Association of proliferation and apoptosis resistance in polycythemia vera erythroblasts with abnormal MAPK and PI3K/AKT pathway signaling.

7086 Background: Polycythemia vera (PV), a myeloproliferative disorder associated with JAK2 mutation, is characterized by erythrocytosis due to dysregulated red blood cell (RBC) production. We investigated the hypothesis that RBC accumulation results from increased precursor proliferation and/or apoptosis resistance associated with abnormal signaling via MAPK and PI3K/AKT pathways.,Peripheral blood CD34+ cells were grown in liquid culture to generate primary erythroid precursors (EBLs) from PV patients and normal controls recruited in an IRB-approved protocol. All patients were positive for the JAK mutation. Studies of proliferation, apoptosis, and protein phosphorylation were performed. To determine effects of MAPK and PI3K/AKT inhibition, cells were treated with inhibitors of MEK (PD98059) and PI3K (LY294002).,Seventeen patients were recruited to the study. In strict serum-free conditions, survival and proliferation of PV EBLs was growth factor-dependent, requiring both erythropoietin (EPO) and stem cell factor. PV EBLs exhibited increased EPO sensitivity, with a proliferation rate 1.6 fold greater than controls at physiologic EPO concentration (P<0.01). EPO-induced ERK1/2 phosphorylation was markedly increased in PV cells compared to controls. EPO induced phosphorylation of AKT in PV but not normal EBLs. PV EBLs were less sensitive than controls to MEK inhibition by a factor of two (P<0.01). Growth factor withdrawal induced a 5.7 fold increase in apoptosis in normal EBLs but only a 2.2 fold increase in PV cells (P<0.01). Inhibition of PI3K during growth factor withdrawal led to a further 1.5-fold increase in apoptosis of normal EBLs (P<0.01), whereas it did not have a significant effect on apoptosis in PV cells. MEK inhibition during growth factor withdrawal did not increase apoptosis in either normal or PV EBLs.,1) PV EBLs containing the JAK2 mutation are not cytokine-independent and exhibit EPO hypersensitivity under strict serum-free conditions, 2) Increased proliferation of PV EBLs is associated with increased EPO-induced ERK1/2 phosphorylation, 3) PV EBLs exhibit apoptosis resistance associated with increased EPO-induced phosphorylation of AKT. No significant financial relationships to disclose.