Intravasation
Intravasation is the invasion of cancer cells through the basal membrane into a blood or lymphatic vessel.[1] Intravasation is one of several carcinogenic events that initiate the escape of cancerous cells from their primary sites.[2] Other mechanisms include invasion through basement membranes, extravasation, and colonization of distant metastatic sites.[2] Cancer cell chemotaxis also relies on this migratory behavior to arrive at a secondary destination designated for cancer cell colonization.[2]
Contributing factors
One of the genes that contributes to intravasation codes for urokinase (uPA), a serine protease that is able to proteolytically degrade various extracellular matrix (ECM) components and the basement membrane around primary tumors.[3] uPA also activates multiple growth factors and matrix metalloproteinases (MMPs) that further contribute to ECM degradation, thus enabling tumor cell invasion and intravasation.[3]
A newly identified metastasis suppressor, p75 neurotrophin receptor (p75NTR), is able to suppress metastasis in part by causing specific proteases, such as uPA, to be downregulated.[3]
Tumor-associated macrophages (TAMs) have been shown to be abundantly present in the microenvironments of metastasizing tumors.[4][5] Studies have revealed that macrophages enhance tumor cell migration and intravasation by secreting chemotactic and chemokinetic factors, promoting angiogenesis, remodeling the ECM, and regulating the formation of collagen fibers.[5][6]
Groups of cells (a macrophage, an endothelial cell, and a tumor cell) collectively known as tumor microenvironment of metastasis (TMEM) can allow tumor cells to enter blood vessels.[7][8]
Active and passive intravasation
Tumors can use both active and passive methods to enter vasculature.[9] Some studies suggest that cancer cells actively move towards blood or lymphatic vessels in response to nutrient or chemokine gradients,[6] while others provide evidence for the hypothesis that metastasis in the early stages is more accidental.[10]
In active intravasation, cancerous cells actively migrate toward and then into nearby blood vessels.[9] The first step in this process is specific adhesion to venular endothelial cells, followed by adherence to proteins of the subendothelial basement membrane, such as laminin and types IV and V collagen.[11] The final step is the adhesion of the metastatic tumor cell to connective tissue elements such as fibronectin, type I collagen, and hyaluronan, which is required for the movement of the tumor cell into the subendothelial stroma and subsequent growth at the secondary site of colonization.[11]
Passive intravasation refers to a process in which tumors metastasize through passive shedding.[9] Evidence for this is seen when the number of tumor cells released into the blood stream increases when the primary tumor experiences trauma.[12] Additionally, cells growing in restricted spaces have been shown to push against each other causing blood and lymphatic vessels to collapse, potentially forcing cells into the vessels.[9]
Epithelial-mesenchymal transition and intravasation
Epithelial-mesenchymal transition (EMT) has been hypothesized to be an absolute requirement for tumor invasion and metastasis.[1] However, both EMT and non-EMT cells have been shown to cooperate to complete the spontaneous metastasis process.[1] EMT cells, with migratory phenotype, degrade the ECM and penetrate local tissue and blood or lymphatic vessels, thereby facilitating intravasation.[1] Non-EMT cells can migrate together with EMT cells to enter the blood or lymphatic vessels.[1] Although both cell types persist in circulation, EMT cells fail to adhere to the vessel wall at the secondary site, while non-EMT cells, which have greater adhesive properties, are able to attach to the vessel wall and extravasate into the secondary site.[1]
References
- ^ a b c d e f Tsuji, Takanori; Soichiro Ibaragi; Guo-Fu Hu (15 September 2009). "Epithelial-Mesenchymal Transition and Cell Cooperativity in Metastasis". Cancer Research. 69 (18): 7135–7139. doi:10.1158/0008-5472.CAN-09-1618.
- ^ a b c Soon, Lilian (2007). "A Discourse on Cancer Cell Chemotaxis: Where to from Here?". IUBMB Life. 59 (2): 60–67. doi:10.1080/15216540701201033. PMID 17454296.
- ^ a b c Iizumi, Megumi; Wen Liu; Sudha K Pai; Eiji Furuta; Kounosuke Watabe (December 2008). "Drug Development Against Metastasis-related Genes and Their Pathways: a Rationale for Cancer Therapy". Biochimica et Biophysica Acta. 1786 (2): 87–104. doi:10.1016/j.bbcan.2008.07.002. PMC 2645343. PMID 18692117.
- ^ Condeelis, John; Jeffrey W. Pollard (27 January 2006). "Macrophages: Obligate Partners for Tumor Cell Migration, Invasion, and Metastasis". Cell. 124 (2): 263–266. doi:10.1016/j.cell.2006.01.007.
- ^ a b Pollard, Jeffrey W. (1 September 2008). "Macrophages Define the Invasive Microenvironment in Breast Cancer". Journal of Leukocyte Biology. 84 (3): 623–630. doi:10.1189/jlb.1107762.
- ^ a b van Zijil, Franziska; Georg Krupitza; Wolfgang Mikulits (October 2011). "Initial Steps of Metastasis: Cell Invasion and Endothelial Transmigration". Mutation Research. 728 (1–2): 23–34. doi:10.1016/j.mrrev.2011.05.002. PMC 4028085. PMID 21605699.
- ^ Rohan; et al. (2014). "Tumor microenvironment of metastasis and risk of distant metastasis of breast cancer". J Natl Cancer Inst. 2014 Jun 3;106(8). pii: dju136. doi:10.1093/jnci/dju136.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Karagiannis; et al. (2017). "Neoadjuvant chemotherapy induces breast cancer metastasis through a TMEM-mediated mechanism". Science Translational Medicine 05 Jul 2017: Vol. 9, Issue 397, eaan0026. doi:10.1126/scitranslmed.aan0026.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ a b c d Bockhorn, Maximilian; Rakesh K Jain; Lance L. Munn (May 2007). "Active Versus Passive Mechanisms in Metastasis: Do Cancer Cells Crawl into Vessels, or Are They Pushed?". The Lancet Oncology. 8 (5): 444–448. doi:10.1016/S1470-2045(07)70140-7.
- ^ Cavallaro, U; G. Christofori (30 November 2001). "Cell Adhesion in Tumor Invasion and Metastasis: Loss of the Glue is Not Enough". Biochimica et Biophysica Acta. 1552 (1): 39–45. doi:10.1016/s0304-419x(01)00038-5.
- ^ a b Zetter, B R. (August 1993). "Adhesion Molecules in Tumor Metastasis". Seminars in Cancer Biology. 4 (4): 219–229.
- ^ Liotta, L A; Saidel, M G; Kleinerman, J (March 1976). "The Significance of Hematogenous Tumor Cell Clumps in the Metastastic Process". Cancer Research. 36 (3): 889–894.