scholarly journals Molecular mechanisms creating bistable switches at cell cycle transitions

Open Biology ◽  
2013 ◽  
Vol 3 (3) ◽  
pp. 120179 ◽  
Author(s):  
Anael Verdugo ◽  
P. K. Vinod ◽  
John J. Tyson ◽  
Bela Novak
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Feedback Loop ◽  
Molecular Mechanisms ◽  
Eukaryotic Cell ◽  
Mitotic Checkpoint ◽  
Toggle Switch ◽  
Inhibitory Protein ◽  
Common Features ◽  
Cellular Decision Making

Progression through the eukaryotic cell cycle is characterized by specific transitions, where cells move irreversibly from stage i −1 of the cycle into stage i . These irreversible cell cycle transitions are regulated by underlying bistable switches, which share some common features. An inhibitory protein stalls progression, and an activatory protein promotes progression. The inhibitor and activator are locked in a double-negative feedback loop, creating a one-way toggle switch that guarantees an irreversible commitment to move forward through the cell cycle, and it opposes regression from stage i to stage i −1. In many cases, the activator is an enzyme that modifies the inhibitor in multiple steps, whereas the hypo-modified inhibitor binds strongly to the activator and resists its enzymatic activity. These interactions are the basis of a reaction motif that provides a simple and generic account of many characteristic properties of cell cycle transitions. To demonstrate this assertion, we apply the motif in detail to the G1/S transition in budding yeast and to the mitotic checkpoint in mammalian cells. Variations of the motif might support irreversible cellular decision-making in other contexts.

scholarly journals Cell growth dilutes the cell cycle inhibitor Rb to trigger cell division

2018 ◽  
Author(s):  
Evgeny Zatulovskiy ◽  
Daniel F. Berenson ◽  
Benjamin R. Topacio ◽  
Jan M. Skotheim
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Cell Growth ◽  
Cell Size ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Inverse Correlation ◽  
Cell Types ◽  
Similar Amount ◽  
Cell Cycle Inhibitor

Cell size is fundamental to function in different cell types across the human body because it sets the scale of organelle structures, biosynthesis, and surface transport1,2. Tiny erythrocytes squeeze through capillaries to transport oxygen, while the million-fold larger oocyte divides without growth to form the ~100 cell pre-implantation embryo. Despite the vast size range across cell types, cells of a given type are typically uniform in size likely because cells are able to accurately couple cell growth to division3–6. While some genes whose disruption in mammalian cells affects cell size have been identified, the molecular mechanisms through which cell growth drives cell division have remained elusive7–12. Here, we show that cell growth acts to dilute the cell cycle inhibitor Rb to drive cell cycle progression from G1 to S phase in human cells. In contrast, other G1/S regulators remained at nearly constant concentration. Rb is a stable protein that is synthesized during S and G2 phases in an amount that is independent of cell size. Equal partitioning to daughter cells of chromatin bound Rb then ensures that all cells at birth inherit a similar amount of Rb protein. RB overexpression increased cell size in tissue culture and a mouse cancer model, while RB deletion decreased cell size and removed the inverse correlation between cell size at birth and the duration of G1 phase. Thus, Rb-dilution by cell growth in G1 provides a long-sought cell autonomous molecular mechanism for cell size homeostasis.

Molecular Mechanisms of Spindle Checkpoint-Apoptosis Linkage and Karyotypic Stability in Stem Cells.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3361-3361
Author(s):  
Charlie Mantel ◽  
Sara Rhorabough ◽  
Ying Guo ◽  
Man-Ryul Lee ◽  
Myung-Kwan Han ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Stem Cells ◽  
Cell Fate ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Spindle Checkpoint ◽  
Cyclin B1 ◽  
Polyploid Cell ◽  
Mitotic Slippage

