GATA Factor-Regulated Samd14 Enhancer Confers Red Blood Cell Regeneration and Survival in Severe Anemia

Abstract

An enhancer with amalgamated E-box and GATA motifs (+9.5) controls expression of the regulator of hematopoiesis GATA-2. While similar GATA-2-occupied elements are common in the genome, occupancy does not predict function, and GATA-2-dependent genetic networks are incompletely defined. A "+9.5-like" element resides in an intron of Samd14 (Samd14-Enh) encoding a sterile alpha motif (SAM) domain protein. Deletion of Samd14-Enh in mice strongly decreased Samd14 expression in bone marrow and spleen. Although steady-state hematopoiesis was normal, Samd14-Enh^-/- mice died in response to severe anemia. Samd14-Enh stimulated stem cell factor/c-Kit signaling, which promotes erythrocyte regeneration. Anemia activated Samd14-Enh by inducing enhancer components and enhancer chromatin accessibility. Thus, a GATA-2/anemia-regulated enhancer controls expression of an SAM domain protein that confers survival in anemia. We propose that Samd14-Enh and an ensemble of anemia-responsive enhancers are essential for erythrocyte regeneration in stress erythropoiesis, a vital process in pathologies, including β-thalassemia, myelodysplastic syndrome, and viral infection.

Keywords: GATA-2; anemia; enhancer; erythroid; hematopoiesis; regeneration.

Figure 1. Samd14-Enh Regulates Samd14 Transcription in Hematopoietic Cells and Tissues In Vivo

(A) ChIP-seq of GATA-2 (GSE29193) and Scl/TAL-1 (GSE36029) occupancy at Samd14 in mouse G1E proerythroblast cells (Trompouki et al., 2011). (B) Sequence validation and genotyping of a 33 base pair deletion in intron 1 of Samd14 (left). Genotypes of offspring from heterozygous matings (right). (C) Relative Samd14 mRNA and primary transcript in bone marrow and brain cerebellum from WT and Samd14-Enh^-/- mice (n = 3). (D) Relative Samd14 mRNA expression in FACS-purified L^-S⁺K⁺, CMP, GMP and MEP populations from bone marrow (n = 3). (E) Flow cytometric analysis of the percentage of CMP, GMP and MEP populations in WT and Samd14-Enh^-/- total bone marrow, using Lin^- Sca^-Kit⁺ cells (n = 3). (F) Representative flow cytometric plot of CD71 and Ter119 staining from bone marrow of WT and Samd14-Enh^-/- mice. (G) Relative expression of Kit, Ptpn11, Rab1 and SlamF1 in WT and Samd14-Enh^-/- cells from bone marrow (n = 3). (H) Representative flow cytometric plot of CD71 and Ter119 staining from WT and Samd14-Enh^-/- cells isolated from E14.5 fetal liver and expanded in vitro for 3 days. (I) Hematologic parameters (white blood cells (WBC), red blood cells (RBC), hemoglobin, platelets) from WT (n = 8) and Samd14-Enh^-/- (n = 10) mice. Statistical significance represented by mean +/- SEM.; **p<0.01, ***p<0.001.

Figure 2. Samd14-Enh Confers Survival in Severe Anemia

(A) Kaplan-Meier survival curve of WT and Samd14-Enh^-/- mice following two doses (one per day) of 60 mg/kg PHZ (n = 16 in each group). (B) Spleen weight of WT and Samd14-Enh^-/- mice 3 days after treatment with vehicle (PBS) or PHZ (100 mg/kg). (C) Hematologic parameters of WT (n = 6) and Samd14-Enh^-/- (n = 6) mice following PHZ treatment (100 mg/kg). (D) Quantification of Burst Forming Unit-Erythroid (BFU-E) colonies 5 days after plating splenic cells (1 × 10⁵) from mice treated with PHZ for 0, 24, 48, or 72 hours (h) in methylcellulose containing Epo, SCF, IL-3, and IL-6. (E) Quantification of BFU-E colonies 5 days after plating, and Colony Forming Unit-Erythroid (CFU-E) colonies 2 days after plating, 1 × 10⁵ cells from mice treated with PHZ for 0 or 72 h in Epo-containing methylcellulose. Statistical significance represented by mean +/- SEM.; *p<0.05. **p<0.01, ***p<0.001.

