Signalling mechanisms in sphingosine 1-phosphate-promoted mesangial cell proliferation.
BACKGROUND
The bioactive sphingolipid sphingosine 1-phosphate (S1P) is formed by the activation of sphingosine kinase (SPHK) in diverse stimuli, such as platelet-derived growth factor (PDGF). S1P acts not only as an extracellular mediator but also as an intracellular second messenger, resulting in the proliferation of various different types of cells. However, the signal transduction mechanism in S1P-induced proliferation of mesangial cells is poorly known.


RESULTS
We examined the signalling mechanisms by which S1P and dihydro-S1P (DHS1P), another S1P receptor agonist, induce mesangial cell proliferation. We first observed that exogenous S1P/DHS1P had additive effects on the PDGF-promoted proliferation of mesangial cells. Treatment of mesangial cells with pertussis toxin almost completely inhibited S1P- and DHS1P-induced, and slightly inhibited PDGF-induced cell proliferation. Additionally, the ERK kinase inhibitor PD98059 partially blocked the proliferation of mesangial cells induced by all these ligands. N,N-dimethylsphingosine, a competitive inhibitor of SPHK, reduced PDGF-induced mesangial cell proliferation, whereas over-expression of SPHK promoted it. We also revealed that PDGF induces SPHK mRNA expression and SPHK activity, suggesting that SPHK, which links the PDGF to the S1P signalling cascade, is, at least in part, involved in PDGF-induced mesangial cell proliferation. Moreover, we found that extracellular S1P stimulates two S1P receptors, EDG3 and EDG5, which leads to cell proliferation and survival.


CONCLUSIONS
The data show that S1P-induced mesangial cell proliferation is mediated by EDG-dependent and -independent signalling pathways. S1P may cooperate with PDGF to increase the proliferation of mesangial cells during pathophysiological processes.
Katsuma
Susumu
S
Department of Molecular, Cell Pharmacology, National Center for Child Health and Development Research Institute, 3-35-31, Taishido, Setagaya-Ku, Tokyo 154-8567, Japan.
Hada
Yuko
Y
Ueda
Toshihiro
T
Shiojima
Satoshi
S
Hirasawa
Akira
A
Tanoue
Akito
A
Takagaki
Kazuchika
K
Ohgi
Tadaaki
T
Yano
Junichi
J
Tsujimoto
Gozoh
G
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002455:Cell Division / Q000502:physiology*; D002478:Cells, Cultured; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D017781:Genes, Immediate-Early; D005920:Glomerular Mesangium / Q000166:cytology* / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008246:Lysophospholipids; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D037342:Pertussis Toxin / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D049312:Receptors, Lysophospholipid; D015398:Signal Transduction / Q000502:physiology*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D005419:Flavonoids; D008246:Lysophospholipids; D010982:Platelet-Derived Growth Factor; D043562:Receptors, G-Protein-Coupled; D049312:Receptors, Lysophospholipid; C060504:dihydrosphingosine 1-phosphate; C060506:sphingosine 1-phosphate; D037342:Pertussis Toxin; D020928:Mitogen-Activated Protein Kinases; D013110:Sphingosine; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one