Previous studies have shown that expression of a membrane targeted chi
meric protein containing the erythropoietin receptor (EpoR) cytoplasmi
c domain fused to the FK506-binding peptide FKBP12 allowed Ba/F3 cells
to be rescued from interleukin-3 (IL-3) deprivation using a dimeric f
orm of FK506, called FK1012. In this report, a similar approach is app
lied to the c-kit receptor. Expression of a membrane targeted fusion p
rotein containing the c-kit receptor linked to one or more copies of F
KBP12 allowed Ba/F3 cells to be switched from IL-3 dependence to FK101
2-dependence. Similar results were obtained using an alternative dimer
izer of FKBP12 domains called AP1510. Pharmacologic dimerization of ch
imeric proteins containing only a single FKBP12 domain confirmed that
receptor dimerization is sufficient for proliferative signaling. Inter
estingly, while the proliferative effects of both FK1012 and AP1510 we
re reversible, FK1012-driven proliferation persisted for several days
after drug withdrawal. Furthermore, much higher concentrations of FK50
6 were required to inhibit FK1012-mediated proliferation than were req
uired to inhibit AP1510-mediated proliferation. The persistence of FK1
012's effect appeared to be specific to clones expressing c-kit-contai
ning fusion proteins. These results suggest that pharmacologically-res
ponsive fusion proteins containing c-kit may be useful for specificall
y and reversibly expanding genetically modified hematopoietic cell pop
ulations, (C) 1998 by The American Society of Hematology.