Retroviral gene transfer of signaling molecules into murine fetal hepatocytes defines distinct roles for the STAT3 and pas pathways during hepatic development

We recently demonstrated that oncostatin M (OSM) in the presence of glucoco rticoid promotes development of fetal hepatic cells in a primary culture sy stem. Our results also suggested that OSM transduces differentiation signal s through gp130, a common subunit of the interleukin (IL)-6 family cytokine receptors. However, an essential downstream pathway required for hepatic d evelopment remains unknown. To address this issue, we expressed signal mole cules by a retroviral expression vector in primary fetal hepatic cells and investigated a signaling pathway essential for OSM-mediated hepatic develop ment. Expression of a dominant-negative form of STAT3 (Delta STAT3), but no t Delta STAT5, 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 a n essential signaling component for OSM-induced hepatic development, while activation of pas appears to negatively regulate this process. Thus, retrov irus-mediated gene transfer is an effective means to analyze function of a gene in primary fetal hepatic culture.