metastasis Flashcards
Whats the difference between benign and malignant tumor?
benign possesses 5 out of 6 hallmarks of cancer except, benign is NOT invasive or leads to metastasis
What are the major characteristics of a malignant tumor?
-detachment and migration
-destruction of tissue barriers
-invasion into the blood and foreign tissues
-survival and proliferation in foreign tissues
-tissue invasion and metastasis
what is the primary cause of cancer morbidity and mortality
metastases
Name experimental models to study metastasis
mouse models
1. xenograft model (human to immuno deficient mice)
2. synegeneic models (mice to immunodeficient mice)
3. chemically induced cancer mouse models
4. genetically engineered mouse models
5. subcutaneous mouse models (tumor implanted subcutanously)
6. orthotopic mouse model (tumor surgically implanted)
Name the 6 steps of the invasion-metastasis cascade
primary tumor formation –>
1. local invasion
2. intravasation
3. survival in the circulation
4. arrest at at distant organ site / extravasation
5. micormetastasis formation
6. metastatic colonization
–> clinically detectable macroscopic metastasis
What happens during local invasion?
- epithelial to mesenchymal transition
- loss of cell- cell adhesion
- cytoskeletal rearrangement
- ECM degradation
Name epithelial markers and mesenchymal markers that play a role in EMT and which role they play
epithelial: E-cadherin
-maintain cell adhesion and polarity, suppress invasion
mesenchymal: N-cadherin
-weak cell adhesion and promote migration and tissue remodeling
What is the difference between epithelial cells and mesenchymal cells?
epithelial vs mesenchymal:
-apical-basal polarity vs lack of polarity
-strong cell adhesion vs weak cell adhesions
- cytokeratin based cytoskeleton vs vimentin based cytoskeleton
What happens during EMT?
- loss of polarity
- loss of cell- to cell and cell to basal lamina junctions
- acquisition of a motile and migratory phenotype
- enabling the invasion of the basal lamina
Where does EMT play an important role besides cancer metastasis and in which animal can this be studied?
EMT
-contributes to formation of connective tissue
-is important for tissue repair/wound healing
-plays a role in embryogenic development
–> can be studied in axolotl
What are cadherins and what is their function?
cadherins are tansmembrane proteins, which are important for formation of adherens junctions. They bind actin intracellularly
What is the p120 protein and what role does it play?
binds to the cytoplasmic tail of cadherin
E-cadherin binds the shorter isoform (compared to n-cadherin)
Which factors play a role in EMT?
- CDH1 gene regulates E-cadherin expression
- TGF-beta, Wnt and Notch activate EMT inducing transcription factors (EMT-TF)
- negative feedback loops involving microRNA to regulate EMT-TF
How does the cytoskelton change in EMT?
Actin filaments: cortical actin filament, stron adhesions –> actin stress fibers, weak adhesions
intermediate filaments: keratin rich –> vimentin rich
microtubules: apical-basal orientation –> orientation towards the leading edge of the cell
Name two isoforms of actin stress fibers
beta (ventral stress fibers) and gamma (dorsal stress fibers)
Describe the actin retrograde flow
- enables controlled, directional cell migration
- actin monomers polymerize at the leading edge of the migrating cell –> pushing force
- after polymerization, actin filaments flow inward (retrograde flow)
- retrograde flow required for actin network organization
- focal adhesions act as molecular clutch
Which MMPs are most important for ECM degradation?
MMP-2 and MMP-9
What is intravasation?
- tumor cells enter blood or lymphatic vessels from the primary tumor site (cross endothelial cell barrier)
- can be active or passive
- highly correlated with tumor angiogenesis
Name 2 ways for tumor cells to enter circulation
- paracellular intravasation
- transcellular intavasation
How does paracellular intravasation work?
