Early Activation of Sphingosine Kinase in Mast Cells and Recruitment to FcεRI Are Mediated by Its Interaction with Lyn Kinase

Abstract

Sphingosine kinase has been recognized as an essential signaling molecule that mediates the intracellular conversion of sphingosine to sphingosine-1-phosphate. In mast cells, induction of sphingosine kinase and generation of sphingosine-1-phosphate have been linked to the initial rise in Ca 2؉ , released from internal stores, and to degranulation. These events either precede or are concomitant with the activation of phospholipase C-␥ and the generation of inositol trisphosphate. Here we show that sphingosine kinase type 1 (SPHK1) interacts directly with the tyrosine kinase Lyn and that this interaction leads to the recruitment of this lipid kinase to the high-affinity receptor for immunoglobulin E (FcRI). The interaction of SPHK1 with Lyn caused enhanced lipid and tyrosine kinase activity. After FcRI triggering, enhanced sphingosine kinase activity was associated with FcRI in sphingolipid-enriched rafts of mast cells. Bone marrow-derived mast cells from Lyn ؊/؊ mice, compared to syngeneic wild-type cells, were defective in the initial induction of SPHK1 activity, and the defect was overcome by retroviral Lyn expression. These findings position the activation of SPHK1 as an FcRI proximal event.In addition to the importance of sphingolipids in membrane structure, the sphingomyelin pathway with its lipid products ceramide, sphingosine (S), and S-1-phosphate (S1P) has been recognized to function in a variety of signaling events (3, 36). Many of the sphingolipids generated along this pathway are secreted and bind specific cellular receptors on a variety of cell types. On the other hand, they also function intracellularly as "second messenger molecules" similar to the various intermediates of phosphoglyceride metabolism (3, 36). Processes such as apoptosis, differentiation, and cell activation are directly regulated or fine-tuned by ceramide and its derivatives. However, in contrast to glycerolipids, the individual concentrations of various intracellular sphingolipids serve to balance cell activation and inactivation. This concept has been termed the sphingolipid rheostat (3). Specific examples include ceramide and S1P, whose relative intracellular concentration regulates apoptosis; S and S1P, which regulates immunoglobulin E-antigen (IgE-Ag) sensitivity in mast cells; and ceramide and ceramide-1-phosphate, which regulates the process of phagocytosis in macrophages (2,14,29,37,42,43). An essential cellular checkpoint in the sphingomyelin signaling pathway is S kinase (SPHK), as its product S1P is able to counteract ceramide as well as S-mediated effects in apoptosis and effector function regulation (e.g., inhibition of cytokine induction by S in mast cells). In humans, two different isoforms and several splice variants of SPHK were described and cloned (34). While activation of SPHK1 has been firmly established (e.g., after FcεRI and Fc␥RI signaling), its relationship to other known mast cell signaling molecules is still unexplored (24, 37). Recent data on Fc␥RI positioned SPHK downstream of phospholipase D, with a de...

Chapter 3 New Insights on Mast Cell Activation via the High Affinity Receptor for IgE

“…However, the evidence gathered to date suggests that a complex interplay of protein kinase-and lipid-derived signals are required in an apparent two step process in which SphKs translocate rapidly to plasma membranes and become active following FcεRI engagement (Olivera and Rivera, 2005;Olivera et al, 2006;Urtz et al, 2004). At the moment it has been difficult to resolve whether the translocation of SphKs to the plasma membrane is essential for activation or whether it is a consequence of activation.…”

“…At the moment it has been difficult to resolve whether the translocation of SphKs to the plasma membrane is essential for activation or whether it is a consequence of activation. Regardless, under circumstances where the stimulation of SphK by FcεRI is impaired there is also no translocation of SphK to membranes Urtz et al, 2004). We now know that the FcεRI-mediated translocation and activation of SphKs requires both Fyn and Lyn (Fig.…”

Role of ABCC1 in export of sphingosine-1-phosphate from mast cells

“…Previous studies with human bone marrow-derived mast cells (29) and RBL-2H3 mast cells (13,16) have shown that SphK1 is primarily cytosolic and is rapidly translocated to the plasma membrane by Ag. Fc RI crosslinking activates both SphK1 and SphK2 and requires the Src protein tyrosine kinases Lyn (33) and Fyn (4). The finding that SCF, an important growth factor required for mast cell survival and differentiation, also activates SphKs (4) further emphasizes the importance of S1P in mast cells.…”

Distinct roles of sphingosine kinases 1 and 2 in human mast-cell functions

“…Following interaction with Lyn, SphK1 is recruited to membrane rafts where conformational changes may occur in both kinases that favor their respective activities. 8 Although activation of both SphK1 and SphK2 required Fyn kinase in murine BMMCs, only SphK1 activation was dependent on the adapter Grb2-associated binder 2 and phosphatidylinositol 3-kinase. 9 Based on results with fetal liver-derived MCs from SphK1 Ϫ/Ϫ , SphK2 Ϫ/Ϫ , and SphK1 Ϫ/Ϫ SphK2 Ϫ/Ϫ mice, it was suggested that SphK2, but not SphK1, may modulate calcium influx and downstream signaling, particularly PKC␣ and ␤, leading to degranulation and the production of eicosanoids and cytokines.…”

“…4 In rodent MCs and human bone marrow-derived mast cells (BMMCs), aggregation of Fc⑀RI leads to activation of both isoforms of sphingosine kinase, SphK1 and SphK2, the enzymes that produce S1P from sphingosine. 4,[6][7][8] Down-regulation of SphK1 but not SphK2 in these MCs inhibits calcium mobilization, degranulation, and migration induced by Ag. 4,6,7 In human BMMCs and murine MCs, SphK1 translocates to the plasma membrane within minutes of Fc⑀RI clustering.…”