Bone resorption is a multistep process initiated by attachment of osteoclasts (OCs) and their precursors to bone, prompting cytoskeletal reorganization and activation of intracellular signaling pathways. The integrin alphavbeta3, which recognizes bone matrix-residing proteins, is essential to osteoclastic bone resorption, and is therefore a potential anti-osteoporosis target. Various molecules, in OC and other cells, associate with or are activated by alphavbeta3 integrin. These molecules are candidates to modulate signaling from the beta3 cytoplasmic tail to the resorptive machinery, and also represent additional potential therapeutic targets. Optimizing this therapeutic goal will depend, however, on detailed analysis of the integrin's molecular structure as it relates to specific components of the resorptive process. Acquisition of alphavbeta3 structure/function data will be best achieved by expressing, in alphavbeta3 null OCs, beta3 integrin mutants whose individual impact on particular events in the resorptive process can be evaluated. We focus on the cytoplasmic domain of the beta3 integrin subunit as it is known, in other circumstances, to regulate cytoskeletal organization and mediate matrix derived signals. We have chosen to examine three alphavbeta3-activated signaling proteins - c-src, PI3-K and RhoA - because inhibition of each blunts bone resorption. Our specific aim is a) to demonstrate that activated c-src, PI3-K and/or RhoA are indeed required for alphavbeta3-mediated bone resorption, and b) to identify the specific components of the beta3 integrin cytoplasmic domain responsible for this activation.