Hallmarks, Heterogeneity, & Cancer Stem Cells

4/10

According to the Canadian Cancer Society, approximately ______ cancer cases can be prevented through healthy living and policies that protect the health of Canadians.

a disease caused by an uncontrolled division of abnormal cells in a part of the body

Cancer is commonly defined as…

a population of abnormal cells showing temporally unrestricted growth preference over normal cells, and such abnormal cells invade surrounding tissues, cross at least one basement membrane zone, grow in the mesenchyme at the primary site, and may metastasize to distant sites

Cancer is defined in the biomedical field as…

sustained proliferative signalling, evading growth suppressors, non-mutational epigenetic reprogramming, avoiding immune destruction, enabling replicative immortality, tumour-promoting inflammation, polymorphic microbiomes, activating invasion and metastasis, inducing or accessing vasculature, senescent cells, genome instability and mutation, resisting cell death, deregulating cellular metabolism, and unlocking phenotypic plasticity

The 14 hallmarks of cancer are:

every cancer is unique but all share some fundamental features, tumours are heterogeneous in space and time, every cancer is constantly adapting to its environment, the phenotype of a cancer is determined by interactions between tumour cells and their neighbours, and tumours are not just cancer cells

The 5 key principles in oncology are:

competition, amensalism, predation, and parasitism

Negative interactions between tumour subpopulations include:

A harms B and B harms A

In a competitive interaction…

A harms B and A is unaffected

In an amensal interaction…

B harms A and A weakly helps B

In a predatory interaction…

A helps B and B weakly harms A

In a parasitic interaction…

commensalism, synergism, and mutualism

Positive interactions between tumour subpopulations include:

A helps B and A is unaffected

In a commensal interaction…

A and B together create novel characteristics in a new population not seen individually

In a synergistic interaction…

A helps B and B helps A

In a mutualistic interaction…

HeLa

Created in 1951, the first human cell line to survive in vitro

Hayflick Limit

The number of times a normal cell can divide

tissue of origin and the age of the donor

A cell’s Hayflick limit is determined by…

measuring cumulative oxidative damage and monitoring chromosome length

A cell measures how often its ancestors have divided through…

Senescence

Permanent loss of replicative potential

Immortalization

Acquisition of an unlimited replicative lifespan

Transformation

Acquisition of growth factor independence and uncontrolled proliferation

metabolically active, growth arrested, accumulation of double-stranded breaks and/or senescence-associated DNA-damage foci (SDF), apoptosis

Senescent cells are ______ but _____ and are characterised by _______. They are resistant to _____.

Senescent

______ cells in a tumour are not benign

Senescence-associated secretory phenotype (SASP)

The complex mixture of inflammatory cytokines, chemokines, growth factors, and proteases that senescent cells secrete, creating a pro-inflammatory environment

secrete microenvironment-modifying factors, inflammatory cells and fibroblasts, tissue remodelling and restructuring, proliferation and tumour progression in nearby pre-malignant cells

In SASP, tumour cells _______ which recruit _______. This induces ________ and stimulates _______

ARF, p53, p16, p16 INK4A, p21 CIP1

_____, _____, and _____ are senescence signals, and ____ and ____ are key cell cycle controllers

ARF, HDM2, HDM2, p21, CDKs, senescence

_____ inhibits _____, and _____ inhibits p53. p53 activates _____, which inhibits ______ and activates ______

CDKs, pRB, E2F, senescence, E2F

p16 inhibits _____, which inhibits _____, which inhibits ______ and activates _____. _____ activates proliferation.

cell crisis, breakage-fusion-bridge cycles, karyotypic instability

Terminal senescence leads to ______ resulting from ______ which causes _____.

Degradation of chromosomal ends

______ during terminal senescence leads to chromosome fusions

genetic catastrophe, apoptosis

Terminal accumulation of unrepaired DNA damage during senescence causes _____, leading to obligate _____

senescence, immortalization via telomerase upregulation, permanent transformation

The steps to escaping a cell’s Hayflick limit are:

protect chromosome ends from degradation, 5-10, repetitive TTAGGG, 3’ ssDNA, T loop and a D loop

Telomere “lassos” _________. They are ____ kb long and are ______ DNA sequences ending with _____. The “lasso” is composed of a ____.

failure to replicate the single-stranded overhang of the lagging chromosome end, causing the loss of 50-100 bp per cell division

The “End-Replication Problem” refers to the…

it lacks a 3’ hydroxyl group, RNA primase leaves an incomplete 3’ end, exonuclease activity removes remaining ssDNA

The single-stranded overhang of the lagging chromosome end can not be replicated because ______, therefore _______ and ______.

double-stranded break repair, exposed ssDNA at the chromosome ends, cell cycle pause, cell cycle arrest, apoptosis

Detection of telomere loss activates ______. Telomere loss is sensed via _______, leading to _____. Inability to “repair” telomeres leads to _____ and _____.

