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Proc Natl Acad Sci U S A. 2018 Mar 6;115(10):2532-2537. doi: 10.1073/pnas.1715345115. Epub 2018 Feb 20.

A comprehensive model for the proliferation-quiescence decision in response to endogenous DNA damage in human cells.

Author information

1
Department of Biochemistry, University of Oxford, OX1 3QU Oxford, United Kingdom; stefan.heldt@bioch.ox.ac.uk bela.novak@bioch.ox.ac.uk.
2
Division of Cancer Biology, The Institute of Cancer Research, SW3 6JB London, United Kingdom.
3
Department of Computational Systems Medicine, Imperial College, SW7 2AZ London, United Kingdom.

Abstract

Human cells that suffer mild DNA damage can enter a reversible state of growth arrest known as quiescence. This decision to temporarily exit the cell cycle is essential to prevent the propagation of mutations, and most cancer cells harbor defects in the underlying control system. Here we present a mechanistic mathematical model to study the proliferation-quiescence decision in nontransformed human cells. We show that two bistable switches, the restriction point (RP) and the G1/S transition, mediate this decision by integrating DNA damage and mitogen signals. In particular, our data suggest that the cyclin-dependent kinase inhibitor p21 (Cip1/Waf1), which is expressed in response to DNA damage, promotes quiescence by blocking positive feedback loops that facilitate G1 progression downstream of serum stimulation. Intriguingly, cells exploit bistability in the RP to convert graded p21 and mitogen signals into an all-or-nothing cell-cycle response. The same mechanism creates a window of opportunity where G1 cells that have passed the RP can revert to quiescence if exposed to DNA damage. We present experimental evidence that cells gradually lose this ability to revert to quiescence as they progress through G1 and that the onset of rapid p21 degradation at the G1/S transition prevents this response altogether, insulating S phase from mild, endogenous DNA damage. Thus, two bistable switches conspire in the early cell cycle to provide both sensitivity and robustness to external stimuli.

KEYWORDS:

DNA damage; cell cycle; live-cell imaging; mathematical modelling; proliferation–quiescence decision

PMID:
29463760
PMCID:
PMC5877942
DOI:
10.1073/pnas.1715345115
[Indexed for MEDLINE]
Free PMC Article

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