Wnt signaling induces transcription, spatial proximity, and translocation of fusion gene partners in human hematopoietic cells

Abstract

Key Points• Wnt/b-catenin signaling increases ETO and Runx1 transcription in human hematopoietic progenitors.• Wnt/b-catenin signaling enhances spatial proximity of ETO and RUNX1 genes and induces the generation of a recurrent translocation event.Chromosomal translocations are frequently associated with a wide variety of cancers, particularly hematologic malignancies. A recurrent chromosomal abnormality in acute myeloid leukemia is the reciprocal translocation t(8;21) that fuses RUNX1 and ETO genes. We report here that Wnt/b-catenin signaling increases the expression of ETO and RUNX1 genes in human hematopoietic progenitors. We found that b-catenin is rapidly recruited into RNA polymerase II transcription factories (RNAPII-Ser5) and that ETO and RUNX1 genes are brought into close spatial proximity upon Wnt3a induction. Notably, long-term treatment of cells with Wnt3a induces the generation a frequent RUNX1-ETO translocation event. Thus, Wnt/b-catenin signaling induces transcription and translocation of RUNX1 and ETO fusion gene partners, opening a novel window to understand the onset/ development of leukemia. (Blood. 2015;126(15):1785-1789) IntroductionOne of the most common chromosomal abnormalities in acute myeloid leukemia (AML) is the reciprocal translocation t(8;21)(q22;q22), which involves the RUNX1 (AML1) and the ETO (RUNX1T1) genes and produces a Runx1-ETO fusion transcript that inhibits Runx1-dependent transcriptional regulation. 1,2 Although RUNX1-ETO translocations could act as initiating events in hematopoietic stem cells (HSCs), after which leukemia clonally evolves through the acquisition of secondary mutations, 3,4 the molecular mechanism and cellular signals that drive the generation of the t(8;21) translocation remain to be elucidated.Although much has been learned in recent years about the onset or development of AML from studies examining Runx1 expression or function, [5][6][7][8] we are still far from a complete understanding of the cellular mechanisms controlling the transcription of its translocation partner, ETO.9-11 Considering that Wnt/b-catenin plays essential roles during the proliferation or differentiation of HSCs and that reactivation of b-catenin signaling is important for selfrenewal of leukemia stem cells, 12-14 we studied whether Wnt/ b-catenin signaling was involved in ETO expression and RUNX1-ETO fusion. Methods Human CD341 cells and cell lines Results and discussionAccording to the current assembly of the human genome (GRCh38), the ETO gene consists of 17 exons distributed over 148 kb ( Figure 1A The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 USC section 1734. For personal use only. on May 11, 2018. by guest www.bloodjournal.org From and its expression generates multiple messenger RNA (mRNA) isoforms by alternative splicing or the use of different promoters. [9][10][11] We searched for core TCF/LEF-binding elements (TBE: CTTTG)...

Concomitant AID Expression and BCL7A Loss Associates With Accelerated Phase Progression and Imatinib Resistance in Chronic Myeloid Leukemia

“…Our case supports the hypothesis that BCL7A deletion induces abnormal Wnt/β-catenin signaling, enhancing the potential for a chromosomal aberration and its persistence in our patient [510]. Loss of the tumor suppressor BCL7A may cooperate with AID activity in disease progression by causing aberrant cell cycle regulation [1].…”

“…The AID gene, located on chromosome 12p13, is associated with genomic instability and ensuing oncogenesis in various human malignancies including CML, AML, and ALL [345]. AID has several non-immunoglobulin targets, including PAX5 and BCL7A [36]; PAX5 can induce TKI resistance and CML progression via AID upregulation [3].…”

“…Specifically, BCL7B suppresses β-catenin expression, causing Wnt signaling inhibition [7]. Importantly, β-catenin deregulation in Wnt signaling is associated with genomic instability that can induce oncogenic translocations in T-cell lymphoma and AML [58]. In CML, β-catenin activation is observed in the AP or BC, and is believed to promote leukemic stem cell generation that facilitates disease progression [9].…”

Replication timing shapes the cancer epigenome and the nature of chromosomal rearrangements

“…In contrast as early-replicating loci are more interactive (Brown et al, 2008;Lieberman-Aiden et al, 2009), and therefore DNA breaks occurring in regions replicating in early S-phase are more likely to result in trans translocations. Our model is supported by studies that show copy number aberration breakpoints generally have the same replication timing and interact long-range (De and Michor, 2011), and that translocation partners are required to be within the same spatial area, transcription (Ugarte et al, 2015) or replication factory (Coll- Bastus et al, 2015), before translocation can occur. A pertinent example for prostate cancer is the TMPRSS2-ERG gene fusion that occurs in ~50-80% of all prostate cancer (Tomlins et al, 2005).…”

Alternative RUNX1 Promoter Regulation by Wnt/β-Catenin Signaling in Leukemia Cells and Human Hematopoietic Progenitors

“…Dependent on tissue context and developmental stage, different signaling pathways modulate Runx1 expression, including the retinoic acid (Tanaka et al, 1995), Notch (Burns et al, 2005), and more recently the Wnt/b-catenin signaling cascade (Wu et al, 2012;Wang et al, 2013;Ugarte et al, 2015). Interestingly, it has been observed that Tcf7, a member of the T-cell factor/lymphoid enhancing factor (TCF/LEF) family of proteins known to mediate Wnt/b-catenin signaling in the nucleus (Clevers and van de Wetering, 1997), is required for a transcriptional program in a mouse EML (Erythroid, Myeloid, and Lymphocytic) multipotential hematopoietic precursor cell-line to produce the alternative P2-proximal Runx1 mRNA isoform (Wu et al, 2012).…”