Retroviral Gene Transfer of Signaling Molecules Into Murine Fetal Hepatocytes Defines Distinct Roles for the Stat3 and Ras Pathways During Hepatic Development

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Abstract
We recently demonstrated that oncostatin M (OSM) in the presence of glucocorticoid promotes development of fetal hepatic cells in a primary culture system. Our results also suggested that OSM transduces differentiation signals through gp130, a common subunit of the interleukin (IL)–6 family cytokine receptors. However, an essential downstream pathway required for hepatic development remains unknown. To address this issue, we expressed signal molecules by a retroviral expression vector in primary fetal hepatic cells and investigated a signaling pathway essential for OSM–mediated hepatic development. Expression of a dominant–negative form of STAT3 (ΔSTAT3), but not ΔSTAT5, suppressed differentiated phenotypes of hepatocytes induced by OSM. On the other hand, dominant–negative forms of Ras (RasN17) and SHP–2(C463A) rather augmented the expression of hepatic differentiation markers, suggesting that the Ras pathway negatively regulates hepatic development. Consistently, expression of a constitutively activated form of Ras (RasV12) inhibited cellular responses to OSM. Our results indicate that STAT3 is an essential signaling component for OSM–induced hepatic development, while activation of Ras appears to negatively regulate this process. Thus, retrovirus–mediated gene transfer is an effective means to analyze function of a gene in primary fetal hepatic culture.
Funding Information
  • Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan
  • Core Research for Evolutionary Science and Technology (CREST), Riken
  • Uehara Memorial Foundation