The stem cell code in oral epithelial tumorigenesis: 'the cancer stem cell shift hypothesis'

Cell State Transitions and Phenotypic Heterogeneity in Luminal Breast Cancer Implicating MicroRNAs as Potential Regulators

Luminal breast cancer subtypes respond poorly to endocrine and trastuzumab treatments due to cellular heterogeneity arising from the phenotype transitions, accounted for mainly by the loss of receptor expression. The origins of basal-like and human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancer subtypes have been attributed to genetic and protein modifications in stem-like cells and luminal progenitor cell populations, respectively. The post-transcriptional regulation of protein expression is known to be influenced by microRNAs (miRNAs) that are deemed to be master regulators of several biological processes in breast tumorigenesis and progression. Our objective was to identify the fractions of luminal breast cancer cells that share stemness potentials and marker profiles and to elucidate the molecular regulatory mechanism that drives transitions between fractions, leading to receptor discordances. Established breast cancer cell lines of all prominent subtypes were screened for the expression of putative cancer stem cell (CSC) markers and drug transporter proteins using a side population (SP) assay. Flow-cytometry-sorted fractions of luminal cancer cells implanted in immunocompromised mice generated a pre-clinical estrogen receptor alpha (ERα+) animal model with multiple tumorigenic fractions displaying differential expression of drug transporters and hormone receptors. Despite an abundance of estrogen receptor 1 (ESR1) gene transcripts, few fractions transitioned to the triple-negative breast cancer (TNBC) phenotype with a visible loss of ER protein expression and a distinct microRNA expression profile that is reportedly enriched in breast CSCs. The translation of this study has the potential to provide novel therapeutic miRNA-based targets to counter the dreaded subtype transitions and the failure of antihormonal therapies in the luminal breast cancer subtype.

Promoter Methylation of Cancer Stem Cell Surface Markers as an Epigenetic Biomarker for Prognosis of Oral Squamous Cell Carcinoma

Growing evidence suggests that genetic and epigenetic factors, including environmental factors, contribute to the development of oral squamous cell carcinoma (OSCC). Here, we investigated the transcriptional silencing of the CD24, CD44, CD133, and CD147 genes, which are well-known cancer stem cell surface markers in various cancer types, including OSCC. We first examined the correlation between the transcriptional expression level and reactivation by 5-aza-2′-deoxycytidine (5-aza-dC) and the promoter methylation levels of the four genes in several OSCC cell lines. We observed promoter hypermethylation for the CD24, CD133, and CD147 genes at 70%, 75%, and 70%, respectively, in OSCC cell lines compared to normal oral mucosa tissues (<53%), indicating that this methylation pattern is cancer-specific, which was confirmed by bisulfite sequencing analysis. More specifically, the expression and methylation profiles of CD133 and CD147 extracted from The Cancer Genome Atlas (TCGA) database were negatively correlated, supporting their epigenetic regulation in primary OSCC tumors. The methylation status of CD133 and CD147 was associated with poor survival in patients with OSCC using the TCGA database. Our findings provide additional insight into the abnormal DNA methylation of CD133 and that CD147 could be used for the diagnosis and therapeutic treatment of patients with OSCC.

The Multiple Roles of CD147 in the Development and Progression of Oral Squamous Cell Carcinoma: An Overview

Cluster of differentiation (CD)147, also termed extracellular matrix metalloprotease inducer or basigin, is a glycoprotein ubiquitously expressed throughout the human body, the oral cavity included. CD147 actively participates in physiological tissue development or growth and has important roles in reactive processes such as inflammation, immunity, and tissue repair. It is worth noting that deregulated expression and/or activity of CD147 is observed in chronic inflammatory or degenerative diseases, as well as in neoplasms. Among the latter, oral squamous cell carcinoma (OSCC) is characterized by an upregulation of CD147 in both the neoplastic and normal cells constituting the tumor mass. Most interestingly, the expression and/or activity of CD147 gradually increase as healthy oral mucosa becomes inflamed; hyperplastic/dysplastic lesions are then set on, and, eventually, OSCC develops. Based on these findings, here we summarize published studies which evaluate whether CD147 could be employed as a marker to monitor OSCC development and progression. Moreover, we describe CD147-promoted cellular and molecular events which are relevant to oral carcinogenesis, with the aim to provide useful information for assessing whether CD147 may be the target of novel therapeutic approaches directed against OSCC.

