A single mutation in arrestin-2 prevents ERK1/2 activation by reducing c-Raf1 binding

Area of Science:

• Molecular and Cellular Biology
• Biochemistry
• Pharmacology

Background:

• Nonvisual arrestins (arrestin-2 and arrestin-3) modulate G protein-coupled receptor (GPCR) signaling and trafficking.
• GPCR-arrestin complexes activate G protein-independent pathways, including extracellular signal-regulated kinase 1/2 (ERK1/2) activation.

Purpose of the Study:

• To investigate the role of specific residues on the nonreceptor-binding surface of arrestin-2 and arrestin-3 in regulating ERK1/2 signaling.
• To create and characterize the first signaling-biased arrestin mutant.

Main Methods:

• Alanine-scanning mutagenesis was performed on conserved residues of arrestin-2 and arrestin-3.
• Binding assays were used to assess interactions between mutant arrestins, receptors, and signaling proteins (c-Raf1, MEK1, ERK2).
• Functional assays in arrestin-2/3 double knockout mouse embryonic fibroblasts were conducted to evaluate ERK1/2 activation.

Main Results:

• An Arg307Ala mutation in arrestin-2 significantly reduced its binding to c-Raf1 but did not affect binding to the receptor, MEK1, or ERK2.
• The Arg307Ala arrestin-2 mutant failed to rescue ERK1/2 activation in knockout cells, indicating a specific role in scaffolding the signaling cascade.
• The homologous Lys308 residue in arrestin-3 has a different orientation and its alanine substitution did not impair c-Raf1 binding or ERK1/2 activation.

Conclusions:

• Residue Arg307 in arrestin-2 is critical for c-Raf1 interaction and essential for scaffolding the c-Raf1-MEK1-ERK1/2 signaling pathway.
• The Arg307Ala mutation creates a signaling-biased arrestin-2, selectively uncoupling it from ERK activation.
• Arrestin-2 and arrestin-3 utilize distinct molecular mechanisms to facilitate ERK1/2 activation despite performing similar functions.