GATA-1 Utilizes Ikaros and Polycomb Repressive Complex 2 To Suppress Hes1 and To Promote Erythropoiesis

Abstract

The transcription factor Hairy Enhancer of Split 1 (HES1), a downstream effector of the Notch signaling pathway, is an important regulator of hematopoiesis. Here, we demonstrate that in primary erythroid cells, Hes1 gene expression is transiently repressed around proerythroblast stage of differentiation. Using mouse erythroleukemia cells, we found that the RNA interference (RNAi)-mediated depletion of HES1 enhances erythroid cell differentiation, suggesting that this protein opposes terminal erythroid differentiation. This is also supported by the decreased primary erythroid cell differentiation upon HES1 upregulation in Ikaros-deficient mice. A comprehensive analysis led us to determine that Ikaros favors Hes1 repression in erythroid cells by facilitating recruitment of the master regulator of erythropoiesis GATA-1 alongside FOG-1, which mediates Hes1 repression. GATA-1 is then necessary for the chromatin binding of the NuRD remodeling complex ATPase MI-2, the transcription factor GFI1B, and the histone H3K27 methyltransferase EZH2 along with Polycomb repressive complex 2. We show that EZH2 is required for the transient repression of Hes1 in erythroid cells. In aggregate, our results describe a mechanism whereby GATA-1 utilizes Ikaros and Polycomb repressive complex 2 to promote Hes1 repression as an important step in erythroid cell differentiation.

ACKNOWLEDGMENTS

We thank J. G. Filep, S. Bottardi, and E. Drobetsky for critical reading of the manuscript; K. Georgopoulos for the Ik^null mouse line; M. Weiss for the G1E-2 and the G1E-ER4 cell lines; F. Grosveld for the MEL C88 cell line; V. Bourgoin for technical assistance; and G. D'Angelo for Wright-Giemsa staining analysis.

This study was supported by a grant from the Canadian Institutes of Health Research (MOP 97738) held by E.M. E.H.B. is supported by NIH R01 DK50107. J.R. is supported by a Fond de la Recherche du Québec en Santé (FRQS) Doctoral Training Award, and E.M. is a scholar of the FRQS.