Interaction between the glucocorticoid and erythropoietin receptors in human erythroid cells.
OBJECTIVE
The aim of this study was to identify whether the rapid membrane-associated pathway of the glucocorticoid receptor (GR) is active in erythroid cells and plays any role in determining the reversible inhibition on erythroid maturation exerted by GR.


METHODS
First we determined the biological effects (inhibition of apoptosis and induction of beta-globin expression) induced in primary erythroblasts by erythropoietin (EPO) and the GR agonist dexamethasone (DXM), alone and in combination. Next, by biochemical analysis, we determined the association between GR and EPO receptor in proerythroblasts generated in vitro from 10 normal adult donors. These studies also analyzed the levels of signal transducers and activators of transcription-5 (STAT-5) phosphorylation induced when the cells were stimulated with DXM alone or in combination with EPO.


RESULTS
DXM antagonized the beta-globin messenger RNA increases, but not the inhibition of apoptosis induced by EPO in primary cells. DXM also antagonized the ability of EPO to induce STAT-5 phosphorylation in these cells. In fact, EPO and DXM alone, but not in combination, induced phosphorylation and nuclear translocation of STAT-5. The inhibition likely occurred through an interaction between the two receptors because GR became associated with the EPO receptor and STAT-5 in cells stimulated with EPO and DXM.


CONCLUSIONS
These data suggest that glucocorticoids inhibit erythroid maturation not only through a transcriptional mechanism, but also through a rapid membrane-associated pathway that interferes with EPO receptor signaling.
Department of Infectious, Parasitic and Immunomediated Diseases, University of Chieti-Pescara, Chieti, Italy.
Emilia
E
Stellacci
Antonella
A
Di Noia
Angela
A
Di Baldassarre
Giovanni
G
Migliaccio
Angela
A
Battistini
Anna Rita
AR
Migliaccio
D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D000328:Adult; D002467:Cell Nucleus / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D004900:Erythroblasts / Q000166:cytology / Q000378:metabolism*; D004921:Erythropoietin / Q000494:pharmacology; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D008297:Male; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D017467:Receptors, Erythropoietin / Q000819:agonists / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000819:agonists / Q000378:metabolism*; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology*; D055544:beta-Globins / Q000096:biosynthesis
D005938:Glucocorticoids; D012333:RNA, Messenger; D017467:Receptors, Erythropoietin; D011965:Receptors, Glucocorticoid; D050799:STAT5 Transcription Factor; D055544:beta-Globins; D004921:Erythropoietin; D003907:Dexamethasone