title: Lysophosphatidylcholine enhances NGF-induced MAPK and Akt signals through the extracellular domain of TrkA in PC12 cells.
abstract: Lysophosphatidylcholine (LPC) is one of the major lysophospholipids mainly generated by phospholipase A2 (PLA2)-mediated hydrolysis of phosphatidylcholine (PC). We previously found that LPC displays neurotrophin-like activity in the rat pheochromocytoma PC12 cells and in cerebellar granule neurons, but the molecular mechanism remains unclear. We report here that LPC specifically enhances nerve growth factor (NGF)-induced signals in PC12 cells. When PC12 cells were treated with NGF, MAPK was phosphorylated, but this phosphorylation was significantly elevated when LPC was added together. In accordance, NGF-induced expression of immediate early genes, c-fos and NGF-IA, was upregulated by LPC. Phosphorylation of the upstream components, MEK and NGF receptor TrkA, was also promoted by LPC, which was in line with increased phosphorylation of Akt. In contrast, LPC did not enhance epidermal growth factor (EGF)-, basic fibroblast growth factor-, or insulin-like growth factor-1-induced signals. Studies using TrkA/EGF receptor chimeras demonstrated that the extracellular domain, but not the transmembrane or intracellular domains, of TrkA is responsible for the effect of LPC. Exogenously-added secretory PLA2 (sPLA2) enhanced NGF-induced MAPK phosphorylation at a comparable level to LPC, suggesting that LPC generated in situ by sPLA2-mediated hydrolysis of membrane PC stimulated NGF-TrkA signal. Taken together, these results indicate a specific role and function of LPC on NGF-TrkA signaling pathway.
authors.affiliation: Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.lastname: Wuhanqimuge
authors.forename: Asako
authors.initials: A
authors.lastname: Itakura
authors.forename: Yuri
authors.initials: Y
authors.lastname: Matsuki
authors.forename: Masato
authors.initials: M
authors.lastname: Tanaka
authors.forename: Manabu
authors.initials: M
authors.lastname: Arioka
keywords: Akt; BDNF, brain-derived neurotrophic factor; CGNs, cerebellar granule neurons; DMEM, Dulbecco’s modified Eagle’s medium; EGF, epidermal growth factor; EGFP, enhanced green fluorescent protein; EGFR, EGF receptor; GPCR, G protein-coupled receptors; IGF-1, insulin-like growth factor-1; LPA, lysophosphatidic acid; LPC, lysophosphatidylcholine; LPE, lysophosphatidylethanolamine; LPS, lysophosphatidylserine; Lysophosphatidylcholine; MAPK, mitogen-activated protein kinase; MEK, mitogen-activated protein kinase kinase; Mitogen-activated protein kinase (MAPK); NGF, nerve growth factor; Nerve growth factor; PC, phosphatidylcholine; PI3K, phosphatidylinositol 3-kinase; PLA2, phospholipase A2; RT-PCR, reverse transcription-polymerase chain reaction; SDS, sodium dodecyl sulfate; TTBS, Tris-buffered saline containing 0.01% Tween 20; TrkA; bFGF, basic fibroblast growth factor; sPLA2, secretory PLA2