Role of Src in ligand-specific regulation of delta-opioid receptor desensitization and internalization

Area of Science:

• Molecular Pharmacology
• Neuroscience
• G protein-coupled receptors (GPCRs)

Background:

• Opioid receptors, a class of GPCRs, mediate responses to endogenous peptides and external alkaloids.
• Differential desensitization and internalization of opioid receptors by various agonists are known but poorly understood.
• Understanding these mechanisms is crucial for developing targeted opioid-based therapeutics.

Purpose of the Study:

• To investigate the distinct signaling events initiated by DPDPE and TIPP at the delta-opioid receptor (deltaOR).
• To elucidate the molecular mechanisms underlying agonist-specific deltaOR desensitization and internalization.
• To identify the role of Src kinase in modulating deltaOR signaling.

Main Methods:

• Compared signaling pathways (adenylyl cyclase inhibition, ERK1/2 activation) of DPDPE and TIPP at deltaOR.
• Assessed receptor desensitization and internalization following ligand stimulation.
• Investigated the involvement of Src kinase, GRK2, and beta-arrestin recruitment and dephosphorylation using specific inhibitors (PP2) and assays.

Main Results:

• Both DPDPE and TIPP inhibited adenylyl cyclase and activated ERK1/2, but only DPDPE induced deltaOR desensitization and internalization.
• DPDPE, unlike TIPP, activated GRK2 via Src phosphorylation and translocation, leading to beta-arrestin recruitment and enhanced dephosphorylation.
• Src inhibition (PP2) abolished DPDPE-induced effects; morphine behaved similarly to TIPP, failing to utilize Src.

Conclusions:

• Agonist-specific utilization of Src kinase is critical for regulating delta-opioid receptor signaling.
• DPDPE enhances beta-arrestin function through dual regulation: promoting recruitment and increasing dephosphorylation via a Src-dependent pathway.
• These findings reveal novel molecular insights into how Src modulates deltaOR responsiveness and receptor trafficking.