SOX2 and nestin expression in human melanoma: an immunohistochemical and experimental study

Species-Specific Transcription Factors Associated with Long Terminal Repeat Promoters of Endogenous Retroviruses: A Comprehensive Review

Endogenous retroviruses (ERVs) became a part of the eukaryotic genome through endogenization millions of years ago. Moreover, they have lost their innate capability of virulence or replication. Nevertheless, in eukaryotic cells, they actively engage in various activities that may be advantageous or disadvantageous to the cells. The mechanisms by which transcription is triggered and implicated in cellular processes are complex. Owing to the diversity in the expression of transcription factors (TFs) in cells and the TF-binding motifs of viruses, the comprehensibility of ERV initiation and its impact on cellular functions are unclear. Currently, several factors are known to be related to their initiation. TFs that bind to the viral long-terminal repeat (LTR) are critical initiators. This review discusses the TFs shown to actively associate with ERV stimulation across species such as humans, mice, pigs, monkeys, zebrafish, Drosophila, and yeast. A comprehensive summary of the expression of previously reported TFs may aid in identifying similarities between animal species and endogenous viruses. Moreover, an in-depth understanding of ERV expression will assist in elucidating their physiological roles in eukaryotic cell development and in clarifying their relationship with endogenous retrovirus-associated diseases.

Uncovering Minimal Pathways in Melanoma Initiation

Cutaneous melanomas are clinically and histologically heterogeneous. Most display activating mutations in Braf or Nras and complete loss of function of one or more tumor suppressor genes. Mouse models that replicate such mutations produce fast-growing, pigmented tumors. However, mice that combine Braf activation with only heterozygous loss of Pten also produce tumors and, as we show here, in an Albino background this occurs even with Braf activation alone. Such tumors arise rarely, grow slowly, and express low levels of pigmentation genes. The timing of their appearance was consistent with a single step stochastic event, but no evidence could be found that it required de novo mutation, suggesting instead the involvement of an epigenetic transition. Single-cell transcriptomic analysis revealed such tumors to be heterogeneous, including a minor cell type we term LNM ( L ow-pigment, N eural- and extracellular M atrix-signature) that displays gene expression resembling "neural crest"-like cell subsets detected in the fast-growing tumors of more heavily-mutated mice, as well as in human biopsy and xenograft samples. We provide evidence that LNM cells pre-exist in normal skin, are expanded by Braf activation, can transition into malignant cells, and persist with malignant cells through multiple rounds of transplantation. We discuss the possibility that LNM cells not only serve as a pre-malignant state in the production of some melanomas, but also as an important intermediate in the development of drug resistance.

Arsenic Impairs Differentiation of Human Induced Pluripotent Stem Cells into Cholinergic Motor Neurons

Arsenic exposure during embryogenesis can lead to improper neurodevelopment and changes in locomotor activity. Additionally, in vitro studies have shown that arsenic inhibits the differentiation of sensory neurons and skeletal muscle. In the current study, human-induced pluripotent stem (iPS) cells were differentiated into motor neurons over 28 days, while being exposed to up to 0.5 μM arsenic. On day 6, neuroepithelial progenitor cells (NEPs) exposed to arsenic had reduced transcript levels of the neural progenitor/stem cell marker nestin (NES) and neuroepithelial progenitor marker SOX1, while levels of these transcripts were increased in motor neuron progenitors (MNPs) at day 12. In day 18 early motor neurons (MNs), choline acetyltransferase (CHAT) expression was reduced two-fold in cells exposed to 0.5 μM arsenic. RNA sequencing demonstrated that the cholinergic synapse pathway was impaired following exposure to 0.5 μM arsenic, and that transcript levels of genes involved in acetylcholine synthesis (CHAT), transport (solute carriers, SLC18A3 and SLC5A7) and degradation (acetylcholinesterase, ACHE) were all downregulated in day 18 early MNs. In day 28 mature motor neurons, arsenic significantly downregulated protein expression of microtubule-associated protein 2 (MAP2) and ChAT by 2.8- and 2.1-fold, respectively, concomitantly with a reduction in neurite length. These results show that exposure to environmentally relevant arsenic concentrations dysregulates the differentiation of human iPS cells into motor neurons and impairs the cholinergic synapse pathway, suggesting that exposure impairs cholinergic function in motor neurons.

Regulation of the TUG1/miR‑145‑5p/SOX2 axis on the migratory and invasive capabilities of melanoma cells

Melanoma is the most prevalent malignancy of cutaneous carcinomas. Taurine-upregulated gene 1 (TUG1), a lncRNA, is a pivotal regulator of cutaneous malignancies. The present study aimed to investigate the impact and possible mechanisms of action of TUG1 behind the progression of melanomas. Reverse transcription-quantitative PCR was conducted to detect the expression levels of TUG1, microRNA (miR)-145-5p and SOX2 in melanoma tissues and cell lines. Cell Counting Kit-8 (CCK-8) assays were performed to measure the proliferative ability of melanoma cells and transwell assays were used to examine the migration and invasion of melanoma cells. Dual luciferase reporter and RNA immunoprecipitation (RIP) assays were utilized to identify the interactions among TUG1, miR-145-5p and SOX2. Western blotting and immunohistochemical assays were performed to determine the expression profile of SOX2. The impact of TUG1 on melanoma tumorigenesis was assessed using tumorigenicity assays. TUG1 expression levels were elevated in melanoma tumor tissues and cell lines. Reduced TUG1 expression levels significantly inhibited the proliferative, migratory and invasive abilities of melanoma cells. The expression levels of miR-145-5p were decreased in melanoma tumor tissues and cell lines. TUG1 directly targeted miR-145-5p and downregulated miR-145-5p. Upregulation of TUG1 counteracted the promotion of the proliferative, migratory and invasive abilities of melanoma cells induced by the overexpression of miR-145-5p. SOX2 was a target of miR-145-5p and its expression was negatively regulated by miR-145-5p, while positively regulated by TUG1. TUG1 regulated SOX2 expression through sponging miR-145-5p. Silencing of TUG1 also inhibited melanoma tumorigenesis in mice. In conclusion, the TUG1/miR-145-5p/SOX2 axis regulated the migration and invasion of melanoma cells.

Movements of Ancient Human Endogenous Retroviruses Detected in SOX2-Expressing Cells

Human endogenous retroviruses (HERVs) occupy approximately 8% of the human genome. HERVs, transcribed in early embryos, are epigenetically silenced in somatic cells, except under pathological conditions. HERV-K is thought to protect embryos from exogenous viral infection. However, uncontrolled HERV-K expression in somatic cells has been implicated in several diseases. Here, we show that SOX2, which plays a key role in maintaining the pluripotency of stem cells, is critical for HERV-K LTR5Hs. HERV-K undergoes retrotransposition within producer cells in the absence of Env expression. Furthermore, we identified new HERV-K integration sites in long-term culture of induced pluripotent stem cells that express SOX2. These results suggest that the strict dependence of HERV-K on SOX2 has allowed HERV-K to protect early embryos during evolution while limiting the potentially harmful effects of HERV-K retrotransposition on host genome integrity in these early embryos. IMPORTANCE Human endogenous retroviruses (HERVs) account for approximately 8% of the human genome; however, the physiological role of HERV-K remains unknown. This study found that HERV-K LTR5Hs and LTR5B were transactivated by SOX2, which is essential for maintaining and reestablishing pluripotency. HERV-K can undergo retrotransposition within producer cells without env expression, and new integration sites may affect cell proliferation. In induced pluripotent stem cells (iPSCs), genomic impairment due to HERV-K retrotransposition has been identified, but it is a rare event. Considering the retention of SOX2-responsive elements in the HERV-K long terminal repeat (LTR) for over 20 million years, we conclude that HERV-K may play important physiological roles in SOX2-expressing cells.

Investigation of the RB1-SOX2 axis constitutes a tool for viral status determination and diagnosis in Merkel cell carcinoma

MCC (Merkel cell carcinoma) is an aggressive neuroendocrine cutaneous neoplasm. Integration of the Merkel cell polyomavirus (MCPyV) is observed in about 80% of the cases, while the remaining 20% are related to UV exposure. Both MCPyV-positive and -negative MCCs-albeit by different mechanisms-are associated with RB1 inactivation leading to overexpression of SOX2, a major contributor to MCC biology. Moreover, although controversial, loss of RB1 expression seems to be restricted to MCPyV-negative cases.The aim of the present study was to assess the performances of RB1 loss and SOX2 expression detected by immunohistochemistry to determine MCPyV status and to diagnose MCC, respectively.Overall, 196 MCC tumors, 233 non-neuroendocrine skin neoplasms and 70 extra-cutaneous neuroendocrine carcinomas (NEC) were included. SOX2 and RB1 expressions were assessed by immunohistochemistry in a tissue micro-array. Diagnostic performances were determined using the likelihood ratio (LHR).RB1 expression loss was evidenced in 27% of the MCC cases, 12% of non-neuroendocrine skin tumors and 63% of extra-cutaneous NEC. Importantly, among MCC cases, RB1 loss was detected in all MCPyV(-) MCCs, while MCPyV( +) cases were consistently RB1-positive (p < 0.001). SOX2 diffuse expression was observed in 92% of the MCC cases and almost never observed in non-neuroendocrine skin epithelial neoplasms (2%, p < 0.0001, LHR +  = 59). Furthermore, SOX2 diffuse staining was more frequently observed in MCCs than in extra-cutaneous NECs (30%, p < 0.001, LHR +  = 3.1).These results confirm RB1 as a robust predictor of MCC viral status and further suggest SOX2 to be a relevant diagnostic marker of MCC.

