Ganglioside GM3 activates ERKs in human lymphocytic cells

In this study we analyzed the signaling pathway triggered by GM3 in lymphoblastoid T-cells. In these cells, GM3 induced cPLA 2 activation, arachidonic acid release, and PKC- � translocation. In order to clarify the upstream molecular signals triggered by GM3, we analyzed the activa- tion of extracellular signal-regulated kinase (ERK)s, a down- stream effector of Ras-regulated cytoplasmic kinase cas- cade. 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 cPLA 2 activation, arachidonic acid release, and PKC- � trans- location, 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. —Garofalo, T., M. Sorice, R. Misasi, B. Cinque, V. Mattei, G. M. Pontieri, M. G. Cifone, and A. Pavan. Ganglioside GM3 activates ERKs in human lymphocytic cells. J. Lipid Res. 2002. 43: 971-978.