Glycosphingolipids of Rat T Cells. Predominance of Asialo-GM1 and GD1c

Abstract

Glycosphingolipids play an important role in the immune response, yet their compositions in T and B cells which mediate cellular and humoral immunity, respectively, have not been elucidated. In this study, characteristic features of glycosphingolipids in rat T lineage cells were revealed by comparing the gangliosides and neutral glycolipids of spleen T- and beta-cell-enriched fractions and thymocytes. In T cells, GD1c(NeuGc,NeuGc), a unique ganglioside synthesized through asialo-GM1 (GA1), was the predominant ganglioside as previously found in thymocytes [Nohara, K., Suzuki, M., Inagaki, F., & Kaya, K. (1991) J. Biochem. (Tokyo) 110, 274-278], and the amount was much higher than in thymocytes. In addition, three other GA1-derived gangliosides were detected in T cells and identified as GM1b(NeuAc), GM1b(NeuGc), and GD1 alpha(NeuAc,NeuAc). In contrast, GD1 alpha(NeuAc,NeuAc) was not discernible in thymocytes, although gangliosides corresponding to GM1b(NeuAc) and GM1b(NeuGc) were detected. The neutral glycolipids of T cells contained almost exclusively GA1, while thymocytes contained much lower amounts. The predominance of these GA1-derived gangliosides was confirmed as a singular feature of T lineage cells by comparison with gangliosides of spleen B-cell-enriched fractions which mainly consisted of gangliosides synthesized through GM3 and GM1. Furthermore, the unique structures, which contain the GM1 core and the extended modification of the lacto series, alpha Gal-LacNAc-GM1, alpha Gal-(LacNAc)2-GM1, and sialyl-LacNAc-GM1, were found in B-cell-enriched fractions. Unexpectedly, the neutral glycolipid composition of the thymocytes resembled that of the B-cell enriched fraction rather than that of the T cells.

Inhibition of Invasiveness and Motility of Human Breast Cancer Cells by Sphingosine-1-Phosphate.

“…This is consistent with the conclusion that SPP, formed in response to PDGF, plays an important role in PDGFregulated motility of human arterial smooth muscle cells [16]. Moreover, we have recently demonstrated that several signaling pathways regulated by SPP, including calcium mobilization, activation of phosphlipase D, and tyrosine phosphorylation of FAK, were clearly independent of Edg-1 expression [23].…”

“…This is consistent with the conclusion that SPP, formed in response to PDGF, plays an important role in PDGFregulated motility of human arterial smooth muscle cells [16]. Moreover, we have recently demonstrated that several signaling pathways regulated by SPP, including calcium mobilization, activation of phosphlipase D, and tyrosine phosphorylation of FAK, were clearly independent of Edg-1 expression [23].It was reported that an increased level of FAK expression is highly correlated with invasion potential of human tumor cells [44,45], suggesting that FAK may be limiting for cell invasion. FAK has been indicated as playing a crucial role in cell migration events [36, 9, 46, 47].…”

“…Some of the effects of exogenously added SPP might be due to binding to a specific cell surface receptor. Recently, we have identified endothelial cell differentiation gene-1 (edg-1) as the G-protein-coupled receptor for SPP [28,23]. However, we could only detect extremely low levels of specific SPP binding (9 fmol/ million cells) and MDA-MB-231 cells have no detectable edg-1 mRNA as determined by RT-PCR and Northern analysis (data not shown).…”

“…Cells were incubated for 30 min at 37°C in the presence of 10 JLIM [ 32 P]SPP (64,000 cpm/nmol), washed with medium containing 0.4 mg/ml fatty acid-free BSA, and then incubated at 37°C for the indicated time [23]. Cells were trypsinized and cellular lipids were extracted as described [24].…”

“…free BSA, and then incubated at 37°C for the indicated time [23]. Cells were trypsinized and cellular lipids were extracted as described [24].…”