PT  - JOURNAL ARTICLE
AU  - Sarah-Jane Watson
AU  - Alastair JH Brown
AU  - Nicholas Holliday
TI  - Differential Signalling by Splice Variants of the Human Free Fatty Acid Receptor, GPR120
AID  - 10.1124/mol.111.077388
DP  - 2012 Jan 26
TA  - Molecular Pharmacology
PG  - mol.111.077388
4099  - http://molpharm.aspetjournals.org/content/early/2012/01/26/mol.111.077388.short
4100  - http://molpharm.aspetjournals.org/content/early/2012/01/26/mol.111.077388.full
AB  - GPR120 is a long chain fatty acid receptor that stimulates incretin hormone release from colonic endocrine cells, and is implicated in macrophage and adipocyte function. The functional consequences of long (L) and short (S) human GPR120 splice variants, which differ by insertion of 16 amino acids in the third intracellular loop, are currently unknown. Here we compare signalling and intracellular trafficking of GPR120S and GPR120L receptors, using calcium mobilization and dynamic mass redistribution (DMR) assays, together with quantitative imaging measurements of β-arrestin2 association and receptor internalization. FLAG or SNAP tagged GPR120S receptors elicited both intracellular calcium mobilization and DMR responses in HEK293 cells, when stimulated with oleic acid, myristic acid or the agonist GW9508. Responses were insensitive to Pertussis toxin, but increases in intracellular calcium were attenuated by 2-APB (2-Aminoethoxydiphenyl borate), an inhibitor of store inositol trisphosphate receptors. Despite equivalent cell surface expression of SNAP-tagged GPR120L receptors, no specific calcium or DMR responses were observed in cells transfected with this isoform. However agonist stimulated GPR120S and GPR120L receptors both recruited β-arrestin2 and underwent robust internalization, with similar agonist potencies in each case. Following oleic acid induced internalization, neither GPR120 isoform recycled rapidly to the cell surface. In both cases confocal microscopy indicated receptor targeting to lysosomal compartments. Thus, the third intracellular loop insertion in GPR120L prevents G protein dependent intracellular calcium and DMR responses, but this receptor isoform remains functionally coupled to the β-arrestin pathway, providing one of the first examples of a native β-arrestin biased receptor