Sox10 Regulates Stem/Progenitor and Mesenchymal Cell States in Mammary Epithelial Cells

Stem Cells and the Differentiation Hierarchy in Mammary Gland Development

The mammary gland is a highly dynamic organ that undergoes profound changes within its epithelium during puberty and the reproductive cycle. These changes are fueled by dedicated stem and progenitor cells. Both short- and long-lived lineage-restricted progenitors have been identified in adult tissue as well as a small pool of multipotent mammary stem cells (MaSCs), reflecting intrinsic complexity within the epithelial hierarchy. While unipotent progenitor cells predominantly execute day-to-day homeostasis and postnatal morphogenesis during puberty and pregnancy, multipotent MaSCs have been implicated in coordinating alveologenesis and long-term ductal maintenance. Nonetheless, the multipotency of stem cells in the adult remains controversial. The advent of large-scale single-cell molecular profiling has revealed striking changes in the gene expression landscape through ontogeny and the presence of transient intermediate populations. An increasing number of lineage cell-fate determination factors and potential niche regulators have now been mapped along the hierarchy, with many implicated in breast carcinogenesis. The emerging diversity among stem and progenitor populations of the mammary epithelium is likely to underpin the heterogeneity that characterizes breast cancer.

Emerging Role of SOX Proteins in Breast Cancer Development and Maintenance

The SOX genes encode a family of more than 20 transcription factors that are critical regulators of embryogenesis and developmental processes and, when aberrantly expressed, have been shown to contribute to tumor development and progression in both an oncogenic and tumor suppressive role. Increasing evidence demonstrates that the SOX proteins play essential roles in multiple cellular processes that mediate or contribute to oncogenic transformation and tumor progression. In the context of breast cancer, SOX proteins function both as oncogenes and tumor suppressors and have been shown to be associated with tumor stage and grade and poor prognosis. Experimental evidence demonstrates that a subset of SOX proteins regulate critical aspects of breast cancer biology including cancer stemness and multiple signaling pathways leading to altered cell proliferation, survival, and tumor development; EMT, cell migration and metastasis; as well as other tumor associated characteristics. This review will summarize the role of SOX family members as important mediators of tumorigenesis in breast cancer, with an emphasis on the triple negative or basal-like subtype of breast cancer, as well as examine the therapeutic potential of these genes and their downstream targets.

Transcriptional regulation of normal human mammary cell heterogeneity and its perturbation in breast cancer

The mammary gland in adult women consists of biologically distinct cell types that differ in their surface phenotypes. Isolation and molecular characterization of these subpopulations of mammary cells have provided extensive insights into their different transcriptional programs and regulation. This information is now serving as a baseline for interpreting the heterogeneous features of human breast cancers. Examination of breast cancer mutational profiles further indicates that most have undergone a complex evolutionary process even before being detected. The consequent intra-tumoral as well as inter-tumoral heterogeneity of these cancers thus poses major challenges to deriving information from early and hence likely pervasive changes in potential therapeutic interest. Recently described reproducible and efficient methods for generating human breast cancers de novo in immunodeficient mice transplanted with genetically altered primary cells now offer a promising alternative to investigate initial stages of human breast cancer development. In this review, we summarize current knowledge about key transcriptional regulatory processes operative in these partially characterized subpopulations of normal human mammary cells and effects of disrupting these processes in experimentally produced human breast cancers.

SOX10 Immunostaining in granulomatous dermatoses and benign reactive lymph nodes

BACKGROUND

SOX10 immunostaining has been considered a highly sensitive and specific marker for melanoma. But there is evidence suggesting that SOX10 positive cells can be present in dermal scars. Therefore, we investigated whether non-melanocytic cell types present in chronic inflammatory processes or benign lymph nodes express SOX10.

METHODS

We retrospectively selected 20 benign lymph nodes and 20 cutaneous granulomatous dermatoses. SOX10, CD68, and Melan-A immunohistochemistry was performed in all cases.

RESULTS

Scattered SOX10 positivity was found in 85% of lymph nodes, specifically in subcapsular and medullary sinuses and in 85% of granulomatous dermatoses. In granulomatous dermatoses, the Melan-A stain did not label the scattered SOX10 positive cells and it was difficult to determine if CD68 was co-expressed on the SOX10 positive cells. In the lymph nodes, the SOX10 positive cells did not co-express Melan-A or CD68.

CONCLUSIONS

We report SOX10 positive cells detected in granulomatous dermatoses and benign lymph nodes. In lymph nodes, SOX10 positive cells were exclusively in subcapsular and medullary sinuses. Therefore, SOX10 is an excellent stain for evaluation of metastatic melanoma with the caveat that positivity in subcapsular and medullary sinuses can be of non-melanocytic origin; the use of additional melanocytic markers is recommended in this situations.

Cell Reprogramming in Tumorigenesis and Its Therapeutic Implications for Breast Cancer

Breast cancer is the most common malignancy in women worldwide and can be categorized into several subtypes according to histopathological parameters or genomic signatures. Such heterogeneity of breast cancer can arise from the reactivation of mammary stem cells in situ during tumorigenesis. Moreover, different breast cancer subtypes exhibit varieties of cancer incidence, therapeutic response, and patient prognosis, suggesting that a specific therapeutic protocol is required for each breast cancer subtype. Recent studies using molecular and cellular assays identified a link between specific genetic/epigenetic alterations and distinct cells of origin of breast cancer subtypes. These alterations include oncogenes, tumor suppressor genes, and cell-lineage determinants, which can induce cell reprogramming (dedifferentiation and transdifferentiation) among two lineage-committed mammary epithelial cells, namely basal and luminal cells. The interconversion of cell states through cell reprogramming into the intermediates of mammary stem cells can give rise to heterogeneous breast cancers that complicate effective therapies of breast cancer. A better understanding of mechanisms underlying cell reprogramming in breast cancer can help in not only elucidating tumorigenesis but also developing therapeutics for breast cancer. This review introduces recent findings on cancer gene-mediated cell reprogramming in breast cancer and discusses the therapeutic potential of targeting cell reprogramming.

