BSc Biomedical Sciences (VU Amsterdam) Oncology pt2 Active Recall
Tips for use :
Bullet-point Question/Answer format
Based on Chapters from “Molecular Biology of Cancer” by Lauren Pecorino,
(Chapters 7, 8, 9, 10, 11, 12 and 13)
Colour the questions RED until you perfect them. Colour them GREEN once you’ve
mastered them. Then, only practice the red question, until they’re all green.
Follow the chapters from the book to view images and visuals corresponding to the notes
Chapter 8: Cancer stem cells and the regulation of self-renewal and differentiation pathways: focus on
colon cancer and leukemias
● What does the cancer “stem cell model” state? Subpopulations of cells within a tumor with stem
cell properties initiate and maintain the cancer phenotype - sustain the tumor
● Where do cancerous stem cells often reside? In stem cell niches - which are distinct
microenvironments in tumors.
○ Give growth factors, physical support, differentiation signalling, etc.
○ Signals from the stem cell niche dictate how much division, and is stem cell dies or not.
● What is ontogeny? Entire developmental history of an organism. Hundreds of specialised cells
must form from the fertilised egg and its unspecialised cells (embryonic stem cells).
● What is the key trait of embryonic stem cells? They are pluripotent - can give rise to any body
cell. Specialisation happens through differentiation. (stem → precursor → differentiated).
○ Stem cells live very long and divide a lot → hence mutations can accumulate
● What determines which kind of cell an embryonic cell differentiates into? The genes that are
expressed in the cell, even though all body cells (except RBCs and germ cells) have the entire
genome. Transcription factors and epigenetics determine the expression.
● In addition to embryonic stem cells, what is another type of stem cell in the adult? Stem cells for
tissue regeneration during an individual’s lifetime. E.g. hemopoietic stem cells, hair follicles, or
breast stem cells in response to pregnancy hormones.
● Stem cells self-renew while also having the ability to give rise to cells that are more committed to
differentiate along a particular cell lineage.
● Do differentiated cells follow the cell cycle? No - most do not. Withdrawal from the cell cycle is
a characteristic of differentiated cells.
● What defect in the “stem cell → differentiated cell” system can cause cancer? Block in
differentiation means a higher net number of stem cells, thus a way for tumors to form in cancers
like leukemia.
● What are the 2 differentiation pathways that can have implications for carcinogenesis?
○ Characteristics of stem cells in normal tissue and in tumors
○ Lineage-specific transcription factors and epigenetics that act as switches for sets of
genes during differentiation.
,Cancer stem cells
● What are 2 defining features of stem cells?
○ Ability to self renew (can divide to create one or more identical copies of itself)
○ Ability to give rise to cells that will become differentiated cell types of one or more
lineages
● What is the classical model for stem cell division?
○ A stem cell divides asymmetrically → 1 stem cell + 1 differentiated cell
○ The fate of the daughters is intrinsically determined (built into the cell’s machinery)
○ This creates a stable hierarchy: Stem cell → progenitor → differentiated cells
○ The stem cell pool size stays constant by design
Cell fate is pre-programmed, not dependent on competition or environment.
● What is the neutral model for stem cell division?
○ Stem cells divide symmetrically or asymmetrically, but outcomes vary:
■ 2 stem cells
■ 1 stem + 1 differentiated
■ 0 stem cells (both differentiate)
○ The outcome depends on external signals + space in the niche
○ Stem cells compete for limited niche slots
Over time, some clones expand, other are lost.
● What kind of division is stem cell division? Asymmetric
● So Key: stem cells compete for niche space, according to the newer neutral model. Based on the
environment, some clones survive and others disappear.
● What is stochastic clonal evolution? Means that clonal success depends on chance + evolution
● Why is the stem cell system so adaptive? Because differentiated cells can de-differentiate and
re-enter the stem cell pool if the niche is empty → shows plasticity and adaptability.
Dangerous because maybe therapy kills all CSCs, but then differentiated cells could turn into
stem again.