SOX2 promotes resistance of melanoma with PD-L1 high expression to T-cell-mediated cytotoxicity that can be reversed by SAHA

BACKGROUND

Immune checkpoint inhibitors (ICIs) induce better tumor regression in melanoma with programmed cell death 1 ligand 1 (PD-L1) high expression, but there has been an upsurge of failed responses. In this study, we aimed to explore the additional mechanisms possibly accounting for ICIs resistance and interventional strategies to overcome the resistance in melanoma with PD-L1 high expression.

METHODS

Melanoma xenografts and cytotoxicity assays were used to investigate function of SOX2 in regulating antitumor immunity. The activity of the janus kinase-signal transducer and activator of transcriptions (JAK-STAT) pathway was investigated by western blots, quantitative PCR and luciferase assay. Epigenetic compounds library screen was employed to identify inhibitors that could decrease SOX2 level. The effect of histone deacetylase inhibitor SAHA in antitumor immunity alone or in combination with immunotherapy was also determined in vitro and in vivo. Prognostic impact of SOX2 was analyzed using transcriptional profiles and clinical data download from the Gene Expression Omnibus and The Cancer Genome Atlas repository.

RESULTS

We uncovered a role of SOX2 in attenuating the sensitivity of melanoma cells to CD8+ T-cell killing. Mechanistically, SOX2 inhibited phosphatases suppressor of cytokine signaling 3 (SOCS3) and protein tyrosine phosphatase non-receptor type 1 (PTPN1) transcription, induced duration activation of the JAK-STAT pathway and thereby overexpression of interferon stimulated genes resistance signature (ISG.RS). By targeting the SOX2-JAK-STAT signaling, SAHA promoted the antitumor efficacy of IFNγ or anti-PD-1 in vitro and in vivo. Moreover, SOX2 was an independent prognostic factor for poor survival and resistant to anti-PD-1 therapy in melanoma with PD-L1 high expression.

CONCLUSIONS

Our data unveiled an additional function of SOX2 causing immune evasion of CD8+ T-cell killing through alleviating the JAK-STAT pathway and ISG.RS expression. We also provided a rationale to explore a novel combination of ICIs with SAHA clinically, especially in melanoma with PD-L1 and SOX2 high expression.

ST3GAL1 is a target of the SOX2-GLI1 transcriptional complex and promotes melanoma metastasis through AXL

Understanding the molecular events controlling melanoma progression is of paramount importance for the development of alternative treatment options for this devastating disease. Here we report a mechanism regulated by the oncogenic SOX2-GLI1 transcriptional complex driving melanoma invasion through the induction of the sialyltransferase ST3GAL1. Using in vitro and in vivo studies, we demonstrate that ST3GAL1 drives melanoma metastasis. Silencing of this enzyme suppresses melanoma invasion and significantly reduces the ability of aggressive melanoma cells to enter the blood stream, colonize distal organs, seed and survive in the metastatic environment. Analysis of glycosylated proteins reveals that the receptor tyrosine kinase AXL is a major effector of ST3GAL1 pro-invasive function. ST3GAL1 induces AXL dimerization and activation that, in turn, promotes melanoma invasion. Our data support a key role of the ST3GAL1-AXL axis as driver of melanoma metastasis, and highlight the therapeutic potential of targeting this axis to treat metastatic melanoma.

Insights into Differentiation of Melanocytes from Human Stem Cells and Their Relevance for Melanoma Treatment

Simple Summary

The reactivation of embryonic developmental programs is crucial for melanoma cells to grow and to metastasize. In order to understand this process better, we first summarize the melanocytic differentiation process both in vivo and in vitro. Secondly, we compare and highlight important similarities between neural crest cell fate during differentiation and tumor cell characteristics during melanoma mestastasis. Finally, we suggest possible therapeutic targets, which could be used to inhibit phenotype switching by developmental cues and hence also suppress the metastatic melanoma spread.

Abstract

Malignant melanoma represents a highly aggressive form of skin cancer. The metastatic process itself is mostly governed by the so-called epithelial mesenchymal transition (EMT), which confers cancer cells migrative, invasive and resistance abilities. Since EMT represents a conserved developmental process, it is worthwhile further examining the nature of early developmental steps fundamental for melanocyte differentiation. This can be done either in vivo by analyzing the physiologic embryo development in different species or by in vitro studies of melanocytic differentiation originating from embryonic human stem cells. Most importantly, external cues drive progenitor cell differentiation, which can be divided in stages favoring neural crest specification or melanocytic differentiation and proliferation. In this review, we describe ectopic factors which drive human pluripotent stem cell differentiation to melanocytes in 2D, as well as in organoid models. Furthermore, we compare developmental mechanisms with processes described to occur during melanoma development. Finally, we suggest differentiation factors as potential co-treatment options for metastatic melanoma patients.

An FGFR/AKT/SOX2 Signaling Axis Controls Pancreatic Cancer Stemness

Cancer stemness is associated with high malignancy and low differentiation, as well as therapeutic resistance of tumors including pancreatic ductal adenocarcinoma (PDAC). Fibroblast growth factors (FGFs) exert pleiotropic effects on a variety of cellular processes and functions including embryonic stem cell pluripotency and cancer cell stemness via the activation of four tyrosine kinase FGF receptors (FGFRs). FGF ligands have been a major component of the cocktail of growth factors contained in the cancer stemness-inducing (CSI) and organoid culture medium. Although FGF/FGFR signaling has been hypothesized to maintain cancer stemness, its function in this process is still unclear. We report that inhibition of FGF/FGFR signaling impairs sphere-forming ability of PDAC in vitro, and knocking down FGFR1 and FGFR2 decreased their tumorigenesis abilities in vivo. Mechanistically, we demonstrated that SOX2 is down-regulated upon loss of FGFR signaling. The overexpression of SOX2 in SOX2-negative cells, which normally do not display stemness capabilities, is sufficient to induce spheroid formation. Additionally, we found that AKT phosphorylation was reduced upon FGFR signaling inhibition. The inhibition of AKT using specific pharmacological inhibitors in the context of CSI medium leads to the loss of spheroid formation associated with loss of SOX2 nuclear expression and increased degradation. We demonstrate that an FGFR/AKT/SOX2 axis controls cancer stemness in PDAC and therefore may represent an important therapeutic target in the fight against this very aggressive form of cancer.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

Differential distribution of the epigenetic marker 5-hydroxymethylcytosine occurs in hair follicle stem cells during bulge activation

BACKGROUND

Hair follicle (HF) cycling is dependent upon activation and differentiation of an epithelial subpopulation of cells with stem-like characteristics. These cells express cytokeratin 15 (CK15) and are sequestered within a specialized niche termed the follicular bulge. The pathways that mediate bulge activation are poorly understood, although growing evidence suggests a role for epigenetic events.

METHODS

Here we investigated murine and human HFs to determine whether a recently described epigenetic hydroxymethylation marker, 5-hmC, known to mediate cell growth and differentiation, may play a role in bulge activation.

RESULTS

We found the bulge region of murine HFs to show variable 5-hmC distribution within the nuclei of CK15-positive stem cells during early anagen, a pattern that was not associated with resting stem cells of telogen follicles, which did not express 5-hmC. Moreover, during phases of early anagen that were induced in an organ culture model, spatial alterations in bulge stem cell 5-hmC reactivity, as assessed by dual labeling, were noted.

CONCLUSIONS

These preliminary findings suggest that 5-hmC may play a dynamic role in bulge activation during anagen growth, and provide a foundation for further experimental inquiry into epigenomic regulation of HF stem cells.

Expression of Potential Dermal Progenitor Cell Markers in the Tumour and Stroma of Skin Adnexal Malignant and Benign Tumours

Stem cells are multipotent cells that maintain the skin epidermis including skin appendages such as hair follicle, sebaceous glands, and sweat glands. There is evidence that reciprocal signalling between the epidermis and the dermis plays an important role in skin development, homeostasis, wound repair, and skin cancer. The origin of skin cancer that derive from skin appendages is still controversial, including basal cell carcinoma and even more of rare tumours such as sebaceous carcinomas and whether those tumours originate from resident tissue stem cells. To investigate whether markers reported to label dermal progenitor cells are preserved in the tumour including the tumour stroma of skin adnexal tumours, we tested 45 human basal cell carcinomas, including superficial, nodular, adenoid, infiltrating, and sclerosing types, and further 38 human tumours of skin appendages including 13 sebaceous adenomas and carcinomas, 20 eccrine sweat gland tumours, and 5 pilomatricomas, syringomas, and hair follicle tumours for the expression of the potential dermal and epidermal cell markers CRABP1, Nestin, and Ephrin B2 and compared these findings with healthy, age-related human epidermis. We detected that CRABP1, Nestin, and Ephrin B2 are expressed in the intratumoural stroma as well as the tumour invasive front of skin tumours of appendages and BCCs.