p21CIP1 Promotes Mammary Cancer-Initiating Cells via Activation of Wnt/TCF1/CyclinD1 Signaling

Cancer stem cells (CSC) generate and sustain tumors due to tumor-initiating potential, resulting in recurrence or metastasis. We showed that knockout of the cell-cycle inhibitor, p21CIP1, in the PyMT mammary tumor model inhibits metastasis; however the mechanism remained unknown. Here, we show a pivotal role for p21 in potentiating a cancer stem-like phenotype. p21 knockout in PyMT mammary tumor cells caused dramatic suppression of CSC properties involving tumorsphere formation, ALDH1 activity, and tumor-initiating potential, which were in turn rescued by p21 overexpression into PyMT/p21 knockout cells. Interestingly, p21 knockout dramatically suppresses Wnt/β-catenin signaling activity, leading to striking inhibition of LEF1 and TCF1 expression. TCF1 knockdown in PyMT cells suppressed tumorsphere formation due to Cyclin D1 attenuation. These data demonstrate that p21 promotes a CSC-like phenotype via activation of Wnt/TCF1/Cyclin D1 signaling. IMPLICATIONS: p21 is a strong promoter of mammary CSCs.

The role of SOX family members in solid tumours and metastasis

Cancer is a heavy burden for humans across the world with high morbidity and mortality. Transcription factors including sex determining region Y (SRY)-related high-mobility group (HMG) box (SOX) proteins are thought to be involved in the regulation of specific biological processes. The deregulation of gene expression programs can lead to cancer development. Here, we review the role of the SOX family in breast cancer, prostate cancer, renal cell carcinoma, thyroid cancer, brain tumours, gastrointestinal and lung tumours as well as the entailing therapeutic implications. The SOX family consists of more than 20 members that mediate DNA binding by the HMG domain and have regulatory functions in development, cell-fate decision, and differentiation. SOX2, SOX4, SOX5, SOX8, SOX9, and SOX18 are up-regulated in different cancer types and have been found to be associated with poor prognosis, while the up-regulation of SOX11 and SOX30 appears to be favourable for the outcome in other cancer types. SOX2, SOX4, SOX5 and other SOX members are involved in tumorigenesis, e.g. SOX2 is markedly up-regulated in chemotherapy resistant cells. The SoxF family (SOX7, SOX17, SOX18) plays an important role in angio- and lymphangiogenesis, with SOX18 seemingly being an attractive target for anti-angiogenic therapy and the treatment of metastatic disease in cancer. In summary, SOX transcription factors play an important role in cancer progression, including tumorigenesis, changes in the tumour microenvironment, and metastasis. Certain SOX proteins are potential molecular markers for cancer prognosis and putative potential therapeutic targets, but further investigations are required to understand their physiological functions.

Sox10 Regulates Plasticity of Epithelial Progenitors toward Secretory Units of Exocrine Glands

Understanding how epithelial progenitors within exocrine glands establish specific cell lineages and form complex functional secretory units is vital for organ regeneration. Here we identify the transcription factor Sox10 as essential for both the maintenance and differentiation of epithelial KIT⁺FGFR2b⁺ progenitors into secretory units, containing acinar, myoepithelial, and intercalated duct cells. The KIT/FGFR2b-Sox10 axis marks the earliest multi-potent and tissue-specific progenitors of exocrine glands. Genetic deletion of epithelial Sox10 leads to loss of secretory units, which reduces organ size and function, but the ductal tree is retained. Intriguingly, the remaining duct progenitors do not compensate for loss of Sox10 and lack plasticity to properly form secretory units. However, overexpression of Sox10 in these ductal progenitors enhances their plasticity toward KIT⁺ progenitors and induces differentiation into secretory units. Therefore, Sox10 controls plasticity and multi-potency of epithelial KIT⁺ cells in secretory organs, such as mammary, lacrimal, and salivary glands.

•

Sox10 marks the initial multi-potent KIT⁺ progenitors of exocrine glandular tissues

•

KIT⁺ progenitors require Sox10 for their maintenance

•

Sox10 is necessary for proper lineage development of secretory units

•

Sox10 is sufficient to induce cell plasticity in non-KIT⁺ epithelial cells

PRAME promotes epithelial-to-mesenchymal transition in triple negative breast cancer

Background

The triple negative breast cancer (TNBC) paradox marks a major challenge in the treatment-decision making process. TNBC patients generally respond better to neoadjuvant chemotherapy compared to other breast cancer patients; however, they have a substantial higher risk of disease recurrence. We evaluated the expression of the tumor-associated antigen PReferentially Antigen expressed in MElanoma (PRAME) as a prognostic biomarker in breast cancer and explored its role in cell migration and invasion, key hallmarks of progressive and metastatic disease.

Methods

TCGA and GTeX datasets were interrogated to assess the expression of PRAME in relation to overall and disease-free survival. The role of PRAME in cell migration and invasion was investigated using gain- and loss-of-function TNBC cell line models.

Results

We show that PRAME promotes migration and invasion of TNBC cells through changes in expression of E-cadherin, N-cadherin, vimentin and ZEB1, core markers of an epithelial-to-mesenchymal transition. Mechanistic analysis of PRAME-overexpressing cells showed an upregulation of 11 genes (SNAI1, TCF4, TWIST1, FOXC2, IL1RN, MMP2, SOX10, WNT11, MMP3, PDGFRB, and JAG1) and downregulation of 2 genes (BMP7 and TSPAN13). Gene ontology analyses revealed enrichment of genes that are dysregulated in ovarian and esophageal cancer and are involved in transcription and apoptosis. In line with this, interrogation of TCGA and GTEx data demonstrated an increased PRAME expression in ovarian and esophageal tumor tissues in addition to breast tumors where it is associated with worse survival.

