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Updated: Jun 7, 2025
A Macrophage-Tumor Spheroid Co-Invasion Assay
Published on: January 24, 2025
Real-time imaging reveals a role for macrophage protrusive motility in melanoma invasion
Gayathri Ramakrishnan1, Veronika Miskolci1, Miranda Hunter2
1Department of Medical Microbiology and Immunology, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI, USA.
Abstract:
Macrophages are primary cells of the innate immune system that mediate tumor progression. However, the motile behavior of macrophages and interactions with tumor cells are not well understood. Here, we exploit the optical transparency of larval zebrafish and perform real-time imaging of macrophage-melanoma interactions. We found that macrophages are highly motile in the tumor microenvironment. Macrophages extend dynamic projections between tumor cells that precede invasive melanoma migration. Modulating macrophage motility with a dominant inhibitory mutation in Rac2 inhibits recruitment to the tumor and impairs tumor invasion. However, a hyperactivating mutation in Rac2 does not affect macrophage recruitment but limits macrophage projections into the melanoma mass and reduces invasive melanoma cell migration. Taken together, these findings reveal a role for Rac2-mediated macrophage protrusive motility in melanoma invasion.
Insights
Macrophages exhibit dynamic motility within tumors, extending projections that precede melanoma invasion. Rac2-mediated protrusive activity is crucial for this macrophage behavior and subsequent tumor cell migration.
Area of Science:
- Immunology
- Cell Biology
- Cancer Research
Background:
- Macrophages are key innate immune cells involved in tumor progression.
- The precise role of macrophage motility and their interaction with tumor cells in invasion remains unclear.
Purpose of the Study:
- To investigate the real-time behavior of macrophages interacting with melanoma cells.
- To elucidate the role of Rac2-mediated macrophage motility in tumor invasion.
Main Methods:
- Utilized optically transparent larval zebrafish for in vivo imaging.
- Performed real-time observation of macrophage-melanoma interactions.
- Employed genetic modulation of Rac2 in macrophages to assess functional impact.
Main Results:
- Macrophages demonstrated high motility within the tumor microenvironment.
- Macrophage projections between tumor cells were observed preceding melanoma migration.
- Inhibitory Rac2 mutation impaired tumor recruitment and invasion.
- Hyperactivating Rac2 mutation reduced macrophage projections and invasive melanoma cell migration.
Conclusions:
- Rac2-mediated macrophage protrusive motility plays a significant role in melanoma invasion.
- Macrophage behavior, specifically their projections, is a critical factor in tumor cell migration.
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