part 2. mechanisms of carcinogenesis chapter 13. Alterations in cell proliferation, cell death, or nutrient supply Jane C. Caldwell PART 2 CHAPTER 13 Introduction these agents – that can be used to 1986; Jayat and Ratinaud, 1993; identify and organize mechanistic in- Stacey and Hitomi, 2008; Irish and Mechanistic data have been in- formation related to cancer induction Doxie, 2014). Although for many of cluded in Volume 100 of the IARC (see Chapter 10, by Smith; see also the human carcinogens Volume 100 Monographs, and they vary with the Smith et al., 2016). One of these 10 of the IARC Monographs contains agent studied. These data are espe- mechanistic categories of data is a more descriptive data under this cat- cially dependent on the type of study composite that includes information egory, primarily as changes in cell and the contemporary understand- on the ability of a carcinogen to alter proliferation, these changes are in- ing of the state of the science at the cell proliferation, cell death, or nutri- herently related to alterations in cell time of publication of the study. ent supply. signalling and/or cell-cycle control. As an outcome of the two-part Alteration of cell proliferation is Many challenges are associated IARC Workshop on Tumour Site identified through assays that detect with the use of data described for Concordance and Mechanisms replicative DNA synthesis, 5-bro- of Carcinogenesis, a mechanistic mo-2′-deoxyuridine (BrdU) labelling, alterations in cell proliferation, cell database was assembled for the proliferating cell nuclear antigen death, or nutrient supply to examine IARC Group 1 carcinogens (see (PCNA) labelling, and hyperplasia mechanistic and tumour site concor- Chapter 22, by Krewski et al.). These or the occurrence of multinucleated dance between humans and experi- agents were examined with regard to cells by light microscopy, and through mental animals. Several key mecha- 10 key characteristics – one or more analysis of some of these end-points nistic characteristics can result in or of which are commonly exhibited by by use of flow cytometry (Gray et al., arise from changes in cell signalling Part 2 • Chapter 13. Alterations in cell proliferation, cell death, or nutrient supply 117 (e.g. inflammation, genotoxicity, and This chapter focuses on issues as- ellers, growth factors, growth factor epigenetic alterations) and can have sociated with the understanding and receptors, signal transducers, and both genetic and epigenetic origins. interpretation of available data for apoptosis regulators (Narayanan There are other levels of interde- this key mechanistic characteristic. et al., 2015). In response to mito- pendence between the key mecha- gens, cell proliferation is triggered by nistic characteristics. Inflammation, Genetic drivers of cell increased translocation into the nu- excessive oxidative stress, and ge- proliferation and apoptosis: cleus of ERK 1 and 2 (ERK1/2), the complex relationships and nomic instability are related (see last proteins in the MAPK/ERK cas- pleiotropic roles of cell Chapter 17, by Kane). Mutagenesis cade. Activating mutations upstream signalling molecules may also underlie some epigenetic or within the ERK1/2 cascade are events that change cell signalling. Cell signalling is a process whereby present in several human cancers, For example, mutations in genes proteins or other chemical messen- but ERK1/2 activation also occurs in involved in the methylation of DNA, gers activate receptors at the cell cancers without mutation of compo- modification of histones, and bind- surface and then transmit signals nents of the cascade (Plotnikov et al., ing of microRNAs to the genome or inside the cell via membrane-to-nu- 2011). to other RNAs may initiate epige- cleus pathways. In healthy adults, Ras, a small upstream guano- netic changes (see Chapter 12, by cell proliferation, cell differentiation, sine-5′-triphosphate (GTP)-binding DeMarini, and Chapter 20, by Rice and cell death determine the size protein in several signalling path- and Herceg). of the proliferating cell population ways, has two isoforms, H-Ras and Cell signalling pathways that reg- in soft tissues, for example surface K-Ras, with different potencies to ulate cell proliferation are not inde- epithelia, mucosal lining cells of ex- activate the MAPK/ERK pathway; pendent of those associated with cretory ducts, columnar epithelia the KRAS gene is more frequent- other key mechanistic characteris- lining the gastrointestinal tract and ly mutated in human cancer, which tics of IARC Group 1 carcinogens. uterus, transitional epithelium of the can result in constitutive activation Many of the genes associated with urinary tract, and bone marrow and (McCubrey et al., 2007). H-Ras cell proliferation are