Examining the CREB Transcriptional Program in Erythropoiesis

The erythropoietin (EPO) signal transduction network regulates a plethora of critical cellular functions during red blood cell maturation including proliferation and iron metabolism. Recently, it has been discovered that EPO signaling also controls heme metabolism through activation of the protein kinase A (PKA) pathway. The activation of PKA by EPO leads to the mitochondrial phosphorylation of the terminal heme enzyme, ferrochelatase (FECH), to ramp up heme production. In addition to FECH, a second principal PKA target is the CREB transcription factor, leading to the hypothesis that the EPO-PKA signaling pathway also regulates gene expression during red cell maturation. Here, we tested this hypothesis using biochemical and bioinformatics approaches. We found that CREB becomes phosphorylated in human and murine erythroid cells in an EPO-dependent manner. Using pharmacologic inhibitors, we confirmed that CREB phosphorylation is downstream of JAK2 and PKA signaling. Moreover, we found enrichment of a previously identified CREB-gene signature within the erythroid transcriptional program. To date, our work suggests that CREB plays a role during red cell development as an effector of EPO signaling. Further work will be required to understand the function of CREB target genes.