Model of ARHGAP25 function. ARHGAP25 opposes CXCL12-CXCR4 signaling, promoting mobilization by converting GTP(active)-Rac to GDP(inactive)-Rac. Phosphorylation of ARHGAP25 on S363 inhibits its ability to inactivate Rac. GDP, guanosine diphosphate; GEF, guanine nucleotide exchange factor; PI3K, phosphatidylinositol 3-kinase; SFTK, Src family tyrosine kinase.