Induction of SOX4 by DNA damage is critical for p53 stabilization and function

The closely related transcription factors Sox4 and Sox11 function as survival factors during spinal cord development

Development of the mouse CNS was reported to be normal in the absence of either Sox4 or its close relative Sox11 despite strong and widespread expression of both transcription factors. In this study, we show that combined absence of both Sox proteins in the mouse leads to severe hypoplasia of the developing spinal cord. Proliferation of neuroepithelial precursor cells in the ventricular zone was unaffected. These cells also acquired their correct positional identity. Both glial and neuronal progenitors were generated and neurons appeared in a similar spatiotemporal pattern as in the wild-type. Rates of cell death were however dramatically increased throughout embryogenesis in the double deficient spinal cord arguing that Sox4 and Sox11 are jointly and redundantly required for cell survival. The absence of pronounced proliferation, patterning, specification, and maturation defects furthermore indicates that the decreased cell survival is not a secondary effect of one of these events. We therefore conclude that the two Sox proteins directly function as pro-survival factors during spinal cord development in neural cell types.

Identification of uniquely expressed transcription factors in highly purified B-cell lymphoma samples

Transcription factors (TFs) are critical for B-cell differentiation, affecting gene expression both by repression and transcriptional activation. Still, this information is not used for classification of B-cell lymphomas (BCLs). Traditionally, BCLs are diagnosed based on a phenotypic resemblance to normal B-cells; assessed by immunohistochemistry or flow cytometry, by using a handful of phenotypic markers. In the last decade, diagnostic and prognostic evaluation has been facilitated by global gene expression profiling (GEP), providing a new powerful means for the classification, prediction of survival, and response to treatment of lymphomas. However, most GEP studies have typically been performed on whole tissue samples, containing varying degrees of tumor cell content, which results in uncertainties in data analysis. In this study, global GEP analyses were performed on highly purified, flow-cytometry sorted tumor-cells from eight subgroups of BCLs. This enabled identification of TFs that can be uniquely associated to the tumor cells of chronic lymphocytic leukemia (CLL), diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), hairy cell leukemia (HCL), and mantle cell lymphoma (MCL). The identified transcription factors influence both the global and specific gene expression of the BCLs and have possible implications for diagnosis and treatment.

SOX4 overexpression regulates the p53-mediated apoptosis in hepatocellular carcinoma: clinical implication and functional analysis in vitro

BACKGROUND AND AIMS

The underlying molecular mechanisms of hepatocellular carcinoma (HCC) remain poorly understood due to its complex development process. The human T cell-specific transcription factor sex-determining region Y-related high-mobility group (HMG) box 4 (SOX4) has been linked to development and tumorigenesis. In this study, we characterized the roles of SOX4 in regulation of the p53 transcription activity and evaluated the expression patterns and prognostic value of the transcription factor SOX4 in HCC.

METHODS

The expression levels of human SOX4 were examined in HCC samples obtained from 58 patients having curative partial hepatectomy. The interaction and effects of SOX4 on the p53 pathway were assessed in HCC cell lines. Luciferase reporter assay to examine p53-mediated transcription of target genes was performed. The association of SOX4 expression level with tumor recurrence and overall survival was evaluated.

RESULTS

We showed that the HMG box domain of SOX4 interacted with p53, resulting in the inhibition of p53-mediated transcription by the Bax promoter. More importantly, SOX4 overexpression led to a significant repression of p53-induced Bax expression and subsequent repression of p53-mediated apoptosis induced by gamma-irradiation. In clinicopathological analysis, nuclear overexpression of SOX4 was observed in 37 out of 58 (63.8%) HCC samples, and this correlated with diminished risk of recurrence (P = 0.014) and improved overall survival time (P = 0.045) in HCC patients.

CONCLUSION

These results suggest that SOX4 contributes to hepatocarcinogenesis by inhibiting p53-mediated apoptosis and that its overexpression might be a useful prognostic marker for survival after surgical resection.

Organogenesis relies on SoxC transcription factors for the survival of neural and mesenchymal progenitors

During organogenesis, neural and mesenchymal progenitor cells give rise to many cell lineages, but their molecular requirements for self-renewal and lineage decisions are incompletely understood. In this study, we show that their survival critically relies on the redundantly acting SoxC transcription factors Sox4, Sox11 and Sox12. The more SoxC alleles that are deleted in mouse embryos, the more severe and widespread organ hypoplasia is. SoxC triple-null embryos die at midgestation unturned and tiny, with normal patterning and lineage specification, but with massively dying neural and mesenchymal progenitor cells. Specific inactivation of SoxC genes in neural and mesenchymal cells leads to selective apoptosis of these cells, suggesting SoxC cell-autonomous roles. Tead2 functionally interacts with SoxC genes in embryonic development, and is a direct target of SoxC proteins. SoxC genes therefore ensure neural and mesenchymal progenitor cell survival, and function in part by activating this transcriptional mediator of the Hippo signalling pathway.

