Signaling through the insulin family of receptors (IR and the insulin-like growth factor I (IGF-I) receptor), transmits molecular information into and throughout the cell. The insulin receptor substrate (IRS) -1 is phosphorylated by and complexes with the activated insulin or IGF-I receptor. It serves to coordinate and amplify signals by acting as a scaffold to which a variety of signaling proteins bind. The IRS family of proteins an emerging role in cell growth and survival. Although the PH and the PTB domains of IRS-1 have been shown to be sufficient for anti-apoptotic and growth properties of insulin, the mechanisms by which this occurs are unknown. Our work seeks to understand possible mechanisms by which the PH domains of IRS proteins contribute to cell survival. Recently, several proteins that interact with the PH domains of IRS-1 and IRS-2 were identified using a yeast two-hybrid system (DB 98). Peptides based on acidic motif found in each of these proteins. This proposal focuses on the molecular interaction between IRS proteins and the acidic motifs identified in these putative PH domain ligands. The specific aims are designed to define this interaction and determine the optimal sequence within these motifs required for interaction with the IRS PH domains. The ability of acidic motifs to mediate functional interaction with the IRS proteins will be investigated in cell culture. Finally, the ability of these peptides to interfere with an IRS-1 survival signal in IGF-1 (or IRS-1) dependent tumors will be investigated in nude mice.