The vasoactive intestinal peptide (VIP) receptor: recent data and hypothesis.

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Pharmacology

Background:

• Vasoactive intestinal peptide (VIP) is a neuropeptide with diverse biological functions.
• VIP exerts its effects by binding to specific membrane receptors, often leading to increased intracellular cyclic AMP.
• VIP receptor structure and function vary across species and tissues.

Purpose of the Study:

• To characterize the VIP binding site on human adenocarcinoma (HT29) cells.
• To compare the HT29 cell VIP receptor structure with those from other tissues and the glucagon receptor.
• To investigate the dynamics of VIP receptor internalization, recycling, and intracellular trafficking.

Main Methods:

• Covalent cross-linking using bifunctional reagents to determine receptor molecular mass.
• Characterization of the VIP binding site on intact HT29 cells.
• Solubilization of the VIP receptor in an active form.
• Study of receptor-mediated endocytosis and intracellular receptor pools.

Main Results:

• The VIP binding site on HT29 cells is a 64 kDa glycoprotein with N-linked oligosaccharide chains.
• VIP binding induces rapid internalization of receptors via endocytosis.
• Receptor internalization leads to decreased cell surface receptors and adenylate cyclase desensitization.
• VIP is degraded in lysosomes, while receptors are recycled to the cell surface.
• Evidence suggests two distinct intracellular pathways for occupied and unoccupied VIP receptors.

Conclusions:

• The HT29 cell line serves as a valuable model for studying VIP receptor dynamics.
• VIP receptor internalization and recycling are complex processes involving intracellular trafficking.
• Understanding these pathways is crucial for elucidating VIP signaling and potential therapeutic interventions.