Cell Polarization by Rho Proteins

During migration, cells establish polarity — a distinct cell front and rear — in response to chemical signals that activate the cell-surface receptors facing the direction of the stimulus.

The activated receptors, further, activate secondary messengers that switch on specific Rho family proteins — Rac, Cdc42, and Rho in different parts of the cell.

The Rac and Cdc42 proteins are locally activated on the side of the cell facing the stimulus.

While Rac triggers actin branching to form lamellipodia, Cdc42 promotes actin polymerization and bundling to form filopodia.

Thus, Rac and Cdc42 help establish the cell's leading edge.

In contrast, Rho is activated at the opposite end of the cell and establishes the trailing edge.

It increases myosin-driven contraction, thereby retracting the rear of the cell during cell migration.

Additionally, Rac inhibits Rho activation at the leading edge. This restricts Rho activity to the rear and maintains Rac activity at the cell front, thus stabilizing the cell's polarity.