Abstract
A transplantable murine leukemia, primarily induced by a biologically cloned Friend helper virus, was shown to induce polycythemia in recipient ICFW mice. A leukemia cell line (IW.32) was established in vitro from this transplantable leukemia. Sodium butyrate and hemin induced erythroid differentiation in these leukemia cells as has already been shown with other erythroleukemia cells. The supernatant of this cell line was devoid of spleen focus-forming virus activity. However, it induced the incorporation of 59Fe in polycythemic mice and the in vitro differentiation of murine and human cfu-e into erythroid colonies. Therefore, these erythroleukemia cells produced a factor with all the biological properties of erythropoietin. The erythropoietic activity of IW.32 supernatant was higher in vitro [equivalent to 0.5-1 international unit (IU) of erythropoietin per ml] than in vivo (0.15-0.3 IU/ml). This erythropoietin-like activity was stable at 100 degrees C for 3 min, which ruled out the possibility that a virus was responsible for these effects. Preliminary studies demonstrated that the biochemical properties of the IW.32 factor are strongly similar to those of Connaught step 3 erythropoietin, thus supporting the hypothesis that the IW.32 factor is indeed an erythropoietin.