During development Sox transcription factors play important roles in the determination of cell fate. In this study Bhattaram and colleagues show that Sox4, Sox11 and Sox12 act redundantly in mouse development and are important for the maintenance of neural and mesenchymal progenitor cells.

POU4F1 is associated with t(8;21) acute myeloid leukemia and contributes directly to its unique transcriptional signature

The t(8;21)(q22;q22) translocation, present in ~5% of adult acute myeloid leukemia (AML) cases, produces the AML1/ETO fusion protein. Dysregulation of the POU domain-containing transcription factor POU4F1 is a recurring abnormality in t(8;21) AML. Here, we show that POU4F1 over-expression is highly correlated with, but not caused by AML1/ETO. AML1/ETO markedly increases the self-renewal capacity of myeloid progenitors from murine bone marrow or fetal liver and drives expansion of these cells in liquid culture. POU4F1 is neither necessary nor sufficient for these AML1/ETO-dependent properties, suggesting that it contributes to leukemia through novel mechanisms. To identify targets of POU4F1, we performed gene expression profiling in primary mouse cells with genetically defined levels of POU4F1 and identified 140 differentially expressed genes. This expression signature was significantly enriched in human t(8;21) AML samples and was sufficient to cluster t(8;21) AML samples in an unsupervised hierarchical analysis. Among the most highly differentially expressed genes, half are known AML1/ETO targets, implying that the unique transcriptional signature of t(8;21) AML is, in part, attributable to POU4F1 and not AML1/ETO itself. These genes provide novel candidates for understanding the biology and developing therapeutic approaches for t(8;21) AML.

Interactions between SOX factors and Wnt/beta-catenin signaling in development and disease

The SOX family of transcription factors have emerged as modulators of canonical Wnt/beta-catenin signaling in diverse development and disease contexts. There are over 20 SOX proteins encoded in the vertebrate genome and recent evidence suggests that many of these can physically interact with beta-catenin and modulate the transcription of Wnt-target genes. The precise mechanisms by which SOX proteins regulate beta-catenin/TCF activity are still being resolved and there is evidence to support a number of models including: protein-protein interactions, the binding of SOX factors to Wnt-target gene promoters, the recruitment of co-repressors or co-activators, modulation of protein stability, and nuclear translocation. In some contexts, Wnt signaling also regulates SOX expression resulting in feedback regulatory loops that fine-tune cellular responses to beta-catenin/TCF activity. In this review, we summarize the examples of Sox-Wnt interactions and examine the underlying mechanisms of this potentially widespread and underappreciated mode of Wnt-regulation.

The Sex-determining region Y-box 4 and homeobox C6 transcriptional networks in prostate cancer progression: crosstalk with the Wnt, Notch, and PI3K pathways

The transforming growth factor beta, Hedgehog, Notch, and Wnt signaling pathways all play critical roles in the development and progression of prostate cancer. It is becoming increasingly apparent that these pathways may intersect with developmentally important transcription factors such as the sex-determining region Y-box 4 (SOX4), homeobox C6, enhancer of zeste 2, and ETS-related gene, which are up-regulated in prostate cancers. For example, identification of the downstream targets of SOX4 and homeobox C6 suggests that these factors may cooperate to activate the Notch pathway and the PI3K/AKT pathway, possibly in response to Wnt signals. PI3K/AKT activation likely occurs indirectly via up-regulation of growth factor receptors, while Notch activation is secondary to up-regulation of Notch pathway components. In addition, SOX4 may affect terminal differentiation via regulation of other transcription factors such as NKX3.1 and MLL, and regulation of components of the microRNA pathway such as Dicer and Argonaute 1. The evidence supporting activation of these pathways in prostate cancer progression suggests that combinations of compounds targeting them may be of benefit to patients with aggressive, metastatic disease.

Critical roles for SoxC transcription factors in development and cancer

Sox4, Sox11 and Sox12 constitute the group C of Sry-related HMG box proteins. They are co-expressed in embryonic neuronal progenitors and in mesenchymal cells in many developing organs. More closely related to each other than to any other proteins, they nevertheless bind DNA and activate transcription in vitro with different efficiencies. Sox4-null embryos and Sox11-null newborns die from heart malformations and the latter display widespread defects, while Sox12-null mice are viable and do not show obvious malformations. Sox4 facilitates differentiation of lymphocytes, pancreatic beta cells, osteoblasts and acts in redundancy with Sox11 to promote neuronal differentiation. Sox4 and Sox11 are upregulated in many tumor types in humans, where their roles in cell survival, proliferation, and metastasis remain controversial. Together, these data hint that Sox4 and Sox11 regulate cell differentiation, proliferation and survival in multiple essential processes, and suggest that they may act in redundancy to control many more developmental, physiological and pathological processes than currently known.