SOX2 as a novel contributor of oxidative metabolism in melanoma cells

BACKGROUND

Deregulated metabolism is a hallmark of cancer and recent evidence underlines that targeting tumor energetics may improve therapy response and patient outcome. Despite the general attitude of cancer cells to exploit the glycolytic pathway even in the presence of oxygen (aerobic glycolysis or "Warburg effect"), tumor metabolism is extremely plastic, and such ability to switch from glycolysis to oxidative phosphorylation (OxPhos) allows cancer cells to survive under hostile microenvironments. Recently, OxPhos has been related with malignant progression, chemo-resistance and metastasis. OxPhos is induced under extracellular acidosis, a well-known characteristic of most solid tumors, included melanoma.

METHODS

To evaluate whether SOX2 modulation is correlated with metabolic changes under standard or acidic conditions, SOX2 was silenced and overexpressed in several melanoma cell lines. To demonstrate that SOX2 directly represses HIF1A expression we used chromatin immunoprecipitation (ChIP) and luciferase assay.

RESULTS

In A375-M6 melanoma cells, extracellular acidosis increases SOX2 expression, that sustains the oxidative cancer metabolism exploited under acidic conditions. By studying non-acidic SSM2c and 501-Mel melanoma cells (high- and very low-SOX2 expressing cells, respectively), we confirmed the metabolic role of SOX2, attributing SOX2-driven OxPhos reprogramming to HIF1α pathway disruption.

CONCLUSIONS

SOX2 contributes to the acquisition of an aggressive oxidative tumor phenotype, endowed with enhanced drug resistance and metastatic ability.

Tyrosinase and nestin immunohistochemical expression in melanocytic nevi as a histopathologic pattern to trace melanocyte differentiation and nevogenesis

While histological analysis represents a powerful tool for the classification of melanocytic lesions as benign or malignant, a clear-cut distinction between a nevus and a melanoma is sometimes a challenging step of the diagnostic process. The immunohistochemical detection of tyrosinase, cardinal melanogenic enzyme during melanocytic maturation, has often been helpful in formulating a differential diagnosis due to the peculiar staining pattern in nevocytes compared with melanoma cells. Tyrosinase distribution in nevi appears to overlap with the cytoarchitectural changes observable within these lesions, that result in epidermal or superficial dermal nevocytes being larger and strongly expressing melanocytic differentiation antigens, such as tyrosinase, compared with deeper dermal nevus cells. Our study aimed to evaluate the immunohistochemical expression pattern of tyrosinase in different histological types of acquired dysplastic melanocytic nevi, including junctional, compound, and intradermal nevi. Moreover, to estimate whether in nevocytes the expression of tyrosinase was associated with their differentiation state, we investigated the expression of two recognized markers of pluripotency, CD34 and nestin. In all examined nevi, our analysis revealed a remarkable immunoreactivity for tyrosinase in junctional and superficial dermal nevocytes and a decreasing gradient of staining in dermal nevocytes, up to become negative in deeper dermis. Meanwhile, junctional and dermal nevocytes were lacking in CD34 protein. Furthermore, nestin immunostaining showed an opposite distribution compared with tyrosinase, leading us to look into the tyrosinase/nestin expression pattern in melanocytic nevus as a tool to better understand the final stages of differentiation of melanocyte precursors toward their ultimate anatomical site into the epidermis.

Fatty Acid Synthase and Acetyl-CoA Carboxylase Are Expressed in Nodal Metastatic Melanoma But Not in Benign Intracapsular Nodal Nevi

BACKGROUND

Melanoma is a potentially lethal form of skin cancer for which the current standard therapy is complete surgical removal of the primary tumor followed by sentinel lymph node biopsy when indicated. Histologic identification of metastatic melanoma in a sentinel node has significant prognostic and therapeutic implications, routinely guiding further surgical management with regional lymphadenectomy. While melanocytes in a lymph node can be identified by routine histopathologic and immunohistochemical examination, the distinction between nodal nevus cells and melanoma can be morphologically problematic. Previous studies have shown that malignant melanoma can over-express metabolic genes such as fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC). This immunohistochemical study aims to compare the utility of FASN and ACC in differentiating sentinel lymph nodes with metastatic melanomas from those with benign nodal nevi in patients with cutaneous melanoma.

MATERIALS AND METHODS

Using antibodies against FASN and ACC, 13 sentinel lymph nodes from 13 patients with metastatic melanoma and 14 lymph nodes harboring benign intracapsular nevi from 14 patients with cutaneous malignant melanoma were examined. A diagnosis of nodal melanoma was based on cytologic atypia and histologic comparison with the primary melanoma. All nodal nevi were intracapsular and not trabecular. Immunohistochemistry for Melan-A, S100, human melanoma black 45 (HMB45), FASN, and ACC were performed. The percentage of melanocytes staining with HMB45, FASN, and ACC was determined and graded in 25% increments; staining intensity was graded as weak, moderate, or strong.

RESULTS

All metastatic melanomas tested had at least 25% tumor cell staining for both FASN and ACC. Greater than 75% of the tumor cells stained with FAS in 7/13 cases and for ACC in 5/12 cases. Intensity of staining was variable; strong staining for FASN and ACC was observed in 69% and 50% of metastatic melanoma, respectively. HMB45 was negative in 40% of nodal melanoma cases all of which stained with FASN and ACC. Capsular nevi were uniformly negative for FASN, ACC, and HMB45 immunoreactivity.

CONCLUSIONS

All metastatic melanoma cases involving sentinel lymph nodes were positive for FASN and ACC while no staining was observed in intracapsular nevi. These findings suggest that FASN and ACC could be used as valuable ancillary stains in the distinction between nodal nevi and metastatic melanoma.

The dark side of SOX2: cancer - a comprehensive overview

The pluripotency-associated transcription factor SOX2 is essential during mammalian embryogenesis and later in life, but SOX2 expression can also be highly detrimental. Over the past 10 years, SOX2 has been shown to be expressed in at least 25 different cancers. This review provides a comprehensive overview of the roles of SOX2 in cancer and focuses on two broad topics. The first delves into the expression and function of SOX2 in cancer focusing on the connection between SOX2 levels and tumor grade as well as patient survival. As part of this discussion, we address the developing connection between SOX2 expression and tumor drug resistance. We also call attention to an under-appreciated property of SOX2, its levels in actively proliferating tumor cells appear to be optimized to maximize tumor growth - too little or too much SOX2 dramatically alters tumor growth. The second topic of this review focuses on the exquisite array of molecular mechanisms that control the expression and transcriptional activity of SOX2. In addition to its complex regulation at the transcriptional level, SOX2 expression and activity are controlled carefully by microRNAs, long non-coding RNAs, and post-translational modifications. In the Conclusion and Future Perspectives section, we point out that there are still important unanswered questions. Addressing these questions is expected to lead to new insights into the functions of SOX2 in cancer, which will help design novels strategies for more effectively treating some of the most deadly cancers.

Expression of monoacylglycerol lipase as a marker of tumour invasion and progression in malignant melanoma

BACKGROUND

Accumulating evidence suggests that the lipid lytic enzyme monoacylglycerol lipase (MAGL) promotes tumour invasion and metastasis through up-regulation of pro-tumorigenic signalling lipids in several tumour cell lines. However, the expression status of MAGL in clinical melanoma tissues and its clinicopathological significance remain unclear.

OBJECTIVE

To correlate the tumour expression status of MAGL with the clinicopathological information of patients with malignant melanoma.

METHODS

Polymerase chain reaction (PCR) array screening was performed, and the results were validated using immunocytochemical analysis of tumour and non-tumour melanocytic cell lines. Immunohistochemical staining for MAGL was performed for 74 melanoma samples, including 48 primary and 26 metastatic tumours, in which the expression of MAGL was determined by evaluating the percentage of MAGL-positive tumour cells and the MAGL staining intensity. Finally, we analysed the association of MAGL expression status with tumour progression, tumour thickness and vascular invasion of the primary lesion.