Conclusions

Our findings indicate that PRAME plays a tumor-promoting role in triple negative breast cancer by increasing cancer cell motility through EMT-gene reprogramming. Therefore, PRAME could serve as a prognostic biomarker and/or therapeutic target in TNBC.

A combination of GATA3 and SOX10 is useful for the diagnosis of metastatic triple-negative breast cancer

In metastatic breast cancer (MBC), it can be difficult to establish the origin if the primary tumor is triple negative or if there is a loss of biomarker expression. SOX10 expression has been reported in primary triple-negative breast cancer but is poorly studied in metastatic lesions. In this study, the diagnostic utility of a panel of SOX10, GATA3, and androgen receptor (AR) in MBC negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 was evaluated and compared with the expression of these markers in the matched primary breast cancer. In a series of 57 triple-negative MBCs, 82% were positive for GATA3, 58% for SOX10, and 25% for AR. Nearly all MBCs (95%) were positive for either GATA3 or SOX10, with 46% dual positive and 5% of cases negative for both markers. Most GATA3-negative MBC cases were SOX10 positive (70%). AR expression was only seen in GATA3-positive MBC (25%) and was significantly more frequent in SOX10-negative MBC (48%) versus SOX10-positive MBC (9%; P = .001). Concordance for GATA3, SOX10, and AR between the primary and metastasis was 89%, 88%, and 80%, respectively. Although GATA3 is a more sensitive lineage marker than SOX10 in MBC, SOX10 is a useful adjunct because it is positive in most GATA3-negative breast metastases. Using both GATA3 and SOX10 is recommended for confirming breast as the site of origin in metastases that lack estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 expression, whereas the addition of AR is not helpful.

Epigenetic and Transcriptomic Profiling of Mammary Gland Development and Tumor Models Disclose Regulators of Cell State Plasticity

Cell state reprogramming during tumor progression complicates accurate diagnosis, compromises therapeutic effectiveness, and fuels metastatic dissemination. We used chromatin accessibility assays and transcriptional profiling during mammary development as an agnostic approach to identify factors that mediate cancer cell state interconversions. We show that fetal and adult basal cells share epigenetic features consistent with multi-lineage differentiation potential. We find that DNA-binding motifs for SOX transcription factors are enriched in chromatin that is accessible in stem/progenitor cells and inaccessible in differentiated cells. In both mouse and human tumors, SOX10 expression correlates with stem/progenitor identity, dedifferentiation, and invasive characteristics. Strikingly, we demonstrate that SOX10 binds to genes that regulate neural crest cell identity, and that SOX10-positive tumor cells exhibit neural crest cell features.

Assessing the efficacy of androgen receptor and Sox10 as independent markers of the triple-negative breast cancer subtype by transcriptome profiling

The Androgen Receptor (AR) has recently garnered a lot of attention as a potential biomarker and therapeutic target in hormone-dependent cancers, including breast cancer. However, several inconsistencies exist within the literature as to which subtypes of breast cancer express AR or whether it can be used to define its own unique subtype. Here, we analyze 1246 invasive breast cancer samples from the Cancer Genome Atlas and show that human breast cancers that have been subtyped based on their HER2, ESR1, or PGR expression contain four clusters of genes that are differentially expressed across all subtypes. We demonstrate that Sox10 is highly expressed in approximately one-third of all HER2/ESR1/PGR-low tumors and is a candidate biomarker of the triple-negative subtype. Although AR expression is acquired in many breast cancer cases, its expression could not define a unique subtype. Despite several reports stating that AR expression is acquired in HER2/ESR1/PGR triple-negative cancers, here we show that a low percentage of these cancers express AR (~20%). In contrast, AR is highly expressed in HER2-positive or ESR1/PGR-positive cancers (> 95%). Although AR expression cannot be used as an independent subtype biomarker, our analysis shows that routine evaluation of AR expression in tumors which express HER2, ESR1 and/or PGR may identify a unique subset of tumors which would benefit from anti-androgen based therapies.

Developmental abnormalities of the otic capsule and inner ear following application of prolyl-hydroxylase inhibitors in chick embryos

BACKGROUND

Naturally hypoxic conditions in amniote embryos play important roles in normal development. We previously showed that a hypoxic condition is required to produce a sufficient amount of neural crest cells (NCCs) during embryogenesis and that promoting a hypoxic response by prolyl-hydroxylase (PHD) inhibitors increases NCCs. Given that PHD inhibitors are considered as a potential treatment for anemia and ischemic diseases, we investigated the phenotypic effect of PHD inhibitors on embryonic development.

METHODS

Chick embryos were administered with PHD inhibitors prior to the induction of NCCs on day 1.5. Three main events relating to hypoxia, NCCs induction, vasculogenesis and chondrogenesis, were examined.

RESULTS

PHD inhibitors caused an increase of Sox10-positive NCCs in vivo. Vasculogenesis was promoted temporarily, although rapid vasculogenesis diminished the effect by day 5 in cephalic and pharyngeal regions. Studies on chondrogenesis at day 7 showed advanced development of the otic capsule, a cartilaginous structure encapsulating the inner ear. Analysis by X-ray micro-computed-tomography (μCT) revealed smaller otic capsule, suggesting premature differentiation. This in turn, deformed the developing semicircular canals within it. Other skeletal structures such as the palate and jaw were unaffected. The localized effect on the otic capsule was considered a result of the multiple effects from the hypoxic responses, increased NCCs and promoted chondrogenesis.

CONCLUSION

Given the wide range of clinical applications being considered for PHD inhibitors, this study provides crucial information to caution and guide use of PHD inhibitors when treating women of childbearing age.

