Internalization and sequestration of the human prostacyclin receptor

Area of Science:

• Pharmacology
• Cell Biology
• Biochemistry

Background:

• Prostacyclin (PGI2) exerts effects via the G protein-coupled IP receptor.
• PKC-mediated phosphorylation of the human IP receptor (hIP) is key to agonist-induced desensitization.
• Regulatory events following hIP desensitization remain unclear.

Purpose of the Study:

• To investigate the mechanisms of agonist-induced sequestration (internalization) of the human IP receptor.
• To determine the role of protein kinase C (PKC) and G protein-coupled receptor kinases (GRKs)/arrestins in hIP trafficking.
• To identify regions of the hIP receptor critical for internalization.

Main Methods:

• Overexpression of HA-tagged and GFP-fused hIP in HEK 293 cells.
• Real-time confocal microscopy to track HAhIP-GFP sequestration upon iloprost stimulation.
• Utilized PKC inhibitors, dominant-negative mutants (dynamin, arrestin-2), and receptor C-terminal deletion mutants.

Main Results:

• Iloprost induced hIP sequestration, partially colocalized with clathrin-coated vesicles.
• Receptor internalization was dependent on dynamin and clathrin-mediated trafficking.
• Internalization occurred independently of PKC activity and Ser-328 phosphorylation.
• The C-terminus of hIP was essential for iloprost-induced internalization.
• GRKs and arrestins did not influence hIP trafficking.

Conclusions:

• Agonist-induced hIP sequestration is mediated by a PKC-independent pathway, distinct from desensitization.
• hIP trafficking requires specific C-terminal determinants and proceeds via a dynamin-dependent, clathrin-mediated endocytotic pathway.
• GRK and arrestin-independent mechanisms govern hIP internalization.