A functional erythropoietin receptor is necessary for the action of thrombopoietin on erythroid cells lacking c-mpl.
OBJECTIVE
We hypothesized that thrombopoietin (TPO) exerts its mitogenic effects on erythroid cells, at least in part, via an interaction of TPO with the cells' erythropoietin receptor (EPO-R).


METHODS
We used BaF3 cells stably transfected with EPO-R to demonstrate that TPO alone is sufficient to support the long-term growth and proliferation of BaF3/EPO-R cells and to develop a TPO-dependent variant, BaF3/EPO-R(T), which is highly sensitive to and dependent on TPO for its proliferation. Northern analysis and RT-PCR were used to verify that both BaF3/EPO-R and BaF3/EPO-R(T) cells express EPO-R but lack c-mpl, the TPO receptor. To confirm that TPO responsiveness of BaF3/EPO-R(T) is due to TPO's interaction with EPO-R, EPO-R was downregulated by antisense mRNA.


RESULTS
Downregulation of EPO-R in BaF3/EPO-R(T) cells abolishes responsiveness to both EPO and TPO. Viability of EPO-treated transfectants decreased from 95% to 36%, while that of TPO-treated transfectants decreased from 95% to 9% by 48 hours. Nontransfected BaF3/EPO-R(T), and BaF3/EPO-R(T) transfected with vector alone, remained viable and grew in either EPO or TPO.


CONCLUSIONS
Our results suggest a functional EPO-R may be necessary and sufficient for TPO to exert its mitogenic effects on erythroid cells.
Rouleau
Cecile
C
Laboratory for Cell and Molecular Biology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Mass 02215, USA.
Cui
Kunyuan
K
Feldman
Laurie
L
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D015672:Erythroid Precursor Cells / Q000187:drug effects*; D051379:Mice; D009363:Neoplasm Proteins / Q000502:physiology*; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D018121:Receptors, Cytokine / Q000502:physiology*; D017467:Receptors, Erythropoietin / Q000502:physiology*; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin / Q000494:pharmacology*
D009363:Neoplasm Proteins; D020319:Oligodeoxyribonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D017467:Receptors, Erythropoietin; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin