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. 2009 Jan 20;106(3):785-90.
doi: 10.1073/pnas.0806196106. Epub 2009 Jan 12.

VSports app下载 - Distinct mechanisms act in concert to mediate cell cycle arrest

Jared E Toettcher  1 , Alexander Loewer, Gerard J Ostheimer, Michael B Yaffe, Bruce Tidor, Galit Lahav
Affiliations

Distinct mechanisms act in concert to mediate cell cycle arrest

"V体育ios版" Jared E Toettcher et al. Proc Natl Acad Sci U S A. .

Abstract

In response to DNA damage, cells arrest at specific stages in the cell cycle. This arrest must fulfill at least 3 requirements: it must be activated promptly; it must be sustained as long as damage is present to prevent loss of genomic information; and after the arrest, cells must re-enter into the appropriate cell cycle phase to ensure proper ploidy VSports手机版. Multiple molecular mechanisms capable of arresting the cell cycle have been identified in mammalian cells; however, it is unknown whether each mechanism meets all 3 requirements or whether they act together to confer specific functions to the arrest. To address this question, we integrated mathematical models describing the cell cycle and the DNA damage signaling networks and tested the contributions of each mechanism to cell cycle arrest and re-entry. Predictions from this model were then tested with quantitative experiments to identify the combined action of arrest mechanisms in irradiated cells. We find that different arrest mechanisms serve indispensable roles in the proper cellular response to DNA damage over time: p53-independent cyclin inactivation confers immediate arrest, whereas p53-dependent cyclin downregulation allows this arrest to be sustained. Additionally, p21-mediated inhibition of cyclin-dependent kinase activity is indispensable for preventing improper cell cycle re-entry and endoreduplication. This work shows that in a complex signaling network, seemingly redundant mechanisms, acting in a concerted fashion, can achieve a specific cellular outcome. .

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Cell cycle and DNA damage models. (A) Diagram of key species in the integrated model of DNA damage signaling (blue) and cell cycle arrest (black). Bridging connections consist of species modulating cell cycle arrest (red). The approximate cell cycle phases are shown below the diagram. Three classes of arrest mechanisms are indicated by numerals: I: G1 arrest by p21 induction; II: G2 arrest by G2 cyclin inactivation; and III: G2 arrest by G2 cyclin transcriptional repression. (B) Cell cycle model simulation showing cyclins E, A, and B and phosphorylated APC. Progression through cell cycle phases and changes in DNA content are indicated above the simulation. (C) Simulation of the DNA damage network after onset of damage at times tD until the repair time tR. Nuclear p53, phospho-Chk2, and Wip1 species are shown. (D-F) Simulation of arrest mechanisms (I-III). Dynamics are influenced by the p53 and Chk2 activity from the DNA damage network shown in C.
Fig. 2.
Fig. 2.
Steady-state cyclin levels during simulated arrest. Rows indicate the arrest mechanism; columns indicate the cyclin measured. In each square both strength and time of arrest application are varied. Arrest strength was varied by scaling the value of the parameters implementing each arrest mechanism over 2 orders of magnitude from the minimum value required to generate arrest (SI Appendix, “Modeling cell cycle arrest”). Colors indicate the ratio of steady-state cyclin levels to their maximum level during normal cycling.
Fig. 3.
Fig. 3.
Cell cycle progression and cyclin levels during arrest. Flow cytometry histograms of DNA content and cyclin levels in HCT p53+/+ (A) and p53−/− (B) cells after IR. Cells were irradiated and stained for DNA content and cyclin levels. Histograms of cyclin levels are gated from the 4N population only. Quantification of apoptotic cells is shown in Fig. S2F.
Fig. 4.
Fig. 4.
Cell cycle model training and prediction. (A) Fractions of G1, S, and G2 cells in freely cycling HCT p53+/+ and HCT p53−/− populations are compared with the amount of time spent by the initial and the fitted model in G1, S, and G2. (B) The ratios of cyclins E and B during IR-induced arrest to their maximum level during normal cycling in both HCT p53+/+ and p53−/− cells, compared with the ratios calculated from model trajectories. (C) Time courses of DNA content after treatment with 10 Gy IR. HCT p53+/+ and p53−/− cells were irradiated, and the fractions of cells with G1, S, and G2 DNA contents were measured by FACS. For apoptotic fraction, see Fig. S2F. (D) Model-generated cell cycle distribution time courses. Individual model trajectories (5 × 102) were simulated from initial conditions distributed through the cell cycle (SI Appendix, “Simulating populations of cells”).
Fig. 5.
Fig. 5.
p21 function in preventing endoreduplication. (A) Model prediction of HCT p21−/− endoreduplication. Individual model trajectories (5 × 102) were simulated from initial conditions distributed through the cell cycle. (B) DNA content profiles for HCT p21−/− cells after irradiation with 10 Gy IR. For apoptotic fraction, see Fig. S2F. (C) Fractions of cells with >G2 DNA content in HCT wild type (wt) and p21−/− cell lines (mean ± SE) as a function of time after irradiation. (D) Fractions of cells with >G2 DNA content after irradiation followed by addition of Cdk1 inhibitor RO-3306 at 16 h after IR (mean ± SE). The increased endoreduplication of p21−/− cells after inhibitor treatment can be explained by a decrease in cells entering mitosis prematurely, creating a larger pool of cells able to undergo a second S phase. (E) Phase contrast images of p21−/− cells 72 h after irradiation. Without added inhibitor, cells are multinucleated (arrow), indicating failures during mitosis. Cells treated with inhibitor are mononucleate but have also undergone endoreduplication.
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References

    1. Murray AW. Recycling the cell cycle: Cyclins revisited. Cell. 2004;116:221–234. - "V体育2025版" PubMed
    1. Tyson JJ. Modeling the cell division cycle: cdc2 and cyclin interactions. Proc Natl Acad Sci USA. 1991;88:7328–7332. - PMC - PubMed
    1. Haberichter T, et al. A systems biology dynamical model of mammalian G1 cell cycle progression. Mol Syst Biol. 2007;3:84. - "VSports app下载" PMC - PubMed
    1. Novak B, Tyson JJ. A model for restriction point control of the mammalian cell cycle. J Theor Biol. 2004;230:563–579. - PubMed (VSports在线直播)
    1. Banin S, et al. Enhanced phosphorylation of p53 by ATM in response to DNA damage. Science. 1998;281:1674–1677. - PubMed

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