Crosstalk between SOXB1 proteins and WNT/β-catenin signaling in NT2/D1 cells

SOX Transcription Factors as Important Regulators of Neuronal and Glial Differentiation During Nervous System Development and Adult Neurogenesis

The SOX proteins belong to the superfamily of transcription factors (TFs) that display properties of both classical TFs and architectural components of chromatin. Since the cloning of the Sox/SOX genes, remarkable progress has been made in illuminating their roles as key players in the regulation of multiple developmental and physiological processes. SOX TFs govern diverse cellular processes during development, such as maintaining the pluripotency of stem cells, cell proliferation, cell fate decisions/germ layer formation as well as terminal cell differentiation into tissues and organs. However, their roles are not limited to development since SOX proteins influence survival, regeneration, cell death and control homeostasis in adult tissues. This review summarized current knowledge of the roles of SOX proteins in control of central nervous system development. Some SOX TFs suspend neural progenitors in proliferative, stem-like state and prevent their differentiation. SOX proteins function as pioneer factors that occupy silenced target genes and keep them in a poised state for activation at subsequent stages of differentiation. At appropriate stage of development, SOX members that maintain stemness are down-regulated in cells that are competent to differentiate, while other SOX members take over their functions and govern the process of differentiation. Distinct SOX members determine down-stream processes of neuronal and glial differentiation. Thus, sequentially acting SOX TFs orchestrate neural lineage development defining neuronal and glial phenotypes. In line with their crucial roles in the nervous system development, deregulation of specific SOX proteins activities is associated with neurodevelopmental disorders (NDDs). The overview of the current knowledge about the link between SOX gene variants and NDDs is presented. We outline the roles of SOX TFs in adult neurogenesis and brain homeostasis and discuss whether impaired adult neurogenesis, detected in neurodegenerative diseases, could be associated with deregulation of SOX proteins activities. We present the current data regarding the interaction between SOX proteins and signaling pathways and microRNAs that play roles in nervous system development. Finally, future research directions that will improve the knowledge about distinct and various roles of SOX TFs in health and diseases are presented and discussed.

SOX3 can promote the malignant behavior of glioblastoma cells

PURPOSE

Glioblastoma is the most common and lethal adult brain tumor. Despite current therapeutic strategies, including surgery, radiation and chemotherapy, the median survival of glioblastoma patients is 15 months. The development of this tumor depends on a sub-population of glioblastoma stem cells governing tumor propagation and therapy resistance. SOX3 plays a role in both normal neural development and carcinogenesis. However, little is known about its role in glioblastoma. Thus, the aim of this work was to elucidate the role of SOX3 in glioblastoma.

METHODS

SOX3 expression was assessed using real-time quantitative PCR (RT-qPCR), Western blotting and immunohistochemistry. MTT, immunocytochemistry and Transwell assays were used to evaluate the effects of exogenous SOX3 overexpression on the viability, proliferation, migration and invasion of glioblastoma cells, respectively. The expression of Hedgehog signaling pathway components and autophagy markers was assessed using RT-qPCR and Western blot analyses, respectively.

RESULTS

Higher levels of SOX3 expression were detected in a subset of primary glioblastoma samples compared to those in non-tumoral brain tissues. Exogenous overexpression of this gene was found to increase the proliferation, viability, migration and invasion of glioblastoma cells. We also found that SOX3 up-regulation was accompanied by an enhanced activity of the Hedgehog signaling pathway and by suppression of autophagy in glioblastoma cells. Additionally, we found that SOX3 expression was elevated in patient-derived glioblastoma stem cells, as well as in oncospheres derived from glioblastoma cell lines, compared to their differentiated counterparts, implying that SOX3 expression is associated with the undifferentiated state of glioblastoma cells.

CONCLUSION

From our data we conclude that SOX3 can promote the malignant behavior of glioblastoma cells.

Epigenetic regulation of human SOX3 gene expression during early phases of neural differentiation of NT2/D1 cells

Sox3/SOX3 is one of the earliest neural markers in vertebrates. Together with the Sox1/SOX1 and Sox2/SOX2 genes it is implicated in the regulation of stem cell identity. In the present study, we performed the first analysis of epigenetic mechanisms (DNA methylation and histone marks) involved in the regulation of the human SOX3 gene expression during RA-induced neural differentiation of NT2/D1 cells. We show that the promoter of the human SOX3 gene is extremely hypomethylated both in undifferentiated NT2/D1 cells and during the early phases of RA-induced neural differentiation. By employing chromatin immunoprecipitation, we analyze several histone modifications across different regions of the SOX3 gene and their dynamics following initiation of differentiation. In the same timeframe we investigate profiles of selected histone marks on the promoters of human SOX1 and SOX2 genes. We demonstrate differences in histone signatures of SOX1, SOX2 and SOX3 genes. Considering the importance of SOXB1 genes in the process of neural differentiation, the present study contributes to a better understanding of epigenetic mechanisms implicated in the regulation of pluripotency maintenance and commitment towards the neural lineage.

Oncogenic activity of SOX1 in glioblastoma

Glioblastoma remains the most common and deadliest type of brain tumor and contains a population of self-renewing, highly tumorigenic glioma stem cells (GSCs), which contributes to tumor initiation and treatment resistance. Developmental programs participating in tissue development and homeostasis re-emerge in GSCs, supporting the development and progression of glioblastoma. SOX1 plays an important role in neural development and neural progenitor pool maintenance. Its impact on glioblastoma remains largely unknown. In this study, we have found that high levels of SOX1 observed in a subset of patients correlate with lower overall survival. At the cellular level, SOX1 expression is elevated in patient-derived GSCs and it is also higher in oncosphere culture compared to differentiation conditions in conventional glioblastoma cell lines. Moreover, genetic inhibition of SOX1 in patient-derived GSCs and conventional cell lines decreases self-renewal and proliferative capacity in vitro and tumor initiation and growth in vivo. Contrarily, SOX1 over-expression moderately promotes self-renewal and proliferation in GSCs. These functions seem to be independent of its activity as Wnt/β-catenin signaling regulator. In summary, these results identify a functional role for SOX1 in regulating glioma cell heterogeneity and plasticity, and suggest SOX1 as a potential target in the GSC population in glioblastoma.