RESULTS

Immunocytochemical analysis revealed that MAGL was expressed in all 12 melanoma cell lines, but not in normal human epidermal melanocytes. In the immunohistochemical analysis, positive staining for MAGL was noted in 32 of 48 (64.5%) primary lesions, 14 of 17 (82.4%) lymph node metastatic lesions and 7 of 9 (77.8%) skin metastatic lesions. Metastatic tumours had a significantly higher staining intensity (P = 0.033 for lymph node, P = 0.010 for skin). In the analysis of primary lesions, higher MAGL expression correlated with greater tumour thickness (P = 0.015) and the presence of vascular invasion (P = 0.017). On further evaluation of MAGL-positive primary lesions, staining intensity of MAGL tended to be higher in deeper areas of the tumour mass.

CONCLUSIONS

The expression of MAGL in tumour cells reflects the aggressiveness of melanoma cells and may serve as a marker of tumour progression.

TGF-β induces SOX2 expression in a time-dependent manner in human melanoma cells

The sry-related high-mobility box (SOX)-2 protein has recently been proven to play a significant role in progression, metastasis, and clinical prognosis spanning several cancer types. Research on the role of SOX2 in melanoma is limited and currently little is known about the mechanistic function of this gene in this context. Here, we observed high expression of SOX2 in both human melanoma cell lines and primary melanomas in contrast to melanocytic nevi. This overexpression in melanoma can, in part, be explained by extra gene copy numbers of SOX2 in primary samples. Interestingly, we were able to induce SOX2 expression, mediated by SOX4, via TGF-β1 stimulation in a time-dependent manner. Moreover, the knockdown of SOX2 impaired TGF-β-induced invasiveness. This phenotype switch can be explained by SOX2-mediated cross talk between TGF-β and non-canonical Wnt signaling. Thus, we propose that SOX2 is involved in the critical TGF-β signaling pathway, which has been shown to correlate with melanoma aggressiveness and metastasis. In conclusion, we have identified a novel downstream factor of TGF-β signaling in melanoma, which may have further implications in the clinic.

Sox2 is not required for melanomagenesis, melanoma growth and melanoma metastasis in vivo

Melanoma is a dangerous form of skin cancer derived from the malignant transformation of melanocytes. The transcription factor SOX2 is not expressed in melanocytes, however, it has been shown to be differentially expressed between benign nevi and malignant melanomas and to be essential for melanoma stem cell maintenance and expansion in vitro and in xenograft models. By using a mouse model in which BRaf^V600E mutation cooperates with Pten loss to induce the development of metastatic melanoma, we investigated if Sox2 is required during the process of melanomagenesis, melanoma growth and metastasis and in the acquisition of resistance to BRAF inhibitors (BRAFi) treatments. We found that deletion of Sox2 specifically in Pten null and BRafV600E-expressing melanocytes did not prevent tumor formation and did not modify the temporal kinetics of melanoma occurrence compared to Sox2 wt mice. In addition, tumor growth was similar between Sox2 wt and Sox2 deleted (del) melanomas. By querying publicly available databases, we did not find statistically significant differences in SOX2 expression levels between benign nevi and melanomas, and analysis on two melanoma patient cohorts confirmed that Sox2 levels did not significantly change between primary and metastatic melanomas. Melanoma cell lines derived from both Sox2 genotypes showed a similar sensitivity to vemurafenib treatment and the same ability to develop vemurafenib resistance in long-term cultures. Development of vemurafenib resistance was not dependent on SOX2 expression also in human melanoma cell lines in vitro. Our findings exclude an oncogenic function for Sox2 during melanoma development and do not support a role for this transcription factor in the acquisition of resistance to BRAFi treatments.

Sox2 is dispensable for primary melanoma and metastasis formation

Tumor initiation and metastasis formation in many cancers have been associated with emergence of a gene expression program normally active in embryonic or organ-specific stem cells. In particular, the stem cell transcription factor Sox2 is not only expressed in a variety of tumors, but is also required for their formation. Melanoma, the most aggressive skin tumor, derives from melanocytes that during development originate from neural crest stem cells. While neural crest stem cells do not express Sox2, expression of this transcription factor has been reported in melanoma. However, the role of Sox2 in melanoma is controversial. To study the requirement of Sox2 for melanoma formation, we therefore performed CRISPR-Cas9-mediated gene inactivation in human melanoma cells. In addition, we conditionally inactivated Sox2 in a genetically engineered mouse model, in which melanoma spontaneously develops in the context of an intact stroma and immune system. Surprisingly, in both models, loss of Sox2 did neither affect melanoma initiation, nor growth, nor metastasis formation. The lack of a tumorigenic role of Sox2 in melanoma might reflect a distinct stem cell program active in neural crest stem cells and during melanoma formation.

Oxidative stress induces the acquisition of cancer stem-like phenotype in breast cancer detectable by using a Sox2 regulatory region-2 (SRR2) reporter

We have previously identified a novel intra-tumoral dichotomy in breast cancer based on the differential responsiveness to a Sox2 reporter (SRR2), with cells responsive to SRR2 (RR) being more stem-like than unresponsive cells (RU). Here, we report that RR cells derived from MCF7 and ZR751 displayed a higher tolerance to oxidative stress than their RU counterparts, supporting the concept that the RR phenotype correlates with cancer stemness. Sox2 is directly implicated in this differential H₂O₂ tolerance, since siRNA knockdown of Sox2 in RR cells leveled this difference. Interestingly, H₂O₂ converted a proportion of RU cells into RR cells, as evidenced by their expression of luciferase and GFP, markers of SRR2 activity. Compared to RU cells, converted RR cells showed a significant increase in mammosphere formation and tolerance to H₂O₂. Converted RR cells also adopted the biochemical features of RR cells, as evidenced by their substantial increase in Sox2-SRR2 binding and the expression of 3 signature genes of RR cells (CD133, GPR49 and MUC15). Lastly, the H₂O₂-induced RU/RR conversion was detectable in a SCID mouse xenograft model and primary tumor cells. To conclude, the H₂O₂-induced RU/RR conversion has provided a novel model to study the acquisition of cancer stemness and plasticity.

Pulsed DC Electric Field-Induced Differentiation of Cortical Neural Precursor Cells

We report the differentiation of neural stem and progenitor cells solely induced by direct current (DC) pulses stimulation. Neural stem and progenitor cells in the adult mammalian brain are promising candidates for the development of therapeutic neuroregeneration strategies. The differentiation of neural stem and progenitor cells depends on various in vivo environmental factors, such as nerve growth factor and endogenous EF. In this study, we demonstrated that the morphologic and phenotypic changes of mouse neural stem and progenitor cells (mNPCs) could be induced solely by exposure to square-wave DC pulses (magnitude 300 mV/mm at frequency of 100-Hz). The DC pulse stimulation was conducted for 48 h, and the morphologic changes of mNPCs were monitored continuously. The length of primary processes and the amount of branching significantly increased after stimulation by DC pulses for 48 h. After DC pulse treatment, the mNPCs differentiated into neurons, astrocytes, and oligodendrocytes simultaneously in stem cell maintenance medium. Our results suggest that simple DC pulse treatment could control the fate of NPCs. With further studies, DC pulses may be applied to manipulate NPC differentiation and may be used for the development of therapeutic strategies that employ NPCs to treat nervous system disorders.

TET2 Negatively Regulates Nestin Expression in Human Melanoma

Although melanoma is an aggressive cancer, the understanding of the virulence-conferring pathways involved remains incomplete. We have demonstrated that loss of ten-eleven translocation methylcytosine dioxygenase (TET2)-mediated 5-hydroxymethylcytosine (5-hmC) is an epigenetic driver of melanoma growth and a biomarker of clinical virulence. We also have determined that the intermediate filament protein nestin correlates with tumorigenic and invasive melanoma growth. Here we examine the relationships between these two biomarkers. Immunohistochemistry staining of nestin and 5-hmC in 53 clinically annotated primary and metastatic patient melanomas revealed a significant negative correlation. Restoration of 5-hmC, as assessed in a human melanoma cell line by introducing full-length TET2 and TET2-mutated constructs, decreased nestin gene and protein expression in vitro. Genome-wide mapping using hydroxymethylated DNA immunoprecipitation sequencing disclosed significantly less 5-hmC binding in the 3' untranslated region of the nestin gene in melanoma compared to nevi, and 5-hmC binding in this region was significantly increased after TET2 overexpression in human melanoma cells in vitro. Our findings provide evidence suggesting that nestin regulation is negatively controlled epigenetically by TET2 via 5-hmC binding at the 3' untranslated region of the nestin gene, providing one potential pathway for understanding melanoma growth characteristics. Studies are now indicated to further define the interplay between 5-hmC, nestin expression, and melanoma virulence.

