Activation and nuclear translocation of ERK1/2 by the formyl peptide receptor is regulated by G protein and is not dependent on beta-arrestin translocation or receptor endocytosis

Abstract

G protein-coupled receptors (GPCRs) transmit diverse cellular signals in response to a large number of stimuli such as chemoattractants, lipids, neurotransmitters, odorants and light. The classical signaling pathway is through heterotrimeric G proteins, but GPCRs can also transmit signals through mechanisms that are not dependent on G proteins. In mammalian cells, the key component for this type of signaling is the family of scaffolding molecules called beta-arrestins. They can function as scaffolds for activation of mitogen-activated protein kinases, including extracellular signal-regulated kinases 1 and 2 (ERK1/2). In this study we examined the role of G protein and beta-arrestin in formyl peptide receptor (FPR)-mediated activation of chemotaxis, receptor endocytosis and ERK1/2 activation using wild type and mutant receptors. Our findings suggest that, unlike certain other GPCRs that can activate ERK1/2 without the involvement of G protein, FPR requires signaling through a G protein-mediated pathway. Previous observations have shown that ERK1/2, activated through G protein, translocates to the nucleus where it stimulates transcription factors. In contrast, the scaffolding protein beta-arrestin retains the activated ERK1/2 in the cytoplasm to allow phosphorylation of cytoplasmic targets. Our experimental data show that both wild-type FPR and a mutant FPR, defective in beta-arrestin binding, induce nuclear translocation of activated ERK1/2 with similar ligand concentration dependence as seen for activation of cytosolic ERK1/2. We propose that FPR-mediated activation of ERK1/2 takes place primarily through G protein and is physiologically important to ensure transcriptional activation of myeloid immunomodulators, such as cytokines.