Down-regulation of Sox10 with specific small interfering RNA promotes transdifferentiation of Schwannoma cells into myofibroblasts

Sex-Determining Region Y Chromosome-Related High-Mobility-Group Box 10 in Cancer: A Potential Therapeutic Target

Sex-determining region Y-related high mobility group-box 10 (SOX10), a member of the SOX family, has recently been highlighted as an essential transcriptional factor involved in developmental biology. Recently, the functionality of SOX 10 has been increasingly revealed by researchers worldwide. It has been reported that SOX10 significantly regulates the proliferation, migration, and apoptosis of tumors and is closely associated with the progression of cancer. In this review, we first introduce the basic background of the SOX family and SOX10 and then discuss the pathophysiological roles of SOX10 in cancer. Besides, we enumerate the application of SOX10 in the pathological diagnosis and therapeutic potential of cancer. Eventually, we summarize the potential directions and perspectives of SOX10 in neoplastic theranostics. The information compiled herein may assist in additional studies and increase the potential of SOX10 as a therapeutic target for cancer.

Regulation of SOX10 stability via ubiquitination-mediated degradation by Fbxw7α modulates melanoma cell migration

Dysregulation of SOX10 was reported to be correlated with the progression of multiple cancer types, including melanocytic tumors and tumors of the nervous system. However, the mechanisms by which SOX10 is dysregulated in these tumors are poorly understood. In this study, we report that SOX10 is a direct substrate of Fbxw7α E3 ubiquitin ligase, a tumor suppressor in multiple cancers. Fbxw7α promotes SOX10 ubiquitination-mediated turnover through CPD domain of SOX10. Besides, GSK3β phosphorylates SOX10 at CPD domain and facilitates Fbxw7α-mediated SOX10 degradation. Moreover, SOX10 protein levels were inversely correlated with Fbxw7α in melanoma cells, and modulation of Fbxw7α levels regulated the expression of SOX10 and its downstream gene MIA. More importantly, SOX10 reversed Fbxw7α-mediated suppression of melanoma cell migration. This study provides evidence that the tumor suppressor Fbxw7α is the E3 ubiquitin ligase responsible for the degradation of SOX10, and suggests that reduced Fbxw7α might contribute to the upregulation of SOX10 in melanoma cells.

NF1 and Neurofibromin: Emerging Players in the Genetic Landscape of Desmoplastic Melanoma

Neurofibromatosis type I (NF1), a monogenic disorder with an autosomal dominant mode of inheritance, is caused by alterations in the NF1 gene which codes for the protein neurofibromin. Functionally, NF1 is a tumor suppressor as it is GTPase-activating protein that negatively regulates the MAPK pathway. More recently, much attention has focused on the role of NF1 and neurofibromin in melanoma as mutations in NF1 have been found to constitute 1 of the 4 distinct genomic categories of melanoma, with the other 3 comprising BRAF, NRAS, and "triple-wild-type" subtypes. In this review, we parse the literature on NF1 and neurofibromin with a view to clarifying and gaining a better understanding of their precise role/s in melanomagenesis. We begin with a historic overview, followed by details regarding structure and function and characterization of neural crest development as a model for genetic reversion in neoplasia. Melanogenesis in NF1 sets the stage for the discussion on the roles of NF1 and neurofibromin in neural crest-derived neoplasms including melanoma with particular emphasis on NF1 and neurofibromin as markers of melanocyte dedifferentiation in desmoplastic melanoma.

SOX10 transactivates S100B to suppress Schwann cell proliferation and to promote myelination

Schwann cells are an important cell source for regenerative therapy for neural disorders. We investigated the role of the transcription factor sex determining region Y (SRY)-box 10 (SOX10) in the proliferation and myelination of Schwann cells. SOX10 is predominantly expressed in rat sciatic nerve-derived Schwann cells and is induced shortly after birth. Among transcription factors known to be important for the differentiation of Schwann cells, SOX10 potently transactivates the S100B promoter. In cultures of Schwann cells, overexpressing SOX10 dramatically induces S100B expression, while knocking down SOX10 with shRNA suppresses S100B expression. Here, we identify three core response elements of SOX10 in the S100B promoter and intron 1 with a putative SOX motif. Knockdown of either SOX10 or S100B enhances the proliferation of Schwann cells. In addition, using dissociated cultures of dorsal root ganglia, we demonstrate that suppressing S100B with shRNA impairs myelination of Schwann cells. These results suggest that the SOX10-S100B signaling axis critically regulates Schwann cell proliferation and myelination, and therefore is a putative therapeutic target for neuronal disorders.

