The stem cell factor SALL4 is an essential transcriptional regulator in mixed lineage leukemia-rearranged leukemogenesis

Abstract

BackgroundThe stem cell factor spalt-like transcription factor 4 (SALL4) plays important roles in normal hematopoiesis and also in leukemogenesis. We previously reported that SALL4 exerts its effect by recruiting important epigenetic factors such as DNA methyltransferases DNMT1 and lysine-specific demethylase 1 (LSD1/KDM1A). Both of these proteins are critically involved in mixed lineage leukemia (MLL)-rearranged (MLL-r) leukemia, which has a very poor clinical prognosis. Recently, SALL4 has been further linked to the functions of MLL and its target gene homeobox A9 (HOXA9). However, it remains unclear whether SALL4 is indeed a key player in MLL-r leukemia pathogenesis.MethodsUsing a mouse bone marrow retroviral transduction/ transplantation approach combined with tamoxifen-inducible, CreERT2-mediated Sall4 gene deletion, we studied SALL4 functions in leukemic transformation that was induced by MLL-AF9—one of the most common MLL-r oncoproteins found in patients. In addition, the underlying transcriptional and epigenetic mechanisms were explored using chromatin immunoprecipitation (ChIP) sequencing (ChIP-Seq), mRNA microarray, qRT-PCR, histone modification, co-immunoprecipitation (co-IP), cell cycle, and apoptosis assays. The effects of SALL4 loss on normal hematopoiesis in mice were also investigated.ResultsIn vitro and in vivo studies revealed that SALL4 expression is critically required for MLL-AF9-induced leukemic transformation and disease progression in mice. Loss of SALL4 in MLL-AF9-transformed cells induced apoptosis and cell cycle arrest at G1. ChIP-Seq assay identified that Sall4 binds to key MLL-AF9 target genes and important MLL-r or non-MLL-r leukemia-related genes. ChIP-PCR assays indicated that SALL4 affects the levels of the histone modification markers H3K79me2/3 and H3K4me3 at MLL-AF9 target gene promoters by physically interacting with DOT1-like histone H3K79 methyltransferase (DOT1l) and LSD1/KDM1A, and thereby regulates transcript expression. Surprisingly, normal Sall4 f/f/CreERT2 mice treated with tamoxifen or vav-Cre-mediated (hematopoietic-specific) Sall4 −/− mice were healthy and displayed no significant hematopoietic defects.ConclusionsOur findings indicate that SALL4 critically contributes to MLL-AF9-induced leukemia, unraveling the underlying transcriptional and epigenetic mechanisms in this disease and suggesting that selectively targeting the SALL4 pathway may be a promising approach for managing human MLL-r leukemia.Electronic supplementary materialThe online version of this article (10.1186/s13045-017-0531-y) contains supplementary material, which is available to authorized users.

Thalidomide Inhibits Human iPSC Mesendoderm Differentiation by Modulating CRBN-dependent Degradation of SALL4

“…The data here suggest that thalidomide-and IMiD-mediated degradation of SALL4 disrupts FOXF1 and SOX17 expression, suggesting FOXF1 and SOX17 may be directly or indirectly regulated by SALL4 at the transcriptional level. To-date, three studies have examined SALL4 by ChIP-Seq to identify its transcriptional targets [57][58][59] . Two separate studies (in mESCs 58 and human CD34+ cells 57 ) demonstrated that SALL4 can bind to the SOX17 promoter 57,58 .…”

“…These data point to a direct interaction between SALL4 and SOX17 that agrees with the SALL4-dependent inhibition of SOX17 expression by thalidomide observed here. Comparatively little is known about transcriptional or functional connections between SALL4 and FOXF1, and only one ChIP-Seq study (out of the three mentioned above) identified that in mouse cells, Sall4 occupies the Foxf1 promoter 59 . Conversely, ChIP-seq of mouse tissue discovered a Gli3 and Tbx5 binding site in the promoter of Foxf1 61 .…”

<p>Sal-Like Protein 4 Transcription Factor: A Significant Diagnostic Biomarker Involved in Childhood ALL Resistance and Relapse</p>

“…SALL4 is a zinc-finger transcriptional factor and a stem cell gene that plays a critical role in the maintenance and selfrenewal of embryonic and hematopoietic stem cells and its expression is normally restricted to embryonic and somatic stem cells. 7,8 While SALL4 plays a key role in hematopoietic differentiation, it is also overexpressed in various human cancers, including hematologic malignancies and subsets of liver, gastric, lung, endometrial, and breast cancers. 25,26 In addition, multiple studies have demonstrated that higher expression levels of SALL4 is associated with drug resistance in some malignancies.…”

“…2,5 Recently, there has been an accumulation of evidence indicating that Sal-like protein 4 transcription factor (SALL4), a stem cell gene, is an oncogene that has a central function in carcinogenesis, chemotherapeutic resistance, and relapse in a variety of cancers. [6][7][8] In some cancers, SALL4 can promote the expression of a subfamily of ABC transporters, through direct or indirect interaction with the promoter, and affect sensitivity to the chemotherapy drug. 9 As a member of the Sal-like (SALL) gene family (SALL1 to SALL4), SALL4 encodes for a C2H2 zinc-finger transcription factor.…”

Function of the Stem Cell Transcription Factor SALL4 in Hematopoiesis

“…These findings indicate that the role of SALL4 and HOXA9 in normal hematopoiesis is to maintain the HSPCs in an undifferentiated stage with self-renewal capacity [37]. Very recently, the roles of SALL4 in normal hematopoiesis have been further explored using conditional gene targeting approaches in mice [46]. Unexpectedly, wild type Sall4 f/f /CreER T2 mice treated with tamoxifen or vav-Cre-mediated (hematopoietic-specific) Sall4 −/− mice were all healthy and displayed no significant hematopoietic defects, which contrasts to previous findings from human CD34+ cell studies.…”