Head and Neck Cancer Stem Cells: The Side Population

The Laryngoscope (Impact Factor: 2.14). 03/2011; 121(3):527 - 533. DOI: 10.1002/lary.21032


The cancer stem cell (CSC) theory concludes that a subpopulation of cancer cells, the cancer stem cells, can self-renew and are responsible for tumor growth. Previous studies have identified cells able to efflux Hoechst 33342 dye as the side population (SP). SP cells and CSCs share many characteristics, suggesting the SP isolated from malignant tumors contains CSCs.
Experimental Study.
The SP was isolated from a head and neck cancer cell line and analyzed for CSC-like characteristics.
The SP demonstrated the ability to reproduce both SP and non-side population (NSP) cells from as few as one cell. The SP had lower expression of active β-catenin and more resistance to 5-fluorouracil; the SP also demonstrated greater expression of Bmi-1 (4.3-fold) and ABCG2 (1.4-fold). SP cells were able to produce tumors in an animal model, whereas NSP were not. SPs were identified in two primary human tumors.
This work adds to the evidence that the SP in head and neck cancer represents cells with CSC properties and provides a method by which CSCs can be isolated and studied. Laryngoscope, 2011

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    • "Conversely, we found CK2 inhibition reciprocally induced TAp73-inducible growth arrest and proapoptotic genes CDKN2A(p21) and PUMA in HNSCC [16; Suppl Figure 1], indicating a pivotal role as a switch regulating genes that determine cell fate. Concordantly, CK2 inhibition attenuated the SP subset, clonogenicity, and sphere formation, linked to CSC phenotype and tumorgenicity in HNSCC and other cancers [6]. We found that CK2 inhibition enhanced TAp73 expression and dependent repression of several known CSC transcription factor genes in two independent lines from an HNSCC subset overexpressing TAp73 with mtTP53. "
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    ABSTRACT: Cancer stem cells (CSC) and genes have been linked to cancer development and therapeutic resistance, but the signaling mechanisms regulating CSC genes and phenotype are incompletely understood. CK2 has emerged as a key signal serine/threonine kinase that modulates diverse signal cascades regulating cell fate and growth. We previously showed that CK2 is often aberrantly expressed and activated in head and neck squamous cell carcinomas (HNSCC), concomitantly with mutant (mt) tumor suppressor TP53, and inactivation of its family member, TAp73. Unexpectedly, we observed that classical stem cell genes Nanog, Sox2, and Oct4, are overexpressed in HNSCC with inactivated TAp73 and mtTP53. However, the potential relationship between CK2, TAp73 inactivation, and CSC phenotype is unknown. We reveal that inhibition of CK2 by pharmacologic inhibitors or siRNA inhibits the expression of CSC genes and side population (SP), while enhancing TAp73 mRNA and protein expression. Conversely, CK2 inhibitor attenuation of CSC protein expression and the SP by was abrogated by TAp73 siRNA. Bioinformatic analysis uncovered a single predicted CK2 threonine phosphorylation site (T27) within the N-terminal transactivation domain of TAp73. Nuclear CK2 and TAp73 interaction, confirmed by co-immunoprecipitation, was attenuated by CK2 inhibitor, or a T27A point-mutation of this predicted CK2 threonine phospho-acceptor site of TAp73. Further, T27A mutation attenuated phosphorylation, while enhancing TAp73 function in repressing CSC gene expression and SP cells. A new CK2 inhibitor, CX-4945, inhibited CSC related SP cells, clonogenic survival, and spheroid formation. Our study unveils a novel regulatory mechanism whereby aberrant CK2 signaling inhibits TAp73 to promote the expression of CSC genes and phenotype.
    Full-text · Article · Oct 2014 · Neoplasia (New York, N.Y.)
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    • "Cancer stem-like side population (SP) cells have been successfully identified in a wide range of solid tumors, including breast cancer [1], [2], hepatocellular carcinoma [3]–[7], lung cancer [8], [9], gastrointestinal cancer [10]–[12], prostate cancer [13], gallbladder cancer [14], ovarian cancer [15], endometrial cancer [16], pancreatic cancer [17], [18], urological cancer [19], [20], glioblastoma [21], melanoma [22], osteosarcoma [23], [24], mesenchymal neoplasms [25], nasopharyngeal cancer [26], oral cancer [27], [28], and other head and neck cancers [29], [30]. However, most of these investigations have been performed using established cancer cell lines. "
