The ovine β-retroviruses enzootic nasal tumor virus (ENTV) and Jaagsiekte sheep retrovirus (JSRV) are the causative agent of enzootic nasal adenocarcinoma (ENA) and ovine pulmonary adenocarcinoma (OPA), respectively, characterized by neoplastic transformation of secretory epithelial cells. The Envelope (Env) proteins of these related betaretroviruses act as oncogenes, in that they can transform fibroblast and epithelial cell lines in culture. In addition, viral vector-mediated expression of the Env proteins for these viruses causes tumors in animals. Here, we investigated what signaling pathways are required for the ENTV transformation in�vitro. We have previously found that Ras–MEK–MAPK and PI3k–Akt–mTOR are involved in JSRV transformation of fibroblast and epithelial cells. In this study, we found that the MEK inhibitor PD98059 and mTOR inhibitor Rapamycin inhibited ENTV transformation in RK3E rat kidney epithelial cells, but the p38 inhibitor SB203580 drastically enhanced transformation, which is quite similar to JSRV transformation. Small molecular inhibitors and dominant negative versions of H-ras and Rac1 indicated a role for both of these molecules in transformation by either virus. These results indicate that the signaling pathways for ENTV and JSRV transformation are quite similar, consistent with the notion that these proteins do not determine the tissue-specificity of the tumors for these viruses.