Inhibitors of phosphoinositide 3-kinase cause defects in the postendocytic sorting of beta2-adrenergic receptors

Exp Cell Res. 2007 Jul 15;313(12):2586-96. doi: 10.1016/j.yexcr.2007.04.034. Epub 2007 May 22.

Abstract

Phosphatidylinositol 3-kinase inhibitors have been shown to affect endocytosis or subsequent intracellular sorting in various receptor systems. Agonist-activated beta(2)-adrenergic receptors undergo desensitization by mechanisms that include the phosphorylation, endocytosis and degradation of receptors. Following endocytosis, most internalized receptors are sorted to the cell surface, but some proportion is sorted to lysosomes for degradation. It is not known what governs the ratio of receptors that recycle versus receptors that undergo degradation. To determine if phosphatidylinositol 3-kinases regulate beta(2)-adrenergic receptor trafficking, HEK293 cells stably expressing these receptors were treated with the phosphatidylinositol 3-kinase inhibitors LY294002 or wortmannin. We then studied agonist-induced receptor endocytosis and postendocytic sorting, including recycling and degradation of the internalized receptors. Both inhibitors amplified the internalization of receptors after exposure to the beta-agonist isoproterenol, which was attributable to the sorting of a significant fraction of receptors to an intracellular compartment from which receptor recycling did not occur. The initial rate of beta(2)-adrenergic receptor endocytosis and the default rate of receptor recycling were not significantly altered. During prolonged exposure to agonist, LY294002 slowed the degradation rate of beta(2)-adrenergic receptors and caused the accumulation of receptors within rab7-positive vesicles. These results suggest that phosphatidylinositol 3-kinase inhibitors (1) cause a misrouting of beta(2)-adrenergic receptors into vesicles that are neither able to efficiently recycle to the surface nor sort to lysosomes, and (2) delays the movement of receptors from late endosomes to lysosomes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 1-Phosphatidylinositol 4-Kinase / antagonists & inhibitors*
  • Adrenergic beta-Agonists / pharmacology
  • Cell Line
  • Chromones / pharmacology*
  • Endocytosis / drug effects*
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Morpholines / pharmacology*
  • Protein Transport / drug effects
  • Receptors, Adrenergic, beta-2 / metabolism*
  • Transferrin / metabolism
  • rab GTP-Binding Proteins / metabolism

Substances

  • Adrenergic beta-Agonists
  • Chromones
  • Morpholines
  • Receptors, Adrenergic, beta-2
  • Transferrin
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins
  • rab7 protein
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • 1-Phosphatidylinositol 4-Kinase
  • rab GTP-Binding Proteins