Targeting stromal remodeling and cancer stem cell plasticity overcomes chemoresistance in triple negative breast cancer

The cellular and molecular basis of stromal cell recruitment, activation and crosstalk in carcinomas is poorly understood, limiting the development of targeted anti-stromal therapies. In mouse models of triple negative breast cancer (TNBC), Hedgehog ligand produced by neoplastic cells reprograms cancer-associated fibroblasts (CAFs) to provide a supportive niche for the acquisition of a chemo-resistant, cancer stem cell (CSC) phenotype via FGF5 expression and production of fibrillar collagen. Stromal treatment of patient-derived xenografts with smoothened inhibitors (SMOi) downregulates CSC markers expression and sensitizes tumors to docetaxel, leading to markedly improved survival and reduced metastatic burden. In the phase I clinical trial EDALINE, 3 of 12 patients with metastatic TNBC derived clinical benefit from combination therapy with the SMOi Sonidegib and docetaxel chemotherapy, with one patient experiencing a complete response. These studies identify Hedgehog signaling to CAFs as a novel mediator of CSC plasticity and an exciting new therapeutic target in TNBC.

Targeting stromal remodeling and cancer stem cell plasticity overcomes chemoresistance in triple negative breast cancer

The cellular and molecular basis of stromal cell recruitment, activation and crosstalk in carcinomas is poorly understood, limiting the development of targeted anti-stromal therapies. In mouse models of triple negative breast cancer (TNBC), Hedgehog ligand produced by neoplastic cells reprograms cancer-associated fibroblasts (CAFs) to provide a supportive niche for the acquisition of a chemo-resistant, cancer stem cell (CSC) phenotype via FGF5 expression and production of fibrillar collagen. Stromal treatment of patient-derived xenografts with smoothened inhibitors (SMOi) downregulates CSC markers expression and sensitizes tumors to docetaxel, leading to markedly improved survival and reduced metastatic burden. In the phase I clinical trial EDALINE, 3 of 12 patients with metastatic TNBC derived clinical benefit from combination therapy with the SMOi Sonidegib and docetaxel chemotherapy, with one patient experiencing a complete response. These studies identify Hedgehog signaling to CAFs as a novel mediator of CSC plasticity and an exciting new therapeutic target in TNBC.

Stromal cell recruitment, activation and crosstalk with cancer cells is poorly understood. Here, the authors demonstrate that cancer cell-derived Hedgehog ligand  triggers stromal remodeling that in turn induces a cancer-stem-cell like, drug-resistant phenotype of nearby cancer cells while treatment with smoothened inhibitors reverses these phenotypes.

Implications of nestin in breast cancer pathogenesis (Review)

The aim of the present review was to summarize the current knowledge of the involvement of nestin in breast cancer (BC) pathogenesis. Nestin is a member of the class VI family of intermediate filament proteins, originally identified as a marker of neural stem cells and subsequently demonstrated to be expressed in BC and other cancer types. In normal breast tissue, nestin is expressed in the basal/myoepithelial cells of the mammary gland. In BC, nestin identifies basal-like tumours and predicts aggressive behaviour and poor prognosis. Nestin expression has also been detected in BC stem cells and newly-formed tumour vessels, being a factor in promoting invasion and metastasis. The present review provides an up-to-date overview of the involvement of nestin in processes facilitating BC pathogenesis and progression.

Clinicopathological, immunohistochemical and molecular correlation of neural crest transcription factor SOX10 expression in triple-negative breast carcinoma

The transcription factor SOX10 mediates the differentiation of neural crest-derived cells, and SOX10 by immunohistochemistry (IHC) is used primarily for the diagnosis of melanoma. SOX10 expression has been previously documented in benign breast myoepithelial cells. However there is limited literature on its expression in triple-negative breast carcinoma (TNBC). The aim was to study the clinical, pathologic and molecular profiles of SOX10+ tumors in TNBC. Tissue microarrays of TNBC were evaluated for SOX10 expression in 48 cases. SOX10 expression was correlated with clinical and pathologic features such as age, grade, and stage. Gene expression was analyzed on RNA extracted from formalin-fixed paraffin-embedded (FFPE) specimens with Affymetrix 2.0 HTA. Co-expression of SOX10 with androgen receptor (AR), WT1, gross cystic disease fluid protein-15 (GCDFP-15), mammaglobin, epidermal growth factor receptor (EGFR), CK5/6 and GATA transcription factor 3 (GATA3) were also assessed. The mean age was 59.38 (range, 28-90 years). Overall, 37.5% cases (18/48) were SOX10+. There was no association between SOX10 expression and age, grade or stage of patients; 6 of 10 (60%) cases of basal-like 1 (BL1), and 5 of 8 cases of unstable (UNS) molecular subtype were SOX10+. One of 5 basal-like-2 (BL2), 1 of 6 immunomodulatory (IM), 1 of 4 mesenchymal (M), 1 of 5 luminal androgen receptor (LAR) and 2 of 8 mesenchymal stem cell (MSL) showed lower frequencies of SOX10 expression. There was negative correlation between SOX10 and AR+ subtypes (P < .002). SOX10 was positively correlated with WT1 (P = .05). SOX10 did not show significant correlation with mammaglobin, GCDFP15, EGFR, CK5/6 and GATA3. SOX10 expression in the basal-like and unstable molecular subtypes supports the concept that these neoplasms show myoepithelial differentiation.

Early lineage segregation of multipotent embryonic mammary gland progenitors

The mammary gland (MG) is composed of basal cells (BCs) and luminal cells (LCs). While it is generally believed that MG arises from embryonic multipotent progenitors (EMPs), it remains unclear when lineage restriction occurs and what are the mechanisms responsible for the switch from multipotency to unipotency during MG morphogenesis. Here, we performed multicolor lineage tracing and assessed the fate of single progenitors and demonstrated the existence of a developmental switch from multipotency to unipotency during embryonic MG development. Molecular profiling and single cell RNA-seq revealed that EMPs express a unique hybrid basal and luminal signature and the factors associated with the different lineages. Sustained p63 expression in EMPs promotes unipotent BC fate and was sufficient to reprogram adult LCs into BCs by promoting an intermediate hybrid multipotent like state. Altogether, this study identifies the timing and the mechanisms mediating the early lineage segregation of multipotent progenitors during MG development.

