AN INTRAMOLECULAR SH3-DOMAIN INTERACTION REGULATES C-ABL ACTIVITY

The ABL1 proto-oncogene encodes a cytoplasmic and nuclear protein tyro sine kinase (c-Abl) that has been implicated in processes of cell diff erentiation, cell division, cell adhesion and stress response(1-4). Al terations of ABL1 by chromosomal rearrangement or viral transduction c an lead to malignant transformation(5,6). Activity of the c-Abl protei n is negatively regulated by its SH3 domain through an unknown mechani sm, and deletion of the SH3 domain turns ABL1 into an oncogene(7-10). We present evidence for an intramolecular inhibitory interaction of th e SH3 domain with the catalytic domain and with the linker between the SH2 and catalytic domain (SH2-CD linker). Site-directed mutations in each of these three elements activate c-Abl. Mutations in the linker c ause a conformational change of the molecule and increase binding of t he SH3 domain to peptide ligands. Individual mutation of two charged r esidues in the SH3 and catalytic domain activates c-Abl, while inhibit ion is restored in the double reciprocal mutant. We propose that regul ators of c-Abl will have opposite effects on its activity depending on their ability to favour or disrupt these intramolecular interactions.