Stem Cell + Cancer Flashcards
How are stem cells characterized
stem cell:
- cells that can self-renew and also can differentiate into other cell types
differentiation:
- development of specialized cell types that carry specific functions.
- driven by differential gene expression
potency (pluripotent vs unipotent)
- possible cell types that a given stem cell can generate
- pluripotent : makes all types
- unipotent: only makes 1 cell type (ex. keratin stem cell)
Relationship between differentiation + potency
- as differentiation goes on, potency decreases
Describe origin of embryonic stem (ES) cells
Embryonic stem cells:
- undifferentiated cell type derived from inner cell mass of an early mammalian embryo
- (pluripotent): can differentiate into any specialized cell types in adult body
Origin:
1. Sperm fertilizes egg to form an early embryo (blastocyst)
- undergoes mitosis quickly + pumps fluid into hollow balls
2. Some cells stick to outside of the blasocyst to serve as a surface (thropoblast = accessory tissues to form placenta + embryonic cavity)
- inner cell mass: embryoblast
- embryoblast within the pre-implantation blastocyst consists of pluripotent / multipotent ES cells
- embryblast splits into epiblast and hypoblast post-implantation
- both epiblast + hypoblast contain stem cells w/ slightly decreased potency
(epiblast cells undergo EMT during gastrulation to form three-layered embryo)
Describe process of gastrulation
a. Define Primitive Streak:
(explain how epithelial to mesenchymal transistions occur here)
Primtive Streak = paracrine factor-induced signaling
1. induces expression of Snail transcription factor –> downregulate E-cadherein (and other cell-cell adhesion) –> shift from anchoring hemidesmosomes to dynamic focal contacts
2. epithelial ectodermal cells transition –> migrator mesenchymal state
3. invade center of embryo (secrete/ deposit large amounts of glycosaminoglycan-rich ECM
(Know where EMT occurs in normal + pathological processes)
Normal:
- EMT tightly regulated in 4 dimensions w/ strong neg feedback (b/c they can be disruptive to epithelial form + function when uncontrolled)
Wound Healing:
- EMT followed by corrective mesenchymal-to-epithelial transformation (tubule _ duct dissolution followed by reformation)
Cancer invasion:
EMT drives cancer cell invasion (uncontrolled) –> comes late in progression of carcinoma (epithelial-derived) tumours
- initial step of metastasis
b. Steps involved in formation of mesoderm from bilaminar disk
1. (after Day 14 to 16 since fertilization): cells from epiblast part of bilaminar disk migrate between the epiblast (ectoderm) and the hypoblast (endoderm)
–> central embryonic tissue layer formed by the migrating fibrblastic cell –> mesoderm (embryonic mesenchyme)
c. Identify 3 germ layers + tissue types originating from each layer
(potency change: these germ layers contain multiotent stem cells, more restricted potency)
1. Epiblast/Ectoderm
ex. Nervous Tissue
- Mesoderm/ Mesenchyme
ex. Connective Tissue - Hypoblast/Endoderm
ex. GI Tract
Explain how many cell lineages originate from multi/pluripotent stem cell
a. Define hematopoietic stem cell
- (HSCs) multipotent stem cells that give rise to other blood cells via hematopoiesis
b. describe the change in potency as HSC differentiate into progenitors and then into lineage-restricted blast cells
HSC –> progenitors (less multipotent)
progenitors –> blast cells (lineage restricted) (blast cells cannot self-renew unlike stem cells)
c. Describe where to find a hematopoietic cord + and the cell types present in these structures
- hematopoietic cords are found in bone marrow
- contains (within hematopoietic niches) in bone marrow: HSCs, lineage progenitors, blast cells, blood cells, and stromal cells
stromal cells: modified connective tissue fibroblast + bone osteoblasts w/ long cell processes (can contact stem/progenitor/blast cells) also produces paracrine factors to regulate hematopoiesis
Describe how hematopoiesis is regulated
a. define paracrine vs endocrine factors and an example of each
Paracrine (short range acting):
(paracrine factors present in hematopoietic niches produced by stromal cells)
- secreted in stromal/ marrow ECM / remain tethetred to surface of stromal cells)
ex. stem cell factor (SCF) acts on hematopoietic stem cells
Endocrine (long range acting):
- hormones produced in another organ that travel to bone marrow via circulator systme
ex. Eryhtropoietin acts on erythroid lineage
i. what are the roles and connection between SCF, c-KIT, and HSCs.
