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Two phases of pseudopod protrusion in tumor cells revealed by a micropipette
C Dong1, S Aznavoorian, L A Liotta
1Bioengineering Program, College of Engineering, Pennsylvania State University, University Park 16802.
Abstract:
Pseudopod protrusion at the leading edge is a characteristic of migrating tumor cells as they traverse vascular subendothelial basement membranes to establish metastases. A micropipette system has been developed to study the dynamics of pseudopod protrusion in individual human melanoma cells in response to type IV collagen, a component of basement membranes. Soluble type IV collagen stimulates chemotaxis of A2058 melanoma cells through a G protein-coupled receptor, and induces an early burst of intracellular calcium (Savarese et al., 1992, J. Biol. Chem. 267, 21928-21935). A micropipette filled with type IV collagen solution (100 micrograms/ml) was positioned so that the tip was adjacent to a cell suspended in Dulbeceo's modified Eagle's medium. Within 10 min, tumor cells generated a pseudopod which entered the micropipette with an average velocity of 0.24 micron/min and proceeded to lengthen for 40 min. Pseudopods from individual cells ranged from 7.5-10 microns at this time and were characterized by an irregular shape which did not fill the lumen of the micropipette. Pretreatment of cells with pertussis toxin (0.5 microgram/ml), which inhibits cell migration by approximately 90% (but not the calcium burst), blocked formation of the irregular, extended pseudopod, while allowing a much smaller outpouching, or bleb, to form. Lengths of such blebs from individual PT-treated cells reached a plateau at approximately 20 min and ranged from 2.2-4.0 microns at the end point. Treatment of cells with bis-(amino-phenoxy)ethane tetraacetic acid (75 microM), an intracellular Ca2+ chelator, blocked initial bleb formation and prevented extension. From these observations we hypothesize that tumor cell pseudopod protrusion induced by soluble type IV collagen takes place in distinct, separable phases: an initial convex, symmetrical outpouching, caused by localized Ca(2+)-activated actin depolymerization and osmotic flux, followed by an extension with an irregular shape, which requires G protein-mediated actin polymerization.
Insights
Tumor cells extend pseudopods to invade tissues. Type IV collagen triggers a two-phase protrusion: an initial calcium-dependent bleb, followed by G protein-driven extension, crucial for metastasis.
Area of Science:
- Cell Biology
- Cancer Metastasis
- Biophysics
Background:
- Tumor cell migration and metastasis involve pseudopod protrusion.
- Type IV collagen is a key component of basement membranes encountered during metastasis.
- Soluble type IV collagen is known to stimulate melanoma cell chemotaxis via G protein-coupled receptors and calcium signaling.
Purpose of the Study:
- To investigate the dynamics of pseudopod protrusion in human melanoma cells stimulated by type IV collagen.
- To elucidate the distinct phases and molecular mechanisms underlying collagen-induced pseudopod extension.
Main Methods:
- Utilized a micropipette system to apply type IV collagen to individual A2058 melanoma cells.
- Measured pseudopod protrusion dynamics, including velocity and length, over time.
- Employed pertussis toxin to inhibit G protein signaling and bis-(amino-phenoxy)ethane tetraacetic acid as a calcium chelator to probe molecular pathways.
Main Results:
- Type IV collagen induced pseudopod protrusion into the micropipette, with an average velocity of 0.24 micron/min and lengths up to 10 microns.
- Pertussis toxin inhibited irregular pseudopod extension but allowed bleb formation, indicating a G protein-dependent extension phase.
- Calcium chelation blocked initial bleb formation and subsequent extension, highlighting the role of calcium in the initial protrusion.
Conclusions:
- Tumor cell pseudopod protrusion by type IV collagen occurs in two phases: an initial calcium-dependent bleb and a subsequent G protein-mediated irregular extension.
- Actin depolymerization and osmotic flux drive the initial bleb, while G protein-mediated actin polymerization drives the extension phase.
- Understanding these distinct phases is critical for developing strategies to inhibit melanoma metastasis.