M.Sc Thesis

M.Sc StudentDvir Liron
SubjectThe Cytoskeleton and the Nucleus Role during Initial Stages
of Metastatic Invasion
DepartmentDepartment of Biotechnology
Supervisor ASSOCIATE PROF. Daphne Weihs
Full Thesis textFull thesis text - English Version


The process of invasion is important during the beginning of the cancer tumor and during cancer metastasis creation. While metastasized, cells detach from the primary tumor and penetrate the extra cellular matrix (ECM). Subsequently, those cells may invade a distant location and initiate a secondary tumor. In addition, cancer cells are more active than normal cells hence, their nucleus position, their intracellular cytoskeleton structure and their intracellular transport may be different from normal cells. Those intracellular components are responsible for the cell mechanics and may have an important role in cancer cell penetration. However, the mechanism in which the cancer cell penetrates the ECM and the role of the nucleus and the intracellular cytoskeleton in the penetration is still unknown. Hence, we focused on the mechanics of cancer cells in the initial stages of penetration by studying cells as they indent a soft substrate, which they cannot degraded or penetrate through its pores. Yet, they can bend and push it while they are indenting it.

In this thesis, We evaluate the initial stages of indentation using model breast-cancer cells, on elastic poly acryl-amide gel with small, sub-micron pores. We evaluated cell's mechanism by imaging the directed fluorescence stained cells that were fixed while indenting a 2-D substrate. Using fluorescent nano-particles embedded in the gel, we were able to identify single cells as they indent the gel since the cells lower the focus of the substrate, indicating that the cells press down on the gel surface. We use three types of human, epithelial breast-cancer cell lines: MDA-MB-231 (high metastatic potential, MP), MDA-MB-468 (low MP) and MCF10-A (benign) as a control. When the cancer cells encounter the gel, a population of those cells adheres to the substrate and attempt penetrating it. We show that only the cancer cells significantly indent the elastic substrate. The high MP cells are differ from low MP and benign cells in several evaluated parameters. First they displayed a larger indentation depth and lower cell height above the gel. Second, their nucleus indent below gel level with larger nucleus volume and it was non-concentric to the cell. Those parameters are in accordance with their highly aggressiveness level. Our results suggest a mechanism with combined roles for both the nucleus and the cytoskeleton that depends on cell aggressiveness. We demonstrated that metastatic cells indent a substrate using a combination of their structural flexibility and ability to dynamically apply forces.