Dual regulation of lysophosphatidic acid (LPA1) receptor signalling by Ral and GRK

Lysophosphatidic acid (LPA) is a major constituent of blood and is involved in a variety of physiological and pathophysiological processes. LPA signals via the ubiquitously expressed G protein-coupled receptors (GPCRs), LPA1 and LPA2 that are specific for LPA. However, in large, the molecular mechanisms that regulate the signalling of these receptors are unknown. We show that the small GTPase RalA associates with both LPA1 and LPA2 in human embryonic kidney (HEK 293) cells and that stimulation of LPA1 receptors with LPA triggers the activation of RalA. While RalA was not found to play a role in the endocytosis of LPA receptors, we reveal that LPA1 receptor stimulation promoted Ral-dependent phospholipase C activity. Furthermore, we found that GRK2 is required for the desensitization of LPA1 and LPA2 and have identified a novel interaction between RalA and GRK2, which is promoted by LPA1 receptor activity. Taken together, these results establish RalA and GRK2 as key regulators of LPA receptor signalling and demonstrate for the first time that LPA1 activity facilitates the formation of a novel protein complex between these two proteins.