scholarly journals Inducers of DNA synthesis: levels higher in transformed cells than in normal cells.

1983 ◽  
Vol 96 (2) ◽  
pp. 571-576 ◽  
Author(s):  
P N Rao ◽  
K L Satya-Prakash
Keyword(s):  
Dna Synthesis ◽  
Sendai Virus ◽  
Transformed Cells ◽  
G1 Phase ◽  
Normal Cells ◽  
Diploid Fibroblasts ◽  
Human Diploid Fibroblasts ◽  
Tumor Viruses ◽  
Latex Beads ◽  
Normal Human

The objective of this study was to determine whether transformed cells have greater DNA synthesis-inducing ability (DSIA) than normal cells when fused with G1 phase cells. HeLa cells synchronized in G1 phase, prelabeled with large latex beads, were fused separately with (a) quiescent human diploid fibroblasts (HDF), (b) HDF partially synchronized in late G1, and random populations of (c) HeLa, (d) WI-38, (e) SV-40 transformed WI-38, (f) CHO, (g) chemically transformed mouse cells (AKR-MCA), and (h) T98G human glioblastoma cells (all prelabeled with small latex beads) using UV-inactivated Sendai virus. The fusion mixture was incubated with [3H] thymidine, sampled at regular intervals, and processed for radioautography. Among the heterodikaryons, the frequency of those with a labeled and an unlabeled nuclei (L/U) were scored as a function of time after fusion. The faster the induction of DNA synthesis in HeLa G1, the steeper the drop in the L/U class and hence the higher DSIA in the S phase cells. The DSIA, which is indicative of the intracellular levels of the inducers of DNA synthesis, was the highest in HeLa and virally transformed WI-38 cells and the lowest in normal human diploid fibroblasts (HDF) while those of chemically and spontaneously transformed cells are intermediate between these two extremes. Higher level of DNA synthesis inducers appears to be one of the pleotropic effects of transformation by DNA tumor viruses. These studies also revealed that initiation of DNA synthesis per se is regulated by the presence of inducers and not by inhibitors.

scholarly journals INHIBITION OF CELL GROWTH IN THE G1 PHASE BY ADENOSINE 3',5'-CYCLIC MONOPHOSPHATE

1974 ◽  
Vol 60 (1) ◽  
pp. 249-257 ◽  
Author(s):  
Jeffrey E. Froehlich ◽  
Martin Rachmeler
Keyword(s):  
Cell Growth ◽  
Dna Synthesis ◽  
Tritiated Thymidine ◽  
S Phase ◽  
Fresh Medium ◽  
G1 Phase ◽  
Cyclic Monophosphate ◽  
Diploid Fibroblasts ◽  
Human Diploid Fibroblasts

Incorporation of tritiated thymidine into acid-precipitable material was used to measure the rate of DNA synthesis in secondary cultures of human diploid fibroblasts. Confluent cultures of human diploid fibroblasts, which are synchronized in the G1 phase due to contact inhibition, were released from growth inhibition either by the addition of fresh medium to the cultures or by trypsinization and replating at nonconfluent densities. Either treatment resulted in a synchronous wave of DNA synthesis beginning 10–15 h after treatment and peaking at 20–25 h. In confluent cultures stimulated by fresh medium, either the addition of 0.25 mM N6, O2-dibutyryl-adenosine 3',5'-cyclic monophosphate (db-cAMP) to the medium in the interval 4–8 h after stimulation or the replacement of the fresh medium in that same 4 h interval with the depleted medium present on the cells for the 2 day period before stimulation delayed the synchronous onset of DNA synthesis in the cultures by about 4 h. In nonconfluent cultures freshly seeded from trypsinized confluent cultures, this same depleted medium obtained after a 2 day incubation of fresh medium on confluent cultures is shown to support the progress of the cells into S phase; however, the addition of 0.25 mM db-cAMP to the medium 3½ h after replating still partially prevented the initiation of DNA synthesis in the cultures. The results are discussed in terms of the role of serum and cAMP in the control of cell growth in fibroblast cultures.