Transitional dynamics of cancer stem cells in invasion and metastasis

At the onset, few cancer cells amidst the tumor bulk, identified as cancer stem cells (CSCs) or early disseminated cancer cells (eDCCs) are capable of survival post conventional therapy and persist as minimal residual disease (MRD). Metastatic subclones emerge both early and late in the life of primary tumor ensuing an ongoing regional clonal evolution of progenitor cells in metastatic and primary tumors. In the last decade, multiple studies proposed various identities of stem-like cells that undergo transitions to adapt to the changing microenvironment as the disease progresses. This review advocates with substantial evidence the dynamic model of tumor propagation by exploring the specific cell types, reversible phenotypic plasticity between the tumorigenic leader seeds and the supporting follower cancer cells both in circulation and in solid tissue to accurately decipher tumor promoting clones and its role in metastatic dissemination and tumor re-growth. (142 words).

Biophysics of Cell-Substrate Interactions Under Shear

Cells adhere to substrates through mechanosensitive focal adhesion complexes. Measurements that probe how cells detach from substrates when they experience an applied force connect molecular-scale aspects of cell adhesion with the biophysical properties of adherent cells. Such forces can be applied through shear devices that flow fluid in a controlled manner across cells. The signaling pathways associated with focal adhesions, in particular those that involve integrins and receptor tyrosine kinases, are complex, receiving mechano-chemical feedback from the sensing of substrate stiffness as well as of external forces. This article reviews the signaling processes involved in mechanosensing and mechanotransduction during cell-substrate interactions, describing the role such signaling plays in cancer metastasis. We examine some recent progress in quantifying the strength of these interactions, describing a novel fluid shear device that allows for the visualization of the cell and its sub-cellular structures under a shear flow. We also summarize related results from a biophysical model for cellular de-adhesion induced by applied forces. Quantifying cell-substrate adhesions under shear should aid in the development of mechano-diagnostic techniques for diseases in which cell-adhesion is mis-regulated, such as cancers.

A novel reporter construct for screening small molecule inhibitors that specifically target self-renewing cancer cells

Cancer stem cells (CSCs) are a subset of cancer cells, which possess self-renewal ability, and lead to tumor progression, metastasis, and resistance to therapy. Live detection and isolation of CSCs are important to understand the biology of CSCs as well as to screen drugs that target them. Even though CSCs are detected using surface markers, there is a lot of inconsistencies for that in a given cancer type. At the same time, self-renewal markers like ALDH1A1, OCT4A and SOX2, which are intracellular molecules, are reliable markers for CSCs in different cancers. In the present study, we generated a reporter construct for self-renewing CSCs, based on ALDH1A1 expression. Oral cancer cells harboring ALDH1A1-DsRed2 were used to screen inhibitors that target CSCs. Our results showed that Comb1, a cocktail of inhibitors for EGF and TGF-β pathways and their intermediates, effectively reduced the DsRed2 population to 34%. Our immunohistochemical analysis on primary oral cancer corroborated the importance of EGF and TGF-β pathways in sustaining CSCs. Since these two pathways are also critical for the self-renewal and differentiation of normal stem cells, Comb1 might abolish them as well. On analysis of the effect of Comb1 on normal murine bone marrow cells, there was no significant change in the stem cell self-renewal and differentiation potential in the treated group compared to untreated cells. To conclude, we claim that ALDH1A1-DsRed2 is a useful tool to detect CSCs, and Comb1 is effective in targeting CSCs without affecting normal stem cells.