Desmoplastic melanoma: an updated immunohistochemical analysis of 40 cases with a proposal for an additional panel of stains for diagnosis

Desmoplastic melanoma (DM) is histologically characterized by a proliferation of spindle melanocytes dispersed in a collagenous stroma that can be mistaken for a variety of neoplasms. The purpose of this study was to analyze 40 cases of DM with a comprehensive panel of immunohistochemical markers (KBA.62, p16, Ezrin, WT-1, MITF-1, SOX-10, CD117, SOX-2, nestin, PNL2, p75, MART-1, gp100 and S100p) to obtain a more complete understanding of the potential use of these antibodies in the diagnosis of DM. We found that all cases of DM expressed p16, WT-1, SOX-10, nestin and S100p and 95% of cases expressed p75. There was variable expression with Ezrin, SOX-2, KBA.62, MART-1 and HMB-45. Most DMs did not express MITF-1, PNL2 and CD117. Conditions that may enter in the histologic differential diagnosis of DM, including dermal scars, fibromatosis and dermatofibromas were also studied. Nearly all control cases also stained positive for p16 but were negative for WT1, SOX10, nestin, p75 and S-100p, as well as for most of the other markers tested. We conclude that a panel of S-100p, WT1, SOX10, p75 and nestin may constitute the optimal panel with the most sensitive and specific combination of immunostain available for the diagnosis of DM.

Correlation of overexpression of nestin with expression of epithelial-mesenchymal transition-related proteins in gastric adenocarcinoma

BACKGROUND

Nestin is associated with neoplastic transformation. However, the mechanisms by which nestin contributes regarding invasion and malignancy of gastric adenocarcinoma (GAC) remain unknown. Recent studies have shown that the epithelial-mesenchymal transition (EMT) is important in invasion and migration of cancer cells. In the present study, we aimed to investigate the expression of nestin and its correlation with EMT-related proteins in GAC.

MATERIALS AND METHODS

The expression of nestin and EMT-related proteins was examined in GAC specimens and cell lines by immunohistochemistry and Western blotting. Clinicopathological features and survival outcomes were retrospectively analyzed.

RESULTS

Positive nestin immunostaining was most obviously detected in the cytoplasm, nucleus or both cytoplasm and nucleus of tumor cells in 19.2% (24/125) of GAC tissues, which was significantly higher than that in normal gastric mucosa tissues (1.7%, 1/60) (p=0.001). Nestin expression was closely related to several clinicopathological factors and EMT-related proteins (E-cadherin, vimentin and Snail) and displayed a poor prognosis. Interestingly, simultaneous cytoplasmic and nuclear nestin expression correlated with EMT-related proteins (E-cadherin, vimentin and Snail) (p<0.05) and lymph node metastasis (p=0.041) and a shorter survival time (p<0.05), but this was not the case with cytoplasmic or nuclear nestin expression.

CONCLUSIONS

Nestin, particularly expression in both cytoplasm and nucleus, might be involved in regulating EMT and malignant progression in GAC, with potential as an unfavorable indicator in tumor diagnosis and a target for clinical therapy.

Regulation of viability, differentiation and death of human melanoma cells carrying neural stem cell biomarkers: a possibility for neural trans-differentiation

During embryonic development, melanoblasts, the precursors of melanocytes, emerge from a subpopulation of the neural crest stem cells and migrate to colonize skin. Melanomas arise during melanoblast differentiation into melanocytes and from young proliferating melanocytes through somatic mutagenesis and epigenetic regulations. In the present study, we used several human melanoma cell lines from the sequential phases of melanoma development (radial growth phase, vertical growth phase and metastatic phase) to compare: (i) the frequency and efficiency of the induction of cell death via apoptosis and necroptosis; (ii) the presence of neural and cancer stem cell biomarkers as well as death receptors, DR5 and FAS, in both adherent and spheroid cultures of melanoma cells; (iii) anti-apoptotic effects of the endogenous production of cytokines and (iv) the ability of melanoma cells to perform neural trans-differentiation. We demonstrated that programed necrosis or necroptosis, could be induced in two metastatic melanoma lines, FEMX and OM431, while the mitochondrial pathway of apoptosis was prevalent in a vast majority of melanoma lines. All melanoma lines used in the current study expressed substantial levels of pluripotency markers, SOX2 and NANOG. There was a trend for increasing expression of Nestin, an early neuroprogenitor marker, during melanoma progression. Most of the melanoma lines, including WM35, FEMX and A375, can grow as a spheroid culture in serum-free media with supplements. It was possible to induce neural trans-differentiation of 1205Lu and OM431 melanoma cells in serum-free media supplemented with insulin. This was confirmed by the expression of neuronal markers, doublecortin and β3-Tubulin, by significant growth of neurites and by the negative regulation of this process by a dominant-negative Rac1N17. These results suggest a relative plasticity of differentiated melanoma cells and a possibility for their neural trans-differentiation without the necessity for preliminary dedifferentiation.

Future perspectives in melanoma research: meeting report from the "Melanoma Bridge": Napoli, December 3rd-6th 2014

The fourth "Melanoma Bridge Meeting" took place in Naples, December 3-6th, 2014. The four topics discussed at this meeting were: Molecular and Immunological Advances, Combination Therapies, News in Immunotherapy, and Tumor Microenvironment and Biomarkers. Until recently systemic therapy for metastatic melanoma patients was ineffective, but recent advances in tumor biology and immunology have led to the development of new targeted and immunotherapeutic agents that prolong progression-free survival (PFS) and overall survival (OS). New therapies, such as mitogen-activated protein kinase (MAPK) pathway inhibitors as well as other signaling pathway inhibitors, are being tested in patients with metastatic melanoma either as monotherapy or in combination, and all have yielded promising results. These include inhibitors of receptor tyrosine kinases (BRAF, MEK, and VEGFR), the phosphatidylinositol 3 kinase (PI3K) pathway [PI3K, AKT, mammalian target of rapamycin (mTOR)], activators of apoptotic pathway, and the cell cycle inhibitors (CDK4/6). Various locoregional interventions including radiotherapy and surgery are still valid approaches in treatment of advanced melanoma that can be integrated with novel therapies. Intrinsic, adaptive and acquired resistance occur with targeted therapy such as BRAF inhibitors, where most responses are short-lived. Given that the reactivation of the MAPK pathway through several distinct mechanisms is responsible for the majority of acquired resistance, it is logical to combine BRAF inhibitors with inhibitors of targets downstream in the MAPK pathway. For example, combination of BRAF/MEK inhibitors (e.g., dabrafenib/trametinib) have been demonstrated to improve survival compared to monotherapy. Application of novel technologies such sequencing have proven useful as a tool for identification of MAPK pathway-alternative resistance mechanism and designing other combinatorial therapies such as those between BRAF and AKT inhibitors. Improved survival rates have also been observed with immune-targeted therapy for patients with metastatic melanoma. Immune-modulating antibodies came to the forefront with anti-CTLA-4, programmed cell death-1 (PD-1) and PD-1 ligand 1 (PD-L1) pathway blocking antibodies that result in durable responses in a subset of melanoma patients. Agents targeting other immune inhibitory (e.g., Tim-3) or immune stimulating (e.g., CD137) receptors and other approaches such as adoptive cell transfer demonstrate clinical benefit in patients with melanoma as well. These agents are being studied in combination with targeted therapies in attempt to produce longer-term responses than those more typically seen with targeted therapy. Other combinations with cytotoxic chemotherapy and inhibitors of angiogenesis are changing the evolving landscape of therapeutic options and are being evaluated to prevent or delay resistance and to further improve survival rates for this patient population. This meeting's specific focus was on advances in combination of targeted therapy and immunotherapy. Both combination targeted therapy approaches and different immunotherapies were discussed. Similarly to the previous meetings, the importance of biomarkers for clinical application as markers for diagnosis, prognosis and prediction of treatment response was an integral part of the meeting. The overall emphasis on biomarkers supports novel concepts toward integrating biomarkers into contemporary clinical management of patients with melanoma across the entire spectrum of disease stage. Translation of the knowledge gained from the biology of tumor microenvironment across different tumors represents a bridge to impact on prognosis and response to therapy in melanoma.

Diagnostic Immunohistochemistry in Cutaneous Neoplasia: An Update

Immunohistochemistry (IHC) is an important adjunct in the diagnosis of neoplastic skin diseases. In addition to the many established IHC markers currently in use, new markers continue to emerge, although their general acceptance and routine application requires robust validation. Here, we summarize the most well-established and commonly used biomarkers along with an array of newer ones reported in the past several decades that either demonstrate or hold high clinical promise in the field of cutaneous pathology. We also highlight recent applications of novel IHC markers in melanoma diagnosis including genetic mutation status markers [e.g. BRAF (v-raf murine sarcoma viral oncogene homolog B) and NRAS (neuroblastoma RAS viral oncogene homolog)] and an epigenetic alteration marker (e.g. 5-hydroxymethylcytosine). We specifically focus on the role of IHC in the differential diagnosis of cutaneous lesions that fall under the following categories: melanoma, epidermal tumors with an intraepidermal epitheliomatous pattern, spindle cell lesions of the dermis, small round blue cell tumors of the dermis, and cutaneous adnexal tumors. While IHC is a valuable tool in diagnostic dermatopathology, marker selection and interpretation must be highly informed by clinical context and the histologic differential diagnosis. With rapid progress in our understanding of the genetic and epigenetic mechanisms of tumorigenesis, new IHC markers will continue to emerge in the field of diagnostic dermatopathology.

