Different mechanisms regulate lysophosphatidic acid (LPA)-dependent versus phorbol ester-dependent internalization of the LPA₁ receptor

Lysophosphatidic acid (LPA) stimulates cells by activation of five G-protein-coupled receptors, termed LPA_1-5. The LPA₁ receptor is the most widely expressed and is a major regulator of cell migration. In this study, we show that phorbol ester (PMA)-induced internalization of the LPA₁ receptor requires clathrin AP-2 complexes, protein kinase C, and a distal dileucine motif (amino acids 352 and 353) in the cytoplasmic tail but not β-arrestin. Agonist-dependent internalization of LPA₁, however, requires a cluster of serine residues (amino acids 341-347) located proximal to the dileucine motif, β-arrestin, and to a lesser extent clathrin AP-2. The serine cluster of LPA₁ is required for β-arrestin2-GFP translocation to the plasma membrane and signal desensitization. In contrast, the dileucine motif (IL) is required for both basal and PMA-induced internalization. Evidence for the β-arrestin independence of PMA-induced internalization of LPA₁ comes from the observations that β-arrestin2-GFP is not recruited to the plasma membrane upon PMA treatment and that LPA₁ is readily internalized in β-arrestin1/2 knock-out mouse embryonic fibroblasts. These results indicate that distinct molecular mechanisms regulate agonist-dependent and PMA-dependent internalization of the LPA₁ receptor.