Hsa-miR-370 inhibited P-selectin-induced cell adhesion in human colon adenocarcinoma cells

Sialyl Lewis x (sLe^x) is a minimal recognition motif for ligands of P-selectin and plays an important role in tumor cell adhesion and migration. Thus, targeting sLe^x could be an effective method to prevent tumor metastasis. In this study, we aimed to identify a microRNA (miRNA) which is capable to suppress the expression of sLe^x. MicroRNAs which may target ST3GAL4 were predicted by the online tools. Colo 320 HSR human colon adenocarcinoma cells were employed. The transcriptional and translational levels of ST3GAL4 were evaluated by western blotting and Real-time quantitative polymerase chain reaction. Cell adhesion and spread were assessed with or without hsa-miR-370 treatment. It was shown that hsa-miR-370 inhibited the expression of sLe^x in colo-320 cells, which repressed the binding of P-selectin, and led to reduced cell attachment and spread. Our results found that P-selectin-induced elevations of p-p38 and p-PI3K levels were significantly inhibited by hsa-miR-370, indicating that repressed sLe^x level is able to reduce the P-selectin binding and therefore eliminating the P-selectin-induced activation of p38 and PI3K signaling. In conclusion, we found that hsa-miR-370 specifically inhibits the expression of sLe^x, represses cell adhesion and spreading in colo-320 cells. Our study provides a possible effective treatment against tumor invasion.

Topical pimecrolimus versus betamethasone for oral lichen planus: a randomized clinical trial

OBJECTIVES

Oral lichen plans (OLP) is a potentially malignant inflammatory mucocutaneous disease. CD133 is an investigated surface marker for cancer stem-like cells (CSCs) that may be involved in tumor initiation in head and neck carcinomas. We compared short-term clinical effectiveness of topical pimecrolimus as selective inflammatory cytokine release inhibitor with betamethasone cream for erosive/atrophic OLP and investigated the influence of this therapy on CD133 expression.

MATERIAL AND METHODS

Thirty patients were randomly assigned into two equal groups to receive topical pimecrolimus (group I) or betamethasone (group II) four times daily for 4 weeks. A marker lesion in each patient were assessed at baseline using clinical score (CS) and visual analog scale (VAS) then at 1, 2, and 4 weeks and after 4 weeks of treatment-free period. CD133 expression was detected in pre- and post-treatment immunostained sections.

RESULTS

Both drugs showed a reduction in CS, VAS, and CD133 expressions after treatment termination (p < 0.001). Pimecrolimus-treated lesions showed significant higher 1st week reduction in severity (33.1% (22.2)), pain score (57.53% (14.27)), less recurrence in follow-up period and less CD133 expression by the end of the 1st 4 weeks compared with betamethasone.

CONCLUSION

Pimecrolimus showed earlier clinical response and less recurrence rate compared with standard topical corticosteroid in symptomatic OLP lesions, and both treatment reduced CD133-positive CSC population.

CLINICAL RELEVANCE

The study proved the benefits of topical pimecrolimus in early management of painful lesions of OLP and its ability to inhibit CSCs, suggesting a possible role in reducing risk of malignant transformation.

Perspectives on oral squamous cell carcinoma prevention-proliferation, position, progression and prediction

Squamous cell carcinoma arising from oral mucosal epithelium remains a lethal and deforming disease due to tumour invasion, oro-facial destruction, cervical lymph node metastasis and ultimate blood-borne dissemination. Worldwide, 300 000 new cases are seen each year, with a recent and significant rise in incidence affecting particularly the young. To rationalize perspectives on preventive strategies in oral cancer management, this study addresses a number of fundamental questions regarding carcinogenesis: proliferation-what epithelial cell changes precede tumour development? Position-why are certain oral sites so predisposed to cancer? Progression-why do some precursor lesions progress to invasive carcinoma and others do not? Prediction-how can we predict individual patient and/or lesion behaviour to prevent disease progression? By improving our understanding of oral carcinogenesis, can we thereby facilitate more effective primary, secondary and tertiary preventive strategies and ultimately reduce the global burden of oral squamous cell carcinoma (OSCC)?

