Blood, Vol. 92 No. 10 (November 15), 1998:
pp. 3848-3856
The C-Terminus of c-Abl Is Required for Proliferation and Viability
Signaling in a c-Abl/Erythropoietin Receptor Fusion Protein
K. Okuda,
A. D'Andrea,
R.A. Van Etten, and
J.D. Griffin
From the Division of Hematologic Malignancies or Pediatric Oncology,
Dana-Farber Cancer Institute, and the Center for Blood Research,
Harvard Medical School, Boston, MA.
Activated ABL oncogenes cause B-cell leukemias in mice and chronic
myelogenous leukemia in humans. However, the mechanism of
transformation is complex and not well understood. A method to rapidly
and reversibly activate c-ABL was created by fusing the
extra-cytoplasmic and transmembrane domain of the erythropoietin (EPO)
receptor with c-ABL (EPO R/ABL). When this chimeric receptor was
expressed in Ba/F3 cells, the addition of EPO resulted in a
dose-dependent activation of c-ABL tyrosine kinase and was strongly antiapoptotic and weakly mitogenic. To evaluate the contributions of
various ABL domains to biochemical signaling and biological effects,
chimeric receptors were constructed in which the ABL SH3 domain was
deleted (
SH3), the SH2 domain was deleted (SH2), the C-terminal
actin-binding domain was deleted (ABD), or kinase activity was
eliminated by a point mutation, K290M (KD). The mutant receptors were
stably expressed in Ba/F3 cells and analyzed for signaling defects,
proliferation, viability, and EPO-induced leukemia in nude mice. When
compared with the ability of the full-length EPO R/ABL receptor to
induce proliferation and support viability in vitro, the SH3 mutant
was equivalent, the SH2 mutant was moderately impaired, and the
ABD and KD mutants were profoundly impaired. None of these cell
lines caused leukemia in mice in the absence of pharmacological doses
of EPO. However, in mice treated with EPO (10 U/d), death from leukemia
occurred rapidly with wild-type and SH3. However, time to death was
prolonged by at least twofold for SH2 and greater than threefold for
ABD. This inducible model of ABL transformation provides a method to link specific signaling defects with specific biological defects and
has shown an important role for the C-terminal actin-binding domain in
proliferation and transformation in the context of this receptor/oncogene.
