title: Ganglioside GM3 activates ERKs in human lymphocytic cells.
abstract: In this study we analyzed the signaling pathway triggered by GM3 in lymphoblastoid T-cells. In these cells, GM3 induced cPLA2 activation, arachidonic acid release, and PKC-delta translocation. In order to clarify the upstream molecular signals triggered by GM3, we analyzed the activation of extracellular signal-regulated kinase (ERK)s, a downstream effector of Ras-regulated cytoplasmic kinase cascade. Our results showed that GM3 treatment led to rapid ERK phosphorylation in lymphoblastoid T-cells, as detected by anti-phospho-p44/42 MAP kinase. Similar findings were found in human peripheral blood lymphocytes. Moreover, we showed that GM3 specifically phosphorylated ERK-2, as revealed by anti-phosphotyrosine reactivity on both cell free lysates and ERKs immunoprecipitates. The role of the CD4 cytoplasmic domain in GM3-triggered signaling pathway was investigated using A2.01/CD4-cyt399 cells, which had been transfected with a mutant form of CD4 lacking the bulk of the cytoplasmic domain. In these cells GM3 induced cPLA2 activation, arachidonic acid release, and PKC-delta translocation, but not CD4 endocytosis, indicating that the CD4 cytoplasmic domain plays a key role in GM3-triggered CD4 endocytosis and the GM3-triggered biochemical pathway is upstream of CD4 phosphorylation. These findings strongly suggest that GM3 triggers a novel signaling pathway involved in the regulation of cellular functions.
authors.affiliation: Dipartimento di Medicina Sperimentale, Università di L'Aquila, Via Vetoio Coppito 2, L'Aquila 67100, Italy.
authors.forename: Tina
authors.initials: T
authors.lastname: Garofalo
authors.forename: Maurizio
authors.initials: M
authors.lastname: Sorice
authors.forename: Roberta
authors.initials: R
authors.lastname: Misasi
authors.forename: Benedetta
authors.initials: B
authors.lastname: Cinque
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Mattei
authors.forename: Giuseppe M
authors.initials: GM
authors.lastname: Pontieri
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Cifone
authors.forename: Antonio
authors.initials: A
authors.lastname: Pavan
mesh_terms: D015704:CD4 Antigens / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D015536:Down-Regulation; D005679:G(M3) Ganglioside / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051745:Protein Kinase C-delta
chemical_list: D015704:CD4 Antigens; D005679:G(M3) Ganglioside; D007527:Isoenzymes; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D020928:Mitogen-Activated Protein Kinases; D010741:Phospholipases A