Key Points • Increasing eIF2a

phosphorylation increases fetal hemoglobin in human primary erythroid progenitors via a post-transcriptional mechanism. • Combining pharmacologic agents that use transcriptional and post-transcriptional mechanisms additively induces fetal hemoglobin. Strategies to increase fetal hemoglobin (HbF) levels can ameliorate symptoms and im-prove the lives of b-hemoglobinopathy patients. Although most studies have focused on induction of g-globin gene expression as an approach to induce HbF, we hypothesized that post-transcriptional regulation of HbF plays an underappreciated yet important role in controlling HbF levels. In the present study, we investigated whether increasing eu-karyotic initiation factor 2a (eIF2a) phosphorylation, a key regulator of protein translation, could enhanceHbFpost-transcriptionally in human primary erythroid cells. Initial analysis using a known inhibitor of eIF2a dephosphorylation, salubrinal, revealed that elevated eIF2a phosphorylation enhanced HbF production without changing globin gene ex-pression, proliferation, or cell differentiation. These results were further supported by the post-transcriptional induction of HbF by other pharmacologic activators of the eIF2a pathway and by genetic inactivation of the negative regulators, GADD34 and CReP. Additionally, we found that this novel mechanism of increasing HbF could be combined with clinically relevant transcriptional activators of g-globin gene expression to additively enhance HbF. Taken together, these findings identify eIF2a phosphorylation as a post-transcriptional regulator of HbF induction that may be pharmacologically targeted, either alone or in combination, inb-hemoglobinopathy patients. (Blood. 2013;122(4):477-485