Mechanism for γ-Globin Induction by SCF Is Via PKCα/ERK1/2/Nrf2 Dependent Signal Pathway To Regulate Down-Stream Transcriptional Regulators NF-Y and COUP-TFII.

Increased fetal hemoglobin has been identified to be associated with stress erythropoiesis. However, the mechanisms underlying γ-globin induction during the rapid expansion of erythroid progenitor cells have not been fully elucidated. Here we examined how intracellular signaling pathway modification of specific transcriptional regulators induced γ-globin expression in vitro cultured erythroid progenitor cells in the presence of erythropoietin and stem cell factor (SCF). We find that γ-globin induced by SCF is through a PKCα-dependent Ras/Raf/Erk1/2 signaling pathway involving activation of the transcription factor NF-Ya and inhibition of the repressor Coup-TFII. Specific inhibition of PKCα with Go6976 blocked both activation of Erk1/2 and p38 MAPK induced by SCF, and abrogated the SCF increased γ-globin gene expression. Activation of Erk1/2 plays a critical role in SCF modulated down-stream transcriptional regulators, involving regulation of γ-globin gene induction. SCF induced nuclear translocation of NF-Ya is required to activate Erk1/2 increased phosphorylation of endogenous Nrf2, which involves up-regulation of thioredoxin, and down-regulation of Coup-TFII. Inhibition of either PKCα or Erk1/2 prevented SCF induced recruitment of NF-Ya, RNA polymerase II and displacement of Coup-TFII repressor from γ-globin-promoter, indicating that the PKCα-Erk1/2 MAPK pathway contributes to SCF induced the γ-globin gene induction in adult erythropoiesis. Furthermore, consistent with this concept, SCF induced the γ-globin gene induction attenuated by inhibition of PKCα or Erk1/2 MAPK. Our data suggest that SCF stimulates the PKCα-Erk1/2 MAPK signaling pathway which regulate the downstream transcriptional activator NF-Ya and repressor Coup-TFII resulting in γ-globin reactivation in adult erythropoiesis. These observations provide the molecular pathways that take part in γ-globin augmentation during “stress erythropoiesis”.