80-95

Telomerase is upregulated in _____% of cancers

holoenzyme complex, human telomerase reverse transcriptase (hTERT), template RNA (hTR/TERC), partially overlaps the TTAGGG end repeat, replicate terminal ssDNA

Telomerase is a _____. It has two core components, ______ and ______ (which ______), and it functions to ______

cell stresses, tolerance or repair of oxidative DNA damage, uncoupling of DNA damage and cell cycle arrest, resistance to apoptosis, and unlimited proliferation

Accumulation of mutations increase tolerance for _____, including changes such as…

order, initiators, promoters

The ____ of mutations matter — ____ must happen before ____

hit pathways with different functions, two initiator mutations, affect the same function, 1 initiator and 1 promoter, affect different functions

Mutations must _______, for example _____ may not cause a cancer if they ______, but ______ can if they _______

Spatial Heterogeneity

Many subclones are present in different locations of a tumour at one point in time as selective pressures are different in different areas of the tumour

Temporal Heterogeneity

Many subclones are present in a tumour over its lifetime as selective pressures vary over both the short and long term

all cells in a tumour have the same tumourigenic potential and susceptibility to mutation (stochastic model) or only the cancer stem cells within a tumour have intrinsic tumourigenic potential (hierarchy model)

Two major mechanisms could explain tumour heterogeneity:

clonal evolution

The stochastic model operates via ______

proceed by different routes, has an equal probability of acquiring a mutation that gives rise to a dominant clone

In the stochastic model, clonal evolution can _______ and every cell ______

Genetic, stable and heritable, epigenetic, medium duration, heritable by a daughter cell, expression, rapid and non-heritable, activation, rapid and non-heritable

_____ (______), _____ (_____ and _____), _____ (______), and _____ (_____) mechanisms of clonal evolution influence cellular composition in a tumour

Plasticity

_____ is key to clonal evolution

Epithelial-Mesenchymal Transition (EMT)

Process where epithelial cells lose cell to cell adhesion and polarity, transforming into migratory, invasive mesenchymal cells with fibroblast-like features

transdifferentiation, polarized epithelial cells, motile mesenchymal cells

EMT involves ______ where _____ become _____

loss of cell-cell junctions, cytoskeletal reorganization, loss of polarity, and acquisition of motility

EMT-induced changes include:

reversible, epigenetic, mutational, embryogenesis and wound healing

EMT is _____ because it is ____, not _____. EMT is a normal part of ______.

Mesenchymal-Epithelial Transition (MET)

Process crucial for establishing distant metastases where cancer cells shift from a motile, invasive mesenchymal state back into a stationary, epithelial-like state

growth factors/cytokines/ECM, adhesion/cortical actin MFs

EMT effectors include ______ and MET effectors include _____.

cancer stem cells

The hierarchy model operates via ______

slow-cycling/senescence, efflux transporters expression, free radicals scavengers, reduced immunogenicity, DNA repair, and anti-apoptotic protein expression

Cancer stem cells (CSCs) share properties with somatic stem cells, including…

each cancer contains only a minority of cells that can give rise to a cancer, and only this minority can self-renew, proliferate indefinitely, and differentiate into all other tumour subclones. Differentiated cells can continue to evolve and proliferate in response to environmental pressures but can not form new tumours.

The cancer stem cell hypothesis states…

outgrowth of normal tissue somatic stem cells, transit amplifying/progenitor cells, or somatic cells

Cancer stem cells come from…

normal tissue somatic stem cells, share many features, there are few somatic stem cells and they divide infrequently

CSCs can come from an outgrowth of ______ — they ______ BUT _________.

transit amplifying/progenitor cells, committed to one cell type but will divide many more times before fully differentiating, more cells, more divisions per cell, increased mutation rate

CSCs can come from _______, which are stem cell progeny that are __________ — ____ + _____ = _______

terminally differentiated cells, de-differentiate and reactivate self-renewal potential, oncogene activation, tumour suppressor inactivation, environmental triggers

CSCs can come from somatic cells, which are _________ that could ______ due to ______ and/or ______ — ______ are key in this process.

growth factors, macrophages/fibroblasts/adipocytes, immune inhibition, macrophages, de-differentiation, macrophages/fibroblasts, proteases, granulocytes

The CSC niche encourages maintenance and differentiation of CSCs via ______ (_______), _______ (______), _______ (_______), and ______ (______)

Hypoxia

_____ is the most significant CSC niche factor

Hypoxia-induced HIF1

______ is essential for CSC maintenance

HIF1a

Represses a negative feedback loop in the Notch pathway, increasing proliferation

epigenetic reprogramming, H3K9me2/3, DNA methylation, gene activity

Hypoxia enables _____ of CSCs to a more active state — there is decreased ______ and _____, and increased _____.

alter their metabolism, aerobic glycolysis, 4 ATP

Hypoxia enables CSCs to ______ towards _____ where 1 glucose yields approximately _____.

Warburg Effect

The shift of cancer cell metabolism to heavily favour aerobic glycolysis instead of using oxidative phosphorylation

pyruvate then lactate, sufficient oxygen for oxphos is present, pyruvate

In aerobic glycolysis, glucose is primarily converted to _____ (even if _____), whereas in oxidative phosphorylation glucose is primarily converted to ______.

glycolytic, high glucose uptake, low oxygen consumption, low mitochondrial mass, low mitochondrial ROS, and high anti-oxidant response

Non-stem, highly proliferative cancer cells have a _____ phenotype characterised by…

oxidative, high oxygen consumption, low glycolytic rates, high mitochondrial mass, high mitochondrial ROS, and high anti-oxidant response

Quiescent cancer stem cells have a _____ phenotype characterised by…

combined, highly metastatic, resistant to therapy, and having increased glycolysis and oxidative phosphorylation rates

Proliferative cancer stem cells have a _____ phenotype characterised as being…

reversible epigenetic plasticity, irreversible hierarchies

Comparing the stochastic and hierarchy models, clonal evolution has _____ while CSCs have ______

Phenotypic plasticity, neutral competition

_____ and _____ determine the products of a CSC division

a limited number of stem cells, compete for a place in the niche, that remain in the niche, both progeny cells differentiate

CSC niche only sustains _______. Stem cell progeny ______ and only cells ______ can be CSCs. If a CSC divides and there is not space in the niche, ______.

rare, quiescent, and hardwired with intrinsic factors

In the classical CSC view, CSCs are…

not rare or quiescent, are guided by niche factors, and have a bidirectional hierarchy

In the updated CSC view, CSCs are…