Erythropoietin-induced erythroid differentiation of K562 cells is accompanied by the nuclear translocation of phosphatidylinositol 3-kinase and intranuclear generation of phosphatidylinositol (3,4,5) trisphosphate.
D-3 phosphorylated inositides are a peculiar class of lipids, synthesized by phosphatidylinositol 3-kinase (PtdIns 3-K), which are also present in the nucleus. In order to clarify a possible role for nuclear D-3 phosphorylated inositides during human erythroid differentiation, we have examined the issue of whether or not, in K562 human erythroleukemia cells, erythropoietin (EPO) may generate nuclear translocation of an active PtdIns 3-K. Immunoprecipitation with an anti-p85 regulatory subunit of PtdIns 3-K, revealed that both the intranuclear amount and the activity of the kinase increased rapidly and transiently in response to EPO. Enzyme translocation was blocked by the specific PtdIns 3-K pharmacological inhibitor, LY294002, which also inhibited erythroid differentiation. In vivo, intranuclear synthesis of phosphatidylinositol (3,4,5) trisphosphate (PtdIns (3,4,5)P(3)) was stimulated by EPO. Almost all PtdIns 3-K that translocated to the nucleus was highly phosphorylated on tyrosine residues of the p85 regulatory subunit. These findings strongly suggest that an important step in the signaling pathways that mediate EPO-induced erythroid differentiation may be represented by the intranuclear translocation of an active PtdIns 3-K.
Neri
Luca M
LM
Dipartimento di Morfologia ed Embriologia, Sezione di Anatomia Umana, Università di Ferrara, via Fossato di Mortara 66, 44100 Ferrara, Italy. l.neri@dns.unife.it
Bortul
Roberta
R
Tabellini
Giovanna
G
Borgatti
Paola
P
Baldini
Giovanna
G
Celeghini
Claudio
C
Capitani
Silvano
S
Martelli
Alberto M
AM
D021581:Active Transport, Cell Nucleus; D015153:Blotting, Western; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism*; D015672:Erythroid Precursor Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D020014:K562 Cells; D007700:Kinetics; D018613:Microscopy, Confocal; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis*; D010766:Phosphorylation
D018129:Phosphatidylinositol Phosphates; C060974:phosphatidylinositol 3,4,5-triphosphate; D004921:Erythropoietin; D019869:Phosphatidylinositol 3-Kinases