Figure 3. Samd14-Enh Mediates Anemia-Dependent Samd14 Expression

(A) Samd14 mRNA levels in WT and Samd14-Enh^-/- spleen and brain from vehicle-treated and PHZ-treated animals (n = 3 in each group). (B) Targeted mass spectrometry using three distinct Samd14 peptides in WT and Samd14-Enh^-/- spleen from vehicle-treated and PHZ-treated animals. Peptide 1 - SASQESTLSDDSTPPSSSPK, Peptide 2 - SLDEDEPPPSPLAR, Peptide 3 - QVDGPQLLQLDGSK. (C) Western blotting of Samd14 in WT and Samd14-Enh^-/- spleen from vehicle- and PHZ-treated animals. (D) Western blot analysis of Samd14 in G1E cells retrovirally infected with an shRNA targeting Samd14 mRNA (shSamd14) relative to control shRNA (shControl). (E) Top, Western blotting of GATA-2 in WT and Samd14-Enh^-/- spleen from vehicle- and PHZ-treated animals. Bottom, densitometric quantitation (n = 3). (F) (top) Experimental strategy to test allele-specific transcription changes in Samd14-Enh and Gata2 +9.5 heterozygous spleen following a 3 d PHZ treatment. Forward primers exclusively anneal to WT or mutant Enh^- alleles of primary transcripts, and reverse primers anneal to both alleles. (bottom) Allele-specific qRT-PCR analysis of Samd14 and Gata2 primary transcripts from Samd14-Enh^+/- and Gata2 +9.5^+/- mice, respectively, in control (n = 3) and PHZ-treated (n = 4) spleen. (G) Hematocrit (left) and Samd14 mRNA (right) in WT and Samd14-Enh^-/- spleen from control and phlebotomized animals (n = 4 in each group). (H) Samd14 mRNA levels in total spleen at 2, 4, 6, 8, 10, 12, and 14 days post-transplantation (n =2). (I) Gata2 mRNA levels in total spleen at 2, 4, 6, 8, 10, 12, and 14 days post-transplantation (n = 2). Statistical significance represented by mean +/- SEM.; *p<0.05 ***p<0.001. (Related to Figure 3)

Figure 4. Samd14-Enh opposes anemia-dependent apoptosis of CD71⁺Ter119^-Kit⁺splenic erythroid progenitor cells

(A) Representative flow cytometric analysis of CD71 and Ter119 staining in WT and Samd14-Enh^-/- spleen following PHZ treatment. (B) Quantitation of the percentage (top) and cell number (bottom) per spleen of CD71⁺Ter119^- and Ter119+ cells in WT and Samd14-Enh^-/- mice. (C) Relative Samd14 mRNA levels in FACS-purified cells from WT spleen and Samd14-Enh^-/- spleen (n = 3). (D) Relative Gata2 mRNA levels in FACS-purified cells from WT spleen and Samd14-Enh-/- spleen (n = 3). (E) Relative Gata1 mRNA levels in FACS-purified cells from WT spleen and Samd14-Enh-/- spleen (n = 3). (F) Relative Kit mRNA levels in FACS-purified cells from WT spleen and Samd14-Enh^-/- spleen (n = 3). (G) Relative Scl/TAL1 mRNA levels in FACS-purified cells from WT spleen and Samd14-Enh^-/- spleen. (H) Flow cytometric analysis of percentages of c-Kit⁺CD71⁺ cells within the Ter119^- population of PHZ-treated spleen (n = 4). (I) Relative Samd14, Gata2, and Scl/TAL1 mRNA levels in FACS-purified cells from WT spleen and Samd14-Enh^-/- spleen. (J) Quantitation of percentages of live (DRAQ7^-AnnexinV^-), early apoptotic (DRAQ7^-AnnexinV⁺), late apoptotic (DRAQ7⁺AnnexinV⁺), and dead (DRAQ7⁺AnnexinV^-) cells in CD71⁺c-Kit⁺Ter119^- cells in PHZ-treated WT and Samd14-Enh^-/- spleen (n = 4). Statistical significance represented by mean +/- SEM.; *p<0.05, ***p<0.001.

