Mutation in erythroid specific transcription factor KLF1 causes Hereditary Spherocytosis in the Nan hemolytic anemia mouse model

Abstract

KLF1 regulates definitive erythropoiesis of red blood cells by facilitating transcription through high affinity binding to CACCC elements within its erythroid specific target genes including those encoding erythrocyte membrane skeleton (EMS) proteins. Deficiencies of EMS proteins in humans lead to the hemolytic anemia Hereditary Spherocytosis (HS) which includes a subpopulation with no known genetic defect. Here we report that a mutation, E339D, in the second zinc finger domain of KLF1 is responsible for HS in the mouse model Nan. The causative nature of this mutation was verified with an allelic test cross between Nan/+ and heterozygous Klf1(+/-) knockout mice. Homology modeling predicted Nan KLF1 binds CACCC elements more tightly, suggesting that Nan KLF1 is a competitive inhibitor of wild-type KLF1. This is the first association of a KLF1 mutation with a disease state in adult mammals and also presents the possibility of being another causative gene for HS in humans.

Erythroid phenotypes associated with KLF1 mutations

“…Interestingly, the two compound heterozygotes (p.S270X::p.K332Q) displayed very high HbF levels (22.1% and 30.9%). In addition, these individuals had high levels of zinc protoporphyrin in their circulation; this was also observed in the Nan mouse [16][17] ( Figure 3). …”

“…Remarkably, an ethylnitrosourea-induced mutation in the homologous position in mouse KLF1 causes the dominant Nan (neonatal anemia) phenotype. [16][17] Heterozygous Nan/+ mice displayed hereditary spherocytosis and severe hemolytic anemia. Expression of erythrocyte membrane skeleton proteins and β-globin was reduced, but embryonic globins were present at aberrantly high levels (Figures 1 and 3).…”

“…For instance, missense mutations of critical residues in the zinc finger domains of KLF1 affect its DNA binding properties and may have a dominant phenotype, as exemplified by the p.E325K mutation in the CDA patients 15 and the p.E339D mutation in the Nan mouse. [16][17] In contrast, the p.K332Q mutation, which also affects the DNA binding properties of KLF1, does not have a dominant effect. 18 Genome-wide assessment of the in vivo binding sites of these mutant KLF1 proteins may help to understand the phenotypic variability.…”

Ten novel mutations in the erythroid transcription factor KLF1 gene associated with increased fetal hemoglobin levels in adults

“…These include the Lutheran blood group, 14 congenital dyserythropoietic anemia, 20 hereditary spherocytosis, 21 high levels of zinc protoporphyrin, 10 HPFH in two families, 9,10 and most recently, borderline increases in Hb A2 levels. 22 The UK population is ethnically diverse and our laboratory receives requests for hemoglobinopathy investigations for individuals who originate from all the malarial regions of the world.…”

Erythropoiesis and globin switching in compound Klf1::Bcl11a mutant mice

“…23 The ethylnitrosurea-induced mouse mutant Nan (neonatal anemia) carries a missense mutation, p.E339D, in the homologous position of mouse KLF1. 39,40 This mutation causes a dominant hemolytic anemia, with markedly increased expression of embryonic globins in adult Nan animals. 40 Collectively, these data support a model in which KLF1 activates b-globin expression and suppresses the embryonic/fetal b-like globin genes.…”