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Erythropoietin rapidly induces tyrosine phosphorylation in the human
erythropoietin-dependent cell line, UT-7
N Komatsu, JW Adamson, K Yamamoto, D Altschuler, M Torti, R Marzocchini and EG Lapetina
Laboratory of Hematopoietic Growth Factors, Lindsley F. Kimball Research
Institute, New York Blood Center, New York.
UT-7 is a human megakaryoblastic cell line capable of growing in
interleukin-3, granulocyte-macrophage colony-stimulating factor, or
erythropoietin (Epo) (Cancer Res 51:341, 1991). We used this cell line and
a selected Epo-dependent subcell line (UT-7/Epo) to study the early signal
transduction events induced by Epo. When UT-7 cells were exposed to Epo,
tyrosine phosphorylation of several proteins (with molecular weight
equivalent to that of p85, p110, and p145) was observed. Protein
phosphorylation occurred in both a dose- and time-dependent manner. p85
showed a marked increase in phosphotyrosine content within 30 seconds;
maximal phosphorylation was observed at 1 minute. Subsequently, tyrosine
phosphorylation of p110 and p145 was observed, beginning at 1 minute and
reaching plateau at 5 minutes. The degree of phosphorylation of these three
proteins gradually decreased thereafter. In addition, in UT-7/Epo cells,
Epo induced tyrosine phosphorylation of other proteins that were not
observed in Epo-induced UT-7 cells. The concentration of Epo required to
induce tyrosine phosphorylation was in the same range of concentration
required to stimulate cell growth. Epo was also able to activate p21ras as
measured by exchange of guanosine diphosphate for guanosine triphosphate.
These data show that tyrosine phosphorylation and P21ras activation are
early signals in the Epo-induced mitogenic pathway.
Volume 80,
Issue 1,
pp. 53-59,
07/01/1992
Copyright © 1992 by The American Society of Hematology
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