The leucine-rich region of Flightless I interacts with R-ras to regulate cell extension formation.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Flightless I (FliI) is a calcium-dependent protein involved in actin dynamics and cell adhesion.
• The precise mechanism of FliI's interaction with Ras proteins in forming cell extensions remains unclear.

Purpose of the Study:

• To elucidate the mechanism by which FliI interacts with Ras proteins to facilitate actin-based cell protrusion formation.
• To define the specific Ras isoforms and protein domains involved in this interaction.

Main Methods:

• Co-immunoprecipitation and pull-down assays to investigate protein-protein interactions.
• Site-directed mutagenesis to identify critical protein regions.
• Small interfering RNA (siRNA) knockdown to assess the functional role of proteins in cell extension formation.
• Expression of truncated G3BP1 proteins to map interaction domains.

Main Results:

• R-Ras, but not other Ras isoforms, specifically associated with the leucine-rich region (LRR) of FliI.
• Mutations in the R-Ras proline-rich region disrupted its binding to FliI.
• Knockdown of G3BP1 or Rasgap120 inhibited cell extension formation and R-Ras/G3BP1 interaction.
• R-Ras bound to the C-terminus of G3BP1 (amino acids 236-466), requiring FliI's LRR.
• Rasgap120 interacted with the N-terminus of G3BP1 (amino acids 1-230).

Conclusions:

• FliI's LRR interacts with R-Ras to promote cell extension formation on collagen.
• FliI is essential for the Rasgap120-G3BP1 interaction, which regulates R-Ras activity and cell protrusion growth.