SALL2 is a poorly characterized transcription factor that belongs to the Spalt‐like family involved in development. Mutations on SALL2 have been associated with ocular coloboma and cancer. In ...cancers, SALL2 is deregulated and is proposed as a tumor suppressor in ovarian cancer. SALL2 has been implicated in stemness, cell death, proliferation, and quiescence. However, mechanisms underlying roles of SALL2 related to cancer remain largely unknown. Here, we investigated the role of SALL2 in cell proliferation using mouse embryo fibroblasts (MEFs) derived from Sall2−/− mice. Compared to Sall2+/+ MEFs, Sall2−/− MEFs exhibit enhanced cell proliferation and faster postmitotic progression through G1 and S phases. Accordingly, Sall2−/− MEFs exhibit higher mRNA and protein levels of cyclins D1 and E1. Chromatin immunoprecipitation and promoter reporter assays showed that SALL2 binds and represses CCND1 and CCNE1 promoters, identifying a novel mechanism by which SALL2 may control cell cycle. In addition, the analysis of tissues from Sall2+/+ and Sall2−/− mice confirmed the inverse correlation between expression of SALL2 and G1‐S cyclins. Consistent with an antiproliferative function of SALL2, immortalized Sall2−/− MEFs showed enhanced growth rate, foci formation, and anchorage‐independent growth, confirming tumor suppressor properties for SALL2. Finally, cancer data analyses show negative correlations between SALL2 and G1‐S cyclins’ mRNA levels in several cancers. Altogether, our results demonstrated that SALL2 is a negative regulator of cell proliferation, an effect mediated in part by repression of G1‐S cyclins’ expression. Our results have implications for the understanding and significance of SALL2 role under physiological and pathological conditions.
SALL2 inhibits cell proliferation by repressing G1‐to S‐phase cell cycle transition. This effect of SALL2 is associated with the transcriptional repression of cyclins D1 and E1.
SALL2, also known as Spalt-like transcription factor 2, is a member of the SALL family of transcription factors involved in development and conserved through evolution. Since its identification in ...1996, findings indicate that SALL2 plays a role in neurogenesis, neuronal differentiation and eye development. Consistently, SALL2 deficiency associates with neural tube defects and coloboma, a congenital eye disease. Relevant to cancer, clinical studies indicate that SALL2 is deregulated in various cancers and is a specific biomarker for Synovial Sarcoma. However, the significance of SALL2 deregulation in this disease is controversial. Here, we present and discuss all available information about SALL2 since its discovery, including isoforms, regulation, targets and functions. We specifically discuss the role of SALL2 in the regulation of cell proliferation and survival within the context of the identified target genes, its interaction with viral oncogenes, and its association with the TP53 tumor suppressor and MYC oncogene. Special attention is given to p53-independent SALL2 regulation of pro-apoptotic genes BAX and PMAIP1, and the implication of these findings on the apoptotic response of cancer cells to therapy. Understanding SALL2 function and the molecular mechanisms governing its expression and activity is critical to comprehend why and how SALL2 could contribute to disease. This knowledge will open new perspectives for the development of molecular targeted approaches in disease.
SALL2 is a transcription factor involved in development and disease. Deregulation of SALL2 has been associated with cancer, suggesting that it plays a role in the disease. However, how SALL2 is ...regulated and why is deregulated in cancer remain poorly understood. We previously showed that the p53 tumor suppressor represses SALL2 under acute genotoxic stress. Here, we investigated the effect of Histone Deacetylase Inhibitor (HDACi) Trichostatin A (TSA), and involvement of Sp1 on expression and function of SALL2 in Jurkat T cells. We show that SALL2 mRNA and protein levels were enhanced under TSA treatment. Both, TSA and ectopic expression of Sp1 transactivated the SALL2 P2 promoter. This transactivation effect was blocked by the Sp1-binding inhibitor mithramycin A. Sp1 bound in vitro and in vivo to the proximal region of the P2 promoter. TSA induced Sp1 binding to the P2 promoter, which correlated with dynamic changes on H4 acetylation and concomitant recruitment of p300 or HDAC1 in a mutually exclusive manner. Our results suggest that TSA-induced Sp1-Lys703 acetylation contributes to the transcriptional activation of the P2 promoter. Finally, using a CRISPR/Cas9 SALL2-KO Jurkat-T cell model and gain of function experiments, we demonstrated that SALL2 upregulation is required for TSA-mediated cell death. Thus, our study identified Sp1 as a novel transcriptional regulator of SALL2, and proposes a novel epigenetic mechanism for SALL2 regulation in Jurkat-T cells. Altogether, our data support SALL2 function as a tumor suppressor, and SALL2 involvement in cell death response to HDACi.