Inhibitor of DNA Binding 4 (ID4) is highly expressed in human melanoma tissues and may function to restrict normal differentiation of melanoma cells

Melanoma tissues and cell lines are heterogeneous, and include cells with invasive, proliferative, stem cell-like, and differentiated properties. Such heterogeneity likely contributes to the aggressiveness of the disease and resistance to therapy. One model suggests that heterogeneity arises from rare cancer stem cells (CSCs) that produce distinct cancer cell lineages. Another model suggests that heterogeneity arises through reversible cellular plasticity, or phenotype-switching. Recent work indicates that phenotype-switching may include the ability of cancer cells to dedifferentiate to a stem cell-like state. We set out to investigate the phenotype-switching capabilities of melanoma cells, and used unbiased methods to identify genes that may control such switching. We developed a system to reversibly synchronize melanoma cells between 2D-monolayer and 3D-stem cell-like growth states. Melanoma cells maintained in the stem cell-like state showed a striking upregulation of a gene set related to development and neural stem cell biology, which included SRY-box 2 (SOX2) and Inhibitor of DNA Binding 4 (ID4). A gene set related to cancer cell motility and invasiveness was concomitantly downregulated. Intense and pervasive ID4 protein expression was detected in human melanoma tissue samples, suggesting disease relevance for this protein. SiRNA knockdown of ID4 inhibited switching from monolayer to 3D-stem cell-like growth, and instead promoted switching to a highly differentiated, neuronal-like morphology. We suggest that ID4 is upregulated in melanoma as part of a stem cell-like program that facilitates further adaptive plasticity. ID4 may contribute to disease by preventing stem cell-like melanoma cells from progressing to a normal differentiated state. This interpretation is guided by the known role of ID4 as a differentiation inhibitor during normal development. The melanoma stem cell-like state may be protected by factors such as ID4, thereby potentially identifying a new therapeutic vulnerability to drive differentiation to the normal cell phenotype.

5-Hydroxymethylcytosine expression in metastatic melanoma versus nodal nevus in sentinel lymph node biopsies

Sentinel lymph node biopsies are conducted to stage patients with newly diagnosed melanomas that have histopathological attributes conferring defined levels of metastatic potential. Because benign nevic cells may also form 'deposits' in lymph nodes (nodal nevus), the pathological evaluation for metastatic melanoma within sentinel lymph nodes can be challenging. Twenty-eight sentinel lymph node biopsy cases containing either metastatic melanoma (N=18) or nodal nevi (N=10) were retrieved from the archives of the Brigham and Women's Hospital, Department of Pathology (2011-2014). In addition, two sentinel lymph node cases that were favored to represent metastatic disease but whose histopathological features were viewed as equivocal, with melanoma favored, were also included. Dual labeling for the melanocyte lineage marker, MART-1, and the epigenetic marker, 5-hydroxymethylcytosine, a functionally significant indicator that has been shown to distinguish benign nevi from melanoma, was performed on all cases using immunohistochemistry and/or direct immunofluorescence. All (18 of 18) metastatic melanoma cases showed complete loss of 5-hydroxymethylcytosine nuclear staining in MART-1-positive cells, and all (10 of 10) nodal nevus cases demonstrated 5-hydroxymethylcytosine nuclear staining in MART-1-positive cells. In addition, 5-hydroxymethylcytosine staining confirmed the favored diagnoses of metastatic melanoma in the two 'equivocal' cases. Thus, 5-hydroxymethylcytosine may be a useful adjunctive marker to distinguish between benign nodal nevi and metastatic melanoma during the evaluation of sentinel lymph node biopsies for metastatic melanoma.

Nestin depletion induces melanoma matrix metalloproteinases and invasion

Matrix metalloproteinases (MMPs) are key biological mediators of processes as diverse as wound healing, embryogenesis, and cancer progression. Although MMPs may be induced through multiple signaling pathways, the precise mechanisms for their regulation in cancer are incompletely understood. Because cytoskeletal changes are known to accompany MMP expression, we sought to examine the potential role of the poorly understood cytoskeletal protein, nestin, in modulating melanoma MMPs. Nestin knockdown (KD) upregulated the expression of specific MMPs and MMP-dependent invasion both through extracellular matrix barriers in vitro and in peritumoral connective tissue of xenografts in vivo. The development of three-dimensional melanospheres that in vitro partially recapitulate noninvasive tumorigenic melanoma growth was inhibited by nestin KD, although ECM invasion by aberrant melanospheres that did form was enhanced. Mechanistically, nestin KD-dependent melanoma invasion was associated with intracellular redistribution of phosphorylated focal adhesion kinase and increased melanoma cell responsiveness to transforming growth factor-beta, both implicated in pathways of melanoma invasion. The results suggest that the heretofore poorly understood intermediate filament, nestin, may serve as a novel mediator of MMPs critical to melanoma virulence.

Profiling gene promoter occupancy of Sox2 in two phenotypically distinct breast cancer cell subsets using chromatin immunoprecipitation and genome-wide promoter microarrays

Introduction

Aberrant expression of the embryonic stem cell marker Sox2 has been reported in breast cancer (BC). We previously identified two phenotypically distinct BC cell subsets separated based on their differential response to a Sox2 transcription activity reporter, namely the reporter-unresponsive (RU) and the more tumorigenic reporter-responsive (RR) cells. We hypothesized that Sox2, as a transcription factor, contributes to their phenotypic differences by mediating differential gene expression in these two cell subsets.

Methods

We used chromatin immunoprecipitation and a human genome-wide promoter microarray (ChIP-chip) to determine the promoter occupancies of Sox2 in the MCF7 RU and RR breast cancer cell populations. We validated our findings with conventional chromatin immunoprecipitation, quantitative reverse transcription polymerase chain reaction (qPCR), and western blotting using cell lines, and also performed qPCR using patient RU and RR samples.

Results

We found a largely mutually exclusive profile of gene promoters bound by Sox2 between RU and RR cells derived from MCF7 (1830 and 456 genes, respectively, with only 62 overlapping genes). Sox2 was bound to stem cell- and cancer-associated genes in RR cells. Using quantitative RT-PCR, we confirmed that 15 such genes, including PROM1 (CD133), BMI1, GPR49 (LGR5), and MUC15, were expressed significantly higher in RR cells. Using siRNA knockdown or enforced expression of Sox2, we found that Sox2 directly contributes to the higher expression of these genes in RR cells. Mucin-15, a novel Sox2 downstream target in BC, contributes to the mammosphere formation of BC cells. Parallel findings were observed in the RU and RR cells derived from patient samples.

Conclusions

In conclusion, our data supports the model that the Sox2 induces differential gene expression in the two distinct cell subsets in BC, and contributes to their phenotypic differences.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0470-2) contains supplementary material, which is available to authorized users.

Sox2 expression involvement in the oncogenicity and radiochemoresistance of oral cancer stem cells

OBJECTIVES

Sox2, a high-mobility-group DNA binding protein, is part of the key set of transcription factors that are involved in the maintenance of pluripotency and self-renewal in undifferentiated stem cells. A recent study has further suggested cancer stem cells (CSCs) are key contributors to radiochemoresistance and are responsible for oral squamous cell carcinoma (OSCC) progression. The aim of this study was to determine the emerging role of Sox2 in radiochemosensitivity of oral CSCs.

METHODS

We determined the function of Sox2 on oncogenicity and radiochemosensitivity of OSCC by overexpression or silencing Sox2 in vitro and in vivo.

RESULTS

Initially, Sox2 expression was increased in OSCC cell lines and OSCC specimens. Upregulated Sox2 is correlated with poor survival outcome of OSCC patients. Overexpression of Sox2 was demonstrated to enhance invasiveness, anchorage-independent growth, xenotransplantation tumourigenicity in OSCC cells. Targeting Sox2 to spheroid cells (SC) and ALDH1+CD44+ cells from OSCC significantly inhibited their CSCs and tumorigenic abilities. Down regulation of SOX2 in OSCC-SC was found to repress invasiveness and diminish epithelail-mesenchymal transition (EMT) traits. Furthermore, silencing Sox2 effectively suppressed the expression of drug-resistance and anti-apoptotic genes and increased the sensitivity of the cells to radiation combined cisplatin treatment. Finally, the in vivo therapeutic efficacy of targeting Sox2 synergistically suppressed tumorigenesis and improved the survival rate when used in combination with radiotherapy and cisplatin in OSCC-SC-transplanted immunocompromised mice.

CONCLUSION

Sox2-mediated CSCs property is associated with the regulation of EMT and Sox2 s as therapeutic target in OSCC.

