Erythroid Krüppel-like factor (EKLF) is an erythroid zinc finger protein identified by its interaction with a CACCC sequence in the ␤-globin promoter, where it establishes local chromatin structure permitting ␤-globin gene transcription. We sought to identify other EKLF target genes and determine the chromatin status of these genes in the presence and absence of EKLF. We identified alpha hemoglobin-stabilizing protein (AHSP) by subtractive hybridization and demonstrated a 95 to 99.9% reduction in AHSP mRNA and the absence of AHSP in EKLF-deficient cells. Chromatin at the AHSP promoter from EKLF-deficient cells lacked a DNase I hypersensitive site and exhibited histone hypoacetylation across the locus compared to hyperacetylation of wild-type chromatin. Wild-type chromatin demonstrated a peak of EKLF binding over a promoter region CACCC box that differs from the EKLF consensus by a nucleotide. In mobility shift assays, the AHSP promoter CACCC site bound EKLF in a manner comparable to the ␤-globin promoter CACCC site, indicating a broader recognition sequence for the EKLF consensus binding site. The AHSP promoter was transactivated by EKLF in K562 cells, which lack EKLF. These results support the hypothesis that EKLF acts as a transcription factor and a chromatin modulator for the AHSP and ␤-globin genes and indicate that EKLF may play similar roles for other erythroid genes.

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Understanding mechanisms controlling expression of the ␣-spectrin gene is important for understanding erythropoiesis, membrane biogenesis, and spectrinlinked hemolytic anemia. We showed previously that a minimal ␣-spectrin promoter directed low levels of expression only in early erythroid development, indicating elements outside the promoter are required for expression in adult erythrocytes. Addition of noncoding exon 1 and intron 1 conferred a 10-fold increase in activity in reporter gene assays. In this report, we used a transgenic mouse model to show that addition of exon 1 and intron 1 to the ␣-spectrin promoter conferred tissue-specific expression of a linked A ␥-globin gene in erythroid cells at all developmental stages. Expression was nearly position-independent, as 21 of 23 lines expressed the transgene, and ␥-globin protein was present in 100% of erythrocytes, indicating uniform expression. Additional in vivo studies revealed that exon 1 functions as an insulator with barrier-element activity. Chromatin immunoprecipitation assays demonstrated that this region was occupied by the upstream stimulatory factors 1/2 (USF1/USF2), similar to the well-characterized chicken HS4 insulator. These data identify the first barrier element described in an erythrocyte membrane protein gene and indicate that exon 1 and intron 1 are excellent candidate regions for mutations in patients with spectrin-linked hemolytic anemia. (Blood. 2009;113:1547-1554) IntroductionSpectrin is the major structural component of the erythrocyte membrane skeleton that maintains cellular shape, regulates the lateral mobility of integral membrane proteins, and provides structural support for the lipid bilayer. 1 It is composed of 2 subunits, ␣-and ␤-spectrin, encoded by separate genes. 1,2 Throughout erythropoiesis, there are significant changes in the synthesis, expression, and membrane assembly of spectrin. Early in erythropoiesis, ␣-spectrin is synthesized in great excess, 3,4 a process controlled at the transcriptional level. 3,5,6 The molecular mechanisms that regulate the erythroid tissue-specific and developmental stage-specific expression of ␣-spectrin, including the mechanisms that control the increase in ␣-spectrin gene transcription to high levels during the early stages of erythropoiesis, are unknown.In the mature erythrocyte, quantitative and qualitative disorders of ␣-spectrin have been associated with inherited hemolytic anemias, including hereditary spherocytosis (HSp), hereditary elliptocytosis (HE), and hereditary pyropoikilocytosis (HPP). [7][8][9][10][11][12] In most recessive HSp and many HPP patients, there is a defect in ␣-spectrin mRNA accumulation associated with spectrin deficiency. 7,13,14 With a few rare exceptions, the cause of the defect in ␣-spectrin expression in erythrocytes of these patients is unknown, even after nucleotide sequence analysis of the exons corresponding to the ␣-spectrin coding region and the minimal promoter region. 15,16 Our previous studies demonstrated that a minimal ␣-spectrin promoter dire...