Transformation by murine sarcoma virus alters the sensitivity of clonal cells derived from NIH/3T3 mouse fibroblasts to interferon

In contrast to normal clonal cells (A5) derived from NIH/3T3 mouse fibroblasts, another clone (A10) derived from the same source was found to be resistant to the anti-lytic-virus activity of IFN and to be deficient in the induction of (2′-5′) oligoadenylate synthetase (2-5A synthetase) by IFN. Following infection of either A5 or A10 cells with Moloney murine sarcoma virus (MSV), a few transformed colonies were isolated, expanded, and tested for their sensitivity to IFN. It is clearly demonstrated that IFN exerts a specific anti-proliferative effect on both MSV-transformed A5 (MA5) and A10 (MA10) cells, as evident by a slower growth rate, a decreased rate of DNA synthesis, and a lower cloning efficiency in its presence. Furthermore, unlike the original A10 cells, the IFN-treated transformed counterpart (MA10 cells), as well as MA5 cells, were protected from the lytic effect of either mengovirus or vesicular stomatitis virus (VSV). In addition, IFN treatment inhibited the release of retroviral particles from the transformed cells. The level of 2-5A synthetase activity in the various transformed cell lines was then determined. Whereas in A10 cells an induction of less than twofold in the enzymatic activity was detected following IFN treatment, a four- to fivefold increase in this activity could be seen in MA10 cells.