 in 293T cells to assess insulin signaling.
- In vitro kinase assays using caveolin-derived peptides and insulin receptor substrate-1.
- Analysis of insulin receptor binding to immobilized caveolin peptides.
Main Results:
- Caveolin-3 overexpression enhanced insulin-stimulated phosphorylation of insulin receptor substrate-1.
- Caveolin-1 and caveolin-3 peptides significantly stimulated insulin receptor kinase activity in vitro.
- Insulin receptor demonstrated binding to immobilized caveolin peptides, inhibited by free caveolin-3.
Conclusions:
- Specific caveolin subtypes (caveolin-1 and -3) directly bind and activate the insulin receptor kinase.
- This interaction activates downstream signaling without affecting insulin receptor auto-phosphorylation.
- Identified a novel mechanism of insulin receptor activation and a new role for caveolin as a signaling activator.