Analysis of viral RNA and proteins expressed by a non producer Friend erythroleukemia cell line (HFL/b cell line)

Friend murine erythroleukemia is a model of virus-induced acute leukemia. RNA and protein viral expression were simultaneously studied in a Friend erythroleukemia murine cell line (HFL/b cells, Freedman et al. (1975) J. expl. Med.142, 212–223), which had lost its capacity of producing infectious virus and was found to contain neither structural p30 nor gp70 envelope-glycoprotein by radioimmunoassay. Presence of the spleen focus-forming virus (SFFV) in these cells was demonstrated by its biological rescue in vivo and in vitro with Moloney-helper leukemia virus (M-MuLV). Molecular hybridization using a DNA complementary to Friend virus complex revealed the presence in cytoplasmic Poly(A) RNA of a major species with the size of the 32S SFFV genome. No. 38S helper Friend Murine Leukemia Virus (F-MuLV) RNA was detected. Viral-encoded polypeptide expression was studied by immunoprecipitation of cell extracts. A first class of polypeptides constituted by two species of 50,000 and 52,000 daltons was precipitated by a goat anti Rauscher gp70 serum and corresponded to the glycoprotein encoded by the SFFV genome. A second class of polypeptides with apparent mobilities of 48,000 and 50,000 daltons was precipitated by anti p15 and anti p12 sera and to a lesser extent by an anti p30 serum. These products were glycosylated in part. Moreover two p37 and p39 products, which disappeared more rapidly than p48gag + p50gag in pulse-chase labeling experiments were also precipitated by anti-gag sera. No other gag-product such as pr65gag was detected, confirming a negative expression of the F-MuLV genome and supporting the idea that all the gag-related products expressed in these cells were coded by SFFV virus.