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Key Event Title
Increase, Cell Proliferation
|Level of Biological Organization|
Key Event Components
|cell proliferation||epithelial cell||increased|
|cell proliferation||mesothelial cell||increased|
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP||Point of Contact||Author Status||OECD Status|
|pH Induced Nasal Tumors||KeyEvent||Justin Teeguarden (send email)||Open for citation & comment||EAGMST Under Review|
|Frustrated phagocytosis-induced lung cancer||KeyEvent||Carole Seidel (send email)||Under development: Not open for comment. Do not cite||Under Development|
|Deposition of energy leading to lung cancer||KeyEvent||Vinita Chauhan (send email)||Open for citation & comment||EAGMST Approved|
|Frustrated phagocytosis leads to malignant mesothelioma||KeyEvent||Penny Nymark (send email)||Under development: Not open for comment. Do not cite|
|AHR leading to lung cancer via NRF2 tox path||KeyEvent||Dianke Yu (send email)||Under development: Not open for comment. Do not cite|
|Ionizing Radiation-Induced AML||KeyEvent||Dag Anders Brede (send email)||Under development: Not open for comment. Do not cite|
|Interaction with lung cells leads to lung cancer||KeyEvent||Penny Nymark (send email)||Under development: Not open for comment. Do not cite|
|Deposition of energy leading to cataracts||KeyEvent||Vinita Chauhan (send email)||Open for citation & comment|
|All life stages||High|
Key Event Description
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
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. 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|
Domain of Applicability
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).
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, https://doi.org/10.1016/j.freeradbiomed.2005.04.028
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, https://doi.org/10.1080/09553002.2018.1439194
Barnard, S. et al. (2022), “Lens Epithelial Cell Proliferation in Response to Ionizing Radiation.”, Radiation Research, Vol. 197/1, Radiation Research Society, United States, https://doi.org/10.1667/RADE-20-00294.1
Barnum, K. and M. O’Connell (2014), “Cell cycle regulation by checkpoints”, in Cell cycle control, Springer, New York, http://doi.org/ 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, https://doi.org/10.1111/jcmm.14489
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, http://dx.doi.org/ 10.1007/978-1-4939-0888-2
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, https://doi.org/10.1371/journal.pone.0098154
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, https://doi.org/10.2307/3571405
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.
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, https://doi.org/10.1667/rr1122.1
Lovicu, J. et al (2014), “Lens epithelial cell proliferation”, in Lens epithelium and posterior capsular opacification, Springer, Tokyo, http://dx.doi.org/ 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, https://doi.org/10.1098/rsob.150011
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, https://doi.org/10.1667/RADE-20-00266.1
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, https://doi.org/10.2307/3577127
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, https://doi.org/10.1111/j.1755-3768.1986.tb06894.x
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, https://doi.org/1016/0047-6374(81)90134-2
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