Interplay of SOX transcription factors and microRNAs in the brain under physiological and pathological conditions

Precise tuning of gene expression,accomplished by regulato ry networks of transcription factors,epigenetic modifiers,and microRNAs,is crucial for the proper neural development and function of the brain cells.The SOX transcription factors are involved in regulating diverse cellular processes during embryonic and adult neurogenesis,such as maintaining the cell stemness,cell prolife ration,cell fate decisions,and terminal diffe rentiation into neurons and glial cells.MicroRNAs represent a class of small non-coding RNAs that play important roles in the regulation of gene expression.Together with other gene regulatory factors,microRNAs regulate different processes during neurogenesis and orchestrate the spatial and temporal expression important for neurodevelopment.The emerging data point to a complex regulatory network between SOX transcription factors and microRNAs that govern distinct cellular activities in the developing and adult brain.Deregulated SOX/mic roRNA interplay in signaling pathways that influence the homeostasis and plasticity in the brain has been revealed in various brain pathologies,including neurodegenerative disorders,traumatic brain injury,and cancer.Therapeutic strategies that target SOX/microRNA interplay have emerged in recent years as a promising tool to target neural tissue regeneration and enhance neuro restoration.N umerous studies have confirmed complex intera ctions between microRNAs and SOX-specific mRNAs regulating key features of glioblastoma.Keeping in mind the crucial roles of SOX genes and microRNAs in neural development,we focus this review on SOX/microRNAs interplay in the brain during development and adulthood in physiological and pathological conditions.Special focus was made on their interplay in brain pathologies to summarize current knowledge and highlight potential future development of molecular therapies.

SOX transcription factors and glioma stem cells:Choosing between stemness and differentiation

Glioblastoma(GBM)is the most common,most aggressive and deadliest brain tumor.Recently,remarkable progress has been made towards understanding the cellular and molecular biology of gliomas.GBM tumor initiation,progression and relapse as well as resistance to treatments are associated with glioma stem cells(GSCs).GSCs exhibit a high proliferation rate and self-renewal capacity and the ability to differentiate into diverse cell types,generating a range of distinct cell types within the tumor,leading to cellular heterogeneity.GBM tumors may contain different subsets of GSCs,and some of them may adopt a quiescent state that protects them against chemotherapy and radiotherapy.GSCs enriched in recurrent gliomas acquire more aggressive and therapy-resistant properties,making them more malignant,able to rapidly spread.The impact of SOX transcription factors(TFs)on brain tumors has been extensively studied in the last decade.Almost all SOX genes are expressed in GBM,and their expression levels are associated with patient prognosis and survival.Numerous SOX TFs are involved in the maintenance of the stemness of GSCs or play a role in the initiation of GSC differentiation.The fine-tuning of SOX gene expression levels controls the balance between cell stemness and differentiation.Therefore,innovative therapies targeting SOX TFs are emerging as promising tools for combatting GBM.Combatting GBM has been a demanding and challenging goal for decades.The current therapeutic strategies have not yet provided a cure for GBM and have only resulted in a slight improvement in patient survival.Novel approaches will require the fine adjustment of multimodal therapeutic strategies that simultaneously target numerous hallmarks of cancer cells to win the battle against GBM.

TG-interacting Factor(TGIF) Downregulates SOX3 Gene Expression in the NT2/D1 Cell Line

SOX3 is a member of the Sox gene family implicated in brain formation and cognitive function. It is considered to be one of the earliest neural markers in vertebrates, playing a role in specifying neuronal fate. Recently, we have established the first link between TALE （three- amino-acid loop extension） proteins, PBX1 （pre-B-cell leukemia homeobox 1） and MEIS1 （myeloid ecotropic viral integration site 1 homologue）, and the expression of the human SOX3 gene. Here we present the evidence that TGIF （TG-interacting factor） is an additional TALE superfamily member involved in the regulation of human SOX3 gene expression in NT2/D1 cells by direct interaction with the consensus binding site that is conserved in primate orthologue promoters. Functional analysis demonstrated that mutation of the TGIF binding site resulted in the activation of SOX3 promoter. TGIF overexpression downregulates SOX3 promoter activity and decreases endogenous SOX3 protein expression in both uninduced and retinoic acid （RA）-induced NT2/D1 ceils. Up to now, this is the first transcription factor identified as a negative regulator of SOX3 gene expression. The obtained results further underscore the significance of TALE proteins as important transcriptional regulators of SOX3 gene expression.