Sphingosine 1-Phosphate and Platelet-derived Growth Factor (PDGF) Act via PDGFβ Receptor-Sphingosine 1-Phosphate Receptor Complexes in Airway Smooth Muscle Cells

Abstract

Platelet-derived growth factor (PDGF) and sphingosine 1-phosphate (S1P) act via PDGF␤ receptor-S1P 1 receptor complexes in airway smooth muscle cells to promote mitogenic signaling. Several lines of evidence support this conclusion. First, both receptors were co-immunoprecipitated from cell lysates with specific anti-S1P 1 antibodies, indicating that they form a complex. Second, treatment of airway smooth muscle cells with PDGF stimulated the phosphorylation of p42/p44 MAPK, and this phosphorylated p42/p44 MAPK associates with the PDGF␤ receptor-S1P 1 receptor complex. Third, treatment of cells with antisense S1P 1 receptor plasmid construct reduced the PDGF-and S1P-dependent activation of p42/p44 MAPK. Fourth, S1P and/or PDGF induced the formation of endocytic vesicles containing both PDGF␤ receptors and S1P 1 receptors, which was required for activation of the p42/ p44 MAPK pathway. PDGF does not induce the release of S1P, suggesting the absence of a sequential mechanism. However, sphingosine kinase 1 is constitutively exported from cells and supports activation of p42/p44 MAPK by exogenous sphingosine. Thus, the presentation of sphingosine from other cell types and its conversion to S1P by the kinase exported from airway smooth muscle cells might enable S1P to act with PDGF on the PDGF␤ receptor-S1P 1 receptor complex to induce biological responses in vivo. These data provide further evidence for a novel mechanism for G-protein-coupled receptor and receptor tyrosine kinase signal integration that is distinct from the transactivation of receptor tyrosine kinases by G-proteincoupled receptor agonists and/or sequential release and action of S1P in response to PDGF. Sphingosine 1-phosphate (S1P)1 is a bioactive lysolipid that has been proposed to have both intracellular and extracellular actions (1). To date, five closely related G-protein-coupled receptors (GPCR), termed S1P 1 -S1P 5 (2) (and formerly named EDG1, EDG5/AGR16/H218, EDG3, EDG6 and EDG8/nrg-1, respectively) have been identified as high affinity S1P receptors (3-9). Further characterization studies confirmed the S1P 1 receptor to be a GPCR with high affinity for S1P that stimulates p42/p44 MAPK and inhibits adenylyl cyclase in cells (10 -13). The S1P 2 and S1P 3 receptors also have high affinity for S1P (14) and are linked via G q to phospholipase C and calcium mobilization and p42/p44 MAPK activation (14, 15) and via G 12 and G 13 to Rhoguanine nucleotide factor and Rho activation. The S1P 4 receptor is lymphoid specific and, in common with the S1P 5 receptor, uses G i/o and G 12 to signal (6, 8).The S1P 1 receptor is implicated in regulating smooth muscle cell migration, proliferation, and vascular maturation. Insight into the function of the S1P 1 receptor was obtained by studies showing that disruption of the s1p 1 gene by homologous recombination in mice results in extensive intra-embryonic hemorrhaging and intrauterine (16). This is caused by incomplete vascular maturation due to the failure of mural cells, vascular smooth muscle cells, and per...

The Insulin-like Growth Factor Type 1 and Insulin-like Growth Factor Type 2/Mannose-6-phosphate Receptors Independently Regulate ERK1/2 Activity in HEK293 Cells

“…Nonetheless, it is clear that heterotrimeric G proteins mediate a subset of signals initiated by diverse non-heptahelical receptors, including the insulin, IGF-1, EGF, and platelet-derived growth factor receptor tyrosine kinases and single membrane-spanning receptors for C-type natriuretic peptide and zona pellucida glycoprotein, integrins, and T cell receptors (49). Apart from our results with the IGF-1 and IGF-2/M6P receptors (31), heterotrimeric G protein activation resulting from SK1-dependent transactivation of S1P receptors has been shown to account for pertussis toxin-sensitive signaling by plateletderived growth factor receptor (50,51). Based on this small but growing body of evidence, it is tempting to speculate that S1P receptor transactivation represents a common mechanism of signal convergence that permits structurally diverse non-GPCRs to access heterotrimeric G protein signaling pathways.…”

Involvement of Smad Signaling in Sphingosine 1-Phosphate-mediated Biological Responses of Keratinocytes

“…Indeed, similar interactions have also been suggested between GPCR and receptor tyrosine kinases, since there exists a transactivation of S1P 1 with the PDGF receptor (26,27,34,54). In these reports, it has been shown that cell migration toward PDGF is dependent on expression of S1P 1 , and moreover PDGF is capable of activating this S1P receptor.…”

“…S1P receptors are also known to cross-communicate with other GPCRs as well as other plasma membrane receptors, including receptor-tyrosine kinases (24 -26). For example, S1P and platelet-derived growth factor (PDGF) have been shown to act via PDGF-␤-and S1P 1 -receptor complexes in airway smooth muscle cells (27).…”

Insulin-like Growth Factors Mediate Heterotrimeric G Protein-dependent ERK1/2 Activation by Transactivating Sphingosine 1-Phosphate Receptors

“…Similar apparently conflicting data exist for the PDGF receptor. Although some evidence suggests that PDGF activates SK1 and causes S1P-dependent S1P receptor activation (36), other data suggest that crosstalk between PDGF and S1P receptors occurs in the context of a physical complex between the two receptors (37,54,55). Whichever model is ultimately correct, both incorporate the notion that a heptahelical S1P receptor functions as an intermediate in PDGF receptor-mediated G protein activation.…”

“…The second model advanced to explain heterotrimeric G protein-dependent signaling by non-GPCRs is that the receptors generate some signal that activates an endogenous GPCR, which in turn catalyzes G protein activation. For example, the platelet-derived growth factor (PDGF) receptor has been shown to activate sphingosine kinase (SK) and cause recruitment of ␤-arrestins to G protein-coupled sphingosine 1-phosphate (S1P) receptors (36,37). However the evidence that this might represent a general model of GPCR transactivation is presently limited.…”