SOX2 and cancer: current research and its implications in the clinic

SOX2 is a gene that encodes for a transcription factor belonging to the SOX gene family and contains a high-mobility group (HMG) domain, which permits highly specific DNA binding. Consequently, SOX2 functions as an activator or suppressor of gene transcription. SOX2 has been described as an essential embryonic stem cell gene and moreover, a necessary factor for induced cellular reprogramming. SOX2 research has only recently switched focus from embryogenesis and development to SOX2’s function in disease. Particularly, the role of SOX2 in cancer pathogenesis has become of interest in the field. To date, studies have shown SOX2 to be amplified in various cancer types and affect cancer cell physiology via involvement in complicated cell signaling and protein-protein interactions. Recent reviews in this field have highlighted SOX2 in mammalian physiology, development and pathology. In this review, we comprehensively compile what is known to date about SOX2’s involvement in cancer biology, focusing on the most recent findings in the fields of cellular signaling and cancer stem cells. Lastly, we underscore the role of SOX2 in the clinic and highlight new findings, which may provide novel clinical applications for SOX2 as a prognostic marker, indicator of metastasis, biomarker or potential therapeutic target in some cancer types.

YB-1 regulates Sox2 to coordinately sustain stemness and tumorigenic properties in a phenotypically distinct subset of breast cancer cells

BACKGROUND

Sox2, a transcription factor and an embryonic stem cell marker, has been implicated in the pathogenesis of breast cancer (BC). YB-1 is another transcription factor that has been shown to promote stemness in BC cells.

METHODS

Western blotting, quantitative PCR, and siRNAs were used to query the regulatory relationships between YB-1, Sox2, and their downstream targets. Chromatin immunoprecipitation was used to detect YB-1 interactions at the Sox2 promoter. Mammosphere and soft agar assays were used to assess the phenotypic consequences of YB-1 knockdown.

RESULTS

Here, we report that YB-1 regulates Sox2. YB-1 was found to bind to the SOX2 promoter and down-regulate its expression in MCF7 and ZR751. The regulatory interaction between YB-1 and Sox2 was drastically different between the two phenotypically distinct cell subsets, purified based on their differential response to a Sox2 reporter. They are referred to as the reporter unresponsive (RU) cells and the reporter responsive (RR) cells. Upon siRNA knockdown of YB-1, RU cells showed an increase in Sox2 expression but no change in Sox2 reporter activity; in contrast, RR cells exhibited increased expression and reporter activity of Sox2. Correlating with these findings, YB-1 knockdown induced a differential response in the expression of genes known to be regulated by both Sox2 and YB-1 (e.g. CCND1 and ITGA6). For instance, in response to YB-1 knockdown, CCND1 and ITGA6 expression were decreased or unchanged in RU cells but paradoxically increased in RR cells. Compared to RU cells, RR cells were significantly more resistant to the suppression of mammosphere formation due to YB-1 knockdown. Importantly, mammospheres derived from parental MCF7 cells treated with YB-1 siRNA knockdown exhibited higher expression levels of SOX2 and its downstream targets.

CONCLUSIONS

To conclude, in a subset of BC cells, namely RR cells, YB-1 regulates Sox2 to coordinately maintain stemness and tumorigenic properties.

SOX2 regulates self-renewal and tumorigenicity of human melanoma-initiating cells

Melanoma is one of the most aggressive types of human cancer, characterized by enhanced heterogeneity and resistance to conventional therapy at advanced stages. We and others have previously shown that HEDGEHOG-GLI (HH-GLI) signaling is required for melanoma growth and for survival and expansion of melanoma-initiating cells (MICs). Recent reports indicate that HH-GLI signaling regulates a set of genes typically expressed in embryonic stem cells, including SOX2 (sex-determining region Y (SRY)-Box2). Here we address the function of SOX2 in human melanomas and MICs and its interaction with HH-GLI signaling. We find that SOX2 is highly expressed in melanoma stem cells. Knockdown of SOX2 sharply decreases self-renewal in melanoma spheres and in putative melanoma stem cells with high aldehyde dehydrogenase activity (ALDH(high)). Conversely, ectopic expression of SOX2 in melanoma cells enhances their self-renewal in vitro. SOX2 silencing also inhibits cell growth and induces apoptosis in melanoma cells. In addition, depletion of SOX2 progressively abrogates tumor growth and leads to a significant decrease in tumor-initiating capability of ALDH(high) MICs upon xenotransplantation, suggesting that SOX2 is required for tumor initiation and for continuous tumor growth. We show that SOX2 is regulated by HH signaling and that the transcription factors GLI1 and GLI2, the downstream effectors of HH-GLI signaling, bind to the proximal promoter region of SOX2 in primary melanoma cells. In functional studies, we find that SOX2 function is required for HH-induced melanoma cell growth and MIC self-renewal in vitro. Thus SOX2 is a critical factor for self-renewal and tumorigenicity of MICs and an important mediator of HH-GLI signaling in melanoma. These findings could provide the basis for novel therapeutic strategies based on the inhibition of SOX2 for the treatment of a subset of human melanomas.

Stem cells and targeted approaches to melanoma cure

Melanoma stem cells, also known as malignant melanoma-initiating cells, are identifiable through expression of specific biomarkers such as ABCB5 (ATP-binding cassette, sub-family B (MDR/TAP), member 5), NGFR (nerve growth factor receptor, CD271) and ALDH (aldehyde dehydrogenase), and drive melanoma initiation and progression based on prolonged self-renewal capacity, vasculogenic differentiation and immune evasion. As we will review here, specific roles of these aggressive subpopulations have been documented in tumorigenic growth, metastatic dissemination, therapeutic resistance, and malignant recurrence. Moreover, recent findings have provided pre-clinical proof-of-concept for the potential therapeutic utility of the melanoma stem cell concept. Therefore, melanoma stem cell-directed therapeutic approaches represent promising novel strategies to improve therapy of this arguably most virulent human cancer.

SOX2 expression associates with stem cell state in human ovarian carcinoma

The SRY-related HMG-box family of transcription factors member SOX2 regulates stemness and pluripotency in embryonic stem cells and plays important roles during early embryogenesis. More recently, SOX2 expression was documented in several tumor types including ovarian carcinoma, suggesting an involvement of SOX2 in regulation of cancer stem cells (CSC). Intriguingly, however, studies exploring the predictive value of SOX2 protein expression with respect to histopathologic and clinical parameters report contradictory results in individual tumors, indicating that SOX2 may play tumor-specific roles. In this report, we analyze the functional relevance of SOX2 expression in human ovarian carcinoma. We report that in human serous ovarian carcinoma (SOC) cells, SOX2 expression increases the expression of CSC markers, the potential to form tumor spheres, and the in vivo tumor-initiating capacity, while leaving cellular proliferation unaltered. Moreover, SOX2-expressing cells display enhanced apoptosis resistance in response to conventional chemotherapies and TRAIL. Hence, our data show that SOX2 associates with stem cell state in ovarian carcinoma and induction of SOX2 imposes CSC properties on SOC cells. We propose the existence of SOX2-expressing ovarian CSCs as a mechanism of tumor aggressiveness and therapy resistance in human SOC.

Diagnostic utility of neural stem and progenitor cell markers nestin and SOX2 in distinguishing nodal melanocytic nevi from metastatic melanomas

Sentinel lymph node evaluation is a critical component of melanoma staging, and lymph node status provides one of the most powerful predictors of melanoma recurrence and survival. One of the well-known diagnostic pitfalls in melanoma sentinel lymph node evaluation is the presence of nodal melanocytic nevi, which has been demonstrated in up to 26% of lymphadenectomy specimens and specifically in melanoma patients. Melanocytic markers enhance the sensitivity of melanoma detection in sentinel lymph nodes. However, established markers such as anti-melan-A/MART1, S100 protein and SOX10 antibodies cannot discriminate melanoma metastasis from nodal nevi. Recent studies have demonstrated strong expression of neural stem/progenitor cell markers nestin and SOX2 in melanoma. In this study, we tested the diagnostic utility of nestin and SOX2 in differentiating metastatic melanomas from nodal nevi. Twenty-three lymph nodes with metastatic melanomas and 17 with nodal nevi were examined. Of the 23 metastatic melanomas, 18 showed diffuse and strong (3+) nestin, 4 showed rare cells with strong (3+) nestin, and one showed diffuse but faint (1+) nestin staining. Nuclear SOX2 was positive in 13 metastatic melanomas. In contrast, 15 nodal nevi showed no nestin, and 2 showed rare cells with very faint (<1+) nestin staining. SOX2 was negative in 13 nodal nevi. Overall, nestin was strongly expressed in metastatic melanomas (n=22/23; 96%), but not in nodal melanocytic nevi (n=15/17; 88%; P<0.0001). SOX2 was also expressed in metastatic melanomas (n=13/23; 57%) but not in the majority of nodal melanocytic nevi (n=13/16; 81%; P=0.02). In one lymph node harboring metastatic melan-A-negative desmoplastic melanoma, nestin and SOX2 strongly highlighted the infiltrating tumor cells, suggesting the potential clinical value of these two markers in desmoplastic melanoma lymph node biopsies. This study provides evidence that nestin and SOX2 can effectively differentiate nodal melanocytic nevi from metastatic melanomas and serve as powerful diagnostic adjuncts in melanoma staging.

