Phosphatidylinositol 4-phosphate 5-kinase alpha is a downstream effector of the small G protein ARF6 in membrane ruffle formation

Synthesis of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P-2], a signalin g phospholipid, is primarily carried out by phosphatidylinositol 4-phosphat e 5-kinase [PI(4)P5K], which has been reported to be regulated by RhoA and Rad. Unexpectedly, we find that the GTP gamma S-dependent activator of PI(4 )P5K alpha is the small G protein ADP-ribosylation factor (ARF) and that th e activation strictly requires phosphatidic acid, the product of phospholip ase D (PLD). In vivo, ARF6, but not ARF1 or ARF5, spatially coincides with PI(4)P5K alpha. This colocalization occurs in ruffling membranes formed upo n AIF(4) and EGF stimulation and is blocked by dominant-negative ARF6. PLD2 similarly translocates to the ruffles, as does the PH domain of phospholip ase C delta 1, indicating locally elevated PI(4,5)P-2. Thus, PI(4)P5K alpha is a downstream effector of ARF6 and when ARF6 is activated by agonist sti mulation, it triggers recruitment of a diverse but interactive set of signa ling molecules into sites of active cytoskeletal and membrane rearrangement .