Mammary Stem Cells and Breast Cancer Stem Cells: Molecular Connections and Clinical Implications

Cancer arises from subpopulations of transformed cells with high tumor initiation and repopulation ability, known as cancer stem cells (CSCs), which share many similarities with their normal counterparts. In the mammary gland, several studies have shown common molecular regulators between adult mammary stem cells (MaSCs) and breast cancer stem cells (bCSCs). Cell plasticity and self-renewal are essential abilities for MaSCs to maintain tissue homeostasis and regenerate the gland after pregnancy. Intriguingly, these properties are similarly executed in breast cancer stem cells to drive tumor initiation, tumor heterogeneity and recurrence after chemotherapy. In addition, both stem cell phenotypes are strongly influenced by external signals from the microenvironment, immune cells and supportive specific niches. This review focuses on the intrinsic and extrinsic connections of MaSC and bCSCs with clinical implications for breast cancer progression and their possible therapeutic applications.

Inhibition of UGT8 suppresses basal-like breast cancer progression by attenuating sulfatide-αVβ5 axis

Cao et al. show that UGT8 promotes BLBC progression through activating sulfatide–αVβ5 axis. ZA is identified as a direct inhibitor of UGT8 and suppresses BLBC progression, suggesting that inhibition of UGT8 offers a promising opportunity for treating BLBC.

Basal-like breast cancer (BLBC) is associated with a poor clinical outcome as a result of the few treatment options and poor therapeutic response. Here, we report that elevated expression of urine diphosphate–galactose ceramide galactosyltransferase (UGT8) specifically occurs in BLBC and predicts poor prognosis in breast cancer patients. UGT8 expression is transcriptionally up-regulated by Sox10, triggering the sulfatide biosynthetic pathway; increased sulfatide activates integrin αVβ5-mediated signaling that contributes to BLBC progression. UGT8 expression promotes, whereas UGT8 knockdown suppresses tumorigenicity and metastasis. Importantly, we identify that zoledronic acid (ZA), a marketed drug for treating osteoporosis and bone metastasis, is a direct inhibitor of UGT8, which blocks the sulfatide biosynthetic pathway. Significantly, a clinically achievable dosage of ZA exhibits apparent inhibitory effect on migration, invasion, and lung metastasis of BLBC cells. Together, our study suggests that UGT8 is a potential prognostic indicator and druggable target of BLBC and that pharmacologic inhibition of UGT8 by ZA offers a promising opportunity for treating this challenging disease.

REC8 inhibits EMT by downregulating EGR1 in gastric cancer cells

REC8 is a component of the meiotic cohesion complex that plays a critical role in chromosome dynamics during meiosis. However, the functional role of REC8 in gastric cancer has not been elucidated. In the present study, REC8 suppressed the growth and metastasis of gastric cancer cells in vitro. Whole Human Genome Oligo Microarray results revealed that a wide range of genes with broad function were targeted by REC8. Among them early growth response-1 (EGR1), a transcription factor and an epithelial-mesenchymal transition (EMT)-associated protein in the AGR-RAGE pathway was significantly downregulated when REC8 was overexpressed in gastric cancer cells. We hypothesized that REC8 inhibits EMT by downregulating EGR1 in gastric cancer cells. Consistent with our prediction, REC8 overexpression decreased EMT in gastric cancer cells, whereas the REC8 ablation reversed these effects. In addition, the phenotypes of EGR1 overexpressed cells were similar to the phenotypes of REC8 ablated cells. Furthermore, we determined that REC8 interacted with EGR1, and inhibited EMT in gastric cancer cells. We thus propose further studies of the pathways associated with REC8 and EGR1 to potentially find novel targets in the treatment for gastric cancer.

Identification and functional analysis of SOX10 phosphorylation sites in melanoma

The transcription factor SOX10 plays an important role in vertebrate neural crest development, including the establishment and maintenance of the melanocyte lineage. SOX10 is also highly expressed in melanoma tumors, and SOX10 expression increases with tumor progression. The suppression of SOX10 in melanoma cells activates TGF-β signaling and can promote resistance to BRAF and MEK inhibitors. Since resistance to BRAF/MEK inhibitors is seen in the majority of melanoma patients, there is an immediate need to assess the underlying biology that mediates resistance and to identify new targets for combinatorial therapeutic approaches. Previously, we demonstrated that SOX10 protein is required for tumor initiation, maintenance and survival. Here, we present data that support phosphorylation as a mechanism employed by melanoma cells to tightly regulate SOX10 expression. Mass spectrometry identified eight phosphorylation sites contained within SOX10, three of which (S24, S45 and T240) were selected for further analysis based on their location within predicted MAPK/CDK binding motifs. SOX10 mutations were generated at these phosphorylation sites to assess their impact on SOX10 protein function in melanoma cells, including transcriptional activation on target promoters, subcellular localization, and stability. These data further our understanding of SOX10 protein regulation and provide critical information for identification of molecular pathways that modulate SOX10 protein levels in melanoma, with the ultimate goal of discovering novel targets for more effective combinatorial therapeutic approaches for melanoma patients.

The SOX11 transcription factor is a critical regulator of basal-like breast cancer growth, invasion, and basal-like gene expression

Basal-like breast cancers (BLBCs) are aggressive breast cancers associated with poor survival. Defining the key drivers of BLBC growth will allow identification of molecules for targeted therapy. In this study, we performed a primary screen integrating multiple assays that compare transcription factor expression and activity in BLBC and non-BLBC at the RNA, DNA, and protein levels. This integrated screen identified 33 transcription factors that were elevated in BLBC in multiple assays comparing mRNA expression, DNA cis-element sequences, or protein DNA-binding activity. In a secondary screen to identify transcription factors critical for BLBC cell growth, 8 of the 33 candidate transcription factors (TFs) were found to be necessary for growth in at least two of three BLBC cell lines. Of these 8 transcription factors, SOX11 was the only transcription factor required for BLBC growth, but not for growth of non-BLBC cells. Our studies demonstrate that SOX11 is a critical regulator of multiple BLBC phenotypes, including growth, migration, invasion, and expression of signature BLBC genes. High SOX11 expression was also found to be an independent prognostic indicator of poor survival in women with breast cancer. These results identify SOX11 as a potential target for the treatment of BLBC, the most aggressive form of breast cancer.