Effect of cytochalasin B on somatic cell hybrids between normal and transformed cells

1985 ◽  
Vol 78 (1) ◽  
pp. 87-96
Author(s):  
I. Hickey ◽  
C. McConville ◽  
M. McMenamin ◽  
R. Neill
Keyword(s):  
Dna Synthesis ◽  
Somatic Cell ◽  
Cytochalasin B ◽  
Nuclear Division ◽  
Transformed Cells ◽  
Somatic Cell Hybrids ◽  
Recessive Character ◽  
Normal Cells ◽  
Cell Hybrids ◽  
Transformed Cell Lines

Cytochalasin B (CB) prevents cytokinesis in animal cells. In normal cells nuclear division and DNA synthesis are also blocked and the cells, held in the G1 phase of the cell cycle, remain either mononucleate or binucleate. In transformed cell lines DNA synthesis and nuclear division continue and the cells become multinucleate. We have examined the response to CB in two sets of somatic cell hybrids made between cells that display multinucleation after CB treatment and cells that do not. In a cross between transformed mouse LMTK cells and normal rat embryo lung cells, very little multinucleation was observed after treatment with CB for 7 days. The ability of the LMTK cells to form clones in soft agar was also significantly reduced in these hybrids. Segregant sub-clones that re-expressed both of these transformation phenotypes were isolated. These had reduced chromosome numbers. A second cross was made between two variants of the BHK cell line, one of which displayed a high level of multinucleation in CB while the other did not. Again the hybrids showed a response similar to that of the non-multinucleating parent. From the results obtained with these two hybrids we conclude that the multinucleation induced in transformed cells by CB behaves as a recessive character in crosses with normal cells.

Complement-dependent induction of DNA synthesis and proliferation of human diploid fibroblasts

1980 ◽  
Vol 105 (3) ◽  
pp. 503-512 ◽  
Author(s):  
Terry I. Korotzer ◽  
James A. Clagett ◽  
William P. Kolb ◽  
Roy C. Page
Keyword(s):  
Dna Synthesis ◽  
Diploid Fibroblasts ◽  
Human Diploid Fibroblasts

scholarly journals Reversible cellular senescence: implications for immortalization of normal human diploid fibroblasts.

1989 ◽  
Vol 9 (7) ◽  
pp. 3088-3092 ◽  
Author(s):  
W E Wright ◽  
O M Pereira-Smith ◽  
J W Shay
Keyword(s):  
Cellular Senescence ◽  
Rare Event ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Diploid Fibroblasts ◽  
Human Diploid Fibroblasts ◽  
Normal Human ◽  
Immortal Cells ◽  
Cellular Dna

IMR-90 normal human diploid fibroblasts, transfected with a steroid inducible mouse mammary tumor virus-driven simian virus 40 T antigen, were carried through crisis to yield an immortal cell line. Growth was dependent on the presence of the inducer (dexamethasone) during both the extended precrisis life span of the cells and after immortalization. After dexamethasone removal, immortal cells divided once or twice and then accumulated in G1. These results are best explained by a two-stage model for cellular senescence. Mortality stage 1 (M1) causes a loss of mitogen responsiveness and arrest near the G1/S interface and can be bypassed or overcome by the cellular DNA synthesis-stimulating activity of T antigen. Mortality stage 2 (M2) is an independent mechanism that is responsible for the failure of cell division during crisis. The inactivation of M2 is a rare event, probably of mutational origin in human cells, independent of or only indirectly related to the expression of T antigen. Under this hypothesis, T-antigen-immortalized cells contain an active but bypassed M1 mechanism and an inactivated M2 mechanism. These cells are dependent on the continued expression of T antigen for the maintenance of immortality for the same reason that precrisis cells are dependent on T antigen for growth: both contain an active M1 mechanism.

Sign in / Sign up

Export Citation Format

Share Document