Activation of the erythropoietin receptor by the Friend spleen focus-forming virus gp55 glycoprotein induces constitutive protein tyrosine phosphorylation.
The erythropoietin receptor (EPO-R) can be activated to signal cell growth by binding either EPO or gp55, the Friend spleen focus-forming virus (SFFV) glycoprotein. EPO binding induces tyrosine kinase activity and rapid tyrosine phosphorylation of several cellular substrates. To test for gp55-induced tyrosine kinase activity, we performed immunoblots on two murine cell lines that stably express EPO-R and gp55. Stimulation of the parental cell line, Ba/F3, with murine interleukin-3 (IL-3) resulted in rapid, dose-dependent tyrosine phosphorylation of a 97-Kd substrate. Stimulation with IL-3 or EPO of the Ba/F3 cells expressing the recombinant EPO-R (Ba/F3-EPO-R) resulted in tyrosine phosphorylation of the same p97 substrate. These latter cells, when transformed to growth factor-independence by the Friend gp55 glycoprotein, exhibited constitutive tyrosine phosphorylation of the 97-Kd substrate. Other growth factor-independent Ba/F3 subclones, transformed with either the oncoprotein, v-abl, or with a constitutively activated EPO-R, also had constitutive phosphorylation of a 97-Kd substrate. In CTLL-2-EPO-R cells, a T-lymphocyte line stably transfected with the EPO-R, the 97-Kd substrate was tyrosine-phosphorylated in response to IL-2 or EPO. The 97-Kd protein was constitutively phosphorylated in CTLL-2-EPO-R-gp55 cells. In conclusion, a 97-Kd protein found in two murine cell lines is tyrosine-phosphorylated in response to multiple growth factors and viral oncoproteins, and appears to be a central phosphoprotein in signal transduction.
Showers
M O
MO
Division of Hematology-Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115.
Moreau
J F
JF
Linnekin
D
D
Druker
B
B
D'Andrea
A D
AD
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D007377:Interleukin-3 / Q000494:pharmacology; D051379:Mice; D008970:Molecular Weight; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D017467:Receptors, Erythropoietin / Q000187:drug effects* / Q000502:physiology*; D011994:Recombinant Proteins / Q000494:pharmacology; D013155:Spleen Focus-Forming Viruses / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014759:Viral Envelope Proteins / Q000378:metabolism*
D007376:Interleukin-2; D007377:Interleukin-3; D010750:Phosphoproteins; D017467:Receptors, Erythropoietin; D011994:Recombinant Proteins; D014759:Viral Envelope Proteins; C078780:glycoprotein gp55, Friend spleen focus-forming virus; D004921:Erythropoietin; D011505:Protein-Tyrosine Kinases; D013755:Tetradecanoylphorbol Acetate