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The relation between protein accumulation and cell cycle traverse of human NHIK 3025 cells in unbalanced growth
Abstract:
Human NHIK 3025 cells, synchronized by mitotic selection, were given 2 mM thymidine, which inhibited DNA synthesis without reducing the rate of protein accumulation. After removal of the thymidine the cells proceeded towards mitosis and cell division, with an S duration 2 hours shorter than, but a G2 and M duration nearly identical to that of the control cells. If cycloheximide (1.25 muM) was present together with thymidine, no net protein accumulation took place during the treatment, and the subsequent duration of S, G2, and M was similar to that of untreated cells. The shortening of S seen after treatment with thymidine alone would therefore indicate that the rate of DNA synthesis depended on the amount of some preaccumulated protein. The postreplicative period in thymidine-treated cells was lengthened by cycloheximide treatment although the protein content had already been doubled. This suggests that proteins required for the traverse of this part of the cell cycle might have to be synthesized after completion of DNA replication. Shortly after removal of thymidine, the rate of protein accumulation declined markedly, indicating the existence of some mechanism for negative control of cell mass. In addition, the daughters of thymidine-treated cells had their cell cycle shortened by 2 hours. As a result, the cells had returned to balanced growth already in the first cell cycle following the induction of unbalanced growth. In conclusion, our experiments suggest that NHIK 3025 cells might require a minimum time in order to traverse the cell cycle, which is independent of cell mass.
Insights
Cell cycle studies reveal that DNA synthesis inhibition by thymidine shortens the S phase, suggesting protein accumulation is key. Cells also exhibit a minimum cell cycle time independent of cell mass.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cell cycle progression is tightly regulated by DNA replication and protein synthesis.
- Understanding the interplay between DNA synthesis, protein accumulation, and cell cycle duration is crucial for cell biology research.
Purpose of the Study:
- To investigate the impact of inhibiting DNA synthesis on cell cycle progression and protein accumulation in human NHIK 3025 cells.
- To determine if protein synthesis is required for the cell cycle traverse after DNA replication inhibition.
Main Methods:
- Synchronization of NHIK 3025 cells using mitotic selection.
- Treatment with thymidine to inhibit DNA synthesis and cycloheximide to inhibit protein accumulation.
- Monitoring of DNA synthesis, protein accumulation, and cell cycle phase durations (S, G2, M).
Main Results:
- Thymidine treatment inhibited DNA synthesis but allowed protein accumulation, leading to a shortened S phase.
- Cycloheximide co-treatment prevented protein accumulation and normalized S, G2, and M phase durations.
- Post-thymidine treatment showed a lengthened post-replicative period with cycloheximide, suggesting post-replication protein synthesis is necessary.
- A negative feedback mechanism for protein accumulation was observed after thymidine removal.
- Daughter cells exhibited a 2-hour shorter cell cycle, returning to balanced growth rapidly.
Conclusions:
- The rate of DNA synthesis is dependent on pre-accumulated proteins.
- Proteins essential for post-replicative cell cycle progression may require synthesis after DNA replication.
- NHIK 3025 cells appear to have a minimum cell cycle duration that is independent of cell mass.