Abstract Ex-vivo expansion of human HSC prior to bone marrow transplantation is still an unrealized goal that could greatly extend the usefulness of this mainstay strategy for treating numerous human hematologic diseases. The safety of this process for potential use in humans depends in large part on the maintenance of karyotypic stability of HSC during expansion, a lack of which could contribute to serious, even fatal, complications such as cancer, and could also contribute to engraftment failure. The spindle checkpoint and its linkage to apoptosis initiation is one of the most important cellular processes that helps maintain chromosomal stability in rapidly proliferating cell populations by removing aneuploid and karyotypically abnormal cells via activation of cell death programs. Detailed understanding of the molecular regulation of this vital cell cycle checkpoint is important to maximize safety of in-vitro HSC expansion techniques. It is widely accepted that mammalian cells enter the next G1-phase with 4N DNA after slippage from prolonged drug-induced mitotic block caused by activation of the transient spindle checkpoint that it is from this state that polyploid/aneuploid cells initiate apoptosis. However, definitive biochemical evidence for G1 is scarce or unconvincing; in part because of methods of protein extraction required for immunoblot analysis that cannot take into account the cell cycle heterogeneity of cell cultures. We used single-cell-intracellular-flow-cytometric analysis to define important factors determining cell fate after mitotic slippage. Results from human and mouse embryonic stem cells that reenter polyploid cell cycles are compared to human somatic hematopoietic cells that die after MS. We now report for the first time that phosphorylation status of pRb, p53, CDK1, and cyclin B1 levels are important for cell fate/apoptosis decision in mitotic-slippage cells, which occurs in a unique, intervening, non-G1, tetraploid subphase. Hyperphosphorylated Rb was extremely abundant in mitotic-slippage cells, a cell signaling event usually associated with early G1-S phase transition. P53 was phosphorylated at sites known to be associated with apoptosis regulation. Cyclin A and B1 were undetectable in mitotic slippage cells; yet, CDK1 was phosphorylated at sites typically associated with its activation. Evidence is also presented raising the possibility of cyclin B1-independent CDK1 activity in mitotic-slippage cells. These findings challenge the current models of spindle checkpoint-apoptosis linkages. Our new model could have important implications for methods to maintain karyotypic stability during ex-vivo HSC expansion.

scholarly journals Cyclin D3-CDK6 Complex Facilitates Tumorigenesis by Regulating the C-Myc/miR-15a/16 Axis in a Feedback Loop in Gastric Cancer

2020 ◽  
Author(s):  
Yeting Hong ◽  
Wei He ◽  
Jianbin Zhang ◽  
Lu Shen ◽  
Chong Yu ◽  
...  
Keyword(s):  
Gastric Cancer ◽  
Cell Cycle ◽  
Cell Proliferation ◽  
Feedback Loop ◽  
Cell Cycle Progression ◽  
Molecular Mechanisms ◽  
Cyclin D3 ◽  
Luciferase Reporter

Abstract Background: Cyclin D3-CDK6 complex is a component of the core cell cycle machinery that regulates cell proliferation. By using Human Protein Atlas database, a higher expression level of this complex was found in gastric cancer. However, the function of this complex in gastric cancer remain poorly understood. This study aims to determine the expression pattern of this complex in gastric cancer and to investigate its biological role during tumorigenesis.Methods: To demonstrate that Cyclin D3-CDK6 regulate the c-Myc/miR-15a/16 axis in a feedback loop in gastric cancer, a series of methods were conducted both in vitro and in vivo experiments, including qRT-PCR, western blot analysis, EdU assay, flow cytometry, luciferase reporter assay and immunohistochemical staining. SPSS and Graphpad prism software were used for data analysis.Results: In this study, we found that Cyclin D3 and CDK6 were significantly upregulated in gastric cancer and correlated with poorer overall survival. Further study proved that this complex significantly promoted cell proliferation and cell cycle progression in vitro and accelerated xenografted tumor growth in vivo. Furthermore, we explored the molecular mechanisms through which the complex mediated Rb phosphorylation and then promoted c-Myc expression in vitro, we also found c-Myc could suppress miR-15a/16 expression in gastric cancer cell. Finally, we found that miR-15a/16 can simultaneously regulate Cyclin D3 and CDK6 expression as direct target genes.Conclusions: Our findings uncover the Cyclin D3-CDK6/c-Myc/miR-15a/16 feedback loop axis as a pivotal role in the regulation of gastric cancer tumorigenesis, and this regulating axis may provide a potential therapeutic target for gastric cancer treatment.