Figure 5. Samd14-Enh Promotes Anemia-Dependent SCF/c-Kit Signaling

(A) Flow cytometric analysis of Ter119-depleted WT control spleen stained with CD71 and c-Kit (left) and quantitation of pAKT in the CD71⁺Kit⁺ cell population. All histograms were normalized to the percentage of the maximal cell number. (B) Flow cytometric analysis of WT PHZ-treated spleen stained with CD71 and c-Kit (top left) and histograms of pAKT in CD71⁺Kit^- cells (bottom left), and pAKT and pERK in CD71⁺Kit⁺ cells (right). (C) Flow cytometric analysis of WT and Samd14-Enh^-/- PHZ-treated spleen stained with CD71 and c-Kit (left) and comparative histogram plots of pAKT and pERK in WT and Samd14-Enh^-/- CD71⁺Kit⁺ SCF-stimulated cells (right). (D) Quantitation of pAKT and pERK MFI in WT and Samd14-Enh^-/- cells (n = 3). Statistical significance represented by mean +/- SEM.; *p<0.05; **p<0.01.

Figure 6. GATA-2-Regulated, Anemia-Responsive +9.5-Like Composite Elements

(A) Models of how anemia impacts transcription of loci containing +9.5-like composite elements. Model 1 assumes that anemia-responsive enhancers are accessible in the absence of anemia, and anemia increases transcription post-chromatin accessibility. Model 2 assumes that anemia increases chromatin accessibility as a regulatory step in anemia-dependent transcriptional activation. (B) Formaldehyde-assisted isolation of regulatory elements (FAIRE) analysis using 4 primer sets at Samd14 in WT cells from vehicle- or PHZ-treated spleen (n = 4). (C) FAIRE analysis using 4 primer sets at Samd14 in Samd14-Enh^-/- cells from vehicle- or PHZ-treated spleen (n = 3). (D) Diagrams illustrating the intronic location of +9.5-like composite elements (arrow) in Bcl2l1, Sox6, Trip4, Bag2, Inpp5d and Pstpip1 (kb, kilobases). (E) GATA-2 ChIP in G1E cells at composite elements. The Necdin promoter served as a negative control (n = 3). (F) Relative mRNA expression at loci containing +9.5-like elements in control and PHZ-treated CD71⁺Ter119^- cells from spleen. (G) Relative mRNA expression at loci containing +9.5-like elements in CD71⁺Ter119^-c-Kit⁺ cells from spleens of control and PHZ-treated mice. (H) FAIRE analysis of +9.5-like loci in CD71⁺Ter119^- cells isolated from vehicle- or PHZ-treated spleen. Pol2ra promoter represents a control with constitutively open chromatin, while the Necdin promoter represents a control with constitutively closed chromatin (n = 3). (I) Relative Samd14 expression in splenic cells treated with Vehicle or Epo (2U/mL) for 4 hours (n = 6) from PHZ-treated WT and Samd14-Enh^-/- mice. Statistical significance represented by mean +/- SEM.; *p<0.05 **p<0.01***p<0.001.

Figure 7. GATA-2- and Anemia-Activated (G2A) Enhancers that Oppose Lethal Anemia Define a Vital Sector of the Hematopoietic Stem and Progenitor Cell Cistrome

(A) Anemia upregulates Samd14 and Gata2 expression in splenic erythroid progenitors, which conforms to a Type I coherent feed-forward loop. Targeted deletion of the intronic GATA-2-regulated Samd14-Enh enhancer disrupts this mechanism, impairs red blood cell regeneration in the context of anemic stress and is lethal. (B) Anemia induces expression of additional genes containing +9.5-like enhancers. Bcl2l1 and Sox6 have established functions to promote stress erythropoiesis (Dumitriu et al., 2010; Koulnis et al., 2012).