Sphingosine-1-phosphate inhibits human keratinocyte proliferation via Akt/protein kinase B inactivation.
Although sphingosine-1-phosphate (S1P) is a well-known mitogen, it has only recently been demonstrated that S1P is able to inhibit cell proliferation in human epidermal keratinocytes and hepatic myofibroblasts. In the present study, we investigated the possible signalling pathways involved in the growth inhibition of human keratinocytes. Our results show that S1P potently inhibits keratinocyte proliferation, and that this leads to the inhibition of DNA synthesis. Interestingly, the prolonged activation of extracellular signal-regulated protein kinase (ERK) and the transient inactivation of Akt/protein kinase B (PKB) were also observed in concert with the inhibition of keratinocyte proliferation by S1P. To verify further the antiproliferative action of S1P, we examined changes in cell cycle-related proteins. S1P inhibited cyclin D(2) synthesis but stimulated p21(WAF1/CIP1) (p21) and p27(KIP1) (p27) synthesis; all are inhibitors of cyclin-dependent kinase. Furthermore, we found that the growth inhibition by S1P was in part abolished by pertussis toxin (PTX) treatment, but that ERK activation and Akt/PKB inhibition were not abrogated, suggesting that S1P functions both intracellularly, as a second messenger, and extracellularly, as a ligand for cell surface receptors. Insulin-like growth factor I (IGF-I) is a well-established human keratinocyte mitogen and is known to stimulate Akt/PKB in various cell types. In the present study, S1P was found to inhibit the keratinocyte proliferation and Akt/PKB activation induced by IGF-I. Our results suggest that S1P may play an important role in the negative regulation of keratinocyte proliferation by inhibiting the Akt/PKB pathway.
Kim
Dong-Seok
DS
Research Division for Human Life Sciences, Seoul National University, 28 Yongon-Dong, Chongno-Gu, Seoul 110-744, South Korea.
Kim
Sook-Young
SY
Kleuser
Burkhard
B
Schäfer-Korting
Monika
M
Kim
Kyu Han
KH
Park
Kyoung-Chan
KC
D000293:Adolescent; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D025461:Feedback, Physiological / Q000187:drug effects / Q000502:physiology; D006131:Growth Inhibitors / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects / Q000201:enzymology*; D008246:Lysophospholipids / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*
D018797:Cell Cycle Proteins; D006131:Growth Inhibitors; D008246:Lysophospholipids; D011518:Proto-Oncogene Proteins; C060506:sphingosine 1-phosphate; D007334:Insulin-Like Growth Factor I; D004247:DNA; D037342:Pertussis Toxin; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D013110:Sphingosine