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•In Jurkat T cells, SALL2 gene is regulated by an epigenetic mechanism that involves p300, HDAC1 and Sp1.•Sp1 directly binds to proximal regions of SALL2-P2 promoter, and its binding increased by Trichostatin A treatment.•TSA and other FDA-approved HDACi upregulate SALL2 expression in Jurkat T cells.•SALL2 is required for the cell death response to TSA treatment in Jurkat T cells.
Abstract
Spalt-like proteins are Zinc finger transcription factors present from C. elegans to vertebrates, with critical roles in development. In vertebrates, four paralogues have been identified ...(Sall1-4), with Sall2 being the most dissimilar member of the family. Sall2 has shown to be important for brain and eye development and–unlike its vertebrate paralogues–it has also been proposed as a tumor suppressor. Sall2 activity promotes cell cycle arrest and cell death and its expression is downregulated in several types of cancer. Despite this, very few Sall2 transcriptional targets have been identified until date.
In agreement with previous reports, characterization of primary and immortalized mouse embryonic fibroblasts (MEFs) showed a proliferative advantage of isogenic Sall2-/- vs Sall2+/+ cells. In order to identify the molecular mechanisms underlying Sall2 function during cell cycle, iMEFs were synchronized at G2/M phase with nocodazole. Flow cytometry, Western blot, and qRT-PCR analyses were performed after nocodazole release. In accordance with the role of Sall2 in promoting cell cycle arrest, a more rapid progression from G2/M to G1/S was noticed in Sall2-deficient cells, which correlates with an increased expression of Cyclin D1 (Ccnd1) and Cyclin E1 (Ccne1). Similar results were obtained in HEK293 and SKOV3 human cell lines, suggesting that Sall2 controls cell cycle progression by downregulating G1-S cyclins. Sall2-mediated repression of CCND1 and CCNE1 was confirmed by luciferase reporter assays. In addition, bioinformatic analysis led to the identification of several putative Sall2 binding sites within CCND1 and CCNE1 promoters. Sall2 binding to CCND1 and CCNE1 promoters was demonstrated by chromatin immunoprecipitation. Analysis of tissues from Sall2+/+ and Sall2-/- mice confirmed the inverse correlation between expression of SALL2 and G1-S cyclins.
Importantly, the same correlation was found in different types of tumor by analyzing publicly available databases, suggesting that Sall2-Cyclin D1-Cyclin E1 axis could be downregulated in cancer. Thus, we have identified two novel Sall2 transcriptional targets at G1-S transition.
Altogether, our findings support the role of Sall2 as a tumor suppressor, by acting as a transcriptional repressor during cell cycle.
Citation Format: Viviana E. Hermosilla, David E. Escobar, Matias I. Hepp, Elizabeth N. Riffo, Ginessa Salgado, Violeta Morin, Mario Galindo, Ariel F. Castro, Roxana Pincheira, Roxana Pincheira. Sall2 transcription factor: A novel regulator of G1-S cyclins abstract. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A32.
The cell type-specific expression of key transcription factors is central to development and disease. Brachyury/T/TBXT is a major transcription factor for gastrulation, tailbud patterning, and ...notochord formation; however, how its expression is controlled in the mammalian notochord has remained elusive. Here, we identify the complement of notochord-specific enhancers in the mammalian Brachyury/T/TBXT gene. Using transgenic assays in zebrafish, axolotl, and mouse, we discover three conserved Brachyury-controlling notochord enhancers, T3, C, and I, in human, mouse, and marsupial genomes. Acting as Brachyury-responsive, auto-regulatory shadow enhancers, in cis deletion of all three enhancers in mouse abolishes Brachyury/T/Tbxt expression selectively in the notochord, causing specific trunk and neural tube defects without gastrulation or tailbud defects. The three Brachyury-driving notochord enhancers are conserved beyond mammals in the brachyury/tbxtb loci of fishes, dating their origin to the last common ancestor of jawed vertebrates. Our data define the vertebrate enhancers for Brachyury/T/TBXTB notochord expression through an auto-regulatory mechanism that conveys robustness and adaptability as ancient basis for axis development.
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