ERYTHROPOIETIN RECEPTORS IN LEUKEMIA

In Friend erythroleukemia, the membrane glycoprotein (gp55) encoded by
Friend spleen focus-forming virus (SFFV) binds as an agonist to murine
erythropoietin receptors (EpoR) to stimulate erythroblastosis. We recently
cloned the human Epo gene and produced helper-free retrovirions that encode
Epo, murine EpoR or gp55. Coinfection of murine IL-3 dependent cells with
the EpoR virus plus either of the other viruses was able to convert the
cells to factor-independent proliferation. Interestingly, erythroblasts of
mice homozygous for Fv-2r have severely reduced mitogenic response to Epo;
and these mice are therefore resistant to both Friend and to Epo virus-
induced erythroleukemias. Mapping indicated that EpoR and Fv-2 genes are
unlinked. We proposed: (1) Use genetic and biochemical methods to analyze
Fv-2 role in EpoR signal transduction. Does Fv-2 encode a second EpoR
subunit or a transducin? Molecularly clone Fv-2. (2) Friend
erythroleukemia is considered restricted to mice. Why? Cannot gp55 bind
to nonmurine EpoR? Or, do other species have an Fv-2rr-like phenotype?
Clone human EpoR. Analyze mitogenic interactions of gp55 and Epo with
human and murine EpoR in factor-dependent cells from humans or mice. (3)
Use methods including mutagenesis to identify active sites for binding and
mitogenesis on Epo and EpoR. (4) Produce a soluble derivative of EpoR in
substantial amounts. Study Epo-sEpoR interaction by physical methods
including cocrystallization and X-ray diffraction. Use sEpoR for a
sensitive Epo assay. Does sEpoR cure Friend erythroleukemia? (5) Analyze
EpoR processing and mitogenic signalling. This project is important for
understanding hematopoietic growth factor receptors in leukemias and it
provides a unique model for learning at the molecular level how host
genetic variation (e.g., Fv-2) controls susceptibility to an oncogenic
protein.