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Regulation of scatter factor/hepatocyte growth factor responses by Ras, Rac, and Rho in MDCK cells
A J Ridley1, P M Comoglio, A Hall
1Institute of Cancer Research, Chester Beatty Laboratories, London, United Kingdom.
Abstract:
Scatter factor/hepatocyte growth factor (SF/HGF) stimulates the motility of epithelial cells, initially inducing centrifugal spreading of cell colonies followed by disruption of cell-cell junctions and subsequent cell scattering. These responses are accompanied by changes in the actin cytoskeleton, including increased membrane ruffling and lamellipodium extension, disappearance of peripheral actin bundles at the edges of colonies, and an overall decrease in stress fibers. The roles of the small GTP-binding proteins Ras, Rac, and Rho in regulating responses to SF/HGF were investigated by microinjection. Inhibition of endogenous Ras proteins prevented SF/HGF-induced actin reorganization, spreading, and scattering, whereas microinjection of activated H-Ras protein stimulated spreading and actin reorganization but not scattering. When a dominant inhibitor of Rac was injected, SF/HGF- and Ras-induced spreading and actin reorganization were prevented, although activated Rac alone did not stimulate either response. Microinjection of activated Rho inhibited spreading and scattering, while inhibition of Rho function led to the disappearance of stress fibers and peripheral bundles but did not prevent SF/HGF-induced motility. We conclude that Ras and Rac act downstream of the SF/HGF receptor p190Met to mediate cell spreading but that an additional signal is required to induce scattering.
Insights
Scatter factor/hepatocyte growth factor (SF/HGF) drives epithelial cell motility. Ras and Rac proteins mediate cell spreading downstream of the SF/HGF receptor, but an additional signal is needed for cell scattering.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Scatter factor/hepatocyte growth factor (SF/HGF) is a key regulator of epithelial cell motility.
- SF/HGF signaling triggers complex cellular responses including cell spreading and scattering.
- These responses involve significant remodeling of the actin cytoskeleton.
Purpose of the Study:
- To investigate the roles of small GTP-binding proteins Ras, Rac, and Rho in SF/HGF-induced epithelial cell responses.
- To elucidate the signaling pathways downstream of the SF/HGF receptor (p190Met) that regulate cell motility.
Main Methods:
- Microinjection of dominant inhibitors and activated forms of Ras, Rac, and Rho proteins into epithelial cells.
- Observation and analysis of cellular responses to SF/HGF, including actin cytoskeleton organization, cell spreading, and cell scattering.
Main Results:
- Inhibition of Ras prevented SF/HGF-induced actin reorganization, spreading, and scattering.
- Activated Ras stimulated spreading and actin reorganization but not scattering.
- Rac inhibition blocked SF/HGF- and Ras-induced spreading and actin reorganization.
- Activated Rho inhibited spreading and scattering; Rho inhibition affected actin bundles but not motility.
- Ras and Rac act downstream of p190Met for cell spreading.
Conclusions:
- Ras and Rac are essential downstream mediators of SF/HGF-induced cell spreading.
- Cell scattering induced by SF/HGF requires an additional signaling pathway beyond Ras and Rac.
- Understanding these pathways is crucial for comprehending epithelial cell dynamics in development and disease.