Novel role for EKLF in megakaryocyte lineage commitment

Abstract

Megakaryocytes and erythroid cells are thought to derive from a common progenitor during hematopoietic differentiation. Although a number of transcriptional regulators are important for this process, they do not explain the bipotential result. We now show by gain-and loss-offunction studies that erythroid Krü ppellike factor (EKLF), a transcription factor whose role in erythroid gene regulation is well established, plays an unexpected directive role in the megakaryocyte lineage. EKLF inhibits the formation of megakaryocytes while at the same time stimulating erythroid differentiation. Quantitative examination of expression during hematopoiesis shows that, unlike genes whose presence is required for establishment of both lineages, EKLF is uniquely down-regulated in megakaryocytes after formation of the megakaryocyte-erythroid progenitor. Expression profiling and molecular analyses support these observations and suggest that megakaryocytic inhibition is achieved, at least in part, by EKLF repression of Fli-1 message levels. IntroductionHematopoiesis is the process by which a self-renewing population of stem cells provide a continuous replenishment of differentiated blood cells by generating progeny with sequentially altered gene expression patterns. [1][2][3] Identification of these cells has relied on selective enrichment by cell-surface markers combined with culture and in vivo cellular assays that enable detection of cells at specific stages of differentiation. Although stem cells are multipotent, individual steps of subsequent differentiative decisions are performed by a series of simpler, even bipotential, decisions whereby one cell type gives rise to 2 or 3 descendants of differing character. 4 This has led to a commonly accepted pattern of parent and progeny relations, 2 although variations of it have recently been suggested 5 (but see Forsberg et al 6 ).A large number of genetic, cellular, and gene expression studies point to the critical importance of cytokine pathways 7 and expression patterns of transcription factors 1,[8][9][10] for establishing and maintaining steady state numbers of lymphoid, myeloid, and erythroid cells that, at the same time, can respond quickly to changes in the organismal environment and increase or decrease the cellularity of specific blood cell types. The megakaryocyte and erythrocyte lineages are proposed to derive from a common precursor, the megakaryocyte-erythroid progenitor (MEP) 4,11,12 (reviewed in Pang et al 13 ). Strikingly, these 2 lineages share a number of commonalities with respect to transcription factors that are absolutely required (eg, GATA1,14,15 FOG1, 16 SCL,17, ). At the same time, the protein partners that form with these factors as differentiation proceeds can be significantly different between lineages. 20 However, because these factors are all positively required for both lineages, we are still left with an incomplete picture of how these lineages are differentially established during hematopoiesis. 13 Erythroid Krüppel-like factor (EKLF; KLF1 21 ) is ...

Functional Interactions between Erythroid Kruppel-like Factor (EKLF/KLF1) and Protein Phosphatase PPM1B/PP2Cβ

“…Given the restricted tissue specificity and temporal regulation of EKLF expression in vivo, it is possible that post-translational regulation and/or protein interactions govern which of the opposing roles EKLF plays in the cell divisions that lead to terminal erythroid differentiation. In addition, EKLF is expressed over a period that encompasses several different stages in hematopoiesis (21,22). Although Pilon et al (2) have demonstrated that EKLF binding to various sites on the genome is dynamic and dependent on differentiation stage, it is not clear which signals trigger these changes.…”

Non-random subcellular distribution of variant EKLF in erythroid cells

“…Although EKLF predominantly serves as a transcriptional activator, protein-protein interactions between EKLF and corepressors, such as mSin3A and HDAC1 [21], can result in the stage-specific repression of EKLF target genes [22]. Recent studies demonstrate that EKLF plays a novel role in negatively regulating megakaryocyte lineage commitment [23]. EKLF is also posttranslationally modified by phosphorylation [24], acetylation [16], ubiquitylation [25], and sumoylation [26].…”

The mammalian zinc finger transcription factor Krüppel‐like factor 3 (KLF3/BKLF)

“…Alternatively, KLF1 may use these repressors to silence conflicting differentiation programs to ensure that progenitor cells follow the erythropoietic lineage. In support of this, KLF1 null cells, which express neither KLF3 nor KLF8, show increased promiscuity toward the megakaryocyte lineage (43)(44)(45). The exact contribution of this KLF network to erythroid development will be revealed by comparative analysis of microarray and ChIP-Seq data from KLF1, KLF3, and KLF8 null tissue.…”