Metastases are the main cause of human cancer deaths. As cancer progresses, tumor cells migrate from the initial tumor mass and spread to vital organs. The microenvironment surrounding the tumor cells is complex, and we are becoming increasingly aware that the microenvironment contains signals that regulate tumor cell migration. We seek to understand what these signals are, which cells send them, and how this communication regulates tumor cell migration in vivo.
As cancer is a dynamic process, to fully understand cancer progression and the regulation of tumor cells, we take advantage of the genetics and the in vivo imaging possible in the zebrafish larvae to discover the cellular mechanism by which cells in the microenvironment influence tumor cell behaviour in vivo. We have demonstrated that the tumor-stromal interactions visualized in mammalian systems are recapitulated in great detail in zebrafish. We found that consistent with mammalian studies, tumor associated macrophages promote tumor cell dissemination in zebrafish. We further found a unique mode of heterotypic communication in which sustained macrophage/tumor cell contacts allow for the transfer of cytoplasmic molecules from macrophages to tumor cells, thereby instructing tumor cell dissemination. We will use this system to further reveal the nature of communication at heterotypic cell contacts in the microenvironment, and how these processes regulate cytoskeletal dynamics of tumor cells in vivo.
Taking advantage of the optical clarity of the zebrafish larvae, in combination with in vitro tissue culture to analyze cellular interactions in real-time, as well as mouse models to test our hypotheses in a mammalian in vivo system, our lab has 2 general goals:
- Dissecting the mechanisms of cell-contact dependent cytoplasmic transfer in development and cancer
- Elucidating extracellular signals regulating tumor cell cytoskeletal dynamics in vivo
Cell-contact dependent cytoplasmic transfer
What is the identity of the cytoplasmic molecules transferred between cells and what is the mechanism by which this transfer occurs?
An intriguing question that stems from our studies is the identification of the cytoplasmic “active ingredients” transferred from macrophages to tumor cells driving dissemination in a cell contact-dependent manner. We are currently using RNA profiling strategies to generate a list of candidate genes to test further with in vitro and in vivo approaches. We will employ high resolution microscopy to resolve cell biological structures that form between cells, as well as visualize mRNA transport between cells. In addition to further illuminating players involved in cell-cell communication, we hope to reveal novel molecules to potentially inhibit in the clinic.
Zebrafish macrophages (red) contacting human melanoma cells (green).
Is cell contact–dependent cytoplasmic transfer a strategy used by many different cell types in different contexts (in both development and disease)?
It has been long been shown that developmental paradigms regulating cell motility are recapitulated in disease. We aim to discover contexts in which cell contact-dependent cytoplasmic transfer occurs during normal development and homeostasis, how this process is regulated, and how it may be hijacked during disease in vivo.
Extracellular signals and cytoskeletal dynamics
What additional signals from stromal cells in the microenvironment regulate tumor cell cytoskeletal dynamics and cell biological decision-making?
In addition to transfer of cytoplasmic molecules, tumor cells communicate with the cells in the environment via extracellular and cell contact mediated signalling. However, the downstream cell biological effects of this signalling are unclear. Thus, the goals of this project are 3-fold: 1. Identify candidate signalling pathways regulating tumor cell metastasis; 2. Identify the specific cells in the microenvironment that take advantage of these signalling pathways to regulate metastasis; and 3. Determine how these signalling pathways regulate cellular behaviour during metastasis. In the course of these experiments, we hope to identify not just signals that regulate a single cytoskeletal event, but signals that regulate how cells switch from one cell behaviour to another during a biological process. These experiments will link heterotypic cell signaling to downstream cytoskeletal responses, a highly regulated process during cancer progression, and will potentially reveal the coordination of two subcellular processes that regulate a single biological step in vivo.
Human melanoma cell expressing TagRFP-T-cortactin (red) to visualize invasive structures as tumor cells migrate near zebrafish blood vessels (green).