Direct and indirect regulation of fetal globin transcript by RNA-binding protein IGF2BP1
Despite extensive investigation, the molecular control of developmental hemoglobin expression remains incompletely elucidated. Hemoglobin switching is controlled by transcription factors, miRNAs, and RNA-binding proteins (RBPs) that enforce gene regulatory changes through development. Here we examine the role of the heterochronically silenced N-6 methyladenosine (m6A) RNA-binding protein IGF2BP1 that was previously described to regulate HBG1/2 indirectly by suppressing BCL11A expression through an unknown mechanism. We find that IGF2BP1 binds and activates HIC2, itself a BCL11A repressor. Furthermore, we identify that IGF2BP1 plays a BCL11A-independent role by direct binding to HBG1/2 to promote its translation. Stop codon-proximal m6A-modified coding sequences within HBG2 transcripts are necessary and sufficient for direct positive regulation mediated by IGF2BP1. This work deepens the mechanistic understanding of hemoglobin switching and suggests a physical relationship between heterochronic RBPs and globin transcripts.