● How do stem cell division models relate to cancer? Tumors often behave more like the neutral +
plastic model than the classical one. Cancer stem cells (CSCs) are usually:
○ Niche dependent (tumor microenvironment matters a lot)
○ Competitive for space/resources
○ Stochastic expansion of clones
○ Plasticity: Non-CSCs can become CSCs again, especially after therapy or injury
● Why are stem cells linked to cancer?
○ Self-renewal increases cancer risk - stem cells divide many times → more chance for
mutations
○ Cancer = dysregulates self renewal
● How can differentiation blocks cause cancer? Usually cells that differentiate stop dividing and
exit the cell cycle. But cancer can block this and leave the cell as immature, which means it has
dividing ability.
● Why are stem cells dangerous mutation targets?
○ They are long lived, unlike many differentiated cells, so they are prone to mutation
accumulation.
○ Divide repeatedly → replication errors.
, ○ Many cancer mutations arise from normal DNA replication errors in stem cells.
● What are CSCs? A tumor is not just a random mass, it's organized like a tissue. It has a small
subset of cells (CSCs) that can self-renew (make more CSCs) or differentiate (make the bulk
tumor cells)
● Why do CSCs matter in the disease stage ? Tumor growth is driven by this minority. More
CSCs → worse prognosis (cancer development). Seen in brain and breast cancer. CSCs =
“roots of the tumor”
● What are the 2 key signalling pathways controlling CSCs? WNT pathway and HH pathway
WNT/Beta-Catenin pathway
● What are WNT proteins? Secreted intracellular signaling molecules that act as ligands to trigger a
specific signal transduction pathway that leads to proliferation.
● Where are WNT proteins made? Inside the cell - are lipid-modified by Porcupine (PORCN) in the
ER, which adds palmitoleic acid. Helps WNT be secreted, and helps it bind to receptors
● What happens when without the WNT acting as a ligand (OFF state)?
○ Destruction complex forms in cytoplasm: APC, AXIN, GSK3beta and Casein Kinase 1
○ Beta-catenin binds this complex
○ It gets phosphorylated (CK1 + GSK3Beta)
○ Then gets ubiquitinated
○ Beta-catenin Destroyed by proteosome
○ No Beta-catenin available in nucleus → TCF/LEF bind DNA → they bind the
Groucho repressor
○ Result: target genes OFF (MYC, cyclin D, etc)
● What happens when the WNT signal is present (pathway ON)?
○ WNT is a ligand that binds the Frizzled receptor and the LRP5/6 coreceptor
○ LRP cytoplasmic tail gets phosphorylated (CK1 + GSK3Beta)
○ This recruits AXIN to the membrane → key effect is that destruction complex is
broken apart
○ Beta-catenin no long degraded → it accumulates in cytoplasm and moves to nucleus
○ Beta-catenin binds TCF/LEF, and replaces Groucho repressor.
○ Result: Target genes turned ON.
● How does negative feedback regulation in the WNT pathway work?
○ WNT activation induces RNF43 and ZNRF3
○ They add ubiquitin to Frizzled receptors
○ Cause receptor degradation
○ Reduces WNT signalling
● How does positive feedback regulation in the WNT pathway work?
○ R-spondin binds LGR5 (or lGR4/6)
○ Blocks RNF43 and ZNRF3
○ Increases receptor levels, and boosts WNT signalling
● Overall, in WNT pathway:
○ OFF → β-catenin destroyed → no proliferation genes
○ ON → β-catenin active → growth genes ON (→ cancer if uncontrolled)
● How does the WNT pathway go wrong in cancer?
, ○ APC mutation (most common and serious) - loss of APC means destruction complex
fails, and Beta-catenin accumulates even without WNT
○ Beta-catenin mutation - cannot be degraded, always active
○ Result: constant MYC and cyclin D activation → uncontrolled proliferation
● What is the clinical relevance of the WNT pathway mutations? 90% of colorectal cancers have
WNT pathway mutations - example is Familial Adenomatous Polyposis
Hedgehog signaling pathway
● What is the HH pathway for? Also a signaling pathway - controls development, stem cell
maintenance and repair. Mostly OFF in adults - when abnormally ON → cancer
● So HH signalling controls whether cells proliferate, survive and migrate
● What are the key players of the HH signaling pathway?
