Igbp1 is part of a positive feedback loop in stem cell factor–dependent, selective mRNA translation initiation inhibiting erythroid differentiation

• Published in: Blood Vol. 112; no. 7; pp. 2750 - 2760
• Main Authors: Grech, Godfrey, Blázquez-Domingo, Montserrat, Kolbus, Andrea, Bakker, Walbert J., Müllner, Ernst W., Beug, Hartmut, von Lindern, Marieke
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.2008
• Subjects: Cell Differentiation - drug effects; Cell Proliferation - drug effects; Cluster Analysis; Enzyme Activation - drug effects; Erythroblasts - cytology; Erythroblasts - drug effects; Erythroid Cells - cytology; Erythroid Cells - drug effects; Erythropoietin - pharmacology; Eukaryotic Initiation Factor-4E - metabolism; Feedback, Physiological - drug effects; Intracellular Signaling Peptides and Proteins - metabolism; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation - drug effects; Polyribosomes - drug effects; Polyribosomes - enzymology; Protein Biosynthesis - drug effects; Protein Kinases - metabolism; Protein-Serine-Threonine Kinases - metabolism; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Stem Cell Factor - pharmacology; TOR Serine-Threonine Kinases; Transforming Growth Factor beta - pharmacology
• ISSN: 0006-4971; 1528-0020; 1528-0020
• DOI: 10.1182/blood-2008-01-133140

Stem cell factor (SCF)–induced activation of phosphoinositide-3-kinase (PI3K) is required for transient amplification of the erythroblast compartment. PI3K stimulates the activation of mTOR (target of rapamycin) and subsequent release of the cap-binding translation initiation factor 4E (eIF4E) from the 4E-binding protein 4EBP, which controls the recruitment of structured mRNAs to polysomes. Enhanced expression of eIF4E renders proliferation of erythroblasts independent of PI3K. To investigate which mRNAs are selectively recruited to polysomes, we compared SCF-dependent gene expression between total and polysome-bound mRNA. This identified 111 genes primarily subject to translational regulation. For 8 of 9 genes studied in more detail, the SCF-induced polysome recruitment of transcripts exceeded 5-fold regulation and was PI3K-dependent and eIF4E-sensitive, whereas total mRNA was not affected by signal transduction. One of the targets, Immunoglobulin binding protein 1 (Igbp1), is a regulatory subunit of protein phosphatase 2A (Pp2a) sustaining mTOR signaling. Constitutive expression of Igbp1 impaired erythroid differentiation, maintained 4EBP and p70S6k phosphorylation, and enhanced polysome recruitment of multiple eIF4E-sensitive mRNAs. Thus, PI3K-dependent polysome recruitment of Igbp1 acts as a positive feedback mechanism on translation initiation underscoring the important regulatory role of selective mRNA recruitment to polysomes in the balance between proliferation and maturation of erythroblasts.