Increased erythropoiesis in polycythemia vera is associated with increased erythroid progenitor proliferation and increased phosphorylation of Akt/PKB.
OBJECTIVE
The aim of this study was to explore the mechanism by which increased erythropoiesis occurs in polycythemia vera (PV).


METHODS
CD34(+) and erythroid colony-forming cells (ECFC) were purified from normal or PV peripheral blood and then incubated in the presence of erythropoietin (EPO) to generate erythroid progenitor cells. Measurement of proliferation by Ki-67 staining, TUNEL assays to measure apoptosis, and Western blots for detection of Akt/PKB and glycogen synthase kinase 3 (GSK3) phosphorylation were performed in both normal and PV erythroid progenitors.


RESULTS
Polycythemia vera erythroid progenitor cells generated 60% more cells compared to normal cells in liquid medium cell cultures. TUNEL assays revealed no difference between PV and normal erythroid progenitors, but Ki-67 staining for cell proliferation showed many more positive cells in the PV samples. A marked increase of phosphorylation of Akt/PKB occurred in the day-8 erythroid progenitors of 4/5 PV patients, compared to normal cells, after incubation with either stem cell factor (SCF) or EPO. PV cells also had much greater glycogen synthase kinase 3 (GSK3) alpha,beta phosphorylation compared to normal cells after incubation with SCF or EPO. These results are parallel to the cellular hypersensitivity of PV cells to SCF and EPO previously reported.


CONCLUSIONS
Increased erythropoiesis in PV is associated with increased cellular proliferation and increased phosphorylation of Akt/PKB and GSK3. This study provides additional insight into the pathogenesis of PV and the regulation of normal erythropoiesis, even though a specific molecular defect of the disease is still not apparent.
Dai
Chunhua
C
Hematology/Oncology Division, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tenn., USA.
Chung
Ik-Joo
IJ
Krantz
Sanford B
SB
D000328:Adult; D018952:Antigens, CD34 / Q000097:blood; D017209:Apoptosis; D002453:Cell Cycle; D002455:Cell Division; D003114:Colony-Forming Units Assay; D004920:Erythropoiesis / Q000502:physiology*; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000097:blood; D000071679:Glycogen Synthase Kinase 3 beta; D006412:Hematopoietic Stem Cells / Q000473:pathology*; D006801:Humans; D019394:Ki-67 Antigen / Q000032:analysis; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D011087:Polycythemia Vera / Q000097:blood* / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012016:Reference Values
D018952:Antigens, CD34; D019394:Ki-67 Antigen; D011518:Proto-Oncogene Proteins; C494918:AKT1 protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha