Interferon and cell division. 8. Effect of interferon on macromolecular synthesis in L1210 Cells in vitro

Inhibition of proliferation of lines derived from human cervical carcinomas by cytotoxic drugs and by recombinant interferons

The authors studied the effects of recombinant interferons (IFN), doxorubicin, and cisplatin against three cell lines derived from human epidermoid cervical carcinomas. These lines were SW 756, containing the genome of human papillomavirus (HPV) type 18, and CaSki and SiHa, containing HPV type 16. IFN-gamma suppressed the growth of all three lines, with a plateau in inhibitory effect beyond a concentration of 1000 units/ml. IFN-alpha was effective in this regard only against SW 756. In this line, the two IFNs together inhibited cell replication to a greater extent than the maximal effect of either IFN alone. Doxorubicin exerted a dose-dependent cytotoxic effect against all the lines, while cisplatin exhibited cytotoxicity only against SW 756. Doxorubicin and IFN-gamma, when used together, acted synergistically against CaSki and SiHa, and in an additive manner against SW 756.

Antitumor effects of interferon

Both natural and recombinant interferons have shown definite antitumor activity in some patients with some malignancies. The history of the development of interferon as an antitumor agent is reviewed, with special attention to its use in mice bearing 'spontaneously' appearing tumors and in mice injected with tumorigenic viruses or transplantable tumor cells. Interferon can inhibit the growth of primary tumors as well as the development of metastases. These experimental results have provided some indications as to the probable optimal regimens of interferon administration in man. Although the mechanisms of interferon's antitumor activity are unknown, it seems likely that interferon can act directly on the tumor cells as well as on the tumor bearing host.

The antitumor effects of interferon

Interferons show antitumor activity in patients with various malignancies. The mechanism(s) of the antitumor effects are not altogether clear. In one experimental animal model discussed herein, mice were injected with Friend erythroleukemia cells and treated with mouse interferon alpha/beta. The results suggest that interferon does not act directly on the tumor cells but acts via host mechanisms that are still ill defined.

Inhibition of cell proliferation by interferons. Relative contributions of changes in protein synthesis and breakdown to growth control of human lymphoblastoid cells

Treatment of the Daudi line of human lymphoblastoid cells with concentrations of human interferons within the physiological range progressively inhibits cell proliferation over 1-4 days. Rigorous measurement of the overall rate of protein synthesis during this period, using a concentration of [3H]phenylalanine sufficient to equalize the specific radioactivity of intracellular and extracellular precursor pools, shows that protein synthesis becomes progressively inhibited as the growth inhibition develops. There is a strong correlation between inhibition of amino acid incorporation and inhibition of cell proliferation. In contrast, we find no evidence for any increase in protein degradation rate under these conditions. These results suggest that interferon treatment of susceptible cells can inhibit protein synthesis even in the absence of virus infection and that this inhibition is of a sufficient magnitude to account for the anti-proliferative effect.

Regulation of protein synthesis in lymphoblastoid cells during inhibition of cell proliferation by human interferons

Treatment of human lymphoblastoid (Daudi) cells with interferons inhibits cell proliferation in culture within 24 h. The failure of cell growth has been shown to be associated with impaired processing and decreased stability of newly replicated DNA. Because there is a close relationship between DNA replication and protein synthesis we have measured protein synthesis in intact Daudi cells. Protein synthesis declined steadily between 24 and 96 h after interferon treatment to a value which is only 20-30% of the rate in control cells. The enzyme 2',5'-oligo(A) synthetase is induced but our data do not support a role for the 2',5'-oligo(A)-activated ribonuclease in the control of translation in this system.

Inhibition of cell division and antibody secretion by murine alpha/beta interferon: effects on plasmacytoma and hybridoma lymphoid cells

Murine alpha/beta interferon (IFN) inhibited the growth of myeloma cells in vitro. Independently of the cell growth inhibition, IFN also reduced the number of antibody secreting myeloma cells as measured by haemolytic plaque assay. The sensitivity of both MOPC 315 plasmacytoma cells and 4F4 hybridoma cells varied, though not to the same extent, depending on the dose of IFN used and the duration of exposure. Inhibition of PFC activity was observed after one day of IFN treatment while inhibition of cell growth was not detected until Day 2 of incubation. A dose of 20 u/ml IFN had no effect on the growth rate of MOPC 315 cells but with 100 u/ml the inhibition of growth was virtually complete. In contrast, an inhibition of PFC activity was observed at all the concentrations tested. The cell growth and PFC activity of 4F4 hybridoma cells, on the other hand, were both inhibited by IFN when used at concentrations as low as 1.25 u/ml. Incubation with higher concentrations of IFN resulted in a progressive reduction in cell growth and PFC activity of 4F4 cells, however to a lesser degree of inhibition compared to that observed with MOPC 315 cells. For example, although virtually 70% of MOPC 315 PFC could be inhibited by culture for two days in the presence of 100 u/ml, it was necessary to use 1,250 u/ml IFN for 4 days incubation before the similar level of PFC inhibition was achieved with 4F4 cells. IFN treatment resulted in an increase in both cellular volume and protein content and this effect was prevented when IFN was previously neutralised by a specific antiserum. IFN-treated cells also showed an inhibition in the incorporation of 3[H]-thymidine but no alteration in the rate of utilization of 35[S]-methionine, when compared with an equal number of control cells.

