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Event: 870

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Increase, Cell Proliferation

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help
Increase, Cell Proliferation
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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Organ term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor).  Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description.  To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons.  If a desired term does not exist, a new term request may be made via Term Requests.  Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Process Object Action
cell proliferation epithelial cell increased
cell proliferation mesothelial cell increased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
pH Induced Nasal Tumors KeyEvent Cataia Ives (send email) Open for citation & comment Under Review
Frustrated phagocytosis-induced lung cancer KeyEvent Arthur Author (send email) Under development: Not open for comment. Do not cite Under Development
Deposition of energy leading to lung cancer KeyEvent Brendan Ferreri-Hanberry (send email) Open for citation & comment WPHA/WNT Endorsed
Frustrated phagocytosis leads to malignant mesothelioma KeyEvent Evgeniia Kazymova (send email) Under development: Not open for comment. Do not cite
AHR leading to lung cancer via NRF2 tox path KeyEvent Allie Always (send email) Under development: Not open for comment. Do not cite
Ionizing Radiation-Induced AML KeyEvent Allie Always (send email) Under development: Not open for comment. Do not cite
Interaction with lung cells leads to lung cancer KeyEvent Evgeniia Kazymova (send email) Under development: Not open for comment. Do not cite
Deposition of energy leading to cataracts KeyEvent Arthur Author (send email) Open for citation & comment

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
rat Rattus norvegicus High NCBI
mouse Mus musculus High NCBI
human Homo sapiens High NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help
Life stage Evidence
All life stages High

Sex Applicability

An indication of the the relevant sex for this KE. More help
Term Evidence
Unspecific High

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

Throughout their life, cells replicate their organelles and genetic information before dividing to form two new daughter cells, in a process known as cellular proliferation. This replicative process is known as the cell cycle and is subdivided into various stages notably, G1, S, G2, and M in mammals. G1 and G2 are gap phases, separating mitosis and DNA synthesis. Differentiated cells typically remain in G1; however, quiescent cells reside in an optional phase just before G1, known as G0.  

Progression through the cycle is dependent on sufficient nutrient availability to provide optimal nucleic acid, protein, and lipid levels, as well as sufficient cell mass. To this end, the cell cycle is mediated by three major checkpoints: the restriction (R) point, or G1/S checkpoint, controlling entry into S phase, the G2/M checkpoint, controlling entry into mitosis, and one more controlling entry into cytokinesis. If conditions are ideal for division, cells will pass the restriction point (G1/S) and begin the activation and expression of genes used for duplicating centrosomes and DNA, eventually leading to proliferation (Cuyàs et al., 2014).  

Various protein complexes, known as cyclins, cyclin-dependent kinases (CDKs), and cyclin-dependent kinase inhibitors (CKIs) regulate passage through each phase by activating and inhibiting specific processes (Lovicu et al., 2014). The CDKs are responsible for controlling progression through the cell cycle. They promote DNA synthesis and mitosis, and therefore cell division (Barnum & O’Connell, 2014). Furthermore, growth factors are required to stimulate cell division, but after passing through the restriction point at G1 they are no longer necessary (Lovicu et al., 2014).  

In the context of cancer, one hallmark is the sustained and uncontrolled cell proliferation (Hanahan et al., 2011, Portt et al., 2011). When cells obtain a growth advantage due to mutations in critical genes that regulate cell cycle progression, they may begin to proliferate excessively, resulting in hyperplasia and potentially leading to the development of a tumor. This is often achieved through oncogene activation and inactivation of tumor suppressor genes (Hanahan et al., 2011). Cell inactivation and the replacement of these cells can initiate clonal expansion (Heidenreich adn Paretzke et al., 2008). 

Sustained atrophy/degeneration olfactory epithelium under the influence of a cytotoxic agent leads to adaptive tissue remodeling. Cell types unique to olfactory epithelium, e.g. olfactory neurons, sustentacular cells and Bowmans glands, are replaced by cell types comprising respiratory epithelium or squamous epithelium.

