THE C-TERMINUS OF C-ABL IS REQUIRED FOR PROLIFERATION AND VIABILITY SIGNALING IN A C-ABL ERYTHROPOIETIN RECEPTOR FUSION PROTEIN

Activated ABL oncogenes cause B-cell leukemias in mice and chronic mye logenous 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 transm embrane domain of the erythropoietin (EPO) receptor with c-ABL (EPO R/ ABL). When this chimeric receptor was expressed in Ba/F3 cells, the ad dition of EPO resulted in a dose-dependent activation of c-ABL tyrosin e kinase and was strongly anti-apoptotic and weakly mitogenic. To eval uate the contributions of various ABL domains to biochemical signaling and biological effects, chimeric receptors were constructed in which the ABL SH3 domain was deleted (Delta SH3), the SH2 domain was deleted (Delta SH2), the C-terminal actin-binding domain was deleted (Delta A BD). or kinase activity was eliminated by a point mutation, K290M (KD) . The mutant receptors were stably expressed in Ba/F3 cells and analyz ed for signaling defects, proliferation, viability, and EPO-induced le ukemia in nude mice. When compared with the ability of the full-length EPO R/ABL receptor to induce proliferation and support viability in v itro, the Delta SH3 mutant was equivalent, the Delta SH2 mutant was mo derately impaired, and the Delta ABD and KD mutants were profoundly im paired. None of these cell lines caused leukemia in mice in the absenc e of pharmacological doses of EPO. However, in mice treated with EPO ( 10 U/d). death from leukemia occurred rapidly with wild-type and Delta SH3. However, time to death was prolonged by at least twofold for Del ta SH2 and greater than threefold for Delta ABD. This inducible model of ABL transformation provides a method to link specific signaling def ects with specific biological defects and has shown an important role for the C-terminal actin-binding domain in proliferation and transform ation in the context of this receptor/oncogene. (C) 1998 by The Americ an Society of Hematology.