Human Interferon and Cell Growth Inhibition. VI. Effect of Different Inhibitors of Cellular Functions on Interferon Activities

Interferon sensitivity of fibroblast cell cultures derived from patients with neoplasms of the head and neck

Interferon (IFN) is a protein with antiviral activity that has been shown to inhibit the growth of many different types of cells. We have measured the IFN sensitivity of nine cell cultures isolated from patients with squamous cell carcinoma and one with malignant melanoma of the head and neck. Normal-appearing fibroblast cultures isolated from these tissues appear quite sensitive to the antiviral effects of IFN. When the encephalomyocarditis virus yield reduction assay is used, these diploid cells are as sensitive to IFN-alpha as are newborn foreskin fibroblast cultures. A similar antiviral effect is seen with IFN-gamma. These cells are relatively insensitive to the antigrowth effect of both IFN preparations as measured by 3H thymidine incorporation and direct observations of cell growth. This is the same relative sensitivity as fibroblasts derived from normal patients. Since these cells are at least 100 times less sensitive to the antigrowth action of the IFNs, it appears unlikely that the IFNs play a significant role in the control of normal fibroblast growth, in contrast to the sensitivity of malignant cell lines.

Characteristics of the induction of two double-stranded RNA-dependent enzymes by interferon in parental and variant L cells

The interferon (IFN)-dependent induction of two double-stranded RNA-dependent enzymes was examined in L cells and an L-cell variant (WDIFN) which is highly resistant to the inhibitory effects of IFN on cellular multiplication. IFN, in a concentration-dependent manner, inhibited the multiplication of parental L cells and induced increased levels of the double-stranded RNA-dependent enzymes in parental L cells. Although WDIFN cells were resistant to the antiproliferative effects of IFN, the cells responded to IFN by increasing their levels of the double-stranded RNA-dependent enzymes. However, the level of activity of each enzyme was lower in the WDIFN line than the parental line when both lines were treated with similar concentrations of IFN. The reduced response of the WDIFN line was not the result of the line being a heterogeneous population of cells nor of IFN being more unstable in the presence of WDIFN cells. In addition there was no evidence that WDIFN cells produced a mitogenic factor that could overcome the antiproliferative effects of IFN, nor that sodium butyrate could increase the sensitivity of WDIFN cells to the antiproliferative effects of IFN.

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.

Human interferon and cell growth inhibition. VII. Reversibility of interferon activities

Interferon (IFN) components isolated from human leukocyte-derived alpha IFN preparations were tested for reversibility of activities in four different human cell lines. As expected, antiviral activity was not reversed by removal of the IFN-containing medium. Growth inhibition by the anticellular component was completely reversible by washing of the cultures, while that of the antiviral component could not be reversed even after careful washing. The results with the components are in agreement with the findings with IFN in the different cell lines. The present study support earlier suggestions that at least two mechanisms of action are involved in growth regulation by IFN in various cell lines.