Neural stem cell differentiation is dictated by distinct actions of nuclear receptor corepressors and histone deacetylases

Signaling factors including retinoic acid (RA) and thyroid hormone (T3) promote neuronal, oligodendrocyte, and astrocyte differentiation of cortical neural stem cells (NSCs). However, the functional specificity of transcriptional repressor checkpoints controlling these differentiation programs remains unclear. Here, we show by genome-wide analysis that histone deacetylase (HDAC)2 and HDAC3 show overlapping and distinct promoter occupancy at neuronal and oligodendrocyte-related genes in NSCs. The absence of HDAC3, but not HDAC2, initiated a neuronal differentiation pathway in NSCs. The ablation of the corepressor NCOR or HDAC2, in conjunction with T3 treatment, resulted in increased expression of oligodendrocyte genes, revealing a direct HDAC2-mediated repression of Sox8 and Sox10 expression. Interestingly, Sox10 was required also for maintaining the more differentiated state by repression of stem cell programming factors such as Sox2 and Sox9. Distinct and nonredundant actions of NCORs and HDACs are thus critical for control of lineage progression and differentiation programs in neural progenitors.

•

ChIP-seq reveals distinct and overlapping occupancy of HDAC2 and HDAC3 in NSCs

•

Absence of NCOR promotes oligodendrocyte differentiation of NSCs

•

HDAC2 controls Sox10 expression in OL differentiation via a SOX2-occupied enhancer

•

Sox10 is required for maintaining the differentiated state in late OL precursors

SOX-10 expression in cutaneous myoepitheliomas and mixed tumors

BACKGROUND

SOX-10 expression can be demonstrated by immunohistochemistry in salivary gland myoepitheliomas, but its expression in cutaneous myoepitheliomas and in cutaneous mixed tumors with prominent myoepithelial cells has not been studied.

METHODS

We assessed the staining pattern of SOX-10 in five cutaneous myoepitheliomas and six cutaneous mixed tumors with a prominent myoepithelial component among both the myoepithelial cells and cells lining lumens. In addition, we examined the staining of S100, microphthalmia-associated transcription factor (MiTF), keratin cocktail, HMK903, smooth muscle actin (SMA) and epithelial membrane antigen (EMA).

RESULTS

SOX-10 positivity was seen in three of five (60%) cutaneous myoepitheliomas and in the myoepithelial cells of all cutaneous mixed tumors. SOX-10 expression on the cells lining the glandular structures in mixed tumors was variable. All myoepitheliomas and mixed tumors stained positively with S100 and negatively with MiTF. Pan-keratin, HMK903, SMA and EMA showed variable expression.

CONCLUSIONS

SOX-10 is a relatively reliable marker for staining cutaneous myoepitheliomas. Cutaneous myoepitheliomas are notoriously difficult to diagnose, and the addition of SOX-10 to the repertoire of stains that can label this tumor is of practical utility. These results further support that cutaneous myoepitheliomas and cutaneous mixed tumors exist on a morphologic and immunophenotypic spectrum.

SOX10 is a novel marker of acinus and intercalated duct differentiation in salivary gland tumors: a clue to the histogenesis for tumor diagnosis

Salivary gland tumors are relatively rare and morphologically diverse and heterogeneous tumors; therefore, histogenesis-based tumor markers are sorely needed to aid in diagnosing and determining the cell type of origin. SRY-related HMG-box 10 (SOX10) protein is a transcription factor known to be crucial in the specification of the neural crest and maintenance of Schwann cells and melanocytes. In addition, positive expression has also been implicated in the major salivary gland. Here, we examined SOX10 expression in various salivary gland tumors to correlate this expression with myoepithelial markers. Overall, 76 malignant and 14 benign tumors were examined. SOX10 expression clearly delineated two distinct subtypes of human salivary gland tumors; acinic cell carcinomas, adenoid cystic carcinomas, epithelial-myoepithelial carcinomas, myoepithelial carcinomas, and pleomorphic adenomas, including the pleomorphic adenoma component of carcinoma, were SOX10 positive, while salivary duct carcinomas, mucoepidermoid carcinomas, an oncocytic carcinoma, Oncocytomas, and Warthin tumors were SOX10 negative. Also, SOX10 was expressed in solid-type or non-specific morphology salivary gland tumors, but was not expressed in poorly differentiated squamous cell carcinomas. In normal human salivary gland tissue, SOX10 expression was specific to the nuclei of acini and both luminal and abluminal cells of intercalated ducts but not in other sites. Moreover, the murine model suggested that SOX10 continued to be expressed from the developmental stage to adulthood in the acinar and both luminal and abluminal intercalated ducts in the major salivary gland. Thus, SOX10 is a novel marker for diagnosing and understanding the histogenesis of salivary gland tumors.

