Molecular regulation of lysophosphatidic acid receptor endocytosis and desensitization

Abstract

Lysophosphatidic Acid (LPA) is a major constituent of serum and is involved in a variety of physiological and pathophysiological processes. LPA signals via the G‐protein coupled receptors (GPCRs), LPA1–3, but the mechanisms regulating LPA receptor desensitization and endocytosis are unknown. GPCRs can internalize via clathrin‐dependent mechanisms and/or lipid rafts and caveolae. We show that Flag‐LPA1 and ‐LPA2 receptors do not partition into lipid rafts of LPA treated human embryonic kidney (HEK) 293 cells suggesting that LPA1 and LPA2 do not internalize via caveolae. Surprisingly, the expression of dynamin‐1 and ‐2 mutant proteins does not affect receptor internalization. We also examined whether RalA and phospholipase Ds, shown to regulate the endocytosis of certain GPCRs, contribute to LPA receptor endocytosis. Although these proteins interact constitutively and co‐localize with both LPA1 and LPA2 in endocytic vesicles, expression of wild‐type or mutant forms of these proteins did not affect receptor internalization. Finally, we observed that the expression of GRK2 and βarrestins mediated the desensitization of LPA1 and LPA2 by attenuating LPA induced inositol phosphate production. In summary, RalA and PLDs may not mediate LPA1 or LPA2 endocytosis, but may act as scaffolding proteins linking the receptors to other signaling pathways.This study is funded by NSERC grant awarded to Dr. M Bhattacharya