Flightless anchors IQGAP1 and R-ras to mediate cell extension formation and matrix remodeling.

Area of Science:

• Cell Biology
• Biochemistry
• Tissue Engineering

Background:

• Fibroblast-mediated tractional remodeling of collagen fibrils is essential for tissue repair and development.
• The formation of cellular extensions by fibroblasts plays a critical role in aligning collagen fibrils.
• Flightless I (FliI), an actin-binding protein, is implicated in cell extension formation and interaction with small GTPases.

Purpose of the Study:

• To investigate the molecular mechanisms by which FliI regulates cell extension formation for collagen remodeling.
• To identify and characterize the interactions between FliI, small GTPases (R-ras, cdc42), and IQGAP1 in fibroblasts.
• To elucidate the role of IQGAP1 in mediating cell extension assembly and collagen alignment.

Main Methods:

• Immunoprecipitation and mass spectrometry to identify FliI-interacting proteins.
• Immunostaining to visualize the colocalization of FliI and IQGAP1.
• siRNA-mediated knockdown of IQGAP1 to assess its functional role.
• Dominant-negative mutant analysis to study the involvement of cdc42 and R-ras.
• Site-directed mutagenesis of FliI and IQGAP1 to map interaction domains.

Main Results:

• Mass spectrometry identified IQGAP1 as a key interactor of FliI, colocalizing at cell adhesions.
• IQGAP1 knockdown significantly reduced cell extension numbers and collagen fibril alignment.
• cdc42 activity was essential for short extensions, while R-ras was required for long extensions.
• IQGAP1 associated with both cdc42 and R-ras via its GAP-related domain.
• The leucine-rich-repeat (LRR) domain of FliI mediated its interaction with cdc42, R-ras, and IQGAP1.

Conclusions:

• FliI interacts with IQGAP1, coordinating with cdc42 and R-ras to regulate cell extension formation.
• This mechanism is critical for fibroblast-driven collagen fibril alignment and tractional remodeling.
• The findings provide insights into the molecular machinery governing cell-matrix interactions and tissue mechanics.