Invasion And Metastasis lecture 15 Flashcards
What does metastasis require?
Metastasis is the spread of a cancer from its tissue of origin
Cell invasion is a process which defines the ability ofcells to navigate through their own tissue or to infiltrate neightbouring tissues.
Cell adhesion, Survival, Proteolysis, Migration, Lymph-/angiogenesis, Immune escape, Homing to target organs
Metastasis is the loss of adhesion and reorganisation of the extracellular matrix and modultaion of cell-ECM adhesion
Describe the metastatic cascade
- Formation of pre-metastatic niche
- Tumour cell must separate from the primary tumour
- Then invades surrounding tissues
- From here they can enter vasculature and become circulating tumour cells (most will die)
- Ones which survive will leave the vasculature via extra-vasation and end up in their target organs
- When activated they proliferate, forming micrometastatis lesions, then form macrometastatic lesions (bad sysmptoms)
How is the pre-metastatic niche formed?
Tumour cells at the primary site will secrete soluble factors or vesicles which reach target organs and begin modifying cells there
-In turn the modified cells at the target organ will start recruiting myeloid derived stem cells which modify the target organ further - it becomes more receptive to seeds from the primary tumour
What is the self-seeding model of metastasis?
- Circulating tumour cells which are able to survive will sometimes return to the tumour
- They are very different to the bulk of the primary cells as they have adapted the foreign environment
- Upon returning they begin modifying primary tumour cells, further facilitating metastatic progression
THere is communication between tumour cells and whatever that surrounds it (macrophages, cancer associated fibroblasts) Tumour cels can supply macrophages with CSF-1 which attract macrogphages and then they secrete EGF which is a growth factor for the tumour - leads to more invasive and proliferative tumour.
Metastasis is very inefficient as most tumour cells die due to not hvaing the correct growth factors, only a few go onto the next stage, cells need growth factors to continue growing.
What is the strcture of cell-cell adhesion plaques
Cytoskelton, linker proteins and adhesion receptors.
Adhesion receptors have large extracellular portions and several transmembrane domains
Cytoskeleton - actin filaments, keratin filaments - allows formation of stable adhesion complexes
Linker proteins - catenine and desmocollins- adhesion receptors bind to linker proteins which link adhesion receptors with cytoskeleton.
Adhesion receptors - interact with one-another by one adhesion recepotr binding exactly the same adhesion receptor in opposing cells
What make up the core of adherence junctions and how do they bind?
E-cadherin and nectin
E-cadherin binding is Ca2+ dependent:
Without Ca2+ it cannot engage in homotypical binding
Protein interactions of cytoplasmic tail allow binding to actin filaments
Nectin binding is Ca2+ independent:
Linker proteins called afadin link nectin to actin filaments
How are adherence junctions formed?
1) Nectin engages with nectin on another cell
2) Afadin connects nectin to the cytoskeleton
3) Ponsin then binds afadin, forming a lateral link between nectin and cadherin complexes
4) When nectin binds its partner a signal is generated through CDC42 and Rac1
5) This leads to reorganisation of actin filaments and lateral recruitment of cadherin complexes to nectin
6) Ponsin helps join the cytoplasmic segments of cadherin and nectin together, causing first round of engagement between opposite cadherins
7) This leads to activation of Rac by E-cadherin, further inducing polymerisation of actin and stabilising the cadherin complex
Loss of adherence junctions causes loss of intercellular adhesion and transcriptional activation which causes increased migration and invasiveness
How can E-cadherin be involved in cancers?
- Loss of E-cadherin leads to invasive lobular carcinomas (breast cancer)
Caused by:
- Repression of expression by Snail and CIP-1
- MMP-induced shedding of E-cadherin from surface of breast cancer cells
2. Mutations leading to reduced expression
Also causes invasive lobular carcinomas
Reduced E-cadherin expression is associated with shortened disease free survival
Loss of E-cadherin causes p120 to activate Cdc42, Pho and Rac, changing actin cytoskeleton, increasing migration and invasion.
Also loss of E-cadherin causes B-cat to dissocaite to LEF/TCF which goes into nucleues and stimulates transcrpition.
Describe the sttructure of cell-ECM adhesion plaques
Has actinfilments and keratin filaments. Also has adhesion recprtors and cytoskeltal linker proteins
Same structure as ahdesion complexes
What does transition into invasive phenotype require?
Modification to Cell-ECM adhesion
- Cells joined to ECM by local adhesion and hemi-desmosomes
- Always has the same structure, this is controlled by:
Integrins:
- Made up of alpha and beta subunit
- Function depends on their ability to bind divalent cations (Mg2+ and Ca2+)
- Important for outside-inside and inside-outside signalling
- To bind their ligands they must be activated from within by Talin (inside-outside signalling)
- Once the integrins bind their ligand conformation is changed again, sending a signal to the cytoplasmic domain
How do tumours overcome the mechanical barriers to invasion?
Basement membrane (comlpex netwrok of interacting proteins which separtates epithetil and endotherial cells from connective tissue) and the stromal environments (made of collagen fibrils and extracellular prroteogycans) are the mechanical barriers
ECM degrading proteins-
Matrix metalloproteinases (MMPS)
Serine proteases activate these They secrete MMP and stimulate stromal cells too
MMP degrade ECM, increase tumour cell migration and release latent growth and chemotactic factors
What happens when tumour cells reach tehir destination on endotherial cells
ONce tumour cells reach destination, they will interact with adhesion recptorson urface of endothelial cells. The attachment of tumour cells and endothelial cells is transient, a signalling cascade is ativated inside tumour cells which allows strong attachment between tumour and endothelial cells. This is mediated by integrins on tumour cells and integrin ligands on endothelial cells allowing strong attachement - tumour cells will be allowed to get out of vasculature by extravation.
How do cancer cells surpass the basemement membrane?
MMPs
- Tumour cells secrete MMP-9 in inactive form
- Can be activated by MMP-2 (but this is also inactive)
- MMP-2 is activated by MT1-MMP (present on surface of tumour cells)
- This allows MMP-2 to activate MMP-9
- MT1-MMP can also activate MMP-7 (also produced by tumour cells AND osteoclasts - this is how cancer cells settle in the bone)
How do tumours home to their target organ
Selective growth
Selective adhesion to sites on the endothelial cells at the organ
Selective chemotaxis of circulating tumour cells to the organ producing soluble attraction factors
Invasion of the endothelium- rolling via weak E/P-selectin - CD44, CEA, PODXL then string ICAM1, VCAM1- integrins the extravasation Or platelet mediated capture followed by growth Selectins tigger biochemical signals that ultimately stop rolling of tumour cells over the endothelium➡️ increase chemokine production➡️ production of MMP➡️ tumour invasion, out of vasculature
How do tumour cells stop on endothelium to invade?
Selectins - carbohydrate binding cell adhesion proteins (L-selectin, P-selectin and E-selectin)
- E-selectin is expressed on the surface of endothelial cells and platelets and used by tumour cells
- Selectins trigger biochemical signals by chemokines that stop rolling of tumour cells over endothelium
- This allows activation of integrin, increased chemokines production and increased MMP production. This allows strong attachment points between the tumour cells and endothelial cells.
- MMP start forming gaps in endothelial cells which allows migration into the tissue and to get inside the stroma of the seconadary organ.
