Differential requirements for the activation domain and FOG-interaction surface of GATA-1 in megakaryocyte gene expression and development - PubMed (original) (raw)

Differential requirements for the activation domain and FOG-interaction surface of GATA-1 in megakaryocyte gene expression and development

Andrew G Muntean et al. Blood. 2005.

Abstract

GATA1 is mutated in patients with 2 different disorders. First, individuals with a GATA1 mutation that blocks the interaction between GATA-1 and its cofactor Friend of GATA-1 (FOG-1) suffer from dyserythropoietic anemia and thrombocytopenia. Second, children with Down syndrome who develop acute megakaryoblastic leukemia harbor mutations in GATA1 that lead to the exclusive expression of a shorter isoform named GATA-1s. To determine the effect of these patient-specific mutations on GATA-1 function, we first compared the gene expression profile between wild-type and GATA-1-deficient megakaryocytes. Next, we introduced either GATA-1s or a FOG-binding mutant (V205G) into GATA-1-deficient megakaryocytes and assessed the effect on differentiation and gene expression. Whereas GATA-1-deficient megakaryocytes failed to undergo terminal differentiation and proliferated excessively in vitro, GATA-1s-expressing cells displayed proplatelet formation and other features of terminal maturation, but continued to proliferate aberrantly. In contrast, megakaryocytes that expressed V205G GATA-1 exhibited reduced proliferation, but failed to undergo maturation. Examination of the expression of megakaryocyte-specific genes in the various rescued cells correlated with the observed phenotypic differences. These studies show that GATA-1 is required for both normal regulation of proliferation and terminal maturation of megakaryocytes, and further, that these functions can be uncoupled by mutations in GATA1.

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Figures

Figure 1.

Figure 1.

Characterization of ΔneoΔHS Gata1 knockdown megakaryocytes. (A-B) Flow cytometric analysis of megakaryocytes cultured from wild-type or GATA-1 knockdown fetal liver cells stained with the anti-CD41 (A) or CD42 (B) antibody. (C) Following in vitro expansion, wild-type and GATA-1–deficient cells were enriched on a BSA gradient and AChE staining was performed to determine the purity of enriched cells. Images were obtained using a Leica DM4000B light microscope equipped with a 20×/0.04 objective lens (Cambridge, United Kingdom). Original magnification, ×200. Images were captured using a mounted Leica DFC320 camera and Leica Firecam version 1.4 software. (D) Ploidy analysis of BSA gradient-purified megakaryocytes was performed by flow cytometry of cells stained with PI. (E) Light microscopy of differentiated cells in culture. The arrow points to proplatelet forms. Images were obtained using a Zeiss Axiovert S100 inverted microscope equipped with a 20×/0.04 objective lens (Thornwood, NY). Original magnification, ×200. Images were captured with a Nikon Coolpix 990 digital camera (Tokyo, Japan).

Figure 2.

Figure 2.

Requirements for GATA-1 in megakaryocyte gene expression. (A) Affymetrix probe set hybridization results for 16 representative genes that were differentially affected by the absence of GATA-1. Highest levels of expression are depicted as yellow squares; the lowest levels or no expression are represented by black squares. (B) Quantitative real-time RT-PCR validation of 16 genes selected from the array data. Data were divided into the following groups: genes that were not significantly affected (P > .05, upper left), ones that were down-regulated 2- to 3-fold (P ranged from < .002 to .02, upper right), those that were reduced more than 5-fold (P < .001, lower left), and genes that were induced in the absence of GATA-1 (GATA-2 and Ets-1, P < .001; myc P < .05; myb P < .5; lower right). Fold changes of gene expression in the GATA-1 knockdown cells (yellow bars) are shown relative to the levels detected in wild-type cells (black bars: wild-type expression was set to 1). Means ± SD for 3 experiments are shown.

Figure 3.

Figure 3.

GATA-1s rescues proplatelet formation, but not the hyperproliferative phenotype. (A) Constructs used in this study. Wild-type or mutant GATA-1 cDNAs were introduced into the MIGR1 vector backbone, which includes an IRES-GFP cassette. (B) GATA-1 expression in the rescued population was determined by qRT-PCR. There was no statistically significant difference between full-length GATA-1 and GATA-1s expression in the reconstitutions, but there was a significant difference between GATA-1 and V205G expression (P < .02). Means ± SD for 3 experiments are shown. (C) Light microscopy for the generation of proplatelet forms by the rescued cells. Notable features include the presence of proplatelets in the GATA-1s rescued cells and the presence of very large megakaryocytes in the population expressing V205G. Original magnification × 320. Images were obtained as described in the legend of Figure 1E. (D) AChE-stained cytospins of an aliquot of the 3-day cultures. Note the presence of a very large AChE-stained megakaryocyte in the population expressing V205G. Original magnification × 200. Images were obtained as described in the legend of Figure 1C. (E) Cell surface expression of CD41 on megakaryocytes after 3 days of in vitro differentiation, assayed by flow cytometry.

Figure 4.

Figure 4.

Megakaryocyte genes fall into several classes based on their requirement for different GATA-1 functional domains. Quantitative RT-PCR analysis of expression of 10 genes in the different rescued populations. These genes fell into 4 classes: (A) genes rescued by wild-type GATA-1 and GATA-1s but not by V205G, (B) genes rescued by GATA-1 and both GATA-1s and V205G, (C) genes rescued by GATA-1 but not GATA-1s or V205G, and (D) genes not significantly affected by wild-type or either of the GATA-1 mutants. Expression in knockdown cells infected with the MIGR1 retrovirus (black bars, far left) was set to 1, whereas the fold changes observed in the wild-type (dark gray bars), GATA-1s (white bars) and V205G (light gray bars, far right) reconstitutions are shown. Means ± SD for 3 experiments are shown.

Figure 5.

Figure 5.

Model of the differential requirements for GATA-1 in megakaryocyte gene expression and development. Committed megakaryocyte progenitors (A) normally display limited proliferation. However, in the absence of GATA-1, or in the presence of GATA-1s, these progenitors hyperproliferate and produce a greater number of CD41+ megakaryocytes, which also express low levels of CD42 (B). In contrast, when the ability of GATA-1 to interact with FOG-1 is disrupted, progenitors expand to a lesser degree. Megakaryocytes then undergo repeated rounds of DNA synthesis without cell division (polyploidization) to generate a polyploid cell (C). Mutagenesis of GATA-1 did not affect the endomitosis of megakaryocytes. However, alterations in GATA-1 led to differential effects on terminal maturation. In the absence of GATA-1, or in the presence of the V205G mutant, terminal maturation was blocked. When GATA-1s was expressed, however, megakaryocytes produced proplatelet forms (D) and were similar to wild-type cells in morphology and gene expression.

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