1. Activating Invasion and Metastasis
Nov 21, 2017

2. Hallmarks of Cancer, 2011

3. Metastasis

4. Metastasis
-The invasion and spread of tumor cells from a primary site to other parts of the body
-Organs have well-delineated
boundaries defined by basement
membranes
-Composed of mostly Extracellular
matrix (ECM)

5. Location of Metastasis
Organotropism – Specific cancers metastasize to specific sites
-Many locations are explained as a result of blood flow
-Organs is close proximity are likely sites of metastasis
-2/3 of metastases

6. Lung Metastases

7. Location of Metastasis
-Metastatic cells need a particular environment
-1/3 of metastases
-”Seed and Soil”
-Factors that affect the “Soil”
-Cell surface molecules/receptors
-ECM
-Neighboring cells
Pre-metastatic niche
-The primary tumor releases tumor-secreted factors that prepare the distant site
-Only 1 in 10,000 metastasizing cells can colonize a distant site

8. Monoclonal Metastasis
Linear
Branched

9. Polyclonal Metastasis
Linear
Branched
Cross-seeding

10. Metastasis

11. Steps of Metastasis Invasion – Breaking through the basement membrane
Intravasation – Entrance into the Bloodstream
Transport within the bloodstream
Extravasation – Exit out of the Bloostream
Colonization – establishment at a distant site
Not all the cells have the same ability to metastasize
-Tumor Microenvironment!!!
Contributions from both the tumor cell and the environment

12. Invasion
Epithelial-Mesenchymal Transition – breaking free of normal cellular constraints and acquiring migratory characteristics
Characteristics of EMT:
-Reversible
-Found in normal
Embryogenesis
-Loss of cell polarity
-Removal of cell-cell junctions
-Changes in cell shape
-Down-regulation of epithelial
Markers, Up-regulation of mesenchymal
Markers
-Increased motility

13. Induction of EMT -Signals from Stroma include:
-Growth Factors (HGF, EGF, PDGF, TGF-β)
-Bind their receptors (Tyrosine kinases) on tumor cells
-Initiates a signaling cascade (MAPK, PI3K)
-Activates transcription factors
-Snail
-Twist

14. Induction of EMT

15. Snail Transcription Factor
-Binds to E-boxes in epithelial genes
-Recruits Polycomb repressor Complex
-Histone modification and epigenetic regulation
-Gene repression (E-cadherin)

16. Twist Transcription Factor
-Helix-Loop-Helix protein
-Inhibition of Twist resulted in loss of metastasis (intravasation)
EMT also produces stem cell-like properties of the cell’s self-renewal

17. Cell Adhesion Molecules (CAM)
Cadherins – calcium-dependent transmembrane glycoproteins that interact via Catenins

18. E-Cadherin -Predominant Cell Adhesion Molecule
-Functions to secure cell-cell adhesion
-Suppresses metastasis, therefore is a tumor suppressor
-Down-regulated during Invasion
-Transfection of E-Cadherin into metastatic cells makes them
non-invasive

19. Extracellular Matrix Remodeling

20. Extracellular Matrix Remodeling
-ECM remodeling is controlled by MMPs that cleave ECM components that are needed for angiogenesis activation
-MMP-mediated degradation of collagen leads to exposure of the Arg-Gly-Asp sites needed for integrin binding

21. Integrin Receptors
-Family of more than 24 heterodimers composed of α and β subunits
-Mediate ECM and intracellular signal transduction
-Ligands include Arg-Gly-Asp tripeptides
-Upon binding the receptors cluster in the membrane
-Kinases such as focal adhesion kinase (FAK) are activated and affect the cytoskeleton

22. Integrin Receptors

23. Integrin Receptors
-Signaling can also go from the inside to the outside
-Altered expression of integrin receptors

24. Rapid Reorganization of the Cytoskeleton

25. Proteases Serine proteases and matrix metalloproteinases (MMPs)
-MMPs can cleave E-cadherin to remove cell-cell junctions
-Often tumor cells induce surrounding cells to produce MMPs
-Extracellular Matrix Metalloproteinase Inducer (EMMPRIN)
-Upregulated in tumor cells
-Also cleave other extracellular proteins, (Endothelial cell growth factors)
-MMPs are upregulated in nearly all tumors, and it’s correlated with its progression

26. Intravasation Steps: Attachment to the Stromal face of the vessel
Degrade the basement membrane using MMPs and proteases
Pass between the endothelial cells into the bloodstream
Tumor-associated macrophages release EGF attracting Tumor cells
Tumor cells release Colony Stimulating Factor -1 (CSF1) attracting tumor-associated macrophages

27. Intravasation

28. Transport in the Bloodstream
Circulating Tumor Cells (CTCs) transport is one way
CTCs travel as single cells or as clumps with platlets, Emboli
-Serve to protect the tumor cells from sheer forces and immune cells
-Certain cancers have favored sites of metastasis
-First-pass organ – the first organ that is downstream from the primary tumor; trapped in the first capillary bed due to size
-Breast cancer to Lung
-Colon and pancreas to Liver