WNT-Mediated Regulation of FOXO1 Constitutes a Critical Axis Maintaining Pubertal Mammary Stem Cell Homeostasis

Puberty is characterized by dynamic tissue remodeling in the mammary gland involving ductal elongation, resolution into the mature epithelial bilayer, and lumen formation. To decipher the cellular mechanisms underlying these processes, we studied the fate of putative stem cells, termed cap cells, present in terminal end buds of pubertal mice. Employing a p63^CreERT2-based lineage-tracing strategy, we identified a unipotent fate for proliferative cap cells that only generated cells with basal features. Furthermore, we observed that dislocated "cap-in-body" cells underwent apoptosis, which aided lumen formation during ductal development. Basal lineage-specific profiling and genetic loss-of-function experiments revealed a critical role for FOXO transcription factors in mediating these proliferative versus apoptotic fates. Importantly, these studies revealed a mode of WNT signaling-mediated FOXO1 inhibition, potentially mediated through AKT. Together, these data suggest that the WNT pathway confers proliferative and survival advantages on cap cells via regulation of FOXO1 localization.

The nuclear receptor ERβ engages AGO2 in regulation of gene transcription, RNA splicing and RISC loading

BACKGROUND

The RNA-binding protein Argonaute 2 (AGO2) is a key effector of RNA-silencing pathways It exerts a pivotal role in microRNA maturation and activity and can modulate chromatin remodeling, transcriptional gene regulation and RNA splicing. Estrogen receptor beta (ERβ) is endowed with oncosuppressive activities, antagonizing hormone-induced carcinogenesis and inhibiting growth and oncogenic functions in luminal-like breast cancers (BCs), where its expression correlates with a better prognosis of the disease.

RESULTS

Applying interaction proteomics coupled to mass spectrometry to characterize nuclear factors cooperating with ERβ in gene regulation, we identify AGO2 as a novel partner of ERβ in human BC cells. ERβ-AGO2 association was confirmed in vitro and in vivo in both the nucleus and cytoplasm and is shown to be RNA-mediated. ChIP-Seq demonstrates AGO2 association with a large number of ERβ binding sites, and total and nascent RNA-Seq in ERβ + vs ERβ - cells, and before and after AGO2 knock-down in ERβ + cells, reveals a widespread involvement of this factor in ERβ-mediated regulation of gene transcription rate and RNA splicing. Moreover, isolation and sequencing by RIP-Seq of ERβ-associated long and small RNAs in the cytoplasm suggests involvement of the nuclear receptor in RISC loading, indicating that it may also be able to directly control mRNA translation efficiency and stability.

CONCLUSIONS

These results demonstrate that AGO2 can act as a pleiotropic functional partner of ERβ, indicating that both factors are endowed with multiple roles in the control of key cellular functions.

Lunatic Fringe and p53 Cooperatively Suppress Mesenchymal Stem-Like Breast Cancer

Claudin-low breast cancer (CLBC) is a poor prognosis molecular subtype showing stemness and mesenchymal features. We previously discovered that deletion of a Notch signaling modulator, Lunatic Fringe (Lfng), in the mouse mammary gland induced a subset of tumors resembling CLBC. Here we report that deletion of one copy of p53 on this background not only accelerated mammary tumor development but also led to a complete penetrance of the mesenchymal stem-like phenotype. All mammary tumors examined in the Lfng/p53 compound mutant mice displayed a mesenchymal/spindloid pathology. These tumors showed high level expressions of epithelial-to-mesenchymal transition (EMT) markers including Vimentin, Twist, and PDGFRα, a gene known to be enriched in CLBC. Prior to tumor onset, Lfng/p53 mutant mammary glands exhibited increased levels of Vimentin and E-cadherin, but decreased expressions of cytokeratin 14 and cytokeratin 8, accompanied by elevated basal cell proliferation and an expanded mammary stem cell-enriched population. Lfng/p53 mutant glands displayed increased accumulation of Notch3 intracellular fragment, up-regulation of Hes5 and down-regulation of Hes1. Analysis in human breast cancer datasets found the lowest HES1 and second lowest LFNG expressions in CLBC among molecular subtypes, and low level of LFNG is associated with poor survival. Immunostaining of human breast cancer tissue array found correlation between survival and LFNG immunoreactivity. Finally, patients carrying TP53 mutations express lower LFNG than patients with wild type TP53. Taken together, these data revealed genetic interaction between Lfng and p53 in mammary tumorigenesis, established a new mouse model resembling CLBC, and may suggest targeting strategy for this disease.

Sox10+ Cells Contribute to Vascular Development in Multiple Organs-Brief Report

OBJECTIVE

Previous genetic lineage tracing studies showed that Sox10+ cells differentiate into vascular mural cells, limited to neural crest-derived blood vessels in craniofacial tissues, aortic arch, pulmonary arch arteries, brachiocephalic, carotid arteries, and thymus. The purpose of this study was to investigate the contribution of Sox10+ cells to the vascular development in other tissues and organs and their relationship with neural crest.

APPROACH AND RESULTS

Using genetic lineage tracing technique based on Cre/LoxP system, we examined blood vessels in the adult organs of the mice expressing Sox10-Cre/Rosa-LoxP-red fluorescent protein or Wnt1-Cre/Rosa-LoxP-red fluorescent protein by immunohistological analysis. In addition to previously reported tissues and organs derived from neural crest, we showed that Sox10+ cells also contributed to vascular mural cells in the lung, spleen, and kidney, which are derived from non-neural crest origin as evidenced by red fluorescent protein-negative blood vessels in these 3 organs of Wnt1-Cre/Rosa-LoxP-red fluorescent protein mice.