c-Kit: transmembrane receptor tyrosine kinase (on surface of stem / progenitor cells)
- binds to SCF produced by stromal cells
- activates self-renewal when binded to SCF
SCF: (ligand that acts in paracrine short range manner –> remain tethered to stromal cell)
- sets up hematopoietic niches within bone marrow
ii. Explain the general signal cascade of SCF binding to KIT in cell proliferation
1. SCF binding activates intrisnic tyrosine kinase activity of Kit receptor
2. activated kit receptors auto-phosphorylate tyrosine residues on intracellular domains
3. phosphorylated tyrosines recruit amplifies (intracellular kinases = Abl) to initate stem/progenitor cell proliferation
4. stimulates G1/S Cdk activity by increasing transcription of cyclin D1
b. How does chronic Abl simtulation result in chronic myelogenous leukemia and how is this prevented by Gleevac (what does Gleevac target + explain effectiveness)
Chronic Abl simulation (chromosomal 9:22 translocation):
- creates huge numbers of immature WBC that crowd out red bloc cell due to driving proliferation of stem/ myeloid progenitor cells)
Gleevac: inhibits Abl activity
(Abl activity is otherwise constitutively activated in chronic myelogenous leukemia)
c. What are hematopoietic niches
- spatially-restricted / localized areas within bone marrow that contain stem/progenitor/blast/stromal cells
- contain moleculary complex hematopoietic synapses (and short range paracrine factors, ECM + adhesion molecules)
hematopoietic synapses: brings hematopoietic stem/ progenitor cells + stromal cells in close contract
Paracrine factor: regulate proliferation/ self renewal in stem/progenitor cell
Describe how erythropoiesis is regulated
a. What is the role of Erythopoietin (EPO)
- increases hematocrit: number of erythrocyte as percentage of blood volume
- therefore drives erythropoiesis
b. Where is it produced and what triggers it. (understand its effect on hemocrit)
- produced in kidney
- triggered when erythrocyte numbers are low:
- blood loss, anemia, physiological need for increased blood (high altitudes)
c. describe effect of EPO on blood viscosity + why EPO blood doping is dangerous
- EPO increases blood viscosity –> shear-based activation of platelets –> intravenous blood clotting
Describe how intestinal epithelial stem cell proliferation is regulated
a. Where are intestinal epithelial stem cellls located?
located at base of intestinal glands (crypts of lieberkuhn)
b. What gave rise to + where these cells move as they differentiate?
- stem cells gave rise to Paneth cells.
Paneth cells:
- remain in the crypts BUT when when they divide, the precrusor cells become differentiated absorptive / secretory goblet cells–> pushed to tip of villi
- detach into lumen of intestine _ die
c. Discuss roles of Paneth cells, where they are located, how the presence / absence of Wnt concentration affects intestinal stem cell proliferation + differentiation
Function:
- secrete antimicrobial peptides
- secrete paracrine factor ‘Wnt’
Wnt:
high concentration: induces Wnt pathway-induced cell proliferation
- increases cyclin expression to drive cell cycle through G1-S phase check point
low concentration: (move out of crypt) –> no Wnt pathway activation
- cells become differentiated into secretory / absorptive cells
- conversely: cells that move downward differentiate into Paneth cells
How do Cancerous lesions evolve over time?
Repeated rounds of mutation + increased genetic instability
–> sustained proliferation / survival within tissue (ex. primary tumour)
(each mutation enchances ability for cell to proliferate and/or survive –> progeny becomes dominate clone in tumour)
–> primary tumour forms cells –> begins to invade surrounding tissues
(localized mass is not deadly –> drives diorganization + dysplasia)
(only deadly when migrating)
How do oncogenes result from gain of function gene mutations / activations?
Gain of function mutations/ changes
–> cause normal, regulated proto-oncogene product to become constitutively activated oncogene product
–> turns on proliferative / survival signaling in tumour cell
- affected cells enter cell cycle independent of growth factor signaling
Types of gain of function mutations:
1. mutation in coding sequence (hyperactive protein made in normal amounts)
- Gene amplification
(normal proteins over-produced) - chromosome rearrangement
(regulator DNA sequence –> normal protein to be overproduced)
(fusion to actively transcribed gene produces hyperactive fusion protein)
ex. (BCR-Abl in chronic myleogenous leukemia can be treated w/ inhibitor of Abl kinase (Gleevac)
- chromosomal rearrangement: fuses protein dimerization domain (BCR) w/ Abl tyrosine kinase gene –> produce hyperactive tyrosine kinase
- BCR-Abl oncogene causes SCF-independent proliferation of hematopoietic myeloid progenior stem cells –> gives rise to chronic myelogenous leukemia
How are tumour suppressors lost during tumourigensis
Normal function:
- products of tumour suppressor genes inhibit proliferation / survival signaling
How is it lost?
- both alleles of tumour suppressor gene must be lost (ex. 2 hit hypothesis)
1. initial loss of function mutation in first allele (recessive mutation)
2. later chromosome loss, gene deletion, second loss of function mutation or epigentic silencing of second allele
ex. APC in colon carcinoma
How does APC work?
APC = tumour supressing gene
- adherens junction linker protein (Beta-Catenin) –> has signal transduction function
- APC destroys Beta Catenin –> prevents proliferation
- Wnt prevents APC –> enables proliferation of stem cells
loss of function mutation –> drive colonic / intestinal epithelial cells through cell cycle @ G1 / S checkpoint
Describe metastasis
Primary tumours have potential to become metastatic form within tissues: ( carcinomas)
Tumour cell invasion (first step in metastasis) driven by inappropriate EMT
Metastatic EMT: changes to multiple signaling pathways downregulated cell-cell adhesion receptor expression t
Metastatic Progression (EMT driven):
1. Primary tumour formation
(tumour cells display hypoxia –> release factors to draw blood vessel to them –> easy pathway via bloodstream)
2. localized invasion
(cells experience dysplasia and eventually –> becomes a carcinoma and then due to inappropriate EMT activation, (metastiatic EMT) , it becomes an invasive carcinoma
3. intravasation (in the blood stream)
4. transport through circulation
- arrest in microvessels of various organs
- extravasation (invades organs)
- formation of micrometastasis
