title: The GPR55 ligand L-alpha-lysophosphatidylinositol promotes RhoA-dependent Ca2+ signaling and NFAT activation.
abstract: The endogenous phospholipid l-alpha-lysophosphatidylinositol (LPI) was recently identified as a novel ligand for the orphan G protein-coupled receptor 55 (GPR55). In this study we define the downstream signaling pathways activated by LPI in a human embryonic kidney (HEK) 293 cell line engineered to stably express recombinant human GPR55. We find that treatment with LPI induces marked GPR55 internalization and stimulates a sustained, oscillatory Ca(2+) release pathway, which is dependent on Galpha13 and requires RhoA activation. We then establish that this signaling cascade leads to the efficient activation of NFAT (nuclear factor of activated T cells) family transcription factors and their nuclear translocation. Analysis of cannabinoid ligand activity at GPR55 revealed no clear effect of the endocannabinoids anandamide and 2-arachidonoylglycerol; however, the classical CB(1) antagonist AM251 evoked GPR55-mediated Ca(2+) signaling. Thus, LPI is a potent and efficacious ligand at GPR55, which is likely to be a key plasma membrane mediator of LPI-mediated signaling events and changes in gene expression.
authors.affiliation: Centre for Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Henstridge
authors.forename: Nariman A B
authors.initials: NA
authors.lastname: Balenga
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Ford
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Ross
authors.forename: Maria
authors.initials: M
authors.lastname: Waldhoer
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Irving