Suppression of the Avian Sarcoma Virus Genome in Hamster-Transformed Cells Made Resistant to 8-Azaguanine

Summary

Hamster cells transformed by the Schmidt-Ruppin strain of avian sarcoma virus [Ha(SR)] were tested for their resistance to a-azaguanine (aza-G). The uncloned resistant cell line Ha(SR)AG-50 proliferated in the presence of 50 μg aza-G/ml in medium supplemented with hypoxanthine, amethopterin, thymidine, and glycine (HATG) and in normal medium. Sixteen single-cell clones were isolated in a medium containing 50 μg aza-G/ml from Ha(SR)AG-50 cells. All cell clones were resistant to aza-G. Two of 16 clones were deficient in hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity; they did not grow in HATG, did not incorporate labeled hypoxanthine, and had negligible HGPRTactivity. The resistance of clones to aza-G was genetically stable. The properties of some aza-G-resistantcell clones were further studied. The aza-Gresistant cells were less tumorigenic in hamsters. Several cell clones were extensively tested for virus genome by fusion with chicken embryo cells and subsequent inoculation of cells to chickens. The virus genome was strongly suppressed in all aza-G-resistant cell clones. The HGPRT deficiency was not connected with virus genome suppression. The group-specific antigen was also inhibited in all aza-G-resistant cell clones compared with the parental clonal cell lines. The relationship of the presence of the virus genome in cells with properties called “transformed phenotype” and tumorigenicity was discussed.