scholarly journals Getting to S: CDK functions and targets on the path to cell-cycle commitment

F1000Research ◽  
2016 ◽  
Vol 5 ◽  
pp. 2374 ◽  
Author(s):  
Robert P. Fisher
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Growth Conditions ◽  
Control Mechanisms ◽  
Cell Fates ◽  
Cycle Arrest ◽  
Distinct Cell ◽  
Cast Doubt ◽  
Multicellular Organisms

How and when eukaryotic cells make the irrevocable commitment to divide remain central questions in the cell-cycle field. Parallel studies in yeast and mammalian cells seemed to suggest analogous control mechanisms operating during the G1 phase—at Start or the restriction (R) point, respectively—to integrate nutritional and developmental signals and decide between distinct cell fates: cell-cycle arrest or exit versus irreversible commitment to a round of division. Recent work has revealed molecular mechanisms underlying this decision-making process in both yeast and mammalian cells but also cast doubt on the nature and timing of cell-cycle commitment in multicellular organisms. These studies suggest an expanded temporal window of mitogen sensing under certain growth conditions, illuminate unexpected obstacles and exit ramps on the path to full cell-cycle commitment, and raise new questions regarding the functions of cyclin-dependent kinases (CDKs) that drive G1 progression and S-phase entry.

Cell cycle regulators in Drosophila: downstream and part of developmental decisions

1997 ◽  
Vol 110 (5) ◽  
pp. 523-528 ◽  
Author(s):  
C.F. Lehner ◽  
M.E. Lane
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Molecular Mechanisms ◽  
Eukaryotic Cell ◽  
Embryonic Cell ◽  
Developmental Phase ◽  
Cell Cycle Regulators ◽  
Egg Extracts ◽  
Extensive Growth ◽  
New Perspective

The molecular identification of an evolutionarily conserved set of cell cycle regulators in yeast, Xenopus egg extracts, and vertebrate cell culture has opened up a new perspective for understanding the mechanisms that regulate cell proliferation during metazoan development. Now we can study how the crucial regulators of eukaryotic cell cycle progression, the various cyclin/cdk complexes (for a recent review see Nigg (1995) BioEssays 17, 471–480), are turned on or off during development. In Drosophila, this analysis is most advanced, in particular in the case of the rather rigidly programmed embryonic cell cycles that generate the cells of the larvae. In addition, this analysis has revealed how the mitotic cycle is transformed into an endocycle which allows the extensive growth of larvae and oocytes. In contrast, we know little about cyclin/cdk regulation during the imaginal proliferation that generates the cells of the adult. Nevertheless, we will also consider this second developmental phase with its conspicuous regulative character, because it will be of great interest for the analysis of the molecular mechanisms that integrate growth and proliferation during development.

scholarly journals Using Budding Yeast to Identify Molecules That Block Cancer Cell ‘Mitotic Slippage’ Only in the Presence of Mitotic Poisons

2021 ◽  
Vol 22 (15) ◽  
pp. 7985
Author(s):  
Scott C. Schuyler ◽  
Hsin-Yu Chen
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Drug Targets ◽  
Budding Yeast ◽  
Eukaryotic Cell ◽  
Mitotic Checkpoint ◽  
Chemotherapeutic Agents ◽  
Cell Cycle Checkpoints ◽  
Yeast Saccharomyces Cerevisiae ◽  
Mitotic Slippage

