Invasion and metastasis Flashcards
What are the 6 steps of the invasion-metastasis cascade?
1) Local invasion
2) Intravasation
3) Migration
4) Extravasation
5) Micrometastasis
6) Colonisation
What is local invasion?
Primary cancer cells invade the surrounding tissue
What is intravasation
Cancer cells enter the circulatory system
What is migration?
Haematogenous transit to distant sites and survival during process
What is extravasation?
Cancer cells exit through the vascular wall into the secondary host site
What is micrometastasis?
The founding of microscopic colonies of cancer cells
What is colonisation?
Cancer cell outgrowth into a tumour of macroscopic size.
What does the metastatic process rely heavily on>
The interaction between cancer cells and their surrounding tumour microenvironment.
What are the types of cancer cell interactions that can occur with the tumour microenvironment?
Contact dependent: Cell-cell and cell-ECM adhesion molecules
Contact independent - Soluble molecules including growth factors, chemokines and cytokines.
What needs to change in a cancer cell for dissemination to occur?
Needs to lose genes that helped it grow in an organised structure alongside the rest of the tumour. Needs to express proteins that can degrade components of the extracellular matrix and proteins that increase invasiveness and motility
What process is key for local invasion and dissemination?
EMT
What triggers EMT?
Epigenetic/genetic changes and heterotypic signals from the stroma (TGFb, Wnt)
What is required for EMT orchestration?
A series of master EMT-inducing transcription factors (Snail, slug, twist)
Is EMT reversible?
Yes - MET
What cellular features change during EMT?
Lose cell polarity (cadherin switch)
Lose cell adhesion (Cadherin, integrin, CD44)
They become isolate motile cells (HGF/SF)
They are able to modulate their environment (MMPs, proteases)
Why is EMT in metastasis not a binary switch?
Because EMT has been reported in collective migration of cells during dissemination. Therefore partial EMT allows cancer cells to gain EMT features whilst maintaining epithelial traits.
What cadherin switch is required in EMT?
E-cadherin to N-cadherin (epithelial to mesenchymal)
How is E-Cadherin expression most commonly inhibited?
Methylation of its promoter or upregulation of the transcriptional repressors SNAIL, SLUG, Zeb1
How do cancers change their expression of cadherin?
They downregulate E-cadherin and upregulate N-cadherin leading to reduced tumour cell adhesion to epithelial cells allowing migration and invasion.
How do epithelial cells become motile?
Hepatocyte growth factor/scatter factor derived mainly from fibroblasts and mesenchymal cells.
Does HGF/SF act in an autocrine or paracrine manner in tumour cells?
Normally paracrine. Tumour cells produce their own HGF causing it to act in an autocrine manner.
What is amoeboid cell migration?
Protease independent method of migration. Cells rely on a loss of polarity and chemotaxis in order to squeeze through the ECM.
What is mesenchymal cell migration?
Protease dependent method of migration. Cancer or stromal cell derived proteases degrade the ECM.
How do collective cells migrate?
In a protease dependent manner. It can occur either as a strand or isolated clusters.
What are common features of collegenases, gelatinases, stromelysins and matrilysins?
1) degradation of at least one component of the basement membrane.
2) Active at physiological pH
3) Require 2 zinc molecules for their activity
4) Inhibited by metal chelators and tissue MMP inhibitors
5) Secreted by zymogens and require extracellular activation
What cell types will produce MMPs
Endothelial cells, leukocytes, macrophages, fibroblasts and tumour cells.
Are MMPs entirely pro-tumour?
No. They also interfere with growth factor signalling, modulate cytokines and chemokines, regulate apoptosis and activate angiogenic factors
Why are serine proteases important?
They degrade several matrix components like gelatin, fibronectin or laminin. Also can activate numerous proforms of MMPs by peptide cleavage. This can aid in invasion etc/
What are the two types of cell adhesion molecules?
Calcium dependent CAMs and calcium independent CAMs.
How do integrins regulate pro-survival and pro-apoptotic signals?
It depends on the ligation status of the surface integrins expressed by a cell. In cells where most of the integrins are ligated, a prosurvival pathway is initiated.
In non-adherent cells in which many of the integrins are unligated, unligated integrins initiate cleavage of caspase 8, triggering apoptosis through integrin mediated cell death. On complete loss of adhesion, cell death is initiated through anoikis
What two stresses do circulating cancer cells encounter?
1) physical changes - associated with life in circulation (loss of attachment, shear stress)
2) Immune attack (mainly by NK cells)
In lung cancer; what cells do circulating tumour cells associate with and what is the result?
Platelets which prevents tumour cell recognition and lysis by NK cells. This is by forcing platelets to secrete TGF-B and PDGF which actively inhibit NK cells. Also, they surround themselves with platelets in order to protect them from shear blood flow stress.
What effect does CTC binding of neutrophils have on cancer cell survival and why?
Promotes survival. Neutrophils adhesion leads to elimination of NK cells and also causes ligation of integrins on cancer cells, preventing apoptosis/anoikis
What cellular process is required for extravasation?
TEM
Why do circulating tumour cell clusters do far better than single cells when it comes to seeding metastatic colonies?
1) physically large enough to lodge themselves in the lumina of capillaries.
2) Maintain a level of cell-adhesion so ligation of integrins is maintained and are more resistant to apoptosis.
How do CTCs induce extravasation?
Elicit ATP secretion from platelets which renders the vasculature more permeable. Also CTCs secrete MMPs and VEGF
What is the seed and soil theory?
The provision of a fertile environment in which compatible tumour cells could grow.
Why is the seed and soil theory the accepted theory?
Organ selectivity of metastatic spread.
What are the determining factors of organ selectivity?
1) Selective chemotaxis - the organ produces some soluble attraction factors to the tumour cells (initiated potentially by the primary tumour)
2) Compatible adhesion - sites on the endothelial luminal surface
3) Appropriate environment - growth factors or ECM (either already found at the secondary site or due to remodelling once the CSCs arrive).
Which cells are most likely to induce metastatic colonization?
Cancer stem cells - whilst all CSCs are capable of forming micrometastasis, only the stem-like population can form a metastatic tumour.
What is required for the induction and maintenance of cancer stem cell properties?
EMT
