Maintenance of stem cell self-renewal in head and neck cancers requires actions of GSK3ß influenced by CD44 and RHAMM.

Cells sorted from head and neck cancers on the basis of their high expression of CD44 have high potency for tumor initiation. These cells are also involved in epithelial to mesenchymal transition (EMT) and we have previously reported that cancer stem cells (CSCs) exist as two biologically distinct phenotypes. Both phenotypes are CD44(high) but one is also ESA(high) and maintains epithelial characteristics, the other is ESA(low) , has mesenchymal characteristics and is migratory. Examining CD44-regulated signal pathways in these cells we show that CD44, and also RHAMM, act to inhibit phosphorylation of glycogen synthase kinase 3ß (GSK3ß). We show that inhibitory phosphorylation reduces the formation of both "tumor spheres" and "holoclone" colonies, functional indicators of stemness. GSK3ß inhibition also reduces the expression of stem cell markers such as Oct4, Sox2, and Nanog and upregulates expression of the differentiation markers Calgranulin B and Involucrin in the CD44(high) /ESA(high) cell fraction. Transition of CSCs out of EMT and back to the epithelial CSC phenotype is induced by GSK3ß knockdown. These results indicate that GSK3ß plays a central role in determining and maintaining the phenotypes and behavior of CSCs in vitro and are likely to be involved in controlling the growth and spread of tumors in vivo.

CD44 staining of cancer stem-like cells is influenced by down-regulation of CD44 variant isoforms and up-regulation of the standard CD44 isoform in the population of cells that have undergone epithelial-to-mesenchymal transition.

CD44 is commonly used as a cell surface marker of cancer stem-like cells in epithelial tumours, and we have previously demonstrated the existence of two different CD44(high) cancer stem-like cell populations in squamous cell carcinoma, one having undergone epithelial-to-mesenchymal transition and the other maintaining an epithelial phenotype. Alternative splicing of CD44 variant exons generates a great many isoforms, and it is not known which isoforms are expressed on the surface of the two different cancer stem-like cell phenotypes. Here, we demonstrate that cancer stem-like cells with an epithelial phenotype predominantly express isoforms containing the variant exons, whereas the cancer stem-like cells that have undergone an epithelial-to-mesenchymal transition down-regulate these variant isoforms and up-regulate expression of the standard CD44 isoform that contains no variant exons. In addition, we find that enzymatic treatments used to dissociate cells from tissue culture or fresh tumour specimens cause destruction of variant CD44 isoforms at the cell surface whereas expression of the standard CD44 isoform is preserved. This results in enrichment within the CD44(high) population of cancer stem-like cells that have undergone an epithelial-to-mesenchymal transition and depletion from the CD44(high) population of cancer stem-like cells that maintain an epithelial phenotype, and therefore greatly effects the characteristics of any cancer stem-like cell population isolated based on expression of CD44. As well as effecting the CD44(high) population, enzymatic treatment also reduces the percentage of the total epithelial cancer cell population staining CD44-positive, with potential implications for studies that aim to use CD44-positive staining as a prognostic indicator. Analyses of the properties of cancer stem-like cells are largely dependent on the ability to accurately identify and assay these populations. It is therefore critical that consideration be given to use of multiple cancer stem-like cell markers and suitable procedures for cell isolation in order that the correct populations are assayed.

Cancer stem cells in squamous cell carcinoma switch between two distinct phenotypes that are preferentially migratory or proliferative.

Epithelial-to-mesenchymal transition (EMT) is an important driver of tumor invasion and metastasis, which causes many cancer deaths. Cancer stem cells (CSC) that maintain and initiate tumors have also been implicated in invasion and metastasis, but whether EMT is an important contributor to CSC function is unclear. In this study, we investigated whether a population of CSCs that have undergone EMT (EMT CSCs) exists in squamous cell carcinoma (SCC). We also determined whether a separate population of CSCs that retain epithelial characteristics (non-EMT CSCs) is also present. Our studies revealed that self-renewing CSCs in SCC include two biologically-distinct phenotypes. One phenotype, termed CD44(high)ESA(high), was proliferative and retained epithelial characteristics (non-EMT CSCs), whereas the other phenotype, termed CD44(high)ESA(low), was migratory and had mesenchymal traits characteristic of EMT CSCs. We found that non-EMT and EMT CSCs could switch their epithelial or mesenchymal traits to reconstitute the cellular heterogeneity which was characteristic of CSCs. However, the ability of EMT CSCs to switch to non-EMT character was restricted to cells that were also ALDH1(+), implying that only ALDH1(+) EMT cells had the ability to seed a new epithelial tumor. Taken together, our findings highlight the identification of two distinct CSC phenotypes and suggest a need to define therapeutic targets that can eradicate both of these variants to achieve effective SCC treatment.