○ Patched - an inhibitor (tumor suppressor)
○ Smoothened - signal activator
○ GLI - turns genes ON or OFF
○ Patched blocks Smoothened → Smoothened controls GLI → GLI controls genes
● What is the default HH pathway state? Usually no HH ligand - pathway OFF
● How does the HH signalling pathway work when no ligand is present?
○ Patch blocks Smoothened (patched sits in the primary cilium, prevents Smoothened
from entering the cilium) → so Smoothened is inactivated
○ GLI is held in the cytoplasm by a complex made of SUFU + Kinases (like PKA, CK1
and GSK3Beta) → these phosphorylate GLI, causing partial proteosome cleave → GLI
becomes a repressor
○ Shortened GLI = repressor form → GLI repressor goes to the nucleus
○ Result: Hedgehog target genes OFF
● How does the HH signalling pathway work when there is a ligand present?
○ HH binds to patched - causes Patched to leave the cilium
○ Smoothened can now enter the cilium → becomes active (key switch flip)
○ Smoothened signalling disrupts SUFU complex - GLI no longer cleaved → full
length GLI accumulates
○ GLI acts as nucleus activator - turns ON genes like cyclin D (prloferation), BCL2 (anti-
apoptosis), VEGF (angiogenesis) and SNAIL (metastasis)
● What is a feature of GLI? It can amplify its own response from even a small signal to create a big
response
● What can go wrong in the HH signalling pathway which can cause cancer?
○ Loss of Patched tumor suppressor - no Smoothened inhibition, pathway is stuck on ON
○ Overactive Smoothened
○ Result: continuous GLI activation, uncontrolled cell growth
● What is Gorlin syndrome? Germline mutation in Patched - patients develop many tumors
● What is the most common cancer linked to the HH pathway? Basal Cell Carcinoma BCC. Almost
all cases have activated HH pathways.
What CSCs explain about tumor behaviour
● What is tumor heterogeneity? Even if a tumor starts from the same cell (same clonal origin), it
contains many cell types → different morphology, gene expression, proliferation rates, etc.
Tips for use :
Bullet-point Question/Answer format
Based on Chapters from “Molecular Biology of Cancer” by Lauren Pecorino,
(Chapters 7, 8, 9, 10, 11, 12 and 13)
Colour the questions RED until you perfect them. Colour them GREEN once you’ve
mastered them. Then, only practice the red question, until they’re all green.
Follow the chapters from the book to view images and visuals corresponding to the notes
Chapter 8: Cancer stem cells and the regulation of self-renewal and differentiation pathways: focus on
colon cancer and leukemias
● What does the cancer “stem cell model” state? Subpopulations of cells within a tumor with stem
cell properties initiate and maintain the cancer phenotype - sustain the tumor
● Where do cancerous stem cells often reside? In stem cell niches - which are distinct
microenvironments in tumors.
○ Give growth factors, physical support, differentiation signalling, etc.
○ Signals from the stem cell niche dictate how much division, and is stem cell dies or not.
● What is ontogeny? Entire developmental history of an organism. Hundreds of specialised cells
must form from the fertilised egg and its unspecialised cells (embryonic stem cells).
● What is the key trait of embryonic stem cells? They are pluripotent - can give rise to any body
cell. Specialisation happens through differentiation. (stem → precursor → differentiated).
○ Stem cells live very long and divide a lot → hence mutations can accumulate
● What determines which kind of cell an embryonic cell differentiates into? The genes that are
expressed in the cell, even though all body cells (except RBCs and germ cells) have the entire
genome. Transcription factors and epigenetics determine the expression.
● In addition to embryonic stem cells, what is another type of stem cell in the adult? Stem cells for
tissue regeneration during an individual’s lifetime. E.g. hemopoietic stem cells, hair follicles, or
breast stem cells in response to pregnancy hormones.
● Stem cells self-renew while also having the ability to give rise to cells that are more committed to
differentiate along a particular cell lineage.
● Do differentiated cells follow the cell cycle? No - most do not. Withdrawal from the cell cycle is
a characteristic of differentiated cells.