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

Two common methods of measuring cell proliferation in vivo are the use of Bromodeoxyuridine (5-bromo-2'-deoxyuridine, BrdU) labeling (Pera, 1977), and Ki67 immunostaining (Grogan, 1988). BrdU is a synthetic analogue of the nucleoside Thymidine. BrDu is incorporated into DNA synthesized during the S1 phase of cell replication and is stable for long periods. Labeling of dividing cells by BrdU is accomplished by infusion, bolus injection, or implantation of osmotic pumps containing BrdU for a period of time sufficient to generate measureable numbers of labeled cells. Tissue sections are stained immunhistochemically with antibodies for BrdU and labeled cells are counted as dividing cells. Similarly, 5-iodo-2'-deoxyuridine (IdU) is another analogue of thymidine used to measure cell proliferation as it is also incorporated into DNA during its synthesis (Devine & Behbehani, 2021). Ki67 is a cellular marker of replication not found in quiescent cells (Roche, 2015). Direct immunohistochemical staining of cells for protein Ki67 using antibodies is an alternative to the use of BrdU, with the benefit of not requiring a separate treatment (injection for pulse-labeling). Cells positive for Ki67 are counted as replicating cells. Replicating cell number is reported per unit tissue area or per cell nuclei (Bogdanffy, 1997). Listed below are common methods for detecting the KE, however there may be other comparable methods that are not listed.

Assay Name References Description OECD Approved Assay
CyQuant Cell Proliferation Assay Jones et al., 2001 DNA-binding dye is added to cell cultures, and the dye signal is measured directly to provide a cell count and thus an indication of cellular proliferation N/A
Nucleotide Analog Incorporation Assays (e.g. BrdU, EdU) Romar et al., 2016, Roche; 2013 Nucleoside analogs are added to cells in culture or injected into animals and become incorporated into the DNA at different rates, depending on the level of cellular proliferation; Antibodies conjugated to a peroxidase or fluorescent tag are used for quantification of the incorporated nucleoside analogs using techniques such as ELISA, flow cytometry, or microscopy Yes (No. 442B)
Cytoplasmic Proliferation Dye Assays Quah & Parish, 2012 Cells are incubated with a cytoplasmic dye of a certain fluorescent intensity; Cell divisions decrease the intensity in such a way that the number of divisions can be calculated using flow cytometry measurements N/A
Colourimetric Dye Assays Vega-Avila & Pugsley, 2011; American Type Culture Collection Cells are incubated with a dye that changes colour following metabolism; Colour change can be measured and extrapolated to cell number and thus provide an indication of cellular proliferation rates N/A
BrdU, Ki67, IdU Quantification - Flow Cytometry  Ligasová et al., 2017; Devine & Behehani, 2021; Kim & Sederstrom, 2015 Measurement of cell proliferation biomarkers by flow cytometry, normalized to total levels of BrdU, Ki67 or IdU.    No

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help

 Cell proliferation is a central process supporting development, tissue homeostasis and carcinogenesis, each of which occur in all vertebrates. This key event has been observed nasal tissues of rats exposed to the chemical initiator vinyl acetate. In general, cell proliferation is necessary in the biological development and reproduction of most organisms. This KE is thus relevant and applicable to all multicellular cell types, tissue types, and taxa.

Life stage applicability: This key event is not life stage specific (Fujimichi and Hamada, 2014; Barnard et al., 2022).

Sex applicability: This key event is not sex specific (Markiewicz et al., 2015).

Evidence for perturbation by a stressor: There is a large body of evidence supporting the effectiveness of ionizing radiation, UV, and mechanical wounding as stressors for increased cell proliferation. These stressors can be subdivided into X-rays (van Sallmann, 1951; Ramsell and Berry, 1966; Richards, 1966; Riley et al., 1988; Riley et al., 1989; Kleiman et al., 2007; Pendergrass et al., 2010; Fujimichi and Hamada, 2014, Markiewicz et al., 2015; Bahia et al., 2018), 60Co γ-rays (Hanna and O’Brien, 1963; Barnard et al., 2022; McCarron et al., 2021), 137Cs γ-rays (Andley and Spector, 2005), neutrons (Richards, 1966; Riley et al., 1988; Riley et al., 1989), 40Ar (Worgul et al., 1986), 56Fe (Riley et al., 1989), UVB (Söderberg et al., 1986; Andley et al., 1994; Cheng et al., 2019), UVC (Trenton and Courtois, 1981), and mechanical wounding (Riley et al., 1989).


