Metastasis Flashcards
what is metastasis?
spread of malignant cells from the primary tumour to othe independent sites within the body
what is angiogenesis?
formation of blood supply (vascularisation) of tumour
occurs following transformation and initial growth of cells
when does the tumour need to form a blood supply and why
angiogenesis must occur to provide support for growth of the tumour mass (required for >1mm in diameter)
at tumour size >1mm, diffusion of nutrients and waste products become rate limiting for continued growth of tumour
how do tumours initiate angiogenesis
synthesis and secretion of pro-angiogenic factors (fibroblast growth factor FGF, vascular endothelial growth factor VEGF) by tumour cells and other non cancerous cell types around the cancer
how do cells become metastatic?
- Initial growth of cancerous cells and formation of a tumour, developing a vascular supply
- Factors produced by cancerous cells and surrounding non-cancerous cell types stimulate morphological changes in cells
- Phenotypic conversion and dedifferentiation of epithelial cells – indicative of carcinoma (epithelial derived cancer)
- Characterised by epithelial mesenchymal transition (EMT) enabling cells to migrate and invade the surrounding tissue; invasion of the vascular and lymphatic system → resulting in metastasis
who proposed the seed and soil hypothesis and what does it describe
Stephen Paget in 1889
distribution of metastasis is not by chance, instead metastases develop only when ‘seed’ and ‘soil’ are compatible
- ‘seeds’ - cancer cells with metastatic ability
- ‘soil’ - microenvironment
explain the bidirectional movement of metastasis and how it can impact recurrence
bi-directional movement of tumour cells between primary and distant tumour sites – metastases have the ability to re-seed the primary tumour site (due to a local environment within each site that is similar and conductive to tumour growth)
Following inital treatment, relapse can occur in the exact same location because the microenvironmetn dictates their location/ survival
what are the three principle factors of the seed and soil hypothesis?
- tumours are heterogenous - made up of cancer cells with subpopulations of host cells exibiting different properties
- metastasis is selective for cancer cells which demonstatre a combination of these particular properties - (in order to succeed in the secondary site)
- success of the resulting metastasis at the secondary site depends on its ability to interact with and utilise the ‘soil’, comprising multiple factors within the microenvironment
(host cells eg epithelial, fibrobalst, endothelial, leukocytes)
(properties eg angiogenic, invasive, metastatic, growth rate)
where does the epithelium sit and what is its major function?
epithelium sits on top of the connective tissure layer (stroma) (basal lamina separates the two
has a barrieer function to protect the underlying tissues and acts selectively to sort molecule between the lumen and underlying tissue
give five common sites of epithelial derived cancer
colon, breast, ovary, lung, prostate, pancrease
development of a cancerous growth within the epithelium leads to…
…disruption of tissue organisation and eventual invasion into the connective tissue layer
what are the stages of epithelial derive cancer from normal to carcinoma
normal epithelium
low grade intraepithelial neoplasia
high grade intraepithelial neoplasia
invasive carcinoma
what are the two key features of epithelial cells
they are polarised (apical and basal) and differentiated
what are the four types of junctions in epithelial tissues?
give examples for each
- tight junctions eg tight junction
- cell-cell anchoring junctions eg adherens junctions and desmosome
- channel forming junctions eg gap junctions
- cell-matrix anchoring junctions eg actin linked cell matrix junction and hemidesmosome
what is a tight junction?
give two components
a tight junction that seals gap between epithelial cells
zipper-like, restricts flow of molecules and water within the intracellular space, maintains an impermeable epithelial barrier
components, occludin, ZO-1
what is an adherens junction?
give two components
a cell-cell anchoring junction that connects actin filament bundles in one cell to that in the next cell
provides lateral adhesion between neighbouring epithelial cells - maintains actin contractile rings and epithelial polarity
components, e-cadherin, alpha actinin
what is a desmosome?
give two components
a cell-cell anchoring junction that connect intermediate filaments in one cell to those in the next cell
linked to intermediate fibres, functions to maintain adhesion and tissue integrity
components+ desmoplakin, cytokeratin
what is a gap junction?
a channel forming jucntion that allows the passage of small water soluble molecules from cell to cell
what junction is found in the zonula occludens?
tight junctions
what junction is found in the zonula adherens?
adherens junctions
what junctions is found in the macula adherens?
desmosome
what is the function of the actin contratile ring
- maintains the adhesion belt between cells
- provides structural support to tissue
- maintains columnar epithelial phenotype
how do e cadherin cell-cell junctions come together and what is their function
Ca2+ dependent homodimerisation of e-cadherin
* provides structural support for tissue organisation
* supports apical/basal polarity of epithelial cells by maintaining actin contractile ring - adhesion belt
Act physically as a belt to support the structure and polarity
how do e cadherin cell-cell junctions come together and what is their function
Ca2+ dependent homodimerisation of e-cadherin
* provides structural support for tissue organisation
* supports apical/basal polarity of epithelial cells by maintaining actin contractile ring - adhesion belt
Act physically as a belt to support the structure and polarity
downregulation of epithelial genes in the epithelial mesenchymal transition leads to what main changes occur
loss of polarity and cuboidal structure (loss of e-cadherin)
cell migration
degredation of the extracellular matrix
what is the epithelial- mesenchymal transition?
