L5: Invasion and metastasis Flashcards
What are the metastatic cascade events?
- Invasion (changes in cell adhesion; enhanced cancer cell migration; ECM degradation); intravasation (basement membrane invasion); circulation (anchorage independent survival); extravasation (basement membrane invasion); colonization (cell adhesion and proliferation)
What is metastatic tropism?
- Cancers metastasis is not random
- The tendency of cancers to metastasise to specific organs
- Different cancers prefer different organs
- Depends highly on pre-metastatic niche
How does premetastatic niche facilitate tumour spread?
The premetastatic niche facilitates tumour spread
- Cancers can precondition distant environments to enable metastasis
- Includes inducing vascular leakage, immune suppression, ECM remodelling at the site of extravasation
- Can have premetastatic niche development at the site of colonization: growth factor liberation, ECM remodelling, exosome delivery
What are the epithelial and mesenhymal features?
Epithelial features:
- Organized in regular columnar morphology
- High degree of cell adhesion
- Cell-cell junctions
- Specialized apical membrane
- Underlying basement membrane
- Cells relatively static
Mesenchymal features:
- Irregular rounded or elongate morphology
- Loss of apico-basal polarity
- Front-back polarity
- Dynamic adhesions
- Lamellipodia and filopodia
- Cells highly motile
What are the molecular regulators of EMT?
- EMT is regulated in many complex ways, there are cotranscriptory regulators: Snail, Slug, Twist, Zeb
- We have microRNAs that co-regulate these transcriptors
- Transcription factors are difficult to target therapeutically
What is a key enzymatic driver of EMT?
Src: a key enzymatic driver of EMT
- Src is a non-receptor tyrosine kinase with both catalytic and scaffolding functions (in addition to transferring phosphate groups on target proteins, it can also bind proteins and help form complexes)
- Disrupts normal epithelial structure and promotes an invasive and mesenchymal phenotype
- Therefore, stimulates cell migration
- Inhibition of Src reduces tumour cell invasion, delaying dissemination and progression of disease
- Recently secured a novel Src inhibitor: eCF506. Very potently reduces breast cancer metastasis in mice
- inhibits both kinase activity and scaffolding properties – which is really effective
What are the adhesion molecules that form cell-to-cell and cell-to-matrix complexes?
- Two superfamilies of cytoskeleton-linked transmembrane adhesion molecules
- Cadherins mainly mediate cell-cell attachment (dynamically disassembled during EMT) disrupts cells contact – allows them to move
- Integrins mainly mediate cell-matrix adhesion (dynamically assembled during EMT)
What forms adherens junctions?
cadherins
What are the types of cadherins? Where are they expressed?
- Cadherins form a diverse family of adhesion proteins
- Tissue specific expression:
o E-cadherins (epithelium)
o N-cadherin (neuron)
o VE-cadherin (vascular endothelium)
o R-cadherin (retina) - This allows cells to form specific cell-cell interactions with the cells that are most relevant for them
How can cancer cells disassemble adherens junctions?
- Cancer cells can disassemble adherens junctions by:
o Phosphorylating cadherins (eg Src)
o Acquiring mutations (eg in E-cadherin’s gene)
o Mutating or removing cadherin-associated factors (beta-catenin)
How can EGFR activation affect regulation of adherens junctions?
- Abberant EGFR activation (very common in cancer) can stimulate beta-catenin and p120-catenin phosphorylation and promote junction disassembly
- Phospho-beta-catenin may antagonize association between alpha-catenin and E-cadherin
- Mediated by excess growth factor production: eg EGF, PDGF, often overexpressed by cancer cells or highly expressed by tumour microenvironment
- potential drug target
How can Src activation affect regulation of adherens junctions?
- Oncogenes such as Src, Yes, Lyn can directly phosphorylate β-catenin and p120-catenin.
- Src can additionally phosphorylate E-cadherin to target it for proteolysis.
- Src is upregulated in several human cancers and correlates with invasion and metastasis.
- Src potential drug target
Describe ECM, its structure, function
Cells reside in an extracellular matrix (ECM)
- ECM is reinforced matrix of structural proteins (collagen, laminin, fibronectin) that are organised as fibrillar structures embedded within a gel containing proteoglycans, glycoproteins, water, growth factors and other metabolites secreted by the cells
- Provides structural support and biochemical signals for multicellular tissue and organ systems.
- Contributes to cell identity and spatial organisation in tissues.
What are integrins?
- Heterodimeric α/β receptor pairs which bind ECM to transmit signals over cell membrane.
- Diversity of ECM proteins requires integrin diversity: at least 18 α-subunits, 8 β-subunits.
- Cells express specific integrins according to their extracellular surroundings.
- Integrins connect ECM to actin cytoskeleton
- Signal bidirectionally: both intracellular and extracellular cues influence integrin state and affinity for ECM proteins / intracellular adaptors
- integrins also coordinate cell migration and movement
What are focal adhesions?
- Focal adhesions are specialized multi-protein complexes that form at the interface between a cell and its extracellular matrix (ECM). These structures physically link the ECM to the intracellular cytoskeleton and serve as hubs for biochemical signaling.
- Concentrated locales of integrin-binding adhesion proteins
- Very diverse family – hundreds of proteins localise at focal adhesions
- Permits functional diversity - integrin adhesion can co-ordinate many cellular processes (primarily migration), because you can recruit many functional proteins to adhesions
What functions does altered integrin expression in can lead to?
o Promote invasion
o Promote metastasis
o Suppress apoptosis
o Drive cell signalling (via downstream adaptors eg focal adhesion kinase)
What is the function of focal adhesions kinases?
FAK is a core adhesion-linked signalling hub:
- Activated by binding active integrins
- Activates Src
- Co-ordinates mitogenic signalling with ECM binding
Very frequently over-expressed in cancer
What happens when focal adhesion kinases are targeted therapeutically?
Therapeutic targeting:
- Inhibits adhesion disassembly
- Inhibits cell migration
- Reduces invasion and metastasis
- Inhibits cancer-mediated immune suppresion
What is the unexpected role for adhesion signalling in non-adherent cells?
- Adhesion signalling complexes (integrins, FAK, etc.) can be internalised through endocytosis.
- Active adhesion signalling prevents anoikis: an adhesion-dependent pathway of apoptosis.
- Rab21-mediated traffic of active adhesion complexes (EEA1-positive)
What is the FAK activation pathway?
Upon integrin activation FAK is recruited to the integrins, FAK autophosphoralates on this Y397 site, which then acts a site for things like Src to come and bind along.
What is actin? How does it form? What is its function?
Actin is a filamentous structure that drives cell movement
- Filamentous (f)-actin forms from actin monomers
- Assembles into fibres which control cell shape and movement
Where from does actin assemble?
- Focal adhesions are sites of Rho GTPase regulation
- Small, monomeric GTPases which regulate factors that control actin polymerisation and cell movement
What are Rho faimily proteins? What is their function?
- Different actin structures are polymerised by different Rho family members
- RhoA (or RhoB/C): form stress fibres: provide elasticity, contractility during migration
- Rac1: forms lamellipodium: broad protrusion at the front of migrating cells.
- Cdc42: forms filopodia: fine, actin-rich processes which protrude intro the microenvironment.
- Co-ordinated action of Rho GTPases controls cell motility.
What are the types of cancer invasion?
- mesenchymal and amoeboid
- Gradient of states from mesenchymal to amoeboid according to:
o Rho status
o Integrin engagement (or lack thereof)
o Surrounding ECM context
o ECM-degrading activity of cancer cells
