Role of Sphingosine-1-phosphate Phosphatase 1 in Epidermal Growth Factor-induced Chemotaxis

Abstract

Sphingosine-1-phosphate (S1P) is the ligand for a family of specific G protein-coupled receptors that regulate a wide variety of cellular functions, including cytoskeletal rearrangements and cell motility. Because of the pivotal role of S1P, its levels are low and tightly regulated in a spatial-temporal manner through its synthesis catalyzed by sphingosine kinases and degradation by an S1P lyase and specific S1P phosphatases (SPP). Surprisingly, down-regulation of SPP-1 enhanced migration toward epidermal growth factor (EGF); conversely, overexpression of SPP-1, which is localized in the endoplasmic reticulum, attenuated migration toward EGF. To determine whether the inhibitory effect on EGF-induced migration was because of decreased S1P or increased ceramide as a consequence of acylation of increased sphingosine by ceramide synthase, we used fumonisin B1, a specific inhibitor of ceramide synthase. Although fumonisin B1 blocked ceramide production and increased sphingosine, it did not reverse the negative effect of SPP-1 expression on EGF-or S1P-induced chemotaxis. EGF activated the epidermal growth factor receptor to the same extent in SPP-1-expressing cells, yet ERK1/2 activation was impaired. In agreement, PD98059, an inhibitor of the ERK-activating enzyme MEK, decreased EGF-stimulated migration. We next examined the possibility that intracellularly generated S1P might be involved in activating a G protein-coupled S1P receptor important for EGF-directed migration. Treatment with pertussis toxin to inactivate G␣ i suppressed EGF-induced migration. Moreover, expression of regulator of G protein signaling 3, which inhibits S1P receptor signaling and completely prevented ERK1/2 activation mediated by S1P receptors, not only reduced migration toward S1P but also markedly reduced migration toward EGF. Collectively, these results suggest that metabolism of S1P by SPP-1 is important for EGF-directed cell migration.The bioactive sphingolipid, sphingosine-1-phosphate (S1P), 1 is a ligand for a family of five specific G protein-coupled receptors (S1P 1 , S1P 2 , S1P 3 , S1P 4 , and S1P 5 ) (1) that are coupled to various G proteins. These receptors regulate diverse cellular processes and have been implicated in cytoskeletal rearrangement and regulation of cell movement (2, 3). The founding member of this receptor family, S1P 1 , couples to a G i pathway (4), and its gene disruption in mice demonstrated an essential function for vascular maturation (5). More recently, several studies have established that S1P 1 is also essential for lymphocyte recirculation and that it regulates egress from peripheral lymphoid organs (6, 7). In addition to its extracellular functions, S1P acts intracellularly to regulate cell survival (8), yet its direct targets have not yet been elucidated.As with other potent lipid mediators, levels of S1P are low and tightly regulated in a spatial-temporal manner. Sphingosine kinase (SphK) catalyzes the synthesis of S1P (2), which can be irreversibly degraded by S1P lyase (9 -11) and reversibly conver...

Recycling of Sphingosine Is Regulated by the Concerted Actions of Sphingosine-1-phosphate Phosphohydrolase 1 and Sphingosine Kinase 2

“…Moreover, increased intracellular and secreted S1P due to down-regulation of SPP-1 regulates "inside-out" S1P signals through its cell surface receptors (18). In agreement, regulation of intracellular levels of S1P by SPP-1 plays an important role in epidermal growth factor-directed cell movement (19).…”

Sphingosine-1-phosphate Phosphatase 1 Regulates Keratinocyte Differentiation and Epidermal Homeostasis

“…SPP1 has been shown to regulate apoptosis by elevating ceramide levels (15), ER-to-Golgi ceramide trafficking (21), and autophagy induced by ER stress (22,23). In addition, its effects on S1P levels influence resistance artery tone (24) and cell migration (25). SPP2 has been found to be elevated during immune responses (26).…”

Involvement of Sphingosine Kinases/Sphingosine-1-Phosphate (S1P)/S1P Receptors in Breast Cancer Subtypes

“…Ceramide, sphingosine and S1P are readily inter-convertible and the balance between these sphingolipids is tightly regulated by SphKs, S1P phosphatase and type 2 phosphatidate phosphohydrolase. These three major sphingolipid metabolites have been the focus of many studies as they possess opposing biological functions where ceramide and sphingosine regulate stress responses such as apoptosis and cell senescence while S1P induces cell migration, survival, proliferation, angiogenesis and inflammation [6][7][8][9]. Therefore, SphKs act as a rheostat of ceramide, sphingosine and S1P; SphKs play a crucial role in determining the fate of a cell.…”

“…These sphingolipids are inter-convertible within cells and their balance is tightly modulated by actions of enzymes including ceramidases, ceramide synthases, SphKs, and S1P phosphatase. The balance of these sphingolipids determine cell fat as ceramide/ sphingosine and S1P possess opposite biological functions where ceramide mediates induction of apoptosis and cell senescence while S1P promotes cell survival, migration and inflammation [6][7][8][9]. S1P can act both intracellularly as second messenger or bind to the five S1PRs to regulate downstream signaling [7,10,11].…”