AJP - Cell Physiology, Vol 262, Issue 5 C1197-C1203, Copyright © 1992 by American Physiological Society
Signal transduction by the erythropoietin receptor: evidence for the activation of phospholipases A2 and C
M. Mason-Garcia, S. Clejan, J. S. Tou and B. S. Beckman
Department of Pharmacology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Erythropoietin (Ep) is the peptide growth factor whose actions on the
erythroid progenitor cell induce terminal differentiation. However, the
intracellular signaling system that is activated by Ep is poorly
understood. Our previous studies have implicated the lipoxygenase
metabolites of arachidonic acid in the actions of Ep. In this study, we
report an early (30 s to 5 min) increase in levels of two lipoxygenase
metabolites: leukotriene B4 (LTB4; 3- to 5-fold) and
12-hydroxyeicosatetraenoic acid (12-HETE; 2-fold). These responses were
blocked by an antibody to Ep, by lipoxygenase inhibitors, or by
1,6-di[O-(carbamoyl)cyclohexanone oxime]hexane (RHC80267), an inhibitor of
diacylglycerol (DAG) lipase. RHC 80267 also significantly inhibited
Ep-mediated proliferation. Ep induced the release of [3H]arachidonic acid
from cellular phospholipids at 5 min and also increased DAG accumulation at
1 min with a maximum increase of 68.2% over control seen at 30 min. No
increase in levels of inositol trisphosphate or phosphatidic acid was
observed in response to Ep. Taken together, these data suggest that the
signal transduction pathway of the Ep receptor includes the activation of
phospholipases A2 and C, resulting in the liberation of DAG and
arachidonate and the subsequent formation of LTB4 and 12-HETE.