Transforming growth factor-β1 may be a key mediator of the fibrogenic properties of neural cells in leprosy

Fibrosis is the main cause of irreversible nerve damage in leprosy. Phenotypic changes in Mycobacterium leprae (ML)-infected Schwann cells (SCs) have been suggested to mediate this process. We found that SC line cultures stimulated with ML upregulated transforming growth factor-β1 (TGF-β1), and that TGF-β1 or ML induced increased numbers of α-smooth muscle actin (α-SMA)-positive cells with characteristic stress fibers. Mycobacterium leprae and TGF-β1 also induced increased type I collagen and fibronectin mRNA and secretion and augmented mRNA levels of SOX9 and ZEB1, which are involved in the epithelial-mesenchymal transition. These effects could be inhibited by the TGF-β1 type I receptor (ALK5) inhibitor, SB-431542. In nerve biopsies from leprosy-infected patients with varying grades of fibrosis (n = 11), type I and III collagen and fibronectin were found in the endoneurium and perineurium, α-SMA-positive cells filled the fibrotic perineurium but not the endoneurium, and CD34-positive fibroblasts predominated in the endoneurium. Results of transcriptional studies of 3 leprosy nerves and 5 controls were consistent with these data, but α-SMA and other mRNA levels were not different from those in the control samples. Our findings suggest that TGF-β1 may orchestrate events, including reprogramming of the SC phenotype, leading to transdifferentiation, connective tissue cell expansion, and fibrogenesis in the evolution of leprosy nerve lesions during some evolutionary stages.

Transdifferentiation: a cell and molecular reprogramming process

Evidence has emerged recently indicating that differentiation is not entirely a one-way process, and that it is possible to convert one cell type to another, both in vitro and in vivo. This phenomenon is called transdifferentiation, and is generally defined as the stable switch of one cell type to another. Transdifferentiation plays critical roles during development and in regeneration pathways in nature. Although this phenomenon occurs rarely in nature, recent studies have been focused on transdifferentiation and the reprogramming ability of cells to produce specific cells with new phenotypes for use in cell therapy and regenerative medicine. Thus, understanding the principles and the mechanism of this process is important for producing desired cell types. Here some well-documented examples of transdifferentiation, and their significance in development and regeneration are reviewed. In addition, transdifferentiation pathways are considered and their potential molecular mechanisms, especially the role of master switch genes, are considered. Finally, the significance of transdifferentiation in regenerative medicine is discussed.

Sox10 controls migration of B16F10 melanoma cells through multiple regulatory target genes

It is believed that the inherent differentiation program of melanocytes during embryogenesis predisposes melanoma cells to high frequency of metastasis. Sox10, a transcription factor expressed in neural crest stem cells and a subset of progeny lineages, plays a key role in the development of melanocytes. We show that B16F10 melanoma cells transfected with siRNAs specific for Sox10 display reduced migratory activity which in turn indicated that a subset of transcriptional regulatory target genes of Sox10 is likely to be involved in migration and metastasis of melanoma cells. We carried out a microarray-based gene expression profiling using a Sox10-specific siRNA to identify relevant regulatory targets and found that multiple genes including melanocortin-1 receptor (Mc1r) partake in the regulation of migration. We provide evidences that the effect of Sox10 on migration is mediated in large part by Mitf, a transcription factor downstream to Sox10. Among the mouse melanoma cell lines examined, however, only B16F10 showed robust down-regulation of Sox10 and inhibition of cell migration indicating that further dissection of dosage effects and/or cell line-specific regulatory networks is necessary. The involvement of Mc1r in migration was studied in detail in vivo using a murine metastasis model. Specifically, B16F10 melanoma cells treated with a specific siRNA showed reduced tendency in metastasizing to and colonizing the lung after being injected in the tail vein. These data reveal a cadre of novel regulators and mediators involved in migration and metastasis of melanoma cells that represents potential targets of therapeutic intervention.