List of the literature that was cited for this KE description. More help

Andley, U. P. et al. (1994), “Modulation of lens epithelial cell proliferation by enhanced prostaglandin synthesis after UVB exposure”, Investigative Ophthalmology & Visual Science, Vol. 35/2, Rockville, pp. 374-381  

Andley, U. and A. Spector (2005), “Peroxide resistance in human and mouse lens epithelial cell lines is related to long-term changes in cell biology and architecture”, Free Radical Biology & Medicine, Vol. 39/6, Elsevier B.V, United States, 

Bahia, S. et al. (2018), “Oxidative and nitrative stress-related changes in human lens epithelial cells following exposure to X-rays”, International journal of radiation biology, Vol. 94/4, England, 

Barnard, S. et al. (2022), “Lens Epithelial Cell Proliferation in Response to Ionizing Radiation.”, Radiation Research, Vol. 197/1, Radiation Research Society, United States, 

Barnum, K. and M. O’Connell (2014), “Cell cycle regulation by checkpoints”, in Cell cycle control, Springer, New York, 10.1007/978-1-4939-0888-2 

Bogdanffy. et al. (1997). “FOUR-WEEK INHALATION CELL PROLIFERATION STUDY OF THE EFFECTS OF VINYL ACETATE ON RAT NASAL EPITHELIUM”, Inhalation Toxicology, Taylor & Francis. 9: 331-350.

Cheng, T. et al. (2019), “lncRNA H19 contributes to oxidative damage repair in the early age-related cataract by regulating miR-29a/TDG axis”, Journal of cellular and molecular medicine, Vol. 23/9, Wiley Subscription Services, Inc. England, 

Cuyàs, E. et al. (2014), “Cell cycle regulation by the nutrient-sensing mammalian target of rapamycin (mTOR) pathway”, in Cell cycle control, Springer, New York, 10.1007/978-1-4939-0888-2 

Devine,R. D, and G. K. Behbehani (2021), “Use of the Pyrimidine Analog, 5-Iodo-2'-Deoxyuridine (IdU) with Cell Cycle Markers to establish Cell Cycle Phases in a Mass Cytometry Platform”, Journal of visualized experiments. (176). doi:10.3791/60556  

Fujimichi, Y. and N. Hamada (2014), “Ionizing irradiation not only inactivates clonogenic potential in primary normal human diploid lens epithelial cells but also stimulates cell proliferation in a subset of this population”, PloS one, Vol. 9/5, e98154, Public Library of Science, United States, 

Grogan. et al. (1988). “Independent prognostic significance of a nuclear proliferation antigen in diffuse large cell lymphomas as determined by the monoclonal antibody Ki-67”, Blood. 71: 1157-1160.

Hanna, C. and J. E. O’Brien (1963), “Lens epithelial cell proliferation and migration in radiation cataracts”, Radiation research, Academic Press, Inc, United States, 

Hanahan, D. & R. A. Weinberg, (2011),” Hallmarks of cancer: the next generation”, Cell. 144(5):646-74. doi: 10.1016/j.cell.2011.02.013.

Heidenreich WF, Paretzke HG. (2008) Promotion of initiated cells by radiation-induced cell inactivation. Radiat Res. Nov;170(5):613-7. doi: 10.1667/RR0957.1. PMID: 18959457.

Jones, J. L. et al. (2001), Sensitive determination of cell number using the CyQUANT cell proliferation assay. Journal of Immunological Methods. 254(1-2), 85-98. Doi:10.1016/s0022-1759(01)00404-5.

Kim, K. H. and Sederstrom J. M. (2015), “Assaying Cell Cycle Status Using Flow Cytometry.” Current protocols in molecular biology, 111:28.6.1-28.6.11., doi:10.1002/0471142727.mb2806s111  

Kleiman, N. J. et al. (2007), “Mrad9 and Atm haplinsufficiency enhance spontaneous and X-ray-induced cataractogenesis in mice”, Radiation research, Vol. 168/5, Radiation Research Society, United States, 

Ligasová, A. et al. (2017), “Cell cycle profiling by image and flow cytometry: The optimised protocol for the detection of replicational activity using 5-Bromo-2'-deoxyuridine, low concentration of hydrochloric acid and exonuclease III.” PloS one, 12(4): e0175880, doi:10.1371/journal.pone.0175880  