An indirect radioimmunoassay for interferon

An indirect radioimmunoassay for testing the antiviral activity of interferon (IFN) is described. Vero cells are seeded in microtitre plates, treated with appropriate dilutions of interferon and challenged with Sindbis virus. Viral yield is measured using specific antibody and radiolabelled protein A. The assay is able to detect IFN levels of 5 international units (I.U.)/ml, has a high degree of reproducibility, and could be easily adapted to various cell and virus combinations. This microsystem is technically simple, allows testing of small volumes of test material, and eliminates subjectivity in reading of end-points.

Interferon increases HLA synthesis in melanoma cells: interferon-resistant and -sensitive cell lines

We report that human leukocyte interferon preparations increase the expression of beta 2-microglobulin by 100-200% on the surface of normal fibroblast and melanoma cell lines sensitive to interferon. This increase in expression can be correlated with an increase in HLA synthesis as measured by incorporation of [35S]methionine in these antigens. This enhanced HLA synthesis, which is 5- to 17-fold, is time dependent and dose related. Synchronized cells in the G0/G1 phase of the cell cycle appear to be more sensitive to this interferon action. Neither an increase in surface expression nor in HLA synthesis is observed in a melanoma cell line resistant to the antiviral and antigrowth effects of interferon. Furthermore, there appears to be a stronger correlation between this increased HLA synthesis and the antiviral function than between it and the antiproliferative action of interferon.

Inhibition of cell division by interferons: Changes in the transport and intracellular metabolism of thymidine in human lymphoblastoid (Daudi) cells

The Daudi line of human lymphoblastoid cells shows a high sensitivity towards growth inhibition by human interferons. In cells pretreated with 70 reference units/ml of an interferon preparation for 48 h, the incorporation of exogenous [3H]thymidine into DNA is inhibited by as much as 85%. We are investigating the extent to which this effect reflects a true inhibition of the rate of DNA synthesis or whether it may be caused by changes in the metabolic utilization of exogenous thymidine by the cells. Interferon treatment results in a 30% inhibition of the rate of membrane transport and a 60% decrease in the rate of phosphorylation of [3H]thymidine in vivo. The latter effect is due to a decrease in V of thymidine kinase without any change in the value of Km for this enzyme. In addition to these changes, incorporation of [3H]uridine into DNA, which occurs as a result of the intracellular conversion of this precursor into thymidine nucleotides, is also inhibited by 75%, whereas RNA labelling by [3H]uridine is decreased by only 15% in interferon-treated cells. Thus several different metabolic events associated with thymidine nucleotide metabolism and DNA synthesis in Daudi cells are disrupted by interferon treatment.

Identification of an interferon in murine placentas

It is becoming increasingly apparent that interferon exerts a major role in cellular regulatory processes. Besides its well known antiviral properties, interferon has been shown to affect cell surface antigen expression, lymphoid cell function, as well as cellular protein synthesis and growth. To date, however, there is little information available on the mechanism of interferon production in vivo except in response to a variety of exogenously administered viral and nonviral systemic inducers. We report here the detection of a pregnancy-associated elevation of interferon, or an interferon-like component, in selected reproductive tissues of mice.

Interferon-mediated effect on ribosomal RNA metabolism

Ribosomal RNA (rRNA) has been shown to be involved in the binding of bacterial messenger RNA (mRNA) and an analogous 18 S rRNA.mRNA complex has been reported in eukaryotic systems. Thus, qualitative changes in host rRNA may be involved in the development of the interferon mediated antiviral state, a process thought to involve the inability of host ribosomes to bind and recognize viral mRNA. Data are reported which suggest that trisomy 21 human fibroblasts respond to human interferon with a marked reduction in cytoplasmic rRNA. [3H]Uridine was used to radioactively label the polysomal RNAs for 24 h beginning 12 h after interferon addition. Subsequent sucrose gradient analysis of the phenol or SDS-extracted RNA revealed that the reduction in radioactive rRNA was nearly complete for the 28 S rRNA. In contrast, considerable residual uridine incorporation was found in the 18 S rRNA species. Corollary data suggesting a net increase in mRNA synthesis and a net decrease in protein synthesis are reported.

Early effect of interferon on mouse leukemia cells cultivated in a chemostat

Mouse interferon preparations inhibited the multiplication of mouse leukemia L 1210 cells cultivated under steady-state conditions in a chemostat. The use of this sensitive and controlled system led to the detection of a rapid inhibition in the incorporation of (3-H)thymidine into cellular acid-precipitable material 2 hr after the addition of interferon, whereas an effect on cell multiplication was not detected until 22 hr later. Interferon exerted only a transitory effect on the incorporation of (3-H)uridine into acid-precipitable material and no effect on the incorporation of 14-C-amino acids into cellular protein. It is suggested that the chemostat offers many advantages for the investigation of those physiologic factors or chemotherapeutic substances that modify cell division.

Relationship between cell kinetic changes and metabolic events during cell senescence in vitro

Cell kinetic studies performed throughout the lifespan of fibroblasts with a limited lifespan in vitro have led to the conclusion that although division slows down, almost all cells are able to divide until the last subcultivation. The prolongation of the division cycle is primarily due to the impariment of mechanisms preceding DNA synthesis and mitosis. An attempt was made to distinguish between primary and secondary changes and to correlate the findings concerning cell kinetics with alterations observed at the molecular level. A decline in protein synthesis was the first modification detected. The two parameters that are always present during cell senescence in vitro, i.e., and increase in cell volume and a decrease in saturation density could be due respectively to a change in cell permeability and a decline in ribosome synthesis. The latter could also be the step responsible for the limited potential of division.