also linked with haematopoietic cells. These pro- has been implicated as contributing apoptosis, inflammation, and several liferating cells replace dead cells to the cancer phenotype, through pleiotropic responses. Dysregulation throughout life. Pathological effects evasion of anti-growth signalling, in the mitogen-activated protein (e.g. injury resulting from hepato- angiogenesis, genetic instability, kinase (MAPK) pathway affects cellular necrosis or partial hepatec- tissue invasion and metastasis, tu- most, if not all, processes involved tomy) and physiological conditions mour-promoting inflammation, and in cancer (Dhillon et al., 2007). The (e.g. estrogen-induced effects on the changes in the tumour microenviron- extracellular signal-regulated kinase endometrium during the menstrual ment (Engström et al., 2015). K-Ras (ERK) pathway of the MAPK family cycle) can involve stimulation of cell promotes metabolic reprogramming, is most commonly associated with proliferation (Engström et al., 2015). activation of proliferative signalling regulation of cell proliferation (Reuter The relationships between cell pathways, glycolysis, reduction of et al., 2010). signalling molecules and pathways oxidative metabolism in the tricar- The ability to use this character- that control cell proliferation and pro- boxylic acid cycle, and channelling of istic to evaluate both mechanistic grammed cell death (apoptosis) are glucose intermediates into anabolic and tumour site concordance is in- complex. Numerous enzymes and pathways, such as the hexosamine fluenced by recent developments in cell signalling pathways are modulat- biosynthesis pathway. cancer research, by the overarching ed during apoptosis, and dysfunction The tumour suppressor protein issue of how carcinogens may ex- of cell death pathways is associated p63, which is activated by DNA dam- press certain characteristics, and with initiation and progression of tum- age, cellular stress, and oncogenic by the question as to the biological origenesis; the products of proto-on- signal transduction, has pleiotropic basis of the differences between cogenes (genes that encode proteins anti-proliferative and metabolic ef- species, strains, target organs, and that stimulate cell proliferation, inhibit fects that include metabolic cell-cy- target cells in cell signalling and apoptosis, or do both) include tran- cle arrest (Robey et al., 2015). cell-cycle control. scription factors, chromatin remod- Numerous pathways have been 118 identified to be involved in disruption trinucleotides that identify amino protein-coding genes, which are like- of resistance to cell death, and p53 acids, and the regulatory code that ly to mediate species differences (Lin has been described as implicated determines how DNA sequences di- et al., 2014). in cell-cycle arrest, apoptosis, reg- rect gene expression are highly con- Human-to-mouse transgenic ex - ulation of metabolism, DNA repair, served between species. However, peri ments demonstrate recapitu - and every pathway linked to these species differ in the composition and lation of human gene regulation in processes (Narayanan et al., 2015). the length of the DNA sequences mice, even in the case of human Disruption of the MAPK cascades, that use this language in the regu- genes that lack murine orthologues. which are central signalling pathways latory regions of their genes (Nitta However, for distinct biological path- that regulate a wide variety of cellular et al., 2015). ways, the expression profiles of processes, is associated with induc- The Mouse ENCODE (Encyclo- many mouse genes diverged from tion and progression of various dis- pedia of DNA Elements) Consortium those of human orthologues (Yue eases, including not only cancer but reported that the degree of conser- et al., 2014). A core set of candidate also diabetes, autoimmune disease, vation is high: the mouse genome is regulatory sequences were con- and developmental abnormalities similar to the human genome in size, served and display similar activity (Plotnikov et al., 2011). structure, and sequence composi- profiles in humans and mice: expres- The role of gene activation in tion, and more than 80% of mouse sion patterns for genes that encode carcinogenesis is also complex and genes have human orthologues. proteins in the nuclear and intracel- PART 2 evolving. Activation of protein kinase The chromatin landscape in a cell lular organelle compartments, and CHAPTER 13 C, which acts as a catalyst for sever- lineage is relatively stable in both genes involved in RNA processing, al cellular functions that are related humans and mice, transcription fac- nucleic acid metabolism, chromatin to cancer (e.g. cell survival, prolif- eration, apoptosis, and migration), tor networks are substantially