PT  - JOURNAL ARTICLE
AU  - Rudi Prihandoko
AU  - Elisa Alvarez-Curto
AU  - Brian D. Hudson
AU  - Adrian J. Butcher
AU  - Trond Ulven
AU  - Ashley M. Miller
AU  - Andrew B. Tobin
AU  - Graeme Milligan
TI  - Distinct Phosphorylation Clusters Determine the Signaling Outcome of Free Fatty Acid Receptor 4/G Protein–Coupled Receptor 120
AID  - 10.1124/mol.115.101949
DP  - 2016 May 01
TA  - Molecular Pharmacology
PG  - 505--520
VI  - 89
IP  - 5
4099  - http://molpharm.aspetjournals.org/content/89/5/505.short
4100  - http://molpharm.aspetjournals.org/content/89/5/505.full
SO  - Mol Pharmacol2016 May 01; 89
AB  - It is established that long-chain free fatty acids including ω-3 fatty acids mediate an array of biologic responses through members of the free fatty acid (FFA) receptor family, which includes FFA4. However, the signaling mechanisms and modes of regulation of this receptor class remain unclear. Here, we employed mass spectrometry to determine that phosphorylation of mouse (m)FFAR4 occurs at five serine and threonine residues clustered in two separable regions of the C-terminal tail, designated cluster 1 (Thr347, Thr349, and Ser350) and cluster 2 (Ser357 and Ser361). Mutation of these phosphoacceptor sites to alanine completely prevented phosphorylation of mFFA4 but did not limit receptor coupling to extracellular signal regulated protein kinase 1 and 2 (ERK1/2) activation. Rather, an inhibitor of Gq/11 proteins completely prevented receptor signaling to ERK1/2. By contrast, the recruitment of arrestin 3, receptor internalization, and activation of Akt were regulated by mFFA4 phosphorylation. The analysis of mFFA4 phosphorylation-dependent signaling was extended further by selective mutations of the phosphoacceptor sites. Mutations within cluster 2 did not affect agonist activation of Akt but instead significantly compromised receptor internalization and arrestin 3 recruitment. Distinctly, mutation of the phosphoacceptor sites within cluster 1 had no effect on receptor internalization and had a less extensive effect on arrestin 3 recruitment but significantly uncoupled the receptor from Akt activation. These unique observations define differential effects on signaling mediated by phosphorylation at distinct locations. This hallmark feature supports the possibility that the signaling outcome of mFFA4 activation can be determined by the pattern of phosphorylation (phosphorylation barcode) at the C terminus of the receptor.