How Actin Polymerization and Myosin II Activity Regulate Focal Adhesion Dynamics in Motile Cells

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Focal adhesions (FAs) are crucial multi-protein complexes mediating cell adhesion to the extracellular matrix.
• FA assembly and maturation are regulated by intracellular tension from actin filaments and phosphorylated myosin II.

Purpose of the Study:

• To investigate the regulatory roles of actin polymerization and myosin II contractility in focal adhesion dynamics.
• To elucidate the minimal requirements for focal adhesion assembly and stability.

Main Methods:

• Live-cell and confocal microscopy were employed to observe FA dynamics.
• Pharmacological inhibitors (ROCK, MLCK, latrunculin B, cytochalasin D) were used to modulate myosin II phosphorylation and actin polymerization.
• Myosin II knockdown was performed to assess its role in FA stability.

Main Results:

• Complete myosin II knockdown led to irreversible FA disassembly.
• Partial inhibition of myosin II or actin polymerization resulted in the formation of smaller, more stable FAs with prolonged lifespans.
• Actin polymerization at the cell edge was identified as the minimal requirement for small FA assembly.

Conclusions:

• Perturbation of the actin-myosin system stabilizes small FAs, contrasting with the dynamic nature of larger FAs formed with myosin II activity.
• Cortical actin organization and myosin II phosphorylation are essential for focal adhesion maintenance and turnover.
• These findings reveal a novel mechanism for regulating FA stability and lifespan through modulation of the actin-myosin cytoskeleton.