Myosin I phosphorylation is increased by chemotactic stimulation

Directed cell migration occurs in response to extracellular cues. Following stimulation of a cell with chemoattractant, a significant rearrangement of the actin cytoskeleton is mediated by intracellular signaling pathways and results in polarization of the cell and movement via pseudopod extension. Amoeboid myosin Is play a critical role in regulating pseudopod formation i n Dictyostelium, and their activity is activated by heavy chain phosphoryla tion. The effect of chemotactic stimulation on the in vivo phosphorylation level of a Dictyostelium myosin I, myoB, was tested. The myoB heavy chain i s phosphorylated in vivo on serine 322 (the myosin TEDS rule phosphorylatio n site) in chemotactically competent cells. The level of myoB phosphorylati on increases following stimulation of starving cells with the chemoattracta nt cAMP, A 3-fold peak increase in the level of phosphorylation is observed at 60 s following stimulation, a time at which the Dictyostelium cell acti vely extends pseudopodia. These findings suggest that chemotactic stimulati on results in increased myoB activity via heavy chain phosphorylation and c ontributes to the global extension of pseudopodia that occurs prior to pola rization and directed motility.