Regulation of Delta-Aminolevulinic Acid Dehydratase by Krüppel-Like Factor 1

Abstract

Krüppel-like factor 1(KLF1) is a hematopoietic-specific zinc finger transcription factor essential for erythroid gene expression. In concert with the transacting factor GATA1, KLF1 modulates the coordinate expression of the genes encoding the multi-enzyme heme biosynthetic pathway during erythroid differentiation. To explore the mechanisms underpinning KLF1 action at the gene loci regulating the first 3 steps in this process, we have exploited the K1-ERp erythroid cell line, in which KLF1 translocates rapidly to the nucleus in response to treatment with 4-OH-Tamoxifen (4-OHT). KLF1 acts as a differentiation-independent transcriptional co-regulator of delta-aminolevulinic acid dehydratase (Alad), but not 5-aminolevulinate synthase gene (Alas2) or porphobilinogen deaminase (Pbgd). Similar to its role at the β-globin promoter, KLF1 induces factor recruitment and chromatin changes at the Alad1b promoter in a temporally-specific manner. In contrast to these changes, we observed a distinct mechanism of histone eviction at the Alad1b promoter. Furthermore, KLF1-dependent events were not modulated by GATA1 factor promoter co-occupancy alone. These results not only enhance our understanding of erythroid-specific modulation of heme biosynthetic regulation by KLF1, but provide a model that will facilitate the elucidation of novel KLF1-dependent events at erythroid gene loci that are independent of GATA1 activity.

EKLF/KLF1, a Tissue-Restricted Integrator of Transcriptional Control, Chromatin Remodeling, and Lineage Determination

“…KLF1 also interacts with chromatin-modifying and -remodeling factors, such as P/CAF, CBP/p300 (44), and the SWI/SNF complex (45,46), the latter likely through its interaction with BRG1 (47)(48)(49)(50) and possibly BAF47/BAF155 (51). Erythroid cells that lack KLF1 exhibit an aberrant chromatin configuration and altered components at KLF1 target promoters, resulting in histone hypoacetylation and loss of DNase hypersensitivity and an absence of CBP, BRG1, TBP, and RNA polymerase II (Pol II) (52).…”

“…In the absence of KLF1, a DNase I-hypersensitive site that is typically present in the promoter is lost, leading to a decrease but not complete loss of acetylated H3 and H4 across most of the AHSP gene, corresponding with loss of expression. KLF1 also directly regulates the erythroid cell-specific Alad(1b) promoter, enhancing the recruitment of other transcription factors, along with BRG1, P300/CBP, and RNA Pol II, that lead to induced changes in the local histone modification and chromatin structure (48). The absence of KLF1 disrupts hypersensitive-site formation at the ␤-globin (55) and E2F2 (19) genes, suggesting that in general, KLF1 plays a role in regulating chromatin conformation of its target loci.…”

Investigating the Molecular Pathogenesis of Inherited Childhood Anaemia

“…Further investigation revealed the extent of KLF1's control of the haemoglobin synthesis pathways. Direct KLF1 target genes in this pathway include Alad (Desgardin et al, 2012), Alas2 (Kramer et al, 2000, Surinya et al, 1997, Pbgd/Hmbs, Urod, Ppox, Abc-me/Abcd10, Abcg2, Bzrap1…”

“…Alad encodes the second enzyme of the haem biosynthetic pathway and is also directly activated by KLF1 (Desgardin et al, 2012). KLF1 binds strongly to the middle of intron 1, and this overlaps a DHS in foetal liver (Figure 3.6B).…”

“…Of these, many are known to be important erythroid genes found in previous studies as KLF1 target genes (Gillinder et al, 2017, Tallack et al, 2012. They encode proteins involved in heme biosynthesis (Alad) (Desgardin et al, 2012, Tallack et al, 2012, cell cycle regulation (E2f2) (Tallack et al, 2009a), blood group antigens (Ermap/Scianna) (Ye et al, 2000) and other Klfs such as Klf10 (Funnell et al, 2012). Interestingly, Gene Ontogeny analysis of inversely regulated genes using the Database for Annotation, Visualization and Integrated Discovery (DAVID) v6.8 (Dennis et al, 2003) shows enrichment for genes involved in positive or negative regulation of cell size and cell growth, but not for other aspects of terminal erythroid cell differentiation ( Figure 5.5B).…”