Developmental regulation of microRNA expression in Schwann cells

Schwann cell differentiation and subsequent myelination of the peripheral nervous system require the action of several transcription factors, including Sox10, which is vital at multiple stages of development. The transition from immature to myelinating Schwann cell is also regulated posttranscriptionally and depends upon Dicer-mediated processing of microRNAs (miRNAs). Although specific miRNA targets have begun to be identified, the mechanisms establishing the dynamic regulation of miRNA expression have not been elucidated. We performed expression profiling studies and identified 225 miRNAs differentially expressed during peripheral myelination. A subset of 9 miRNAs is positively regulated by Sox10, including miR-338 which has been implicated in oligodendrocyte maturation. In vivo chromatin immunoprecipitation (ChIP) of sciatic nerve cells revealed a Sox10 binding site upstream of an alternate promoter within the Aatk gene, which hosts miR-338. Sox10 occupied this site in spinal cord ChIP experiments, suggesting a similar regulatory mechanism in oligodendrocytes. Cancer profiling studies have identified clusters of miRNAs that regulate proliferation, termed "oncomirs." In Schwann cells, the expression of many of these proproliferative miRNAs was reduced in the absence of Sox10. Finally, Schwann cells with reduced Sox10 and oncomir expression have an increase in the CDK inhibitor p21 and a concomitant reduction in cell proliferation.

Cellular origin and developmental mechanisms during the formation of skin melanocytes

Melanocytes are derived from the neural crest (NC), which are transient multipotent cells arising by delamination from the developing dorsal neural tube. During recent years, signaling systems and molecular mechanisms of melanocyte development have been studied in detail, but the exact diversification of the NC into melanocytes and how they migrate, expand and disperse in the skin have not been fully understood. The recent finding that Schwann cell precursors (SCPs) of the growing nerve represents a stem cell niche from which various cell types, including Schwann cells, endoneural fibroblasts and melanocytes arise has exposed new knowledge on the cellular basis for melanocyte development. This opens for the identification of new factors and reinterpretation of old data on cell fate instructive, proliferative, survival and cell homing factors participating in melanocyte development.

The Yin and Yang of Sox proteins: Activation and repression in development and disease

The general view of development consists of the acquisition of committed/differentiated phenotypes following a period of self-renewal and progenitor expansion. Lineage specification and progression are phenomena of antagonistic events, silencing tissue-specific gene expression in precursors to allow self-renewal and multipotentiality, and subsequently suppressing proliferation and embryonic gene expression to promote the restricted expression of tissue-specific genes during maturation. The high mobility group-containing Sox family of transcription factors constitutes one of the earliest classes of genes to be expressed during embryonic development. These proteins not only are indispensable for progenitor cell specification but also are critical for terminal differentiation of multiple cell types in a wide variety of lineages. Sox transcription factors are now known to induce or repress progenitor cell characteristics and cell proliferation or to activate the expression of tissue-specific genes. Sox proteins fulfill their diverse functions in developmental regulation by distinct molecular mechanisms. Not surprisingly, in addition to DNA binding and bending, Sox transcription factors also interact with different protein partners to function as coactivators or corepressors of downstream target genes. Here we seek to provide an overview of the current knowledge of Sox gene functional mechanisms, in an effort to understand their roles in both development and pathology.

Sox10 promotes the survival of cochlear progenitors during the establishment of the organ of Corti

Transcription factors of the SoxE family are critical players that underlie various embryological processes. However, little is known about their function during inner ear development. Here, we show that Sox10 is initially expressed throughout the otic vesicle epithelium and becomes later restricted to supporting cells as cell differentiation proceeds in the organ of Corti. Morphological analyses of Sox10 mutant mice reveal a significant shortening of the cochlear duct likely resulting from the progressive depletion of cochlear progenitors. While Sox10 appears dispensable for the differentiation and patterning of the inner ear prosensory progenitors, our data support a critical role for this transcription factor in the promotion of their survival. We provide genetic evidences that Sox10, in a concentration-dependant manner, could play a role in the regulation of Jagged1, a gene known to be important for inner ear prosensory development. Together, our results demonstrate that Sox10 regulates the biology of early cochlear progenitors during inner ear development, but, in contrast to neural crest-derived cells, this transcription factor is dispensable for their differentiation. Evidence also suggests that this effect occurs via the activation of the Jagged1 gene.

