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While a multiplicity of cellular and biochemical effects are mediated by interferons on cultured cells, the mechanisms involved in the direct growth-inhibitory activity of interferons remain problematic. We have previously found that variants in cAMP metabolism in a macrophage cell line, J774.2, were at least 50-fold less sensitive to the growth inhibitory activity of interferons (IFN) than the parental clone. To test the hypothesis that cAMP mediates the growth inhibition produced by IFN in these cells, interferon-resistant variants were selected and characterized with respect to cAMP synthesis and function. Approximately one-third of the IFN-resistant clones were found to be resistant to growth inhibition produced by cholera toxin, but not 8Br-cAMP. IFN was fully able to protect all of the interferon-resistant/choleratoxin-resistant (IFNr/CTr) clones against infection by vesicular stomatitis virus and markedly stimulated 2', 5'-oligodenylate synthetase activity. These IFNr/CTr variants were shown to have a defect in adenylate cyclase. The remaining IFN-resistant clones were fully susceptible to the growth-inhibitory effects of cholera toxin because their basal and stimulated adenylate cyclase activity is similar to that of the parental clone. IFN failed to protect these IFNr/choleratoxin sensitive clones against infection by vesicular stomatitis virus and failed to stimulate 2', 5-oligodenylate synthetase, suggesting that they have defective or deficient IFN receptors. In addition, IFN failed to increase intracellular cAMP levels in both IFNr/CTr and IFNr/choleratoxin sensitive clones. These results provide firm genetic and biochemical evidence that the growth inhibitory effects of IFN on this cell line are mediated by cAMP.
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