Studies On The Role Of Cancer Stem Cells in Head And Neck Squamous Cell Carcinoma
IR@IICB: CSIR-Indian Institute of Chemical Biology, Kolkata
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| Title |
Studies On The Role Of Cancer Stem Cells in Head And Neck
Squamous Cell Carcinoma
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| Creator |
Ghuwalewala, Sangeeta
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| Subject |
Molecular & Human Genetics
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| Description |
Almost all epithelial tumors contain cancer stem-like cells, which possesses a unique property of self-renewal and differentiation. In oral cancer, several biomarkers including cell surface molecules have been exploited for the identification of this highly tumorigeneic population. Implicit is the role of CD44 in defining CSCs but CD24 is not well-explored in Oral Squamous Cell Carcinoma (OSCC). Here we show that CD44highCD24low cells isolated from the oral cancer cell lines, not only express stem cell related genes but also exhibit Epithelial-to-Mesenchymal transition (EMT) characteristics. This CD44highCD24low population gives rise to all other cell types upon differentiation. Typical Cancer Stem Cell (CSC) phenotypes like increased colony formation, sphere forming ability, migration and invasion were also confirmed in CD44highCD24low cells. These cells also showed enhanced resistance to apoptosis inducing stimuli owing to their slow-cycling state and high expression of drug transporters. Comparison with CD44highCD24high population revealed significantly enhanced stem-like characteristics of CD24low cells. To validate our findings in-vivo, we determined the relative expression of CD44 and CD24 in clinical samples of OSCC patients. CD44 expression was consistently high whereas CD24 showed significantly lower expression in tumor tissues. Moreover, whole transcriptome profiling reveals the gene-specific signatures of CSCs in OSCC. We conclude that CD44highCD24low represents cancer stem-like cells in Oral Squamous Cell Carcinoma. Deregulation of microRNAs (miRNAs) has been implicated in tumor development, but whether or how it regulates stemness in OSCC remains unclear. Here we report that miR-146a is significantly up-regulated in CSCs derived from oral cancer cell lines and primary tumors. Moreover, ectopic expression of miR-146a resulted in enhanced expression of CSC markers and self-renewing potential. Interestingly, miR-146a was found to induce CSC characteristics by stabilizing β-catenin that coincides with the loss of E-cadherin and CD24. Thus miR-146a is also linked with epithelial-mesenchymal transition (EMT) in addition to activated wnt signaling. Further, we identified and validated CD24 as a novel functional target of miR-146a and found that CD24 over-expression rescued miR-146a driven CSC properties. Detailed mechanistic investigations revealed an inverse relation between CD24 and β-catenin which is regulated by AKT activity. We hereby show that CD24 inhibits AKT leading to β-xx. catenin degradation. Our data also confirmed a positive feedback loop in β-catenin mediated trans-activation of miR-146a that possibly contributes to stem cell homeostasis. Taken together, our study suggests that miR-146a plays a critical role in regulating stemness properties in OSCC through CD24-AKT-β-catenin axis. Another means of epigenetic regulation that actively participate in cellular re-programming of cancer stem cells is bivalent chromatin modification. In this context, role of PRC2 (Polycomb Repressor Complex 2) has been found to be evident in mediating H3K27me3 modification, with effect on transcriptional repression of the developmental regulators. We have shown that EED, a component of PRC2, is moderately up-regulated in CSCs and when, transiently over-expressed in bulk cells, induces CSC markers. Based on our observations, we hypothesize that PRC2 promotes re-programming via Oct4highSox2low molecular signature, which probably defines the intermediate committed cells (progenitors) in OSCC. Here we have shown activation of Notch pathway to play an important role in mediating CSC-like phenotype, which is EZH2 dependent. Notch activation by PRC2 is probably the underlying mechanism of induced EMT and stemness in OSCC cells. Overall, the epigenetic means of CSC regulation emerge as a significant mechanism of modulating CSC plasticity. These results may provide insights into the CSC-based therapeutic intervention in oral cancers in general.
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| Date |
2016
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| Type |
Thesis
NonPeerReviewed |
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| Format |
application/pdf
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| Identifier |
http://www.eprints.iicb.res.in/2585/1/Sangeeta_THESIS.pdf
Ghuwalewala, Sangeeta (2016) Studies On The Role Of Cancer Stem Cells in Head And Neck Squamous Cell Carcinoma. PhD thesis, C U. |
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| Relation |
http://www.eprints.iicb.res.in/2585/
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