Lovicu, J. et al (2014), “Lens epithelial cell proliferation”, in Lens epithelium and posterior capsular opacification, Springer, Tokyo, 10.1007/978-4-431-54300-8_4 

Markiewicz, E. et al. (2015), “Nonlinear ionizing radiation-induced changes in eye lens cell proliferation, cyclin K1 expression and lens shape”, Open biology, Vol. 5/4, The Royal Society, England, 

McCarron, R. A. et al. (2021), “Radiation-induced lens opacity and cataractogenesis: a lifetime study using mice of varying genetic backgrounds”, Radiation research, Vol. 197/1, Radiation Research Society, United States, 

Pendergrass, W. et al. (2010), “X-ray induced cataract is preceded by LEC loss, and coincident with accumulation of cortical DNA, and ROS; similarities with age-related cataracts”, Molecular vision, Vol. 16, Molecular Vision, United States, pp. 1496-1513 

Pera, Mattias and Detzer (1977). “Methods for determining the proliferation kinetics of cells by means of 5-bromodeoxyuridine”, Cell Tissue Kinet.10: 255-264. Doi: 10.1111/j.1365-2184.1977.tb00293.x.

Portt, L. et al. (2011), “Anti-apoptosis and cell survival: a review”, Biochim Biophys Acta. 21813(1):238-59. doi: 10.1016/j.bbamcr.2010.10.010.

Quah, J. C. B. & R. C. Parish (2012), “New and improved methods for measuring lymphocyte proliferation in vitro and in vivo using CFSE-like fluorescent dyes”, Journal of Immunological Methods. 379(1-2), 1-14. doi: 10.1016/j.jim.2012.02.012.

Ramsell, T. G. and R. J. Berry (1966), “Recovery from X-ray damage to the lens. The effects of fractionated X-ray doses observed in rabbit lens epithelium irradiated in vivo”, British Journal of Radiology, Vol. 39/467, England, pp. 853-858 

Riley, E. F. et al. (1988), “Recovery of murine lens epithelial cells from single and fractionated doses of X rays and neutrons”, Radiation Research, Vol. 114/3, Academic Press Inc, Oak Brook, 

Riley, E. F. et al. (1989), “Comparison of recovery from potential mitotic abnormality in mitotically quiescent lens cells after X, neutron, and 56Fe irradiations”, Radiation Research, Vol. 119/2, United States, pp. 232-254 

Richards, R. D. (1966), “Changes in lens epithelium after X-ray or neutron irradiation (mouse and rabbit)”, Transactions of the American Ophthalmological Society, Vol. 64, United States, pp. 700-734 

Roche Applied Science, (2013), “Cell Proliferation Elisa, BrdU (Colourmetric) ». Version 16

Romar, A. G., S. T. Kupper & J. S. Divito (2015), “Research Techniques Made Simple: Techniques to Assess Cell Proliferation”,  Journal of Investigative Dermatology. 136(1), e1-7. doi: 10.1016/j.jid.2015.11.020.

Söderberg, P. G. et al. (1986), “Unscheduled DNA synthesis in lens epithelium after in vivo exposure to UV radiation in the 300 nm wavelength region”, Acta Ophthalmologica, Vol. 64/2, Blackwell Publishing Ltd, Oxford, UK, 

Trenton, J. A. and Y. Courtois (1981), “Evolution of the distribution, proliferation and ultraviolet repair capacity of rat lens epithelial cells as a function of maturation and aging”, Mechanisms of Ageing and Development, Vol. 15/3, Elsevier, Ireland, 

Vega-Avila, E. & K. M. Pugsley (2011), “An Overview of Colorimetric Assay Methods Used to Assess Survival or Proliferation of Mammalian Cells”, Proc. West. Pharmacol. Soc. 54, 10-4.

von Sallmann, L. (1951), “Experimental studies on early lens changes after x-ray irradiation III. Effect of X-radiation on mitotic activity and nuclear fragmentation of lens epithelium in normal and cysteine-treated rabbits”, Transactions of the American Ophthalmological Society, Vol. 48, United States, pp. 228-242 

Worgul, B. V. et al. (1986), “Accelerated heavy particles and the lens II. Cytopathological changes”, Investigative Ophthalmology and Visual Science, Vol 27/1, pp. 108-114