An 18K protein from ascites hepatoma cell depolymerizes actin filaments rapidly

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• Actin cytoskeleton dynamics are crucial for cellular functions.
• Identifying novel actin-binding proteins can reveal new regulatory mechanisms.

Purpose of the Study:

• To isolate and characterize novel actin-binding proteins from ascites hepatoma cells.
• To elucidate the mechanism of action of a purified 18,000 molecular weight (18K) actin-binding protein.

Main Methods:

• DNase I affinity chromatography, DEAE cellulose, hydroxyapatite, and Sephadex G-75 gel filtration for protein purification.
• Viscosity measurements, fluorescence intensity assays, DNase I inhibition assays, chemical cross-linking, sedimentation assays, and electron microscopy to study protein function.

Main Results:

• A novel 18K protein was purified that inhibits actin polymerization and depolymerizes actin filaments.
• The 18K protein binds to both monomeric actin and actin filaments, forming a 1:1 complex with monomers.
• Electron microscopy revealed that the 18K protein reduces filament quantity and distorts existing filaments.

Conclusions:

• The 18K protein is a potent regulator of actin dynamics, affecting both actin monomers and filaments.
• This protein's interaction with actin is independent of Ca2+ ions and affects both tumor and muscle actin.
• The 18K protein represents a potential target for understanding and manipulating cell structure in cancer.