- MMP mediate remodelling of endothelial junctions
- transmigration of tumor cells through endothelial cell junctions
How can circulating tumor cells (CTC) survive in the circulation? What can kill them?
killing:
- CTC are vulnerable to death induced by shear stress and turbulance
- immune system (NK cells)
How to escape NK
- platelet coating (reduced shear stress)
- tumor cells secrete immunomodulatory molecules
- tumor cells can shed NKG2D ligands
- stromal cells or myeloid.derived suppressor cells can secrete immunosuppressive molecules
what influences where a tumor might extravastates?
vessel structure
Name three types of endothelium that might influence extravasation and which is used by tumors
- continous endothelium
- fenestrated endothelium –> used
- discontinous endothelium –> common sites of metastasis
describe extravasation
- initial attachment and rolling –> expression of E/P-Selectin
- Arrest and adhesion –> CTCs express integrins which bind to endothelial receptors
- transmigration
descibe the state of early attachement in extravasation
- interaction of endothelial selectin with CD44
- cancer cells use different cell shapes during intra- and extravasation
describe stabloe adhesion and arrest in extravasation
- HGF signalling increases expression of integrins and CD44
- CDC42 controls beta1 integrin expression
- RAC1 stimulates beta1 integrin activity
What is the role of Rho GTPases? How are they regulated?
-regulate cell migrate, intra- and extravasation
-regulate cytoskeletal rearrangement
-GAPs and GEF mediate molecular switch between inactive state (GDP bound) and active state (GTP bound)
Name GEFs that play a role in regulating RhoGTPase in extravasation
Tiam1 and P-Rex1
Explain tissue tropism in metastasus using breast cancer as example
- breats cancer cedlls express chemokine receptor 4 on their surface
- breast cancer cells are arrested in organs that produce high level of chemokine receptor 4 ligand
- binding of liganf leads to migration of cancer cells into normal tissue
- breast cancer cells do not metastazie to organs to produce low levels of ligand like kidney
Which receptors are important for attraction based cell migration in metastasis?
chemokine receptors
Explain the seed and soil theory
- spread of cancer cells is not random
- pro-metastatic tumor cells colonize to specific organ sites
this depends on interaction between cancer cells and the microenvironment at a distinct organ
What is the pre-metastatic niche (PMN)?
tumor secreted factors and extracellular vesicles shed by the primary tumor induce formation of a PMN before metastatic seeding occurs:
- clot formation and vascular disruption (vascular leakiness)
- local increase in cytokines to aid extravasation
- ECM is deposited and remodelled (fibronectin accumulates and MMPs are secreted)
- inflammatory cell recruitment
Explain the metastatic niche. How is it established and what does it faciltate?
established metastatic niche due to
- bone marrow derived cell recruitment
- ECM changes
- inflammation
facilitates
- CTC adhesion to endothelium
- extravasation
- metastatic out growth
What is tumor cell dormacy? By what is it controlled?
cancer dormacy is a stage in tumor progression in which residual disease remains asymptomatic for a prolonged period of time
cells reside in G0-G1 arrest
this is controlled by the niche
describe the dormant cancer life cycle
- niche engagement and programming
- immune cloaking: immune evasion
- reactivation and relapse
name potential mechanism involved in tumor dormacy
- oncogene inactivcation
- lack of angiogenic switch
- lack of growth stimulation
- host polymophism that delay growth
- inhibition of proliferation
- need for additional genomic alterations
- aberrations in adhesion factor signaling
- immunological factors
What are micrometastasis and how can they be visualized?
they are too small to be seen with imaging tests and can only be visualized by microscopy
Describe the change from micro- to macrometastasus
- changes in TME canlead to (re)activation of dormant micrometastasis –> metastatic outgrowth
- mesenchymal to epithelial transition (MET)
What is MET?
Mesenchymal to epithelial transition:
- loss of mesenchymal characteristics (migratory) to epithelial characteristics (stationary)
What is the Warburg effect?
cancerous cells preferentially use aerobic glycolysis for energy production rather than oxidative phoshorylation –> less ATP/glc generated
What is the significance of PK-M2 in metastasis?
PK: catalyzes final step of glycolysis
Tumor PK-M2 is dimeric instead of the usual tetrameric form –> slower enzymatic activity –> pyruvate production slowed down –> lactate formation enhanced