CONCLUSIONS

This study demonstrates that Sox10+ cells contribute to pericytes and smooth muscle cells in most parts of the body, including those from neural crest and non-neural crest, which has significant implications in vascular remodeling under physiological and pathological conditions.

BPTF Maintains Chromatin Accessibility and the Self-Renewal Capacity of Mammary Gland Stem Cells

Chromatin remodeling is a key requirement for transcriptional control of cellular differentiation. However, the factors that alter chromatin architecture in mammary stem cells (MaSCs) are poorly understood. Here, we show that BPTF, the largest subunit of the NURF chromatin remodeling complex, is essential for MaSC self-renewal and differentiation of mammary epithelial cells (MECs). BPTF depletion arrests cells at a previously undefined stage of epithelial differentiation that is associated with an incapacity to achieve the luminal cell fate. Moreover, genome-wide analysis of DNA accessibility following genetic or chemical inhibition, suggests a role for BPTF in maintaining the open chromatin landscape at enhancers regions in MECs. Collectively, our study implicates BPTF in maintaining the unique epigenetic state of MaSCs.

Direct reprogramming with SOX factors: masters of cell fate

Over the last decade significant advances have been made toward reprogramming the fate of somatic cells, typically by overexpression of cell lineage-determinant transcription factors. As key regulators of cell fate, the SOX family of transcription factors has emerged as potent drivers of direct somatic cell reprogramming into multiple lineages, in some cases as the sole overexpressed factor. The vast capacity of SOX factors, especially those of the SOXB1, E and F subclasses, to reprogram cell fate is enlightening our understanding of organismal development, cancer and disease, and offers tremendous potential for regenerative medicine and cell-based therapies. Understanding the molecular mechanisms through which SOX factors reprogram cell fate is essential to optimize the development of novel somatic cell transdifferentiation strategies.

MYB fusions and CD markers as tools for authentication and purification of cancer stem cells from salivary adenoid cystic carcinoma

Cancer stem cells (CSC) are considered the major cause of aggressive tumor behavior, recurrence, metastases, and resistance to radiation, making them an attractive therapeutic target. However, isolation of CSC from tumor tissue and their characterization are challenging due to uncertainty about their molecular markers and conditions for their propagation. Adenoid cystic carcinoma (ACC), which arises predominantly in the salivary glands, is a slow-growing but relentless tumor that frequently invades nerves and metastasizes. New effective treatment approaches for ACC have not emerged over the last 40years. Previously, based on a highly conserved SOX10 gene signature that we identified in the majority of ACC tumors, we suggested the existence in ACC of SOX10+ cells with neural stem properties and corroborated this hypothesis via isolation from ACC tissue a novel population of CSC, termed ACC-CSC. These cells activated NOTCH1 signaling and co-expressed SOX10 and other ACC-intrinsic neural crest stem cell markers with CD133, a CSC cell surface marker, suggesting that ACC is driven by a previously uncharacterized population of SOX10+/CD133+ cells with neural stem cell properties. Here, we authenticated ACC identity of our primary cultures by demonstrating that most of them harbor MYB-NFIB fusions, which are found in 86% of ACC. We demonstrated using CyTOF, a novel mass cytometry technology, that these cells express high β-catenin and STAT3 levels and are marked by CD24 and CD44. Finally, to streamline development of ACC cell lines, we developed RT-PCR tests for distinguishing mouse and human cells and used immunomagnetic cell sorting to eliminate mouse cells from long-term cell cultures. Overall, this study describes a new population of CSC that activates signaling pathways associated with poor prognosis, validates their ACC identity, and optimizes approaches that can be used for purification of ACC-CSC and generation of cell lines.

Lgr5 is a marker for fetal mammary stem cells, but is not essential for stem cell activity or tumorigenesis

The search for the bipotent mammary stem cells that drive mammary development requires markers to enable their prospective isolation. There is general agreement that bipotent mouse mammary stem cells are abundant in late fetal development, but their existence in the adult is vigorously debated. Among markers useful for mammary stem cell identification, the Wnt co-receptor Lgr5 has been suggested by some to be both "necessary and sufficient" for bipotency and transplantation of adult mammary stem cell activity, though other studies disagree. Importantly, the relevance of Lgr5 to the bipotency of fetal mammary stem cells has not been studied. We show here that expression of a fluorescent protein driven by the endogenous Lgr5 promoter enables significant fetal mammary stem cell enrichment. We used lineage tracing to demonstrate embryonic cells expressing Lgr5 are bipotent, while their adult counterparts are myoepithelial restricted. Importantly, our data conclusively demonstrate that Lgr5 is dispensable for both fetal and adult mammary stem cell activity and for the development of mammary tumors.

Cell state plasticity, stem cells, EMT, and the generation of intra-tumoral heterogeneity

Cellular heterogeneity in cancer represents a significant challenge. In order to develop effective and lasting therapies, it is essential to understand the source of this heterogeneity, and its role in tumor progression and therapy resistance. Here, we consider not only genetic and epigenetic mechanisms, but also inflammation and cell state reprogramming in creating tumor heterogeneity. We discuss similarities between normal mammary epithelial developmental states and various breast cancer molecular sub-types, and the cells that are thought to propagate them. We emphasize that while stem cell phenotypes and mesenchymal character have often been conflated, existing data suggest that the combination of intrinsic genetic and epigenetic changes, and microenvironmental influences generate multiple types of tumor propagating cells distinguishable by their positions along a continuum of epithelial to mesenchymal, stem to differentiated and embryonic to mature cell states. Consequently, in addition to the prospect of stem cell-directed tumor therapies, there is a need to understand interrelationships between stem cell, epithelial–mesenchymal, and tumor-associated reprogramming events to develop new therapies that mitigate cell state plasticity and minimize the evolution of tumor heterogeneity.