● What defect in the “stem cell → differentiated cell” system can cause cancer? Block in
differentiation means a higher net number of stem cells, thus a way for tumors to form in cancers
like leukemia.
● What are the 2 differentiation pathways that can have implications for carcinogenesis?
○ Characteristics of stem cells in normal tissue and in tumors
○ Lineage-specific transcription factors and epigenetics that act as switches for sets of
genes during differentiation.
,Cancer stem cells
● What are 2 defining features of stem cells?
○ Ability to self renew (can divide to create one or more identical copies of itself)
○ Ability to give rise to cells that will become differentiated cell types of one or more
lineages
● What is the classical model for stem cell division?
○ A stem cell divides asymmetrically → 1 stem cell + 1 differentiated cell
○ The fate of the daughters is intrinsically determined (built into the cell’s machinery)
○ This creates a stable hierarchy: Stem cell → progenitor → differentiated cells
○ The stem cell pool size stays constant by design
Cell fate is pre-programmed, not dependent on competition or environment.
● What is the neutral model for stem cell division?
○ Stem cells divide symmetrically or asymmetrically, but outcomes vary:
■ 2 stem cells
■ 1 stem + 1 differentiated
■ 0 stem cells (both differentiate)
○ The outcome depends on external signals + space in the niche
○ Stem cells compete for limited niche slots
Over time, some clones expand, other are lost.
● What kind of division is stem cell division? Asymmetric
● So Key: stem cells compete for niche space, according to the newer neutral model. Based on the
environment, some clones survive and others disappear.
● What is stochastic clonal evolution? Means that clonal success depends on chance + evolution
● Why is the stem cell system so adaptive? Because differentiated cells can de-differentiate and
re-enter the stem cell pool if the niche is empty → shows plasticity and adaptability.
Dangerous because maybe therapy kills all CSCs, but then differentiated cells could turn into
stem again.
● How do stem cell division models relate to cancer? Tumors often behave more like the neutral +
plastic model than the classical one. Cancer stem cells (CSCs) are usually:
○ Niche dependent (tumor microenvironment matters a lot)
○ Competitive for space/resources
○ Stochastic expansion of clones
○ Plasticity: Non-CSCs can become CSCs again, especially after therapy or injury
● Why are stem cells linked to cancer?
○ Self-renewal increases cancer risk - stem cells divide many times → more chance for
mutations
○ Cancer = dysregulates self renewal
● How can differentiation blocks cause cancer? Usually cells that differentiate stop dividing and
exit the cell cycle. But cancer can block this and leave the cell as immature, which means it has
dividing ability.
● Why are stem cells dangerous mutation targets?
○ They are long lived, unlike many differentiated cells, so they are prone to mutation
accumulation.
○ Divide repeatedly → replication errors.
, ○ Many cancer mutations arise from normal DNA replication errors in stem cells.
● What are CSCs? A tumor is not just a random mass, it's organized like a tissue. It has a small
subset of cells (CSCs) that can self-renew (make more CSCs) or differentiate (make the bulk
tumor cells)
● Why do CSCs matter in the disease stage ? Tumor growth is driven by this minority. More
CSCs → worse prognosis (cancer development). Seen in brain and breast cancer. CSCs =
“roots of the tumor”
● What are the 2 key signalling pathways controlling CSCs? WNT pathway and HH pathway
WNT/Beta-Catenin pathway
● What are WNT proteins? Secreted intracellular signaling molecules that act as ligands to trigger a
specific signal transduction pathway that leads to proliferation.
● Where are WNT proteins made? Inside the cell - are lipid-modified by Porcupine (PORCN) in the
ER, which adds palmitoleic acid. Helps WNT be secreted, and helps it bind to receptors
● What happens when without the WNT acting as a ligand (OFF state)?
○ Destruction complex forms in cytoplasm: APC, AXIN, GSK3beta and Casein Kinase 1
○ Beta-catenin binds this complex
○ It gets phosphorylated (CK1 + GSK3Beta)
○ Then gets ubiquitinated
○ Beta-catenin Destroyed by proteosome
○ No Beta-catenin available in nucleus → TCF/LEF bind DNA → they bind the
Groucho repressor
○ Result: target genes OFF (MYC, cyclin D, etc)
● What happens when the WNT signal is present (pathway ON)?
