ARHGAP25 acts as a regulator of HSPC mobilization. Phosphorylation of serine 363 modulates ARHGAP25 activity and inhibits the ability of ARHGAP25 to suppress Rac-dependent downstream functions. Inhibition of ARHGAP25 activity leads to an augmentation of CXCL12 signaling and marrow retention. GDP, guanosine diphosphate; GEF, guanine nucleotide exchange factor; GTP, guanosine triphosphate; PI3K, phosphatidylinositol 3-kinase; SFTK, Src family tyrosine kinase. See Figure 5 in the article by Wang et al that begins on page 1465.