Retrovirus gene expression during the cell cycle. I. Virus production, synthesis, and expression of viral proteins in Rauscher murine leukemia virus-infected mouse cells

Abstract

Synchronized mouse cells (JLS-V9) chronically infected with Rauscher murine leukemia virus were used to study virus production, the synthesis of gag and env precursor proteins, and the expression of env protein on the cell surface during the cell cycle. The amount of virus released into the medium by synchronized cells during a 30-min interval was determined by using the XC plaque assay and by measuring reverse transcriptase activity. The results show that virus production occurs during mitosis. Labeling of the cell surface of synchronized cells with 125I or with fluorescein-conjugated antiserum shows that the amount of gp 70env on the cell surface parallels cellular growth. Therefore, the cell cycle-dependent release of virus is not accompanied by similar variations in the amount of viral envelope protein on the cell surface. Immunoprecipitation of cells labeled with [35S]methionine, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was used to measure viral protein synthesis during the cell cycle. The rate of synthesis of gag precursor proteins show three maximums corresponding to the G1, middle S, and late S to G2 phases of the cell cycle. The rate of synthesis of env precursor proteins does not change, suggesting that in these cells the synthesis of these two gene products is controlled separately.

Antiviral activity obtained from aqueous extracts of the Chilean soapbark tree (Quillaja saponaria Molina)

“…Briefly, radioisotopelabelled virus was prepared by infecting the indicated host cell line at an m.o.i. of 20 in the presence of 35 S-methionine/cysteine (20 mCi ml 21 ) for 48 h and the viruses were extracted from cell debris as described by Balazs & Caldarella (1981). The ability of each virus to attach to their host cells was determined by adding 1610 6 c.p.m.…”

Regulation of Moloney murine leukemia virus replication in chronically infected cells arrested at the G0/G1 phase

“…At this presumed point in the GO/Gl phase, MuLV may be produced in the absence of cell proliferation. It should be noted, however, that during cell proliferation, MuLV is produced predominantly during the M phase (3,19,20,23). An alternative possibility is that butyric acid uncoupled the block on MuLV that was imposed by cell cycle arrest.…”

“…The dependence of retrovirus replication on cell proliferation is a well-documented phenomenon. The productive infection of murine leukemia viruses (MuLV) is aborted in serum-starved, GO/Gl-phase-arrested cells both at the level of proviral DNA synthesis (11) and during virus production from the chronically infected cells (3,10,23,27). Although virus production is inhibited in the chronically infected GO/Gl-arrested cells, viral RNA and protein synthesis are unaffected (10,27).…”

“…Release of the cells from GO/G1 arrest by the addition of serum results in a resumption of Moloney MuLV (MMuLV) production. Although complex patterns of virus regulation in the synchronized cultures have been observed, maximal MuLV production coincides with the M phase of the cell cycle (3,10,20,23).…”

In vitro growth inhibition of murine leukemia cells by antibody specific for the major envelope glycoprotein (gp71) of friend leukemia virus

“…It should be noted that differential expression of cellsurface antigens relative to the cell cycle has been reported for a wide variety of determinants on tumor cells (Sumner et al, 1973, Drewinko andBurk, 1977;Balazs and Caldarella, 1981), including those involved in other C'-independent antibody-mediated growth suppression systems. However, whereas the thymus leukemia (TL) allodifferentiation antigen is preferentially expressed on ASL-1w murine thymoma cells during the S phase of the cell cycle (Williams et al, 19791, anti-TL antibodyinhibited ASL-lw cells are blocked in GZ .…”