Progression of cutaneous melanoma: implications for treatment

The survival rates of melanoma, like any type of cancer, become worse with advancing stage. Spectrum theory is most consistent with the progression of melanoma from the primary site to the in-transit locations, regional or sentinel lymph nodes and beyond to the distant sites. Therefore, early diagnosis and surgical treatment before its spread is the most effective treatment. Recently, new approaches have revolutionized the diagnosis and treatment of melanoma. Genomic profiling and sequencing will form the basis for molecular taxonomy for more accurate subgrouping of melanoma patients in the future. New insights of molecular mechanisms of metastasis are summarized in this review article. Sentinel lymph node biopsy has become a standard of care for staging primary melanoma without the need for a more morbid complete regional lymph node dissection. With recent developments in molecular biology and genomics, novel molecular targeted therapy is being developed through clinical trials.

Loss of microRNA-200a and c, and microRNA-203 expression at the invasive front of primary cutaneous melanoma is associated with increased thickness and disease progression

Loss of E-cadherin expression in melanoma correlates with increased tumor thickness and reduced disease-free survival. The molecular mechanisms underpinning its differential expression in melanoma tissue remain elusive. MicroRNAs (miRNAs) have been implicated in tumor progression and regulation of E-cadherin expression. Here, we demonstrate a significant correlation between tumor thickness and loss of expression of miR-200a, miR-200c, and miR-203 in a series of 23 frozen primary melanomas, where it was confirmed in two subsequent validation series (series 1: six nevi, 15 primary melanomas, and 16 metastases; series 2: 11 matched pairs of primary melanomas and metastases). Decreased levels of miR-200a, miR-200c, and miR-203 correlated with increasing thickness in the combined validation series (P = 0.024, 0.033, and 0.031, respectively). In addition, progressive loss of miR-200a expression with disease progression was observed in series 1 (P < 0.001) and in series 2 (P = 0.029). MiR-200 in situ hybridization and E-cadherin immunohistochemistry demonstrated reduced expression of both at the deep invasive margin of the tumor. Furthermore, a functional validation study using an anti-miR200 strategy demonstrated that loss of miR-200 expression in melanoma cell lines reduced E-cadherin expression. Collectively, our data point towards an important role for miR-200 and miR203 expression in regulating E-cadherin during melanoma progression.

Stem cell media culture of melanoma results in the induction of a nonrepresentative neural expression profile

The ability of cell lines to accurately represent cancer is a major concern in preclinical research. Culture of glioma cells as neurospheres in stem cell media (SCM) has been shown to better represent the genotype and phenotype of primary glioblastoma in comparison to serum cell lines. Despite the use of neurosphere-like models of many malignancies, there has been no robust analysis of whether other cancers benefit from a more representative phenotype and genotype when cultured in SCM. We analyzed the growth properties, transcriptional profile, and genotype of melanoma cells grown de novo in SCM, as while melanocytes share a common precursor with neural cells, melanoma frequently demonstrates divergent behavior in cancer stem cell assays. SCM culture of melanoma cells induced a neural lineage gene expression profile that was not representative of matched patient tissue samples and which could be induced in serum cell lines by switching them into SCM. There was no enrichment for expression of putative melanoma stem cell markers, but the SCM expression profile did overlap significantly with that of SCM cultures of glioma, suggesting that the observed phenotype is media-specific rather than melanoma-specific. Xenografts derived from either culture condition provided the best representation of melanoma in situ. Finally, SCM culture of melanoma did not prevent ongoing acquisition of DNA copy number abnormalities. In conclusion, SCM culture of melanoma does not provide a better representation of the phenotype or genotype of metastatic melanoma, and the resulting neural bias could potentially confound therapeutic target identification.

Novel biomarkers and therapeutic targets for optimizing the therapeutic management of melanomas

Cutaneous malignant melanoma is the most aggressive form of skin cancer with an extremely poor survival rate for the patients diagnosed with locally invasive and metastatic disease states. Intensive research has led in last few years to an improvement of the early detection and curative treatment of primary cutaneous melanomas that are confined to the skin by tumor surgical resection. However, locally advanced and disseminated melanomas are generally resistant to conventional treatments, including ionizing radiation, systemic chemotherapy, immunotherapy and/or adjuvant stem cell-based therapies, and result in the death of patients. The rapid progression of primary melanomas to locally invasive and/or metastatic disease states remains a major obstacle for an early effective diagnosis and a curative therapeutic intervention for melanoma patients. Importantly, recent advances in the melanoma research have led to the identification of different gene products that are often implicated in the malignant transformation of melanocytic cells into melanoma cells, including melanoma stem/progenitor cells, during melanoma initiation and progression to locally advanced and metastatic disease states. The frequent deregulated genes products encompass the oncogenic B-RafV600E and N-RasQ61R mutants, different receptor tyrosine kinases and developmental pathways such as epidermal growth factor receptor (EGFR), stem cell-like factor (SCF) receptor KIT, hedgehog, Wnt/β-catenin, Notch, stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) and vascular endothelial growth factor (VEGF)/VEGFR receptor. These growth factors can cooperate to activate distinct tumorigenic downstream signaling elements and epithelial-mesenchymal transition (EMT)-associated molecules, including phosphatidylinositol 3’-kinase (PI3K)/Akt/ molecular target of rapamycin (mTOR), nuclear factor-kappaB (NF-κB), macrophage inhibitory cytokine-1 (MIC-1), vimentin, snail and twist. Of therapeutic relevance, these deregulated signal transduction components constitute new potential biomarkers and therapeutic targets of great clinical interest for improving the efficacy of current diagnostic and prognostic methods and management of patients diagnosed with locally advanced, metastatic and/or relapsed melanomas.

Sex-determining region Y-box 2 expression predicts poor prognosis in human ovarian carcinoma

Sex-determining region Y-box 2 is proposed to be a key transcription factor in embryonic stem cells. The known roles of sex-determining region Y-box 2 in development and cell differentiation suggest that it is relevant to the aberrant growth of tumor cells. Thus, sex-determining region Y-box 2 may play an important role in tumor progression. However, its clinical significance in human ovarian carcinoma has been uncertain until recently. The aim of the present study was to clarify the clinical role of sex-determining region Y-box 2 expression in ovarian carcinoma. Immunohistochemical staining of 540 human ovarian carcinoma samples for sex-determining region Y-box 2 was performed using tissue microarray. The associations among sex-determining region Y-box 2 expression and clinical factors (diagnosis, tumor grade, International Federation of Gynecology and Obstetrics stage, and response to chemotherapy), overall survival, and disease-free survival were analyzed. We observed sex-determining region Y-box 2 expression in 15% of the ovarian carcinoma samples. Use of the Fisher exact test suggested that sex-determining region Y-box 2 expression was associated with high-grade carcinoma (P = .009), especially high-grade serous carcinoma (P = .048); International Federation of Gynecology and Obstetrics stage (II-IV; P = .005); and malignant mixed müllerian tumors (P = .048). Sex-determining region Y-box 2 expression was also associated with decreased disease-free survival durations (P = .035; log-rank test). Our results showed that sex-determining region Y-box 2 expression may be a potential marker related to tumor recurrence, as implicated by its role in cancer stem cells.

SOX2 contributes to melanoma cell invasion

The mechanisms of melanoma invasion are poorly understood despite extensive inquiry. SRY (sex determining region Y)-box 2 (SOX2) is an embryonic stem cell transcription factor that has recently been discovered to be expressed in human melanoma where it is associated with dermal invasion and primary tumor thickness. To assess the potential role of SOX2 expression in melanoma invasion, we examined patient melanomas and humanized melanoma xenografts, and noted preferential SOX2 expression in cells that interfaced and infiltrated dermal stroma. Experimental knockdown (KD) of SOX2 mRNA and protein in A2058 melanoma cells with high constitutive SOX2 expression resulted in 4.5-fold decreased invasiveness in vitro compared with controls (P<0.0001). Conversely, when G361 cells that normally express low SOX2 were transduced to overexpress SOX2 mRNA and protein, a 3.8-fold increase in invasiveness was observed (P=0.0004). Among 84 invasion-related genes, RT-PCR screening revealed that SOX2 KD resulted in striking decrease in matrix metalloproteinase-3 (MMP-3), an endopeptidase associated with cleavage of the extracellular matrix. Quantitatively, SOX2 KD diminished MMP-3 mRNA by 87.8%. MMP-3 KD in SOX2-expressing A2058 cells served to inhibit invasion, although to a lesser degree than SOX2 KD. Finally, immunostaining of patient and xenograft melanomas revealed coordinate SOX2 and MMP-3 expression in regions of stromal infiltration. These data implicate SOX2 expression in melanoma invasion, and suggest a role for MMP-3 as one potential mediator of this process.