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PubMed1985

Permanent expression of p53 in FR 3T3 rat cells but cell cycle-dependent association with large-T antigen in simian virus 40 transformants.

The p53 oncogene is thought to play a role in the proliferation of normal and transformed cells and its expression was postulated to be cell cycle dependent. Using flow cytofluorimetry sorting of populations of exponentially growing cells, coupled to a radioimmune assay, we have investigated the accumulation of p53 along the cell cycle in normal FR 3T3 rat cells as well as in two types of SV40-transformed derivatives, one of which only expresses the large-T protein during the G2 phase of the cell cycle. p53 was accumulated at a constant level throughout the cell cycle in FR 3T3 cells. Its level and stability increased to different extents in the two types of transformants. However, the formation of complexes between p53 and large-T was modulated by the G2-restricted accumulation of large-T, thus leading to a differential increase in the levels of p53 both in exponentially growing cells and along the cell cycle. This increase in the levels of p53 appeared to be regulated at a post-transcriptional level.

Animals↗

PubMed1984

Cell cycle-dependent expression of early viral genes in one group of simian virus 40-transformed rat cells.

SV40-transformed FR 3T3 rat cells were previously shown to exhibit different patterns of accumulation of the virus-coded T-antigen. One group of transformants accumulates T-antigen throughout the cell cycle, whereas in another group, only the cells in the G2 phase of the cell cycle are stained by immunofluorescence with anti-T antigen antibodies. We investigated the mechanism involved by determining the amounts of early SV40 RNA during the cell cycle. Cells in the various phases of the cell cycle were sorted from an asynchronously growing population using a flow cytofluorimeter. Determination of the amounts of viral RNA in the different nuclear and cytoplasmic RNA fractions showed that in transformants with a G2-restricted accumulation of T-antigen, viral RNA was present in G2, to some extent in S, but could not be detected in cells in G1. In contrast, equivalent amounts of viral RNA were detected in all the phases of the cell cycle in the other group of transformants. Cell sorting, performed after pulse-labeling the cells for 2 h with [35S]methionine, confirmed that translation of the viral mRNAs occurred only in G2 in the first group of transformants, and throughout the cell cycle in the second group.

Animals↗