M. Warmuth et al., THE SRC FAMILY KINASE HCK INTERACTS WITH BCR-ABL BY A KINASE-INDEPENDENT MECHANISM AND PHOSPHORYLATES THE GRB2-BINDING SITE OF BCR, The Journal of biological chemistry, 272(52), 1997, pp. 33260-33270
bcr-abl, the oncogene causing chronic myeloid leukemia, encodes a fusi
on protein with constitutively active tyrosine kinase and transforming
capacity in hematopoietic cells. Various intracellular signaling inte
rmediates become activated and/or associate by/with Bcr-Abl, including
the Src family kinase Hck. To elucidate some of the structural requir
ements and functional consequences of the association of Bcr-Abl with
Hcb, their interaction was investigated in transiently transfected COS
7 cells. Neither the complex formation of Hck kinase with Bcr-Abl nor
the activation of Hck by Bcr-Abl was dependent on the Abl kinase activ
ity. Both inactivating point mutations of Hck and dephosphorylation of
Hck enhanced its complex formation with Bcr-Abl, indicating that thei
r physical interaction was negatively regulated by Hck (auto)phosphory
lation. Finally, experiments with a series of kinase negative Bcr-Abl
mutants showed that Hck phosphorylated Bcr-Abl and induced the binding
of Grb2 to Tyr(177) of Bcr-Abl. Taken together, our results suggest t
hat Bcr-Abl preferentially binds inactive forms of Hck by an Abl kinas
e-independent mechanism. This physical interaction stimulates the Hck
tyrosine kinase, which may then phosphorylate the Grb2-binding site in
Bcr-Abl.