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    ABSTRACT: Cancer stem-like side population (SP) cells have been identified in many solid tumors; however, most of these investigations are performed using established cancer cell lines. Cancer cells in tumor tissue containing fibroblasts and many other types of cells are much more complex than any cancer cell line. Although SP cells were identified in the laryngeal squamous cell carcinoma (LSCC) cell line Hep-2 in our pilot study, it is unknown whether the LSCC tissue contains SP cells. In this study, LSCC cells (LSCCs) were primary cultured and purified from a surgically resected LSCC specimen derived from a well-differentiated epiglottic neoplasm of a Chinese male. This was followed by the verification of epithelium-specific characteristics, such as ultrastructure and biomarkers. A distinct SP subpopulation (4.45±1.07%) was isolated by Hoechst 33342 efflux analysis from cultured LSCCs by using a flow cytometer. Cancer stem cell (CSC)-associated assays, including expression of self-renewal and CSC marker genes, proliferation, differentiation, spheroid formation, chemotherapy resistance, and tumorigenicity were then conducted between SP and non-SP (NSP) LSCCs. In vitro and in vivo assays revealed that SP cells manifested preferential expression of self-renewal and CSC marker genes, higher capacity for proliferation, differentiation, and spheroid formation; enhanced resistance to chemotherapy; and greater xenograft tumorigenicity in immunodeficient mice compared with NSP cells. These findings suggest that the primary cultured and purified LSCCs contain cancer stem-like SP cells, which may serve as a valuable model for CSC research in LSCC.
    Full-text · Article · Jun 2013 · PLoS ONE
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    • "They are involved in resistance to chemotherapy because of their ability to efflux the drug from the cell and prevent the action of the chemotherapeutic agent.58 Cells of head and neck carcinoma were isolated using this method and exhibited increased clonogenicity and tumorigenicity in xenotransplantation.59–60 "
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    ABSTRACT: Cancer stem cells (CSCs), also called "cells that start the tumor," represent in themselves one of the most topical and controversial issues in the field of cancer research. Tumor stem cells are able to self-propagate in vitro (self-renewal), giving rise both to other tumor stem cells and most advanced cells in the line of differentiation (asymmetric division). A final characteristic is tumorigenicity, a fundamental property, which outlines the tumor stem cell as the only cell able to initiate the formation of a tumor when implanted in immune-deficient mice. The hypothesis of a hierarchical organization of tumor cells dates back more than 40 years, but only in 1997, thanks to the work of John Dick and Dominique Bonnet, was there the formal proof of such an organization in acute myeloid leukemia. Following this, many other research groups were able to isolate CSCs, by appropriate selection markers, in various malignancies, such as breast, brain, colon, pancreas, and liver cancers and in melanoma. To date, however, it is not possible to isolate stem cells from all types of neoplasia, particularly in solid tumors. From a therapeutic point of view, the concept of tumor stem cells implies a complete revision of conventional antineoplastic treatment. Conventional cytotoxic agents are designed to target actively proliferating cells. In the majority of cases, this is not sufficient to eliminate the CSCs, which thanks to their reduced proliferative activity and/or the presence of proteins capable of extruding chemotherapeutics from the cell are not targeted. Therefore, the theory of cancer stem cells can pose new paradigms in terms of cancer treatment. Potential approaches, even in the very early experimental stages, relate to the selective inhibition of pathways connected with self-renewal, or more specifically based on the presence of specific surface markers for selective cytotoxic agent vehicles. Finally, some research groups are trying to induce these cells to differentiate, thus making them easier to remove. For all these reasons, we have collected existing literature on head and neck cancer stem cells that correlate the biological characteristics of this subpopulation of cancer cells with the clinical behavior of tumors.
    Full-text · Article · Nov 2012 · OncoTargets and Therapy
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