Activating Invasion and Metastasis Nov 21, 2017

Hallmarks of Cancer, 2011

Metastasis

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)

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

Lung Metastases

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

Monoclonal Metastasis Linear Branched

Polyclonal Metastasis Linear Branched Cross-seeding

Metastasis

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

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

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

Induction of EMT

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

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

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

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

Extracellular Matrix Remodeling

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

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

Integrin Receptors

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

Rapid Reorganization of the Cytoskeleton

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

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

Intravasation

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