Mechanism governing heme synthesis reveals a GATA factor/heme circuit that controls differentiation. (23rd December 2015)

• Record Type: Journal Article
• Authors: Tanimura, Nobuyuki; Miller, Eli; Igarashi, Kazuhiko; Yang, David; Burstyn, Judith N; Dewey, Colin N; Bresnick, Emery H
• Is Part Of: EMBO reports. Volume 17:Number 2(2016:Feb.)
• Page Start: 249
• Page End: 265
• Publication Date: 2015-12-23
• Subjects: Bach1 -- GATA factor -- heme -- network -- transcriptome; Molecular biology -- Periodicals; Molecular Biology -- Periodicals; Molecular biology; Periodicals; 572.8
• DOI: 10.15252/embr.201541465
• Languages: English
• ISSNs: 1469-221X

Abstract

Abstract: Metal ion‐containing macromolecules have fundamental roles in essentially all biological processes throughout the evolutionary tree. For example, iron‐containing heme is a cofactor in enzyme catalysis and electron transfer and an essential hemoglobin constituent. To meet the intense demand for hemoglobin assembly in red blood cells, the cell type‐specific factor GATA‐1 activates transcription of Alas2, encoding the rate‐limiting enzyme in heme biosynthesis, 5‐aminolevulinic acid synthase‐2 (ALAS‐2). Using genetic editing to unravel mechanisms governing heme biosynthesis, we discovered a GATA factor‐ and heme‐dependent circuit that establishes the erythroid cell transcriptome. CRISPR/Cas9‐mediated ablation of two Alas2 intronic cis elements strongly reduces GATA‐1‐induced Alas2 transcription, heme biosynthesis, and surprisingly, GATA‐1 regulation of other vital constituents of the erythroid cell transcriptome. Bypassing ALAS‐2 function in Alas2 cis element‐mutant cells by providing its catalytic product 5‐aminolevulinic acid rescues heme biosynthesis and the GATA‐1‐dependent genetic network. Heme amplifies GATA‐1 function by downregulating the heme‐sensing transcriptional repressor Bach1 and via a Bach1‐insensitive mechanism. Through this dual mechanism, heme and a master regulator collaborate to orchestrate a cell type‐specific transcriptional program that promotes cellular differentiation. Synopsis: This study shows that heme amplifies GATA‐1 activity at select target genes to establish the erythroid cell transcriptome. GATA‐1/heme‐activated genes are repressed through mechanisms involving the heme‐regulated repressor Bach1 or a Bach1‐insensitive mechanism. Deletion of two Alas2 intronic GATA motifs severely decreases Alas2 expression, impairs heme biosynthesis, and dysregulates the erythroid cell transcriptome. 5‐aminolevulinic acid (5‐ALA), a product of Alas2, restores heme biosynthesis and expression of a cohort of GATA‐1‐regulated genes. The transcriptional repressor Bach1 accumulates in heme‐deficient erythroid cells and represses a cohort of the GATA‐1/heme‐activated genes. A distinct cohort of the GATA‐1/heme‐activated genes are repressed in a Bach1‐independent manner. Abstract : This study shows that heme amplifies GATA‐1 activity at select target genes to establish the erythroid cell transcriptome. GATA‐1/heme‐activated genes are repressed through mechanisms involving the heme‐regulated repressor Bach1 or a Bach1‐insensitive mechanism.