Activating Invasion and Metastasis Nov 28, 2017

Hallmarks of Cancer, 2011

Metastasis

Extravasation The exit of a tumor cell from a blood or lymphatic vessel Steps are opposite of Intravasation Attachment to the endothelial side of the blood vessel Pass through the endothelial cells and basement membrane Migrate into the surrounding stroma The mechanisms differ because of the cell approaches the endothelium from opposite sides

Extravasation Supports the “Seed and Soil” theory

Extravasation Upon binding to E-selectin, Signaling between the tumor cell and endothelial cell is bidirectional In endothelial cells , E-selectin induces tyrosine phosphorylation and modifies the cell’s shape In tumor cells, Stress-activated protein kinase-2 (SAPK2/p38), a MAPK isoform in induced, important for transendothelial migration Other molecules on tumor cells include CD44 and MUC1

Extravasation Transendothelial migration -VEGF has been implicated from in vitro studies Migration -Proteases are important -MMP9

Metastatic Colonization Sites of Metastasis is influenced by: Location of Extravasation Ability of tumor cells to adapt to the new environment Metastatic Colonization is the establishment of a progressively growing tumor at a distant site To Grow or Not to Grow???

Metastatic Colonization “Not to Grow” Tumor cells which have reached a secondary site but have not grown are called disseminated tumor cells -Can occur early during carcinogenesis Micrometastases -Remain dormant for years -Maintain a balance between proliferation and apoptosis -Angiogenesis is not initiated -Molecular factors induce quiescence (stable blood vessels) -Need to undergo a mesenchymal-to-epithelial transition (a reversal of EMT)

Pre-Metastatic Niche and Exosomes “To Grow” Tumor-specific factors are released from the primary tumor facilitate changes to the microenvironment of a distant and future site of colonization before tumor cells arrive

Exosomes Small vesicles (30-100nm) that carry protein and nucleic acids Characteristics: -Important for intercellular communication -Carry DNA, RNA, and protein Horizontal transfer - Exosome transfer can educate and change the behavior of the receiving cells

Exosomes Experiments: Mice treated with concentrated tumor exosomes, there was an increase in the number of metastases Reduced exosome production via RNA interference, caused a decrease in the number of metastases Pancreatic exosomes promote liver metastases -Pancreatic exosomes fuse with Kupffer cells in the liver -Kupffer cells upregulate TFG-β -Results in expression of fibronectin in liver stellate cells -Fibronectin recruits bone-marrow-derived cells -Pre-metastatic niche ready to accept pancreatic tumor cells

Evidence for Horizontal Transfer -Potential recipient cells would express GFP if it received the CRE-recombinase -When exposed to CRE-containing exosomes, the cells fluoresced green

Exosome Composition

Metastasis Suppressor Genes -Expressed in low levels in metastatic cells -Inhibit overt metastasis without affecting the growth of the primary tumor -Regulation of Growth of metastatic cells at secondary sites -Maintain these cells as noon-proliferating dormant cells -Therefore, Loss of function, promotes metastasis

Metastasis Suppressor Genes -23 metastasis suppressor genes identified -NM23 -a nucleoside disphosphate kinase and a histidine kinase -MKK4 (mitogen-activated protein kinase-kinase 4) -induces apoptosis in response to a stressful environment miRNAs -miR-335 and miR-126 -Promote dormancy of micrometastatic colonies

Exosomes Video https://www.youtube.com/watch?v=eSwG5O_kiOQ