Novel proteins that regulate cell extension formation in fibroblasts

Area of Science:

• Cell Biology
• Biochemistry
• Extracellular Matrix Dynamics

Background:

• Cell extensions are vital for matrix remodeling in wound healing and cancer invasion.
• The precise regulation of cell extension formation remains poorly understood.

Purpose of the Study:

• To identify novel proteins involved in cell extension formation over collagen.
• To elucidate the regulatory mechanisms governing these proteins' recruitment into cell extensions.

Main Methods:

• Tandem mass-tagged mass spectrometry of purified cell extensions from 3T3 fibroblasts.
• siRNA knockdown of identified proteins and assessment of cell extension formation and collagen remodeling on collagen gels.
• Immunostaining and immunoblotting to confirm protein localization.
• Inhibition of TGF-β RI kinase, Smad3, and ROCK-II signaling pathways.

Main Results:

• Importin-5, PDLIM5, and PSMC4 were identified as significantly enriched in cell extensions.
• Knockdown of these proteins markedly reduced cell extension formation, collagen compaction, and pericellular collagen degradation.
• PDLIM5 recruitment was modulated by TGF-β, Smad3, and ROCK-II pathways, while PSMC4 and importin-5 were regulated by Smad3 and ROCK-II.

Conclusions:

• Importin-5, PDLIM5, and PSMC4 are novel, essential regulators of cell extension formation and matrix remodeling.
• The recruitment of these proteins into cell extensions is dependent on Smad3 and ROCK signaling pathways.