a genetic reprogramming event driven by transciptional regulation
reversible phenotypic conversion of polarised (differentiated) epithelial cells to unpolarised mesenchymal cells
at what stage in cancer progression does EMT occur
just before intravasation
what effect does the tumour microenvironment have on EMT?
TME provides factors and different cell types that prommote cancer cell dedifferentiation and metastasis
* growth factors: HGF, EGF
* extracellular matrix: laminin, fibronectin
* macrophages
* matrix metalloproteases
* Pro-inflammatory cytokines TNFalpha, IL1beta, TGFbeta1
* hypoxia
what are the functions of TGFbeta1 in normal epithelium
growth inhibition
apoptosis
genomic stability
just helps maintain the epithelium
what are the functions of TGFbeta1 in normal epithelium
growth inhibition
apoptosis
genomic stability
just helps maintain the epithelium
what are the roles of TGFbeta1 in invasive/metastatic cancer
EMT
invasion/ motility
survival
angiogenesis
immunosuppression
what changes in the actin organisation when cells are treated with TGFbeta1
epithelial tissue has a cortical actin ring
mesenchyal/tgfbeta1has actin stress fibres
what are the differences between epithelal and mesenchymal cells?
epithelial - low cell motility and cell-cell adhesion, Ecadherin
mesenchymal - high cell motility, cell-ECM adhesion, ECM production and deposition, vimentin
what factors around cancer activate the latent form of TGFbeta1
MMPs
ROS
acidic pH
ECM
TGFbeta1 is kept in latent (inactive) form in complex with what other protein
with latent associated peptide (LAP) derived from N-terminal region of TGFbeta1 precursor
TGFbeta1 is kept in latent (inactive) form in complex with what other protein
with latent associated peptide (LAP) derived from N-terminal region of TGFbeta1 precursor
what occurs whenTGFbeta1 is converted form the latent form to the active/mature form
binding of tgfbeta to type 2 causes stabilisation of
heterodimerisation of type 1 and type 2 receptors
type 2 receptor is a consituitively active kinase and recruits and phosphorylates type 1 receptors.
This causes recruitment and phosphorylation of R-SMAD (Smad2/3) allowing it to bind SMAD 4 and translocate into the nucelus to modulation of gene expression
Activating genes involved in EMT regulation (Snail, Zeb, Twist)
how is EMT regulated?
What are the three major genes?
by transcriptional reprogramming
of ZEB1/2, SNAIL and TWIST
what signalling factors activate ZEB1/2 SNAIL and TWIST
Wnt
Transforming growth factor beta 1 (TGFb1)
Notch
Epidermal growth factor (EGF)
Hepatocyte growth factor (HGF)
Tumour necrosis factor alpha (TNFa)
whats the relationship between p53 and the roles of ZEB, snail, twist master regulators during cancer
1) ZEB1 – activates DNA repair pathways, promotes cell survival → in an EMT-independent and dependent manner
2) p53 inhibits ZEB1 expression via microRNA 200 – upon p53 deletion, ZEB1 becomes active and is able to induce EMT; p53 represses Snail expression
what three signalling mechanisms feed into EMT regulation
TGFbeta - leading to Smad2/3 phosphorylation and activation and transcription of Snail ZEB & twist
Wnt - to Dsh inhibiting GSK-3beta which inhibits Snail, ZEB & twist
Growth factors - leading to Ras then MAPK activating Snail ZEB & Twist. Ras also activates P13K/AKT which inhibits GSK-3beta
SNAIL, ZEB and twist are all genes contributing to suppression of epithelial markers and activation of mesenchymal markers
how is microRNA 200 involved in EMT
P53 activates miR-200
microRNA 200 negatively regulates expression of ZEB1, thus inhibiting EMT
Phosphorylation occurs mostly on which three amino acids
serine, threonine or tyrosine
give four types of ubiquitin chains
mono
K63
K48
K11
what two ways can snail be targetted for degredation
(repress snail expression)
- phosphorylation by GSK3beta
- p53 activation of MDM2 (a ubiquitin ligase)
How does activated GSK3beta repress snail expression
Snail can be phosphorylated at 1st site by GSK3beta which leads to its translocation out of the nucleus
In the cytoplasm, Snail subsequently gets phosphorylation by GSK3beta at 2nd site, leading to its ubiquitination and targetting to the proteosome for degredation