○ WNT is a ligand that binds the Frizzled receptor and the LRP5/6 coreceptor
○ LRP cytoplasmic tail gets phosphorylated (CK1 + GSK3Beta)
○ This recruits AXIN to the membrane → key effect is that destruction complex is
broken apart
○ Beta-catenin no long degraded → it accumulates in cytoplasm and moves to nucleus
○ Beta-catenin binds TCF/LEF, and replaces Groucho repressor.
○ Result: Target genes turned ON.
● How does negative feedback regulation in the WNT pathway work?
○ WNT activation induces RNF43 and ZNRF3
○ They add ubiquitin to Frizzled receptors
○ Cause receptor degradation
○ Reduces WNT signalling
● How does positive feedback regulation in the WNT pathway work?
○ R-spondin binds LGR5 (or lGR4/6)
○ Blocks RNF43 and ZNRF3
○ Increases receptor levels, and boosts WNT signalling
● Overall, in WNT pathway:
○ OFF → β-catenin destroyed → no proliferation genes
○ ON → β-catenin active → growth genes ON (→ cancer if uncontrolled)
● How does the WNT pathway go wrong in cancer?
, ○ APC mutation (most common and serious) - loss of APC means destruction complex
fails, and Beta-catenin accumulates even without WNT
○ Beta-catenin mutation - cannot be degraded, always active
○ Result: constant MYC and cyclin D activation → uncontrolled proliferation
● What is the clinical relevance of the WNT pathway mutations? 90% of colorectal cancers have
WNT pathway mutations - example is Familial Adenomatous Polyposis
Hedgehog signaling pathway
● What is the HH pathway for? Also a signaling pathway - controls development, stem cell
maintenance and repair. Mostly OFF in adults - when abnormally ON → cancer
● So HH signalling controls whether cells proliferate, survive and migrate
● What are the key players of the HH signaling pathway?
○ Patched - an inhibitor (tumor suppressor)
○ Smoothened - signal activator
○ GLI - turns genes ON or OFF
○ Patched blocks Smoothened → Smoothened controls GLI → GLI controls genes
● What is the default HH pathway state? Usually no HH ligand - pathway OFF
● How does the HH signalling pathway work when no ligand is present?
○ Patch blocks Smoothened (patched sits in the primary cilium, prevents Smoothened
from entering the cilium) → so Smoothened is inactivated
○ GLI is held in the cytoplasm by a complex made of SUFU + Kinases (like PKA, CK1
and GSK3Beta) → these phosphorylate GLI, causing partial proteosome cleave → GLI
becomes a repressor
○ Shortened GLI = repressor form → GLI repressor goes to the nucleus
○ Result: Hedgehog target genes OFF
● How does the HH signalling pathway work when there is a ligand present?
○ HH binds to patched - causes Patched to leave the cilium
○ Smoothened can now enter the cilium → becomes active (key switch flip)
○ Smoothened signalling disrupts SUFU complex - GLI no longer cleaved → full
length GLI accumulates
○ GLI acts as nucleus activator - turns ON genes like cyclin D (prloferation), BCL2 (anti-
apoptosis), VEGF (angiogenesis) and SNAIL (metastasis)
● What is a feature of GLI? It can amplify its own response from even a small signal to create a big
response
● What can go wrong in the HH signalling pathway which can cause cancer?
○ Loss of Patched tumor suppressor - no Smoothened inhibition, pathway is stuck on ON
○ Overactive Smoothened
○ Result: continuous GLI activation, uncontrolled cell growth
● What is Gorlin syndrome? Germline mutation in Patched - patients develop many tumors
● What is the most common cancer linked to the HH pathway? Basal Cell Carcinoma BCC. Almost
all cases have activated HH pathways.
What CSCs explain about tumor behaviour
● What is tumor heterogeneity? Even if a tumor starts from the same cell (same clonal origin), it
contains many cell types → different morphology, gene expression, proliferation rates, etc.
