MUTANT FORMS OF GROWTH FACTOR-BINDING PROTEIN-2 REVERSE BCR-ABL-INDUCED TRANSFORMATION

Growth factor-binding protein 2 (Grb2) is an adaptor protein that link s tyrosine kinases to Ras, BCR-ABL is a tyrosine kinase oncoprotein th at is implicated in the pathogenesis of Philadelphia chromosome (Ph(1) )-positive leukemias. Grb2 forms a complex with BCR-ABL and the nucleo tide exchange factor Sos that leads to the activation of the Ras proto oncogene, In this report we demonstrate that Grb2 mutant proteins lack ing amino- or carboxyl-terminal src homology SH3 domains suppress BCR- ABL-induced Pas activation and reverse the oncogenic phenotype, The Gr b2 SH3-deletion mutant proteins bind to BCR-ABL and do not impair tyro sine kinase activity. Expression of the Grb2 SH3-deletion mutant prote ins in BCR-ABL-transformed Rat-1 fibroblasts and in the human Ph(1)-po sitive leukemic cell line K562 inhibits their ability to grow as foci in soft agar and form tumors in nude mice. Furthermore, expression of the Grb2 SH3-deletion mutants in K562 cells induced their differentiat ion. Because Ras plays an important role in signaling by receptor and nonreceptor tyrosine kinases, the use of interfering mutant Grb2 prote ins may be applied to block the proliferation of other cancers that de pend in part on activated tyrosine kinases for growth.