Phosphorylation of ARHGAP19 by CDK1 and ROCK regulates its subcellular localization and function during mitosis.

ARHGAP19 is a hematopoietic-specific Rho GTPase-activating protein (RhoGAP) that acts through the RhoA/ROCK pathway to critically regulate cell elongation and cytokinesis during lymphocyte mitosis. We report here that, during mitosis progression, ARHGAP19 is sequentially phosphorylated by the RhoA-activated kinases ROCK1 and ROCK2 (hereafter ROCK) on serine residue 422, and by CDK1 on threonine residues 404 and 476. The phosphorylation of ARHGAP19 by ROCK occurs before mitosis onset and generates a binding site for 14-3-3 family proteins. ARHGAP19 is then phosphorylated by CDK1 in prometaphase. The docking of 14-3-3 proteins to phosphorylated S422 protects ARHGAP19 from dephosphorylation of the threonine sites and prevents ARHGAP19 from relocating to the plasma membrane during prophase and metaphase, thus allowing RhoA to become activated. Disruption of these phosphorylation sites results in premature localization of ARHGAP19 at the cell membrane and in its enrichment to the equatorial cortex in anaphase leading to cytokinesis failure and cell multinucleation.