Antiproliferative property of sphingosine 1-phosphate in rat hepatocytes involves activation of Rho via Edg-5.
OBJECTIVE
Sphingosine 1-phosphate (S1P), a ligand for G protein-coupled endothelial differentiation gene-1 (Edg-1), Edg-3, Edg-5, Edg-6, and Edg-8, elicits a variety of responses by cells. Prominent among these is cell proliferation. S1P is abundantly stored in platelets and released upon their activation, suggesting that S1P plays a pathophysiologic role in vivo. Because the major part of injected S1P was distributed into the liver in mice, we wondered whether the liver would be one of its targets. The effects of S1P on hepatocytes, the major constituent cells in the liver, were examined.


RESULTS
Northern blot analysis revealed the expression of Edg-1 and Edg-5 messenger RNA (mRNA) in cultured rat hepatocytes, in which S1P decreased DNA synthesis induced by hepatocyte growth factor (HGF) or epidermal growth factor (EGF) without affecting total protein synthesis. This inhibitory effect was attenuated by inactivation of small GTPase Rho with C3 exotoxin but not by inactivation of G(i) with pertussis toxin. Moreover, in the presence of JTE-013, a newly developed and specific binding antagonist for Edg-5, the inhibitory effect was also cancelled. Finally, the administration of S1P after 70% partial hepatectomy in rats reduced the peak of DNA synthesis in hepatocytes with increased Rho activity. Furthermore, Edg-5 but not Edg-1 mRNA expression was enhanced in hepatocytes 24-72 hours after partial hepatectomy, which coincides with decreasing hepatocyte proliferation.


CONCLUSIONS
S1P has an antiproliferative property in rat hepatocytes by activating Rho via Edg-5. Our results raise the possibility that S1P is a negative regulator in liver regeneration.
Ikeda
Hitoshi
H
Department of Gastroenterology, University of Tokyo, Japan. ikeda-1im@h.u-tokyo.ac.jp
Satoh
Hiroaki
H
Yanase
Mikio
M
Inoue
Yukiko
Y
Tomiya
Tomoaki
T
Arai
Masahiro
M
Tejima
Kazuaki
K
Nagashima
Kayo
K
Maekawa
Hisato
H
Yahagi
Naohisa
N
Yatomi
Yutaka
Y
Sakurada
Soutaro
S
Takuwa
Yoh
Y
Ogata
Itsuro
I
Kimura
Satoshi
S
Fujiwara
Kenji
K
D036002:ADP Ribose Transferases / Q000494:pharmacology; D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D006224:Cricetinae; D004247:DNA / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008115:Liver Regeneration / Q000502:physiology; D008246:Lysophospholipids; D008297:Male; D037342:Pertussis Toxin / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled; D049312:Receptors, Lysophospholipid; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000502:physiology*
C471998:JTE 013; D008246:Lysophospholipids; D011720:Pyrazoles; D011725:Pyridines; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D049312:Receptors, Lysophospholipid; C060506:sphingosine 1-phosphate; D004247:DNA; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D037342:Pertussis Toxin; D001905:Botulinum Toxins; D020741:rho GTP-Binding Proteins; D013110:Sphingosine