Research on the budding yeast Saccharomyces cerevisiae has yielded fundamental discoveries on highly conserved biological pathways and yeast remains the best-studied eukaryotic cell in the world. Studies on the mitotic cell cycle and the discovery of cell cycle checkpoints in budding yeast has led to a detailed, although incomplete, understanding of eukaryotic cell cycle progression. In multicellular eukaryotic organisms, uncontrolled aberrant cell division is the defining feature of cancer. Some of the most successful classes of anti-cancer chemotherapeutic agents are mitotic poisons. Mitotic poisons are thought to function by inducing a mitotic spindle checkpoint-dependent cell cycle arrest, via the assembly of the highly conserved mitotic checkpoint complex (MCC), leading to apoptosis. Even in the presence of mitotic poisons, some cancer cells continue cell division via ‘mitotic slippage’, which may correlate with a cancer becoming refractory to mitotic poison chemotherapeutic treatments. In this review, knowledge about budding yeast cell cycle control is explored to suggest novel potential drug targets, namely, specific regions in the highly conserved anaphase-promoting complex/cyclosome (APC/C) subunits Apc1 and/or Apc5, and in a specific N-terminal region in the APC/C co-factor cell division cycle 20 (Cdc20), which may yield molecules which block ‘mitotic slippage’ only in the presence of mitotic poisons.

scholarly journals When Yeast Cells Change their Mind: Cell Cycle 'Start' is Reversible under Starvation

2021 ◽  
Author(s):  
Deniz Irvali ◽  
Fabian P. Schlottmann ◽  
Prathibha Muralidhara ◽  
Iliya Nadelson ◽  
N. Ezgi Wood ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Live Cell Imaging ◽  
Feedback Loop ◽  
Cell Imaging ◽  
Yeast Cells ◽  
Nutrient Depletion ◽  
Restriction Point ◽  
Cell Cycle Inhibitor ◽  
Nutrient Signaling

Eukaryotic cells decide in late G1 whether to commit to another round of genome duplication and division. This point of irreversible cell cycle commitment is a molecular switch termed 'Restriction Point' in mammals and 'Start' in budding yeast. At Start, yeast cells integrate multiple signals such as pheromones, osmolarity, and nutrients. If sufficient nutrients are lacking, cells will not pass Start. However, how the cells respond to nutrient depletion after they have made the Start decision, remains poorly understood. Here, we analyze by live cell imaging how post-Start yeast cells respond to nutrient depletion. We monitor fluorescently labelled Whi5, the cell cycle inhibitor whose export from the nucleus determines Start. Surprisingly, we find that cells that have passed Start can re-import Whi5 back into the nucleus. This occurs when cells are faced with starvation up to 20 minutes after Start. In these cells, the positive feedback loop is interrupted, Whi5 re-binds DNA, and CDK activation occurs a second time once nutrients are replenished. Cells which re-import Whi5 also become sensitive to mating pheromone again, and thus behave like pre-Start cells. In summary, we show that upon starvation the commitment decision at Start can be reversed. We therefore propose that in yeast, as has been suggested for mammalian cells, cell cycle commitment is a multi-step process, where irreversibility in face of nutrient signaling is only reached approximately 20 minutes after CDK activation at Start.

scholarly journals Gains of 12p13.31 delay WNT-mediated initiation of hPSC differentiation and promote residual pluripotency in a cell cycle dependent manner

2021 ◽  
Author(s):  
Alexander Keller ◽  
Yingnan Lei ◽  
Nuša Krivec ◽  
Edouard Couvreu De Deckersberg ◽  
Dominika Dziedzicka ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Wnt Signaling ◽  
Feedback Loop ◽  
Molecular Mechanisms ◽  
Physical Interaction ◽  
Dependent Manner ◽  
Pluripotent Cells ◽  
Primary Driver ◽  
A Cell ◽  
Cycle Dependent