Expression Profiling of Clinical Specimens Supports the Existence of Neural Progenitor-Like Stem Cells in Basal Breast Cancers

BACKGROUND

We previously characterized in salivary adenoid cystic carcinoma (ACC) a novel population of cancer stem cells (CSCs) marked by coexpression of 2 stemness genes, sex-determining region Y (SRY)-related HMG box-containing factor 10 (SOX10) and CD133. We also reported that in ACC and basal-like breast carcinoma (BBC), a triple-negative breast cancer subtype, expression of SOX10 similarly demarcates a highly conserved gene signature enriched with neural stem cell genes. On the basis of these findings, we hypothesized that BBC might be likewise driven by SOX10-positive (SOX10⁺)/CD133⁺ cells with neural stem cell properties.

MATERIALS AND METHODS

To validate our hypothesis on clinical data, we used a novel approach to meta-analysis that merges gene expression data from independent breast cancer studies and ranks genes according to statistical significance of their coexpression with the gene of interest. Genes that showed strong association with CD133/PROM1 as well as SOX10 were validated across different platforms and data sets and analyzed for enrichment with genes involved in neurogenesis.

RESULTS

We identified in clinical breast cancer data sets a highly conserved SOX10/PROM1 gene signature that contains neural stem cell markers common for Schwann cells, ACC, BBC, and melanoma. Identification of tripartite motif-containing 2 (TRIM2), TRIM29, MPZL2, potassium calcium-activated channel subfamily N member 4 (KCNN4), and V-set domain containing T cell activation inhibitor 1 (VTCN1)/B7 homolog 4 (B7H4) within this signature provides insight into molecular mechanisms of CSC maintenance.

CONCLUSION

Our results suggest that BBC is driven by SOX10⁺/CD133⁺ cells that express neural stem cell-specific markers and share molecular similarities with CSCs of neural crest origin. Our study provides clinically relevant information on possible drivers of these cells that might facilitate development of CSC-targeting therapies against this cancer distinguished with poor prognosis and resistance to conventional therapies.

Sox10+ adult stem cells contribute to biomaterial encapsulation and microvascularization

Implanted biomaterials and biomedical devices generally induce foreign body reaction and end up with encapsulation by a dense avascular fibrous layer enriched in extracellular matrix. Fibroblasts/myofibroblasts are thought to be the major cell type involved in encapsulation, but it is unclear whether and how stem cells contribute to this process. Here we show, for the first time, that Sox10⁺ adult stem cells contribute to both encapsulation and microvessel formation. Sox10⁺ adult stem cells were found sparsely in the stroma of subcutaneous loose connective tissues. Upon subcutaneous biomaterial implantation, Sox10⁺ stem cells were activated and recruited to the biomaterial scaffold, and differentiated into fibroblasts and then myofibroblasts. This differentiation process from Sox10⁺ stem cells to myofibroblasts could be recapitulated in vitro. On the other hand, Sox10⁺ stem cells could differentiate into perivascular cells to stabilize newly formed microvessels. Sox10⁺ stem cells and endothelial cells in three-dimensional co-culture self-assembled into microvessels, and platelet-derived growth factor had chemotactic effect on Sox10⁺ stem cells. Transplanted Sox10⁺ stem cells differentiated into smooth muscle cells to stabilize functional microvessels. These findings demonstrate the critical role of adult stem cells in tissue remodeling and unravel the complexity of stem cell fate determination.

Single Molecule Bioelectronics and Their Application to Amplification-Free Measurement of DNA Lengths

As biosensing devices shrink smaller and smaller, they approach a scale in which single molecule electronic sensing becomes possible. Here, we review the operation of single-enzyme transistors made using single-walled carbon nanotubes. These novel hybrid devices transduce the motions and catalytic activity of a single protein into an electronic signal for real-time monitoring of the protein’s activity. Analysis of these electronic signals reveals new insights into enzyme function and proves the electronic technique to be complementary to other single-molecule methods based on fluorescence. As one example of the nanocircuit technique, we have studied the Klenow Fragment (KF) of DNA polymerase I as it catalytically processes single-stranded DNA templates. The fidelity of DNA polymerases makes them a key component in many DNA sequencing techniques, and here we demonstrate that KF nanocircuits readily resolve DNA polymerization with single-base sensitivity. Consequently, template lengths can be directly counted from electronic recordings of KF’s base-by-base activity. After measuring as few as 20 copies, the template length can be determined with <1 base pair resolution, and different template lengths can be identified and enumerated in solutions containing template mixtures.

High expression of Sox10 correlates with tumor aggressiveness and poor prognosis in human nasopharyngeal carcinoma

Purpose

The aim of the study was to detect the expression of Sox10 in human nasopharyngeal carcinoma (NPC) and investigate the relationship between its expression and the clinicopathological characteristics of NPC patients.

Patients and methods

Tumor specimens (n=105) were retrospectively collected from patients with NPC diagnosed between 2004 and 2005 who presented at Hunan Cancer Hospital. Immunohistochemistry analyses were performed to characterize the expression of Sox10 in NPC. Kaplan–Meier survival and Cox regression analyses were employed to evaluate the prognosis of 105 NPC patients.

Results

The results showed that Sox10 was markedly overexpressed in human NPC tissues. Analysis of clinicopathological parameters showed that high Sox10 expression was significantly correlated with the clinical stage (P=0.032), T classification (P=0.034), and lymph node metastasis (P=0.03). Cox regression analyses further showed that Sox10 expression was an independent prognostic factor for overall survival (P=0.005). This is the first time Sox10 has shown its importance in predicting NPC progressiveness and survival outcomes.

Conclusion

Sox10 serves as a potential biomarker for NPC patients. It may hopefully become a novel therapeutic target for NPC patients.