Stepwise phosphorylation of BLT1 defines complex assemblies with β-arrestin serving distinct functions

Area of Science:

• Biochemistry
• Cellular Signaling
• Molecular Pharmacology

Background:

• G protein-coupled receptors (GPCRs) mediate cellular responses to diverse stimuli.
• Leukotriene B4 receptor 1 (BLT1) phosphorylation at Thr308 and Ser310 modulates ligand affinity.
• The precise role of BLT1 phosphorylation in signal transduction remains elusive.

Purpose of the Study:

• To elucidate the sequential BLT1-engaged beta-arrestin conformations.
• To investigate the impact of these conformations on downstream signal transduction.
• To understand the mechanisms underlying ligand-dependent GPCR signaling.

Main Methods:

• Utilized BLT1 as a model GPCR system.
• Investigated phosphorylation events at Thr308 and Ser310 residues.
• Analyzed beta-arrestin engagement and conformational changes.
• Examined downstream signaling pathways including ERK1/2, PI3K/AKT.

Main Results:

• LTB4 stimulation induces sequential BLT1 phosphorylation and distinct beta-arrestin complexes.
• Low LTB4 concentrations trigger Ser310 phosphorylation, beta-arrestin binding, and ERK1/2 deactivation.
• High LTB4 concentrations lead to Thr308 phosphorylation, altering beta-arrestin conformation and activating PI3K/AKT signaling.
• Specific beta-arrestin regions (finger loop, N domain) mediate distinct interactions.

Conclusions:

• Stepwise BLT1 phosphorylation dictates the formation of distinct beta-arrestin-GPCR complexes.
• These distinct complexes mediate differential signal transduction outcomes.
• This provides a novel mechanism for fine-tuning cellular responses to LTB4.