Sox10: a pan-schwannian and melanocytic marker

S100 protein is a sensitive marker for melanomas and peripheral nerve sheath tumors. It is, however, expressed by other mesenchymal and epithelial tumors. Despite its low specificity, S100 protein is valuable for the diagnosis of desmoplastic melanomas and peripheral nerve sheath tumors, for which no specific marker is available. Sox10 is a neural crest transcription factor crucial for specification, maturation, and maintenance of Schwann cells and melanocytes. Anti-Sox10 antibody was applied to a variety of neural crest-derived tumors, mesenchymal and epithelial neoplasms, and normal tissues. Sox10 nuclear expression was found in 76 of 78 melanomas (97%) and 38 of 77 malignant peripheral nerve sheath tumors (49%) whereas S100 protein was expressed in 71 melanomas (91%) and 23 malignant peripheral nerve sheath tumors (30%). Sox10 was diffusely expressed in schwannomas and neurofibromas. Sox10 reaction was seen only in sustentacular cells of pheochromocytomas/paragangliomas, and occasionally carcinoid tumors from various organs, but it was not seen in the tumor cells. In normal tissues, Sox10 was expressed in Schwann cells, melanocytes, and myoepithelial cells of salivary, bronchial, and mammary glands. Sox10 reaction was not identified in any other mesenchymal and epithelial tumors except for myoepitheliomas and diffuse astrocytomas. Sox10 was expressed by metastatic melanomas and nodal capsular nevus in sentinel lymph nodes, but not by other lymph node components such as dendritic cells. Our results indicate that Sox10 will serve as a more sensitive and specific marker for the diagnosis of melanocytic and schwannian tumors than S100 protein.

Identification of direct regulatory targets of the transcription factor Sox10 based on function and conservation

Background

Sox10, a member of the Sry-related HMG-Box gene family, is a critical transcription factor for several important cell lineages, most notably the neural crest stem cells and the derivative peripheral glial cells and melanocytes. Thus far, only a handful of direct target genes are known for this transcription factor limiting our understanding of the biological network it governs.

Results

We describe identification of multiple direct regulatory target genes of Sox10 through a procedure based on function and conservation. By combining RNA interference technique and DNA microarray technology, we have identified a set of genes that show significant down-regulation upon introduction of Sox10 specific siRNA into Schwannoma cells. Subsequent comparative genomics analyses led to potential binding sites for Sox10 protein conserved across several mammalian species within the genomic region proximal to these genes. Multiple sites belonging to 4 different genes (proteolipid protein, Sox10, extracellular superoxide dismutase, and pleiotrophin) were shown to directly interact with Sox10 by chromatin immunoprecipitation assay. We further confirmed the direct regulation through the identified cis-element for one of the genes, extracellular superoxide dismutase, using electrophoretic mobility shift assay and reporter assay.

Conclusion

In sum, the process of combining differential expression profiling and comparative genomics successfully led to further defining the role of Sox10, a critical transcription factor for the development of peripheral glia. Our strategy utilizing relatively accessible techniques and tools should be applicable to studying the function of other transcription factors.

Morphological and functional characterizations of Schwann cells stimulated with Mycobacterium leprae

Nerve damage, a characteristic of leprosy, is the cause of patient deformities and a consequence of Schwann cells (SC) infection by Mycobacterium leprae. Although function/dysfunction of SC in human diseases like leprosy is difficult to study, many in vitro models, including SC lines derived from rat and/or human Schwannomas, have been employed. ST88-14 is one of the cell lineages used by many researchers as a model for M. leprae/SC interaction. However, it is necessary to establish the values and limitations of the generated data on the effects of M. leprae in these SC. After evaluating the cell line phenotype in the present study, it is close to non-myelinating SC, making this lineage an ideal model for M. leprae/SC interaction. It was also observed that both M. leprae and PGL-1, a mycobacterial cell-wall component, induced low levels of apoptosis in ST88-14 by a mechanism independent of Bcl-2 family members.