Analysis of MicroRNA-mRNA Interactions in Stem Cell-Enriched Fraction of Oral Squamous Cell Carcinoma

This study is an integrated analysis of the transcriptome profile microRNA (miRNA) and its experimentally validated mRNA targets differentially expressed in the tumorigenic stem-like fraction of oral squamous cell carcinoma (OSCC). We had previously reported the coexistence of multiple drug-resistant tumorigenic fractions, termed side population (SP1, SP2, and MP2), and a nontumorigenic fraction, termed main population (MP1), in oral cancer. These fractions displayed a self-renewal, regenerative potential and expressed known stemness-related cell surface markers despite functional differences. Flow cytometrically sorted pure fractions of SP1 and MP1 cells were subjected to differential expression analysis of both mRNAs and miRNAs. A significant upregulation of genes associated with inflammation, cell survival, cell proliferation, drug transporters, and antiapoptotic pathways, in addition to enhanced transcriptome reprogramming mediated by DNA-histone binding proteins and pattern recognition receptor-mediated signaling, was found to play a crucial role in the transformation of the nontumorigenic MP1 fraction to the tumorigenic SP1 fraction. We also identified several differentially expressed miRNAs that specifically target genes distinctive of tumorigenic SP1 fraction. miRNA-mediated downregulation of stemness-associated markers CD44 and CD147 and upregulation of CD151 may also account for the emergence and persistence of multiple tumorigenic stem cell fractions with varying degrees of malignancy. The phenotypic switch of cancer cells to stem-like OSCC cells mediated by transcriptomal regulation is effectual in addressing biological tumor heterogeneity and subsequent therapeutic resistance leading to a minimal residual disease (MRD) condition in oral cancer. A detailed study of the interplay of miRNAs, mRNA, and the cellular phases involved in the gradual transition of nontumorigenic cancer cells to tumorigenic stem-like cells in solid tumors would enable detection and development of a treatment regimen that targets and successfully eliminates multiple, drug-resistant fractions of cancer cells.

Expression of SOX2 in oral squamous cell carcinoma and the association with lymph node metastasis

Oral squamous cell carcinomas (OSCCs) are a growing problem in the world. The various existing treatments have not markedly improved the survival rate of patients with OSCC during the past three decades. Novel treatment strategies are required. Sex determining region Y-box 2 (SOX2) is a transcription factor that is involved in the maintenance of embryonic stem cell pluripotency and in multiple developmental processes. SOX2 expression was indicated to act as a prognostic factor in various types of tumors, including breast, colorectal, gastric and lung cancer and glioblastoma, and as a link between malignancy and stemness. Cancer stem cells (CSCs) may be responsible for the genesis, growth and metastatic spread of tumors. The poor survival outcomes for OSCC patients may be attributable to a poor selection of target cells for treatment, as current oral cancer therapies are generally aimed at the global mass of tumor. Therefore, the consideration that novel approaches to oral cancer may be targeted using SOX2 and CSCs appears reasonable. In order to better understand the oncogenic roles and the corresponding signal transduction pathways of the SOX2 protein, the present study emphasizes the role of SOX2 in OSCC, including the proteins associated with OSCC, and reviews the literature regarding the role of SOX2 in lymph node metastasis. The aim of the present study is to provide a reference for future studies that engage in research on the aforementioned subject.

Expression of ALDH1A1 and CD44 in primary head and neck squamous cell carcinoma and their value for carcinogenesis, tumor progression and cancer stem cell identification

In head and neck squamous cell carcinoma (HNSCC), aldehyde dehydrogenase 1 family, member A1 (ALDH1A1) and hyaluronan receptor cluster of differentiation 44 (CD44) are often used as cancer stem cell (CSC) markers. The aim of the present study was to examine the relevance of these proteins for HNSCC in general and for the identification of CSCs. Tumors from 48 patients with primary HNSCC were analyzed for the expression of ALDH1A1 and CD44. Additionally, the association of the proteins with the proliferation rate and epidermal growth factor receptor (EGFR) expression was analyzed. ALDH1A1 was expressed in 54.2% of the carcinoma samples while CD44 was expressed in 89.6% of the carcinoma samples. Most notably, these proteins were often not expressed exclusively in a subpopulation, but also in the majority of tumor cells (ALDH1A1: 30.8% of ALDH1A1⁺ tumors; CD44: 65.1% of CD44⁺ tumors). Furthermore, patients with ALDH1A1⁺ tumors exhibited worse survival rates. CD44 and EGFR expression patterns were overlapping within the tumors and the expression rates were significantly connected. Ki-67⁺ tumor cells often expressed CD44. ALDH1A1 and CD44 expression patterns only partly overlapped. Consequently, ALDH1A1 and CD44 play significant roles in carcinogenesis and tumor progression. Within the present study, CD44 appeared to interact with EGFR and was more often expressed in primary HNSCC than the marker ALDH1A1. However, ALDH1A1 was a better marker to define a subpopulation of tumor cells. Finally, neither ALDH1A1 nor CD44, alone or combined, were sufficient to determine the CSC population in HNSCC.

