MicroRNA expression profiles of cancer stem cells in head and neck squamous cell carcinoma.

Increasing evidence indicates that cancer stem cells have essential roles in tumor initiation, progression, metastasis and resistance to chemo-radiation. Recent research has pointed out biological importance of microRNAs in cancer stem cell dysregulation. Total number of mature microRNAs in human genome increased to more than 2,500 with the recent up-date of the database. However, currently no information is available regarding microRNA expression profiles of cancer stem cells in head and neck squamous cell carcinoma (HNSCC). Increased ALDH1 activity has been demonstrated as a reliable marker for isolation of cancer stem cells. Therefore, we evaluated the microRNA expression profile of ALDH1-high subpopulations in the HNSCC cell lines UTSCC-9 and UTSCC-90. Initially, we examined cancer stem cell properties of ALDH1-high subpopulations in both cell lines. We analyzed expression of stemness markers, sphere formation capacity and xenograft transplantation into NOD/SCID mice. Our findings validated that ALDH1-high subpopulations showed significantly increased tumor-initiating ability. Furthermore, we investigated the microRNA expression profile of HNSCC stem cells using microRNA array and confirmed the results by quantitative real-time PCR. We found that expressions of miR­424, let-7a, miR­6836, miR­6873 and miR­7152 were downregulated, whereas miR­147b was upregulated with statistical significance in the ALDH1-high subpopulation. In conclusion, we identified a subset of microRNAs that were differentially expressed in ALDH1-high subpopulation, providing new microRNA targets to study dysregulation of HNSCC-initiating cells and develop therapeutic strategies aimed at eradicating the tumorigenic stem cells in HNSCC.

Role of miR-200c/miR-141 in the regulation of epithelial-mesenchymal transition and migration in head and neck squamous cell carcinoma.

Epithelial-mesenchymal-transition (EMT) is a critical step in tumor invasion and metastasis, while its fate is mainly defined by the balanced expression between the miR-200 family and ZEB transcription factors. In this study, we observed a reciprocal correlation between miR-200c/mir-141 and ZEB1, as well as between ZEB2 and E-cadherin expression in a panel of 13 head and neck squamous cell carcinoma (HNSCC) cell lines. We also confirmed that the enforced expression of miR-200c and miR-141 significantly reduced the migration capacity of HNSCC cells. Accordingly, the enforced expression of miR-200c and mir-141 resulted in a significant upregulation in E-cadherin expression, contrary to the significant downregulation in ZEB1 expression in 3 cell lines (UTSCC-24A, UTSCC-24B and UTSCC-6A cells). Another pair of cell lines, UTSCC-60A and UTSCC­ 60B failed to show a significant change in the expression of E-cadherin or ZEB1/ZEB2 during the enforced expression of miR-200c/miR-141. To address the issue, we focused on the hypermethylation status of the ZEB1/2 promoters, which have both been shown to include wide CpG islands. We observed a marked upregulation in both ZEB1 and ZEB2 mRNA expression following treatment with a demethylating agent in both pairs of UTSCC cell lines. In conclusion, our findings confirm the existence of a reciprocal correlation between the mir-200 family and the ZEB family, and demonstrate the role of the miR-200 family in EMT, as well as in the migration and invasion ability of HNSCC cells. Furthermore, our data suggest that the promoter hypermethylation of ZEB1 and ZEB2 may play an essential role and may overshadow the effects of the miR-200 family in the regulation of EMT during carcinogenesis.