A pinboard by
Matias Hepp

Postdoc, Universidad de Concepcion


Finding specific target genes of Sall2 isoforms in normal and genotoxic stress conditions

Gene expression is regulated in part by transcription factors which form one of the most important mechanisms regulating the differentiation, development and cellular homeostasis. A transcription factor, called Sall2, member of the Spalt-sal genes involved in normal development, has not been well characterized, with little information available about its regulation and specific targets. Recently, mutations in Sall2 have been associated with genetic diseases such as ocular coloboma and Alport syndrome. Moreover, there are now more evidence to suggest that Sall2 has an important role in cancer. Like, as Sall2 expression is deregulated in various cancers including synovial sarcoma, Wilm's tumor, ovarian cancer, testicular cancer and others. Several studies, including our data, suggest that Sall2 is a tumor suppressor. However, this suppressor function remains controversial. Because, Sall2 is increased in some cancers, Sall2 Knockout's mice show no spontaneous tumor formation and recently Sall2 was identified as one of the four essential transcription factors for formation of glioblastoma, which together suggests a oncogenic role for Sall2. That's where we wonder "How could explain this controversy?". One way is, Sall2 gene contains two alternative promoters (P1 and P2), conserved between human and mouse and could form two Sall2 isoforms, called E1 and E1A. These isoforms differ only in the N-terminal domain. However, bioinformatic analysis of these domains predicts that Sall2 isoforms differ in their regulation and function. According to this assumption, it was shown that E1 isoform can interact with NuRD complex, but not E1A, that can act as a transcriptional repressor. In addition, unpublished data from our lab suggest that only the E1A isoform can induce transcription of the proapoptotic gene NOXA1. However, controversial roles proposed for Sall2 function in a normal and pathological state, that could be resolved through an understanding of expression, regulation, and function of Sall2 isoforms. Therefore, we propose that by using complementary approaches include stable modifying genome (genome editing) for Sall2 isoforms, ChIP-seq analysis, and bioinformatics analysis, identifying Sall2 isoform-specific target genes in normal and in response to genotoxic stress. Until now, I have 3 published paper in this area. In addition, there are 2 papers submitted in review.


Wild type p53 transcriptionally represses the SALL2 transcription factor under genotoxic stress.

Abstract: SALL2- a member of the Spalt gene family- is a poorly characterized transcription factor found deregulated in various cancers, which suggests it plays a role in the disease. We previously identified SALL2 as a novel interacting protein of neurotrophin receptors and showed that it plays a role in neuronal function, which does not necessarily explain why or how SALL2 is deregulated in cancer. Previous evidences indicate that SALL2 gene is regulated by the WT1 and AP4 transcription factors. Here, we identified SALL2 as a novel downstream target of the p53 tumor suppressor protein. Bioinformatic analysis of the SALL2 gene revealed several putative p53 half sites along the promoter region. Either overexpression of wild-type p53 or induction of the endogenous p53 by the genotoxic agent doxorubicin repressed SALL2 promoter activity in various cell lines. However R175H, R249S, and R248W p53 mutants, frequently found in the tumors of cancer patients, were unable to repress SALL2 promoter activity, suggesting that p53 specific binding to DNA is important for the regulation of SALL2. Electrophoretic mobility shift assay demonstrated binding of p53 to one of the identified p53 half sites in the Sall2 promoter, and chromatin immunoprecipitation analysis confirmed in vivo interaction of p53 with the promoter region of Sall2 containing this half site. Importantly, by using a p53ER (TAM) knockin model expressing a variant of p53 that is completely dependent on 4-hydroxy-tamoxifen for its activity, we show that p53 activation diminished SALL2 RNA and protein levels during genotoxic cellular stress in primary mouse embryo fibroblasts (MEFs) and radiosensitive tissues in vivo. Thus, our finding indicates that p53 represses SALL2 expression in a context-specific manner, adding knowledge to the understanding of SALL2 gene regulation, and to a potential mechanism for its deregulation in cancer.

Pub.: 17 Sep '13, Pinned: 30 Aug '17

Sall2 is required for proapoptotic Noxa expression and genotoxic stress-induced apoptosis by doxorubicin.

Abstract: The Sall2 transcription factor is deregulated in several cancers; however, little is known about its cellular functions, including its target genes. Recently, we demonstrated that p53 directly regulates Sall2 expression under genotoxic stress. Here, we investigated the role of Sall2 in the context of cellular response to genotoxic stress. In addition, we further examined the Sall2-p53 relationship during genotoxic stress in primary mouse embryo fibroblasts (MEFs), which are derived from Sall2 knockout mice separately, or in combination with the p53ERTAM knock-in mice. We found that the levels of Sall2 mRNA and protein are dynamically modulated in response to doxorubicin. At early times of stress, Sall2 is downregulated, but increases under extension of the stress in a p53-independent manner. Based on caspase-3/7 activities, expression of cleaved poly (ADP-ribose) polymerase, expression of cleaved caspase-3 and induction of proapoptotic proteins, Sall2 expression was correlated with cellular apoptosis. Consequently, Sall2-/- MEFs have decreased apoptosis, which relates with increased cell viability in response to doxorubicin. Importantly, Sall2 was required for apoptosis even in the presence of fully activated p53. Searching for putative Sall2 targets that could mediate its role in apoptosis, we identified proapoptotic NOXA/PMAIP1 (phorbol-12-myristate-13-acetate-induced protein 1). We demonstrated that Sall2 positively regulates Noxa promoter activity. Conserved putative Sall2-binding sites at the NOXA promoter were validated in vitro by electrophoretic mobility shift assay and in vivo by ChIP experiments, identifying NOXA as a novel Sall2 target. In agreement, induction of Noxa protein and mRNA in response to doxorubicin was significantly decreased in Sall2-/- MEFs. In addition, studies in leukemia Jurkat T cells support the existence of the Sall2/Noxa axis, and the significance of this axis on the apoptotic response to doxorubicin in cancer cells. Our study highlights the relevance of Sall2 in the apoptotic response to extended genotoxic stress, which is important for understanding its role in normal physiology and disease.

Pub.: 17 Jul '15, Pinned: 30 Aug '17

Developmental SALL2 transcription factor: a new player in cancer.

Abstract: 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.

Pub.: 22 Apr '17, Pinned: 30 Aug '17