The effects of treatment with human beta-interferon on the stimulation of thymidine uptake and DNA synthesis by colchicine in human fibroblasts.

The marked inhibition by beta-interferon (IFN) of colchicine-induced incorporation of [3H]-thymidine into DNA of human fetal lung fibroblasts reflects inhibition of uptake of labeled precursor, rather than an effect on DNA synthesis per se. The percent of cells in S phase as measured with flow cytometry was unchanged by a concentration of IFN that reduced the uptake of labeled thymidine by 50% at 30 h after treatment.

Chromosomal aberrations in muntjac cells resulting from exposure to interferon.

Cells of the Indian deer (Muntiacus muntjac) are sensitive to the antiviral and antiproliferative action of human beta-interferon (beta-IFN). Because of their low diploid chromosome number and readily identifiable chromosomes, they provide a convenient model system in which to test for the ability of IFN treatment to result in chromosome abnormalities. Increases in the frequencies of chromosome gaps and breaks have been observed after 72 h of treatment with IFN at a concentration of 100 U/ml. At IFN concentrations of 10-100 U/ml, there is a higher proportion of aberrations in the X chromosome than would be expected in a random distribution. At 1,000-1,700 U/ml IFN, there is an increase in the proportion of cells with multiple abnormalities over that observed at 0-100 U/ml IFN, and the distribution of aberrations appears to be random.

Effects of beta interferon on human fibroblasts at different population doubling levels. Proliferation, cell volume, thymidine uptake, and DNA synthesis.

Cellular aging had no effect on the ability of beta interferon to increase cell volume and population doubling time in 76-109 cells, a line of human skin fibroblasts. However, DNA synthesis in cells at high population doubling levels (PDL 55-70) was inhibited after 72 h of beta interferon treatment (1,000 U/ml) while no inhibition of DNA synthesis was observed in cells at middle population doubling levels (PDL 30-40).

Effect of simian virus 40 on the temporal and spatial organization of DNA replication in Muntjac cells.

We examined the effects of simian virus 40 infection on the temporal and spatial organization of initiation sites for DNA replication in Muntjac cells by means of light microscopic DNA fiber autoradiography. Initiation at multiple sites along the DNA fiber in virus-infected confluent Muntjac cells was more nearly synchronous than in serum-deprived controls, although temporal control in the infected cells did not reach the level observed in cells incubated in serum-enriched medium. Initiation sites in virus-infected cells appeared to be spatially closer together than in either uninfected serum-deprived or uninfected serum-enriched cells. This change did not appear to be the result of the induction or repression by simian virus 40 of clusters of replication units with new and different organizations.

Effects of reovirus infection on the spatial and temporal organization of DNA replication in L cells.

DNA fiber autoradiography was used to analyze the spatial and temporal organization of activated initiation sites for DNA replication in mouse L929 cells infected with reovirus type 3 (Dearing strain) and in uninfected control cells. Cells were labeled for 10 min with 3H-thymidine at high specific activity followed by 3 h of low specific activity labeling. Reovirus infection causes no change in the rate of replication fork progression, but increases both the mean distance between activated initiation sites by approximately 30% and the nonrandomness in the spatial distribution of the sites along the DNA fibers. Significant synchronization of initiation in adjacent activated sites was detected on DNA fibers from uninfected cells and from reovirus-infected cells. The mean relative initiation time for pairs of initiation events which had occurred prior to high specific activity labeling did not differ significantly between the infected and uninfected cells. The data are consistent with the interpretation that reovirus infection shuts off initiation sites in a coordinated fashion, possibly by preventing activation of entire clusters of potential initiation sites.

Temporal organization of replication in DNA fibers of mammalian cells.

The extent of coordinate control over the multiple initiation events in DNA replication has been investigated in three mammalian cell lines by DNA fiber autoradiography. Quantitative estimates have been obtained of the degree of synchrony among initiations occurring on stretches of DNA. Synchrony decreases markedly with increasing distance between initiation sites in MDBK (bovine) and L929 (mouse) cells, but only slightly in muntjac cells. Possible control mechanisms for the initiation process are discussed.