Stem cell characteristics of cell sub-populations in cell lines derived from head and neck cancers of Fanconi anemia patients.

Increasing evidence indicates that cancer growth is driven by a sub-population of self-renewing cancer stem cells (CSCs) and that clinical problems of tumor recurrence after therapy may be related to differential resistance of CSCs to therapeutic elimination. Fanconi anemia (FA) is an autosomal recessive disorder associated with deficiencies of DNA repair and a greatly enhanced risk of hematopoietic malignancies and of head and neck squamous cell carcinoma (HNSCC). In FA patients, lack of DNA repair complicates therapies acting through DNA damage and alternative approaches, such as targeting signaling pathways associated with stem cell maintenance, might be of particular benefit. To assess effects of FA gene defects on the expression of stem cell properties, CSC patterns in cell lines derived from FA-related and sporadic HNSCC were compared. As for sporadic cell lines, FA cell lines showed colony morphologies associated with stem cell patterns. In all cell lines, cells with strong staining for CD44 (CD44(high) ) showed lower rates of apoptosis and a greater DNA damage induced block in the G2 phase of the cell cycle than CD44(low) cells. Mitomycin C, and UVB increased overall rates of apoptosis for both sporadic and FA cell lines, although FA cells tended to be more sensitive to apoptotic induction. Fluorescence activated cell sorting, immunohistochemistry, and QPCR indicated distinctly different patterns of gene expression of CD44(high) and CD44(low) cells in both sporadic and FA cell lines.

Normal and malignant epithelial cells with stem-like properties have an extended G2 cell cycle phase that is associated with apoptotic resistance.

BACKGROUND: Subsets of cells with stem-like properties have been previously isolated from human epithelial cancers and their resistance to apoptosis-inducing stimuli has been related to carcinoma recurrence and treatment failure. The aim of this study was to investigate the mechanisms of resistance to apoptosis-inducing agents of cells with stem-like properties in both normal and malignant human epithelia. METHODS: Cells isolated from fresh human head and neck carcinomas (n = 11), cell lines derived from head and neck, prostate and breast human carcinomas (n = 7), and from normal human oral mucosa (n = 5), were exposed to various apoptosis-inducing stimuli (UV, Tumour Necrosis Factor, Cisplatin, Etoposide, and Neocarzinostatin). Flow cytometry for CD44 and epithelial-specific antigen (ESA) expression, colony morphology, tumour sphere formation and rapid adherence assays were used to identify the subset of cells with stem-like properties. Apoptosis, cell cycle and expression of various cell cycle checkpoint proteins were assessed (Western Blot, qPCR). The role of G2-checkpoint regulators Chk1 and Chk2 was investigated by use of debromohymenialdisine (DBH) and siRNA. RESULTS: In both cancer biopsies and carcinoma cell lines a subset of CD44(high) cells showed increased clonogenicity, a significantly lower rate of apoptosis, and a significantly higher proportion of cells in the G2-phase of the cell cycle. An inverse correlation between the percentage of cells in G2-phase and the rate of apoptosis was found. Pulse-chase with iododeoxyuridine (IdU) demonstrated that CD44(high) carcinoma cells spent longer time in G2, even in un-treated controls. These cells expressed higher levels of G2 checkpoint proteins, and their release from G2 with BDH or Chk1 siRNA increased their rate of apoptosis. Low passage cultures of normal keratinocytes were also found to contain a subset of CD44(high) cells showing increased clonogenicity, and a similar pattern of G2-block associated with apoptotic resistance. CONCLUSIONS: These data indicate that both normal and malignant human epithelial cells with stem-like properties show greater resistance to apoptosis associated with extended G2 cell cycle phase, and that this property is not a consequence of neoplastic transformation. Targeting G2 checkpoint proteins releases these cells from the G2-block and makes them more prone to apoptosis, implying an opportunity for improved therapeutic approaches.