The biological function and clinical utilization of CD147 in human diseases: a review of the current scientific literature

CD147 or EMMPRIN is a member of the immunoglobulin superfamily in humans. It is widely expressed in human tumors and plays a central role in the progression of many cancers by stimulating the secretion of matrix metalloproteinases (MMPs) and cytokines. CD147 regulates cell proliferation, apoptosis, and tumor cell migration, metastasis and differentiation, especially under hypoxic conditions. CD147 is also important to many organ systems. This review will provide a detailed overview of the discovery, characterization, molecular structure, diverse biological functions and regulatory mechanisms of CD147 in human physiological and pathological processes. In particular, recent studies have demonstrated the potential application of CD147 not only as a phenotypic marker of activated regulatory T cells but also as a potential diagnostic marker for early-stage disease. Moreover, CD147 is recognized as an effective therapeutic target for hepatocellular carcinoma (HCC) and other cancers, and exciting clinical progress has been made in HCC treatment using CD147-directed monoclonal antibodies.

Oral epithelial stem cells - implications in normal development and cancer metastasis

Oral mucosa is continuously exposed to environmental forces and has to be constantly renewed. Accordingly, the oral mucosa epithelium contains a large reservoir of epithelial stem cells necessary for tissue homeostasis. Despite considerable scientific advances in stem cell behavior in a number of tissues, fewer studies have been devoted to the stem cells in the oral epithelium. Most of oral mucosa stem cells studies are focused on identifying cancer stem cells (CSC) in oral squamous cell carcinomas (OSCCs) among other head and neck cancers. OSCCs are the most prevalent epithelial tumors of the head and neck region, marked by their aggressiveness and invasiveness. Due to their highly tumorigenic properties, it has been suggested that CSC may be the critical population of cancer cells in the development of OSCC metastasis. This review presents a brief overview of epithelium stem cells with implications in oral health, and the clinical implications of the CSC concept in OSCC metastatic dissemination.

Side population cells as prototype of chemoresistant, tumor-initiating cells

Classically, isolation of CSCs from tumors exploits the detection of cell surface markers associated with normal stem cells. Invariable expression of these cell surface markers in almost all proliferating tumor cells that albeit impart specific functionality, the universality, and clinical credibility of CSC phenotype based on markers is still dubious. Side Population (SP) cells, as defined by Hoechst dye exclusion in flow cytometry, have been identified in many solid tumors and cell lines and the SP phenotype can be considered as an enriched source of stem cells as well as an alternative source for the isolation of cancer stem cells especially when molecular markers for stem cells are unknown. SP cells may be responsible for the maintenance and propagation of tumors and the proportion of SP cells may be a predictor of patient outcome. Several of these markers used in cell sorting have emerged as prognostic markers of disease progression though it is seen that the development of new CSC-targeted strategies is often hindered by poor understanding of their regulatory networks and functions. This review intends to appraise the experimental progress towards enhanced isolation and drug screening based on property of acquired chemoresistance of cancer stem cells.

