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  • Title: Interferon-mediated antiviral state in human MRC5 cells in the absence of detectable levels of 2-5A synthetase and protein kinase.
    Author: Meurs E, Hovanessian AG, Montagnier L.
    Journal: J Interferon Res; 1981 Feb; 1(2):219-32. PubMed ID: 6180053.
    Abstract:
    Treatment of human HeLa and MRC5 cells with human alpha (leukocyte) and beta (fibroblast) interferon results in the development of an antiviral state against two types of viruses: vesicular stomatitis virus (rhabdovirus) and encephalomyocarditis virus (picornavirus). These cells, however, differ in their ability to synthesize the two double-stranded (ds) RNA-dependent enzymatic activities, pppA(2'p5'A)n synthetase (2-5A synthetase) and protein kinase which have been reported to be induced in several cell lines by interferon. Both the 2-5A synthetase and the protein kinase are enhanced by several fold in HeLa cells on treatment with interferon. In contrast, neither the 2-5A synthetase nor the protein kinase can be detected in MRC5 cell treated or not treated with interferon. The lack of detection of the 2-5A synthetase in MRC5 cells is not associated with the absence of the other components of the 2-5A system (2-5A dependent nuclease and 2'-phosphodiesterase). We have previously shown that MRC5 cells are sensitive to the action of 2-5A and furthermore the inhibitory action of 2-5A on these cells is transient. Mixing experiments between HeLa and MRC5 cell fractions after partial purification on columns of poly(I).poly(C)-Sepharose, showed that the absence of detection of the protein kinase activity in MRC5 cells cannot be attributed to the presence of phosphatases or other inhibitors of phosphorylation in control or interferon-treated MRC5 cell extracts. In addition, we show that the interferon-mediated protein kinase activity in HeLa cell extracts can be precipitated by treatment at pH 5, a procedure which leads to an enhanced level of detectable protein kinase activity in general. Once again, however, MRC5 cell extracts fail to show any interferon-mediated protein kinase activity. These results suggest that either the two enzyme activities are not necessary for the development of the antiviral response induced by interferon or the intracellular events leading to the establishment of the antiviral state vary from one cell system to the other.
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