lecture 8 - invasion Flashcards
What is the difference between invasion and metastasis?
Cancers can spread through the body by two mechanisms:
Invasion is migration and penetration into neighbouring tissues.
Metastasis involves penetration of lymphatic or blood vessels, circulation and colonisation of normal tissues at a distant site.
What is the metastatic cascade?
Metastasis is a multi-step process.
Metastasis encompasses tumour growth/angiogenesis, detachment/invasion, transport in circulation, arrest in distant organs, extravasation, and establishment at secondary sites.
Invasion is an early step in the metastatic cascade.
Primary tumour grows, there is proliferation and angiogenesis is required for the tumour to grow above a certain size. There is detachment and invasion of some of those cells, they gain access to the circulation, might form emboli within the circulation, transport through the circulation and arrest in distal organs, adhere to vessel wall, escape out of vessel through extravasation and establish favourable microenvironment at metastatic site, proliferate and form metastases. Once cancers reach this stage of multiple metastases they become more difficult to treat – both drug resistant and difficult to operate on
Describe cross-talk and feedback in metastasis
Mesenchymal stem cells (MSCs) in the tumor stroma can secrete CCL5 (chemokine ligand 5) in response to signals released by cancer cells - CCL5 then acts on the cancer cells - stimulates invasive behaviour.
Conclusion: Malignancy does not arise in a cell-autonomous manner
Implication: The invasion-metastasis cascade may be acquired without additional mutations beyond those that were needed for primary tumor formation.
Analyses of tumor cell genomes can only reveal part of the story.
Feedback loop between cancer cells and mesenchymal stem cells
Heterotypic signalling taking place between tumour cells and other cells within the tumour
Carcinoma cells can secrete chemotactic factors – act on circulating monocytes which are passing through the tumour environment – causes co-option of these monocytes
Tumour-associated macrophages can then also secrete growth factors eg EGF, proteases, angiogenic factors – which then act back on the tumour and the cancer cells
More carcinoma cells recruit more monocytes
Positive feedback – promotes invasive tumour
Describe cell adhesion molecules
There are multiple classes of cell adhesion molecules (CAMs) expressed on cancer cells.
These include: cadherins, integrins, immunoglobulin superfamily cell adhesion molecules.
Some CAMs are involved in cell-ECM adhesion. Others are involved in cell-cell adhesion (cis and trans).
Invading cancer cells experience changing tissue environments and matrix components - adapt by altering CAM expression (e.g. there are >22 types of alternately expressed integrins).
Cancer cells with interact with and adhere to components of ECM
Cis on same cell, trans on different cells
Describe integrin signalling complexes
Integrins assemble as ⍺ and β heterodimers.
There are multiple signal transduction proteins associated with, or activated by, integrins.
Signalling molecules, e.g. FAK, bind to and recruit additional signalling molecules.
Creates a complex signalling network that is closely connected to the cytoskeleton.
Integrins themselves assemble as alpha/beta heterodimers, activate multiple signal transduction pathways
Signalling molecules recruited to points of adhesion (focal adhesion)
Describe the functional role of adhesion molecules
Adhesion molecules regulate cell shape.
Altered adhesion can lead to loss of attachment to other cells and/or the extracellular matrix.
Changes in adhesion molecule expression can cause loss of anti-growth signaling.
Altered CAM profile can facilitate migration and anchorage to cells/substrates at new sites.
Loss of attachment important for cells escaping tumour
E-cadherin can cause contact inhibition, preventing cell growth and inhibition
Image on left has more epithelial-like phenotype, cells adhered to each other
On the right E-cadherin is knocked down, causes change in cell morphology more mesenchymal-like
What is the epithelial to mesenchymal transition (EMT) ?
During embryonic morphogenesis (and wound healing), signals from neighbouring cells trigger expression of transcription factors that promote an epithelial-mesenchymal transition.
This is co-opted by cancer cells.
Quiescence: Epithelial cell-to-cell adhesion molecule E-cadherin maintains quiescent state and suppresses invasion and metastasis.
Loss of E-cadherin makes cells more invasive
When E-cadherin is present is suppresses activity of B-catenin
B-catenin activates txn factors
What is the link between EMT and E-cadherin?
EMT can occur via mutation of the E-cadherin or β-catenin genes; transcriptional repression; proteolysis of the extracellular cadherin domain.
The result is a loss of adhesion.
At the same time there is upregulation of adhesion molecules associated with mesenchymal cell migration such as N-cadherin.
EMT can occur via several different mechanisms
Loss of E-cadherin associated with increased local invasion
Describe invasion
Invasion is migration and penetration into neighbouring tissues.
The spread of cancer requires reorganisation and proteolysis of the extracellular matrix (ECM).
Protease genes are upregulated.
Protease inhibitor genes are downregulated.
Inactive proteases are converted into active enzymes.
Proteases facilitate invasion into nearby tissue.
Intravasation: penetration of blood vessel walls.
Cancer cells have to reorganise ECM to create space for themselves
Once they start to invade they break through the basal lamina in between the tumour and the stroma
Intravasation involves cancer cells entering the blood vessels
What are Matrix metalloproteinases (MMPs)?
Family of zinc- or calcium-dependent enzymes that degrade virtually all components of the ECM.
Minimal unit contains a propeptide domain and a catalytic domain.
Can be be secreted or membrane-bound (MT-MMP).
Membrane anchorage can be via transmembrane domains or GPI anchor.
Invasion requires protease activity
Membrane bound = MT-MMP
Describe the role of MMPs and survival
Upregulated in almost every type of cancer.
Expression induced by oncogenes, e.g. c-myc, c-ras.
Increase tumour progression, e.g. MMP-3 overexpression causes severe mammary hyperplasia in mice.
Often associated with poor survival, e.g. stromal MMP-9 expression reduces RFS by 20%.
High expression of MMPs in tumour = bad news
Experiment here used mouse model – researchers overexpressed/upregulated MMP-3 in the mammary gland of mice – caused very severe phenotype
Mammary hyperplasia – akin to early stage tumour
Clinical studies have shown MMP expression associated with poor survival
RFS = recurrence free survival
What are Cathepsin proteases?
Proteases such as cathepsin-B degrade collagens in connective tissue.
Allow penetration of the basal lamina and the stroma, to support exit from organs and entry to the circulatory system: intravasation.
Normally housed in membrane-bound vesicles (lysosomes) inside the cell (function to degrade cellular proteins).
Cancer cells express cathepsin-B on their surface membranes as well.
Heterotypic contribution from non-cancer cells: macrophages at the tumor periphery support local invasion by supplying matrix-degrading enzymes such as metalloproteinases and cathepsin proteases.
Describe patterns of invasion
There are multiple types of invasion.
Mesenchymal invasion: regulated by EMT.
Collective invasion: groups of cells advance into adjacent tissues.
Usually not metastatic.
Typical of squamous cell carcinomas.
Amoeboid invasion: morphological plasticity allows cells to squeeze through existing gaps rather than digest the ECM to create a path for themselves.
Coopted proinvasive inflammatory cells: tumours attract cells that secrete ECM-degrading enzymes.
