Periodic Reporting for period 1 - MechTransition (Regulatory mechanisms controlling a new mechanical Epithelial to Mesenchymal Transition in zebrafish)
Período documentado: 2020-09-01 hasta 2022-08-31
Although metastasis is the predominant cause of mortality in patients with cancer, how tumour cells invade to form metastases is not well understood. For a cancer cell to metastasise, it must first invade from sites where most solid tumours originate, the epithelia, the skin that lines our organs, and then trans-differentiate to acquire a malignant phenotype. The prevailing metastasis model suggests that as cells mutate to become cancerous, they first form primary tumours from which accumulate mutations that disrupt these epithelia to become more motile (mesenchymal) cells that can move through the body in a process typically referred to as Epithelial-to-Mesenchymal Transition (EMT). Despite this model, our understanding of how tumour cells invade and transition to become a rogue migratory cell has been hindered by our ability to see this process live in real organisms. To visualise this process live, we have developed the transparent embryonic zebrafish skin as a model for the simple epithelia where cancers form, allowing us to directly film cell invasion. By following oncogenically transformed cells within this transparent skin, we found that cells can invade directly from the epithelium before they become actual cancers and independently from primary tumour masses. To do this, they co-opt a process that normally drives epithelial cell death - a process we discovered- called epithelial cell extrusion. Moreover, oncogenic hijacking of this process not only allows cells to invade and migrate throughout the body, but it also causes the cells to simultaneously pinch off the top of the cell, containing essential components that dictate their epithelial behaviour. Thus, invasion causes these cells to lose epithelial traits and become primordial. These cells then transition to a variety of different, more aggressive cell types that form big internal cell masses, similar to metastatic tumours. In this proposal I investigated how these primordial cells become mesenchymal and aggressive to metastasise.
During this project I used cell and molecular biology tools combined with fluorescence microscopy and image analysis to understand how can cancer cells that invade directly from the epithelium transform into mesenchymal cells and colonise other tissues. The main results from the study are briefly discussed below.
• Cancer cells invade by basal extrusion and deform as they migrate through the body. I found that as cancer cells invade by basal extrusion and migrate throughout the tight spaces inside the body, they become greatly deformed. I discovered that this confinement causes the cell nucleus, the round organelle that contains the DNA in the cell, to become compressed and elongated. These compressed cells frequently show signs of DNA damage, presumably due to the nuclear deformation, which has been previously linked to invasion in breast cancer.
• Deformation of cells and their nuclei promotes mesenchymal transition. I found that altering confinement that the cells experience when they invade the body, affects the ability of cells to acquire aggressive migratory traits. I decreased their confinement by genetically reducing the density of the connective tissue, and observed fewer invading cells became mesenchymal. Alternatively, physically compressing the embryos caused more cells to acquire aggressive mesenchymal traits. Thus, the mechanical confinement that the cancer cells encounter as they migrate can directly impact their potential to colonise other tissues.
• Increasing confinement and cell deformation results in more internal cell masses. Finally, I found that increasing confinement caused more internal cell masses to later form, whereas decreasing confinement resulted in fewer.
Together, my findings suggest a model where the mechanical invasion not only strips cells of their original epithelial characteristics, but the mechanical confinement they later encounter acts as a mechanical gymnasium, which either kills the cells or makes them more aggressive and able to form distant metastases. This work has been published in the peer reviewed scientific journal, iScience and we have published a review article discussing aspects of the project in Current Opinion in Genetics & Development.
• Cancer cells invade by basal extrusion and deform as they migrate through the body. I found that as cancer cells invade by basal extrusion and migrate throughout the tight spaces inside the body, they become greatly deformed. I discovered that this confinement causes the cell nucleus, the round organelle that contains the DNA in the cell, to become compressed and elongated. These compressed cells frequently show signs of DNA damage, presumably due to the nuclear deformation, which has been previously linked to invasion in breast cancer.
• Deformation of cells and their nuclei promotes mesenchymal transition. I found that altering confinement that the cells experience when they invade the body, affects the ability of cells to acquire aggressive migratory traits. I decreased their confinement by genetically reducing the density of the connective tissue, and observed fewer invading cells became mesenchymal. Alternatively, physically compressing the embryos caused more cells to acquire aggressive mesenchymal traits. Thus, the mechanical confinement that the cancer cells encounter as they migrate can directly impact their potential to colonise other tissues.
• Increasing confinement and cell deformation results in more internal cell masses. Finally, I found that increasing confinement caused more internal cell masses to later form, whereas decreasing confinement resulted in fewer.
Together, my findings suggest a model where the mechanical invasion not only strips cells of their original epithelial characteristics, but the mechanical confinement they later encounter acts as a mechanical gymnasium, which either kills the cells or makes them more aggressive and able to form distant metastases. This work has been published in the peer reviewed scientific journal, iScience and we have published a review article discussing aspects of the project in Current Opinion in Genetics & Development.
Our new EMT model represents a paradigm shift in our understanding of how tumour cells initiate metastasis and become distinct cell types. Using our original approach to visualize and study the invasion of transformed cells in vivo, our work has shed light on the mechanisms that cancer cells use to disseminate and overtake certain organs. A new mechanical understanding for how cell transition into more aggressive, mesenchymal types that have been historically difficult to target with current chemotherapies may shed new light on how to better target these cell types. We anticipate that our work will have an impact across different fields, including Cancer Biology, Mechanobiology and Cell Biology.