Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena complex

Area of Science:

• Cell Biology
• Molecular Biology
• Cytoskeleton Dynamics

Background:

• Rho GTPases, including Cdc42, regulate actin cytoskeleton organization.
• Cdc42 is known to control filopodia formation at the cell periphery.
• The precise molecular mechanisms underlying Cdc42-mediated filopodia formation are not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanism by which Cdc42 regulates filopodia formation.
• To identify downstream effector proteins of Cdc42 involved in cytoskeletal organization.

Main Methods:

• Investigated the interaction between Cdc42 and IRSp53 using biochemical assays.
• Utilized overexpression studies in fibroblasts to assess the role of IRSp53 and its fragments in filopodia formation.
• Employed affinity chromatography to identify proteins interacting with IRSp53.

Main Results:

• Identified IRSp53 as a Cdc42-interacting protein that binds via a partial CRIB motif.
• Demonstrated that IRSp53 overexpression induces filopodia formation, which can be inhibited by an N-terminal fragment of IRSp53.
• Discovered Mena, an Ena/VASP family member, as an IRSp53-interacting protein, with both proteins synergistically promoting filopodia.

Conclusions:

• Cdc42 binding to IRSp53's CRIB motif relieves autoinhibition by the N-terminus.
• This interaction facilitates the recruitment of Mena to IRSp53.
• The IRSp53:Mena complex is crucial for initiating actin filament assembly and driving filopodia formation.