Modulation of protein tyrosine phosphatase 1B by erythropoietin in UT-7 cell line.
OBJECTIVE
Since the reversible phosphorylation of tyrosyl residues is a critical event in cellular signaling pathways activated by erythropoietin (Epo), attention has been focused on protein tyrosine phosphatases (PTPs) and their coordinated action with protein tyrosine kinases. The prototypic member of the PTP family is PTP1B, a widely expressed non-receptor PTP located both in cytosol and intracellular membranes via its hydrophobic C-terminal targeting sequence. PTP1B has been implicated in the regulation of signaling pathways involving tyrosine phosphorylation induced by growth factors, cytokines, and hormones, such as the downregulation of erythropoietin and insulin receptors. However, little is known about which factor modulates the activity of this enzyme.


METHODS
The effect of Epo on PTP1B expression was studied in the UT-7 Epo-dependent cell line. PTP1B expression was analyzed under different conditions by Real-Time PCR and Western blot, while PTP1B phosphatase activity was determined by a p-nitrophenylphosphate hydrolysis assay.


RESULTS
Epo rapidly induced an increased expression of PTP1B which was associated with higher PTP1B tyrosine phosphorylation and phosphatase activity. The action of Epo on PTP1B induction involved Janus Kinase 2 (JAK2) and Phosphatidylinositol-3 kinase (PI3K).


CONCLUSIONS
The results allow us to suggest for the first time that, besides modulating Epo/Epo receptor signaling, PTP1B undergoes feedback regulation by Epo.
Callero
Mariana A
MA
Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina. mcallero@qb.fcen.uba.ar
Pérez
Gladys M
GM
Vittori
Daniela C
DC
Pregi
Nicolás
N
Nesse
Alcira B
AB
D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation; D004921:Erythropoietin / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic; D053614:Janus Kinase 2 / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D020032:Tyrphostins / Q000494:pharmacology
D004921:Erythropoietin; D053614:Janus Kinase 2; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide