The Rap-1 Antioncogene in Breast Cancer

This project aims to devise strategies to antagonize the promitogenic action of Ras and thereby suppress the transforming activity of the Erb2 oncogene found in 70% of human breast adenocarcinomas. We have focused on the identification and characterization of proteins that interact with Rap-1 and Ras through their effector loop in GTP-dependent fashion. We have carried out an extensive two-hybrid screening for proteins that bind to Ras and Rap 1. This has yielded the known Ras-Rap partners and a novel set of noncatalytic polypeptides which have provided the main focus of our efforts. The first of these to be characterized was the polypeptide known as AF-6; this binds more avidly to Rap 1-GTP than to Ras-GTP. Of greater interest is the polypeptide NORE-1, which binds to Ras-GTP at its carboxyterminus and encodes a centrally located zinc finger, and an aminoterminal proline rich domain. High affinity antibodies to NORE-1 cross-react with a family of polypeptides, some of which bind to Ras-GTP in vivo after growth factor stimulation. Recently, a candidate tumor suppressor locus on chromosome 3p21 (frequently deleted in Breast Cancer) was identified as a protein RDA32, a 271AA polypeptide that is 55% identical to NORE1. Ongoing work is focused ca the biologic activation of the NORE-1 family of Ras effectors and their possible role in the negative regulation of cell growth.