Protein kinase B (c-Akt), phosphatidylinositol 3-kinase, and STAT5 are activated by erythropoietin (EPO) in HCD57 erythroid cells but are constitutively active in an EPO-independent, apoptosis-resistant subclone (HCD57-SREI cells).
We found that erythropoietin (EPO) and stem cell factor (SCF) activated protein kinase B (PKB/Akt) in EPO-dependent HCD57 erythroid cells. To better understand signals controlling proliferation and viability, erythroid cells that resist apoptosis in the absence of EPO were subcloned and characterized (HCD57-SREI cells). Constitutive activations of PKB/Akt, STAT5a, and STAT5b were noted in these EPO-independent cells. PI3-kinase activity was an upstream activator of PKB/Akt because the PI3-kinase inhibitor LY294002 blocked both constitutive PKB/Akt and factor-dependent PKB/Akt activity. The LY294002 study showed that proliferation and viability of both HCD57-SREI and HCD57 cells correlated with the activity of PKB/Akt; however, PKB/Akt activity alone did not protect these cells from apoptosis. Treatment of HCD57 cells with SCF also activated PKB/Akt, but did not protect from apoptosis. This result suggested that PKB/PI3-kinase activity is necessary but not sufficient to promote viability and/or proliferation. Constitutive STAT5 activity, activated through an unknown pathway not including JAK2 or EPOR, may act in concert with the constitutive PI3-kinase/PKB/Akt pathway to protect the EPO-independent HCD57-SREI cells from apoptosis and promote limited proliferation.
Bao
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H
Department of Pharmacology and Toxicology, Medical College of Virginia campus of Virginia Commonwealth University, Richmond, VA, USA.
Jacobs-Helber
S M
SM
Lawson
A E
AE
Penta
K
K
Wickrema
A
A
Sawyer
S T
ST
D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism* / Q000473:pathology; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D008894:Milk Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
D004268:DNA-Binding Proteins; D004921:Erythropoietin; D008894:Milk Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; C494092:STAT5A protein, human; C494095:STAT5B protein, human; C494918:AKT1 protein, human