The small GTPase Rac1 is essential for the aberrant growth properties and invasive behavior of transformed cells. The long term goals of our laboratory are to elucidate the signaling pathways that are governed by Rac1 to stimulate cell proliferation and invasion. Rac1 regulates a number of cellular functions that are likely to play a role in malignant transformation. These include the inhibition of receptor-mediated endocytosis and the stimulation of lamellipodia formation. Endocytosis contributes to the down-regulation of growth factor receptors and inhibition of endocytic trafficking has been shown to enhance cell proliferation. Lamellipodia are thought to be important for cell motility. He recently identified the phosphatidylinositol 5'-phosphastase synaptojanin 2 as a novel effector of Rac1. Synaptojanins have been implicated in the regulation of receptor-mediated endocytosis and the organization of the actin cytoskeleton, processes that are known to by modulated by phosphatidylinositol metabolism. The overall objective of this proposal is to examine the hypothesis that synaptojanin 2 functions downstream of Rac1 in the regulation of endocytic trafficking and actin dynamics and that these functions in turn contribute to cell transformation and invasion. In Aim 1 he will study the molecular mechanisms of the regulation of synaptojanin 2 by Rac1. In Aim 2 he will examine whether synaptojanin 2 mediates the effects of Rac1 on endocytosis and actin cytoskeleton dynamics. To test these hypothesis, he will use two distinct antisense strategies to inhibit expression of synaptorjanin 2. He will complement this approach, he will stimulate synapotjanin 2 activity in cells using expression of a version of synaptojanin 2 that is Rac-1 independent. In Aim 3 he will use similar strategies to examine the hypothesis that synaptojanin 2 functions downstream of Rac1 in the regulation of cell proliferation and invasion. These studies will contribute to the understanding of the molecular of cancer. Identifying a role for synaptojanin 2 in the regulation of either cell transformation or invasion would suggest novel avenues for cancer therapy.