This is a renewal of the PI's RO1 application, which characterized MBP-1, a c-myc binding protein isolated from a HeLa cell library. This gene is ubiquitously expressed in normal human tissues and has been localized to human chromosome1. Ectopic expression of MBP-1 induces apoptotic cell death, reduced c-myc expression, and suppression of biological properties associated with tumorigenicity of breast cancer cell. Building on the preliminary studies reported in this application, the PI proposes the following specific Aims: To characterize MBP-1 interacting protein and study the mechanism of its functional activities. To investigate the mechanism by which it induces apoptosis To test the biological effect of MBP-1 disruption in KO mice To determine whether adenovirus-mediated MBP-1 gene transfer can regress tumor growth in vivo.