Isolation and Biological Characterization of Mouse LM Fibroblast Variants Resistant to the Cytotoxicity of Polyriboinosinic{middle dot}Polyribocytidylic Acid after Interferon Treatment

Abstract

SUMMARYMouse LM fibroblasts growing continuously in the absence of serum have an increased sensitivity to the cytotoxicity of poly(rI).poly(rC) after interferon (IFN) exposure. This has allowed the isolation by an enrichment procedure of several independent and stable variant clones (IFN + I. C) g which are resistant to such a treatment. One of the resistant variants has been more extensively characterized as far as IFN action and IFN production are concerned. It behaves identically to the wildtype parent except for the spontaneous release of low amounts of IF N. The target of the mutation probably resides in a late step in the development of the cytotoxic response as revealed by microinjection techniques. The (IFN + I. C) g variants characterized here thus appear different from mutants in the IFN system isolated so far.

Requirement for Endocytosis of Poly(rI).Poly(rC) to Generate Toxicity on Interferon-treated LM Cells

“…1 (b) shows that the toxic effect of poly(rI).poly(rC) was not improved above 2 ~tg/ml. Previous experiments had already demonstrated that IFN-treatment allowed effective lysis at 1000 units/ml and above (Faure et al, 1984). In most experiments described here, poly(rI), poly(rC) was used at 5/.tg/ml and IFN at 1000 units/ml.…”

“…The experimental conditions leading to lysis induced by poly(rI).poly(rC) on IFN-treated cells have been described previously (Faure et al, 1984). Long term exposure of IFN-treated cells to poly(rI), poly(rC) results in lysis of up to 90~ of the cells.…”

“…In order to gain information about the cytotoxicity of dsRNA for IFN-treated cells, independent variants resistant to lysis induced by combined treatment of IFN and poly(rI), poly(rC) were isolated Which spontaneously secrete small amounts of IFN (Faure et al, 1984). Characterization of these variants indicates that both IFN production and the lytic mechanism share a common stage (De Clercq & De Somer, 1975).…”

An Antiviral State Induced in HeLa Cells by Microinjected Poly(rI){middle dot}Poly(rC)

“…This would explain the incomplete neutralization by IFN antibodies we observed. However, our own experiments (Faure et al, 1984;P. G. Milhaud, M. Silhol, T. Salehzada & B. Lebleu, unpublished results) at least do not favour an involvement of cell cytotoxicity of microinjected poly(rI).poly(rC) apart from the low (< 10~) cell mortality inherent in the microinjection procedure itself.…”

“…Studies by our group on the toxicity of poly(rI), poly(rC) for IFN-treated murine cells (Faure et al, 1984;P. G. Milhaud, M. Silhol, T. Salehzada & B. Lebleu, unpublished) strongly suggest the involvement of fluid-phase endocytosis.…”