We have identified three members of the AGAP subfamily of ASAP family ADP-ribosylation factor GTPaseactivating proteins (Arf GAPs). In addition to the Arf GAP domain, these proteins contain GTP-binding protein-like, ankyrin repeat and pleckstrin homology domains. Here, we have characterized the ubiquitously expressed AGAP1/KIAA1099. AGAP1 had Arf GAP activity toward Arf1>Arf5>Arf6. Phosphatidylinositol 4,5-bisphosphate and phosphatidic acid synergistically stimulated GAP activity. As found for other ASAP family Arf GAPs, the pleckstrin homology domain was necessary for activity. Deletion of the GTP-binding proteinlike domain affected lipid dependence of Arf GAP activity. In vivo effects of AGAP1 were distinct from other ASAP family Arf GAPs. Overexpressed AGAP1 induced the formation of and was associated with punctate structures containing the endocytic markers transferrin and Rab4. AP1 was redistributed from the transGolgi to the punctate structures. Like other ASAP family members, AGAP1 overexpression inhibited the formation of PDGF-induced ruffles. However, distinct from other ASAP family members, AGAP1 also induced the loss of actin stress fibers. Thus, AGAP1 is a phosphoinositide-dependent Arf GAP that impacts both the endocytic compartment and actin.

We have identified ARAP1 and ARAP2 and examined ARAP1 as a possible link between phosphoinositide-, Arf-, and Rho-mediated cell signaling. ARAP1 contains Arf GAP, Rho GAP, Ankyrin repeat, Ras-associating, and five PH domains. In vitro, ARAP1 had Rho GAP and phosphatidylinositol (3,4,5) trisphosphate (PIP3)-dependent Arf GAP activity. ARAP1 associated with the Golgi. The Rho GAP activity mediated cell rounding and loss of stress fibers when ARAP1 was overexpressed. The Arf GAP activity mediated changes in the Golgi apparatus and the formation of filopodia, the latter a consequence of increased cellular activity of Cdc42. The Arf GAP and Rho GAP activities both contributed to inhibiting cell spreading. Thus, ARAP1 is a PIP3-dependent Arf GAP that regulates Arf-, Rho-, and Cdc42-dependent cell activities.

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