Though gains of chromosome 12p13.31 are highly recurrent in hPSC, their impact on differentiation is poorly understood. We identify a reduction in differentiation capacity towards all three germ layers and a subpopulation of residual pluripotent cells that appear during hepatic specification. These cells form as a result of the overexpression of NANOG and GDF3, whereby NANOG as the primary driver delays activation of WNT signaling, partly as a result of a direct physical interaction with TCF7. Entry into the residual state is determined by cell cycle position at the onset of differentiation and is maintained by a feedback loop between NANOG and GDF3. These findings highlight the ability of genetically abnormal hPSC to escape correct differentiation and to form residual pluripotent cells, an important risk in the safe clinical translation of hPSC. Our results further refine the molecular mechanisms that underpin the exit from pluripotency and onset of differentiation.

scholarly journals Pleiotropic molecular effects of the Mycobacterium ulcerans virulence factor mycolactone underlying the cell death and immunosuppression seen in Buruli ulcer

2014 ◽  
Vol 42 (1) ◽  
pp. 177-183 ◽  
Author(s):  
Belinda Hall ◽  
Rachel Simmonds
Keyword(s):  
Cell Death ◽  
Virulence Factor ◽  
Cell Biology ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Prolonged Exposure ◽  
Buruli Ulcer ◽  
Eukaryotic Cell ◽  
Cellular Systems ◽  
Mycobacterium Ulcerans

Mycolactone is a polyketide macrolide lipid-like secondary metabolite synthesized by Mycobacterium ulcerans, the causative agent of BU (Buruli ulcer), and is the only virulence factor for this pathogen identified to date. Prolonged exposure to high concentrations of mycolactone is cytotoxic to diverse mammalian cells (albeit with varying efficiency), whereas at lower doses it has a spectrum of immunosuppressive activities. Combined, these pleiotropic properties have a powerful influence on local and systemic cellular function that should explain the pathophysiology of BU disease. The last decade has seen significant advances in our understanding of the molecular mechanisms underlying these effects in a range of different cell types. The present review focuses on the current state of our knowledge of mycolactone function, and its molecular and cellular targets, and seeks to identify commonalities between the different functional and cellular systems. Since mycolactone influences fundamental cellular processes (cell division, cell death and inflammation), getting to the root of how mycolactone achieves this could have a profound impact on our understanding of eukaryotic cell biology.

scholarly journals Competition in the chaperone-client network subordinates cell-cycle entry to growth and stress

2019 ◽  
Vol 2 (2) ◽  
pp. e201800277 ◽  
Author(s):  
David F Moreno ◽  
Eva Parisi ◽  
Galal Yahya ◽  
Federico Vaggi ◽  
Attila Csikász-Nagy ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Growth Rate ◽  
Mammalian Cells ◽  
Molecular Mechanisms ◽  
Growth Potential ◽  
Nuclear Accumulation ◽  
Single Cell Level ◽  
Cell Level ◽  
Cell Cycle Entry ◽  
Biosynthetic Machinery

The precise coordination of growth and proliferation has a universal prevalence in cell homeostasis. As a prominent property, cell size is modulated by the coordination between these processes in bacterial, yeast, and mammalian cells, but the underlying molecular mechanisms are largely unknown. Here, we show that multifunctional chaperone systems play a concerted and limiting role in cell-cycle entry, specifically driving nuclear accumulation of the G1 Cdk–cyclin complex. Based on these findings, we establish and test a molecular competition model that recapitulates cell-cycle-entry dependence on growth rate. As key predictions at a single-cell level, we show that availability of the Ydj1 chaperone and nuclear accumulation of the G1 cyclin Cln3 are inversely dependent on growth rate and readily respond to changes in protein synthesis and stress conditions that alter protein folding requirements. Thus, chaperone workload would subordinate Start to the biosynthetic machinery and dynamically adjust proliferation to the growth potential of the cell.

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