Co-expression of CD44+/RANKL+ tumor cells in the carcinogenesis of oral squamous cell carcinoma

Receptor activator of nuclear factor-kappa (RANK)/receptor activator of nuclear factor-kappa B ligand (RANKL) signaling helps putative cancer stem cells (CSC) to maintain their stemness. Expression of CD44 and RANKL was analyzed in oral squamous cell carcinoma specimen (n = 191). Moreover, RANKL expression was measured in cancer cell lines (BICR3, BICR56) by immunohistochemistry and western blot analysis. Scanned images were digitally analyzed using ImageJ and the immunomembrane plug-in. CD44 and RANKL expression on protein level was correlated with clinical characteristics and impact on survival. RANKL was co-labeled with CD44 in immunohistochemical and immunofluorescence double labeling experiments. Although high CD44+/RANKL+ co-expression was significantly associated with clinicopathological factors and worse survival, multivariate analysis did not demonstrate high CD44+/RANKL+ co-expression as independent prognostic factor. Immunohistochemical and immunofluorescence double labeling experiments revealed RANKL expression by CD44+ cancer cells. RANKL specificity was confirmed by western blot analysis. For the first time, this study provides evidence that RANKL expression in OSCC might be associated with disease recurrence and a cell compartment measured by CD44+/RANKL+ co-expression within the mucosal epithelial basal layer cells.

Areca nut extract induces pyknotic necrosis in serum-starved oral cells via increasing reactive oxygen species and inhibiting GSK3β: an implication for cytopathic effects in betel quid chewers

Areca nut has been proven to be correlated with various pathologic alterations in oral cavity. However, the mechanisms for such cytopathic effects are still elusive due mostly to the limitations of cell culture systems. Here we discovered that areca nut extract (ANE) induced production of autophagosome vacuoles in cells cultured with rich medium but induced pyknosis and ballooning, two morphological alterations frequently observed in betel quid chewers, in cells under a serum-free culture condition. Permeability of the serum-starved cells to propidium iodide (PI) confirmed ANE induced novel necrosis with pyknosis (pyknotic necrosis), providing a possible explanation for inflammatory infiltration in chewers’ mucosa. In these serum-starved cells, ANE strongly induced reactive oxygen species (ROS), which acted as a key switch for the initiation of pyknotic necrosis. Calcium flux was also involved in the morphological alterations. Besides, inhibition of GSK3β by SB216763 significantly exacerbated the pyknotic necrosis either induced by ANE or H₂O₂ in serum-starved cells, suggesting that GSK3β is a critical regulator for ANE/ROS-mediated pyknotic necrosis. Interestingly, LC3-II transition and PARP cleavage were still detected in the serum-starved cells after ANE treatment, suggesting concurrent activation of apoptotic and autophagic pathways. Finally, insulin could counteract the effect of ANE-induced pyknotic necrosis. Taken together, these data provide a platform for studying ANE-induced cytopathogenesis and the first clinical implication for several pathological alterations, such as ballooning and inflammatory infiltration, in betel quid chewers.

FGF2 mediates DNA repair in epidermoid carcinoma cells exposed to ionizing radiation

Purpose

Fibroblast growth factor 2 (FGF2) is a well-known survival factor. However, its role in DNA repair is poorly documented. The present study was designed to investigate in epidermoid carcinoma cells the potential role of FGF2 in DNA repair.

Materials and methods

The side population (SP) with cancer stem cell-like properties and the main population (MP) were isolated from human A431 squamous carcinoma cells. Radiation-induced DNA damage and repair were assessed using the alkaline comet assay. FGF2 expression was quantified by enzyme linked immunosorbent assay (ELISA).

Results

SP cells exhibited rapid repair of radiation induced DNA damage and a high constitutive level of nuclear FGF2. Blocking FGF2 signaling abrogated the rapid DNA repair. In contrast, in MP cells, a slower repair of damage was associated with low basal expression of FGF2. Moreover, the addition of exogenous FGF2 accelerated DNA repair in MP cells. When irradiated, SP cells secreted FGF2, whereas MP cells did not.

Conclusions

FGF2 was found to mediate DNA repair in epidermoid carcinoma cells. We postulate that carcinoma stem cells would be intrinsically primed to rapidly repair DNA damage by a high constitutive level of nuclear FGF2. In contrast, the main population with a low FGF2 content exhibits a lower repair rate which can be increased by exogenous FGF2.