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Mol Cell Biol, March 1998, p. 1172-1180, Vol. 18, No. 3
Department of Retroviral Regulation,
Received 13 August 1997/Returned for modification 28 September
1997/Accepted 1 December 1997
Abnormal erythropoietin (EPO)-independent cell growth is induced
after infection of erythroid progenitor cells with a polycythemic strain of Friend virus (FVp). Binding of its Env-related
glycoprotein (gp55) to the EPO receptor (EPOR) mimics the activation of
the EPOR with EPO. We investigated the gp55-EPOR signaling in
erythroblastoid cells from mice infected with FVp and in
cells of FVp-induced or gp55-transgenic-mouse-derived
erythroleukemia cell lines, comparing it with the EPO-EPOR signaling in
EPO-responsive erythroblastoid cells. While the Janus protein tyrosine
kinase JAK2 and the transcription factor STAT5 became tyrosine
phosphorylated with the EPO stimulation in EPO-responsive
erythroblastoid cells from anemic mice, JAK1 and STAT5 were
constitutively tyrosine phosphorylated in all of these FVp
gp55-induced erythroblastoid or erythroleukemic cells. Moreover, this
constitutively tyrosine-phosphorylated STAT5 was unable to bind to its
specific DNA sequences and did not translocate to the nucleus. Nuclear
translocation and DNA binding of this STAT5 species required EPO
stimulation. These findings clearly indicate that the FVp
gp55-EPOR signaling is distinct from the EPO-EPOR signaling and suggest
that STAT5 may not play an essential role in the transmission of the
cell growth signals in FVp gp55-induced erythroleukemia
cells.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Erythropoietin and Friend Virus gp55 Activate
Different JAK/STAT Pathways through the Erythropoietin Receptor
in Erythroid Cells
*
Corresponding author. Mailing address: Department of
Retroviral Regulation, Tokyo Medical and Dental University Medical
Research Division, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113, Japan. Phone: 81-3-5803-5159. Fax: 81-3-3814-7172. E-mail:
y.ikawa.mbch{at}med.tmd.ac.jp.
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