Actin assembly in response to extracellular signals: role of capping proteins, thymosin beta 4 and profilin.

In motile non-muscle cells, G-actin sequestering proteins, capping proteins and profilin regulate actin assembly in response to extracellular signals. The regulation of actin sequestration/assembly is performed via the control of the concentration of free G-actin at steady-state. The increase in free G-actin mediated by capping proteins results in an increased sequestration of actin. When barbed ends are uncapped upon cell stimulation, the participation of profilin-actin in filament assembly causes a decrease in free G-actin, which results in the depletion of the pool of sequestered actin and concomitant increase in the F-actin pool.