Cell cycle study on the effect of interferon on synchronized mouse embryo fibroblasts

Mechanisms of nitrosothiol-induced antimitogenesis in aortic smooth muscle cells

The purpose of this work was to investigate the effect of a nitrosothiol vasodilator, S-nitroso-N-acetylpenicillamine (SNAP), on serum-induced cell proliferation, thymidine uptake, RNA synthesis, protein synthesis and thymidine kinase activity in a cultured rat aortic smooth muscle cell line. SNAP decreased the rate of serum-stimulated cell proliferation, thymidine uptake and incorporation, uridine and leucine incorporation and thymidine kinase activity in concentration-dependent fashion. The threshold concentration of SNAP for inhibition of cell proliferation and thymidine uptake was similar and in the range of 1-3 microM. Uridine incorporation, indicative of RNA synthesis, was inhibited beginning at 10 microM SNAP, whereas leucine incorporation, indicative of protein synthesis, and thymidine kinase activity, an enzyme of importance to DNA synthesis, were inhibited beginning at 100 microM SNAP. These results indicate that inhibition of cell proliferation induced by relatively low concentrations of SNAP (1-10 microM) is independent of inhibition of protein synthesis or thymidine kinase activity, whereas higher concentrations of SNAP may inhibit cell proliferation by decreasing protein synthesis.

Molecular expression of the negative growth factor murine beta-galactoside binding protein (mGBP)

Characterisation of the negative growth factor mGBP at molecular and biological levels indicates that the protein has no lectin nature and suggests instead a participation in the cytokine network. The protein is shown to be expressed as a monomer in two forms, one of which is non-covalently linked to a glycan complex. This confers greater efficiency to the inhibitor and may favour a paracrine role. The two monomeric forms may oxidise into tetramers which retain biological activity, but lack ability to link to specific saccharide residues.

Cell cycle regulation (G1) by autocrine interferon and dissociation between autocrine interferon and 2',5'-oligoadenylate synthetase expression

In tertiary MEF undergoing cell cycle progression, autocrine interferon (IFN) is released and constitutive levels of 2',5'-oligoadenylate (2-5A) synthetase activity, low through the cell cycle, surge into a peak within S phase. Treatment of MEF with the autocrine IFN they produce elicits a 2-5A synthetase response from cells positioned in G0 but not from cells in G1 and from cells in S phase. Neutralization of the autocrine IFN by antibody shortens the length of G1 leaving unaltered the kinetics of progression through S and G2 and has no effect on the S phase-linked expression of 2-5A synthetase activity. The growth controlling effect of the autocrine IFN has been mapped to the second part of G1.

Identification of an autocrine negative growth factor: mouse beta-galactoside-binding protein is a cytostatic factor and cell growth regulator

Murine beta-galactoside-binding protein, a protein classified as a soluble lectin, is shown to be a cell growth-regulatory molecule and a cytostatic factor. The growth-inhibitory effect is not related to lectin properties, and competition assays indicate that the protein binds to specific cell surface receptors with high affinity. It exerts control in G0 and at G2, both as a regulator of cell replication and as a cytostatic factor.

Cell cycle regulation (G1) by autocrine interferon and dissociation between autocrine interferon and 2',5'-oligoadenylate synthetase expression

In tertiary MEF undergoing cell cycle progression, autocrine interferon (IFN) is released and constitutive levels of 2',5'-oligoadenylate (2-5A) synthetase activity, low through the cell cycle, surge into a peak within S phase. Treatment of MEF with the autocrine IFN they produce elicits a 2-5A synthetase response from cells positioned in G0 but not from cells in G1 and from cells in S phase. Neutralization of the autocrine IFN by antibody shortens the length of G1 leaving unaltered the kinetics of progression through S and G2 and has no effect on the S phase-linked expression of 2-5A synthetase activity. The growth controlling effect of the autocrine IFN has been mapped to the second part of G1.

Expression of the 2-5A system during the cell cycle

To determine whether the 2-5A system has a role in the regulation of cell growth we have examined all constituents of the 2-5A pathway in mouse embryo fibroblasts undergoing one cycle of division at the tertiary stage under conditions where a high degree of uniformity is maintained within each stage of the cycle. Levels of the 2-5A synthetase increased up to tenfold late in S phase and declined as cells moved through G2. A similar but smaller increase in the 2-5A-dependent ribonuclease was observed, whereas activity of the 2'5' phosphodiesterase was highest in quiescent cells. At the time of maximum synthetase levels no phosphorylated 2-5A could be detected in the intact cell. Endogenous interferon (IFN) was found in the culture supernatants in increasing concentration with cell cycle progression and addition of antibodies to IFN reduced the increase in synthetase seen in late S. Treatment of cells with a growth inhibitor that cells produce also affected synthetase activity.

Interferon inhibition of thymidine incorporation into DNA through effects on thymidine transport and uptake

Replenishment of medium after 72 hr of growth of HeLa-S3 cells in dense suspension cultures increased [3H]-thymidine uptake into cells and incorporation into DNA, with the levels reaching a peak approximately 12 hr following medium change; beta interferon inhibits the enhanced uptake of [3H]-thymidine and labeling of DNA in a dose-dependent manner. Some reduction in these processes is observed at a concentration as low as 1 u/ml, and approximately 75% inhibition at 640 u/ml. Kinetic analysis has revealed that the rate of labeling of the acid-soluble pool with [3H]-thymidine, measured either at 22 degrees C or 37 degrees C, is reduced in interferon-treated (640 u/ml, 24 hr) HeLa-S3 cells. At 22 degrees C, the initial rate of thymidine transport at a high (500 microM) thymidine concentration, determined within the first 30 sec of [3H]-thymidine addition was depressed by 44% in interferon-treated HeLa cells. At 37 degrees C, labeled precursors accumulate in acid-soluble material for approximately 8 min after the addition of [3H]-thymidine, after which an apparent equilibrium level is attained. At this temperature, the rate of thymidine uptake and the apparent equilibrium level attained were depressed by 70% in interferon-treated HeLa cells. The reduced incorporation of [3H]-thymidine into DNA in interferon-treated HeLa-S3 cells can be largely explained by interferon inhibition of thymidine transport and phosphorylation.

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).