Journal of Pharmacological Sciences (Jan 2004)

Enhancement of Sphingosine 1-Phosphate-Induced Phospholipase C Activation During G0-G1 Transition in Rat Hepatocytes

  • Dong-Soon Im,
  • Hideaki Tomura,
  • Masayuki Tobe,
  • Koichi Sato,
  • Fumikazu Okajima

DOI
https://doi.org/10.1254/jphs.fpj04007x
Journal volume & issue
Vol. 95, no. 2
pp. 284 – 290

Abstract

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We previously reported that sphingosine 1-phosphate (S1P) induces inhibition of adenylyl cyclase and activation of phospholipase C via independent G protein-coupled receptors in adult rat hepatocytes. Although S1P activation of phospholipase C and subsequent increase of intracellular Ca2+ concentration were enhanced during the primary culture of hepatocytes, S1P inhibition of adenylyl cyclase remained unchanged. Here, we addressed whether enhancement of S1P-induced actions is dependent on change of status from the differentiated (G0) phase to proliferating (G1/S) phase in hepatocytes. By employing cell-density-dependency of the transition (G0-G1) of hepatocytes in primary culture in vitro, it was found that the enhancement of phospholipase C activation by S1P was dependent on cell density and correlated to the G0-G1 transition. The correlation was further confirmed in vivo by 70% hepatectomy as a proliferating hepatocytes model. Northern blot analysis suggested an enhanced expression of S1P2 receptor in proliferating hepatocytes. Keywords:: hepatocyte, sphingosine 1-phosphate, phospholipase C, G protein-coupled receptor, cell cycle