Elsevier

Molecular Metabolism

Volume 5, Issue 5, May 2016, Pages 366-378
Molecular Metabolism

Original article
Inter-domain tagging implicates caveolin-1 in insulin receptor trafficking and Erk signaling bias in pancreatic beta-cells

https://doi.org/10.1016/j.molmet.2016.01.009Get rights and content
Under a Creative Commons license
open access

Highlights

  • Insulin receptors are tagged between domains to maintain the functionality and endogenous intracellular trafficking patterns.

  • Insulin receptors have virtually no co-localization with classical endocytosis markers, but co-localize with Cav11.

  • Insulin receptor internalization and anti-apoptotic Erk signaling are modulated by phosphorylated Cav1.

Abstract

Objective

The role and mechanisms of insulin receptor internalization remain incompletely understood. Previous trafficking studies of insulin receptors involved fluorescent protein tagging at their termini, manipulations that may be expected to result in dysfunctional receptors. Our objective was to determine the trafficking route and molecular mechanisms of functional tagged insulin receptors and endogenous insulin receptors in pancreatic beta-cells.

Methods

We generated functional insulin receptors tagged with pH-resistant fluorescent proteins between domains. Confocal, TIRF and STED imaging revealed a trafficking pattern of inter-domain tagged insulin receptors and endogenous insulin receptors detected with antibodies.

Results

Surprisingly, interdomain-tagged and endogenous insulin receptors in beta-cells bypassed classical Rab5a- or Rab7-mediated endocytic routes. Instead, we found that removal of insulin receptors from the plasma membrane involved tyrosine-phosphorylated caveolin-1, prior to trafficking within flotillin-1-positive structures to lysosomes. Multiple methods of inhibiting caveolin-1 significantly reduced Erk activation in vitro or in vivo, while leaving Akt signaling mostly intact.

Conclusions

We conclude that phosphorylated caveolin-1 plays a role in insulin receptor internalization towards lysosomes through flotillin-1-positive structures and that caveolin-1 helps bias physiological beta-cell insulin signaling towards Erk activation.

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Keywords

Insulin receptor internalization
Insulin resistance
Pancreatic islet beta-cells
Autocrine insulin signaling

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