The RNA-Degrading Exosome Complex Is an Endogenous Suppressor of Erythroid Maturation

• Published in: Blood 2014-12, Vol.124 (21), p.2659-2659
• Main Authors: McIver, Skye C, Kang, Yoon-A, DeVilbiss, Andrew W, O’Driscoll, Chelsea A, Yang, David T., Ghaffari, Saghi, Bresnick, Emery H
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V124.21.2659.2659

Complex genetic networks control hematopoietic stem cell differentiation into progenitors that give rise to billions of erythrocytes daily. We demonstrated that the master regulator of erythropoiesis, GATA-1, induces expression of genes encoding components of the autophagy machinery. In this context, the Forkhead transcription factor, Foxo3, amplified GATA-1-mediated transcriptional activation. We conducted studies to assess whether the GATA-1/Foxo3 cooperativity is restricted to the control of autophagy, or if it more broadly impacts the erythroid cell transcriptome. Analysis of the GATA-1/Foxo3-dependent transcriptome in erythroid cells revealed a target gene ensemble extending beyond autophagy, but representing only a small fraction of the complex GATA-1-dependent target gene ensemble. GATA-1/Foxo3 repressed expression of genes encoding two exosome complex components, Exosc5 and Exosc8. The exosome complex functions in one of the major RNA degradation pathways in diverse cell types, mediates splicing and degradation of mRNAs and non-coding RNAs, and functions in epigenetic gene regulation. As the role of the exosome complex in erythropoiesis, and more broadly in hematopoiesis, had not been described previously, we conducted biological and mechanistic studies to determine whether the endogenous exosome complex has important roles in the development and/or function of erythroid cells. Strikingly, downregulating expression of endogenous exosome components, Exosc8, Exosc9 and the catalytic component Dis3 dramatically increased the percentage of primary erythroid precursor cells in the R4 (polychromatic and orthrochromatic orthrochromatic) population from 1% in control cells to 30%, 28% and 16% respectively. We have extended these initial findings to explore key mechanistic and biological questions. Using the exosome complex high-resolution crystal structure as a guide, we are conducting loss-of-function studies to establish whether additional exosome complex components that serve structural roles in the complex (Exosc4 and Exosc7), bind RNA substrates (Exosc1), and degrade RNAs (Dis3L and Exosc10) are also important determinants of erythroid maturation. Initial studies indicate that multiple components suppress maturation, but differ quantitatively in their importance. Studies are underway to test the hypothesis that downregulating Exosc8 or Exosc9 severely disrupts the integrity of the exosome complex, whereas certain other components are less critical for