Stem cell marker (Nanog) and Stat-3 signaling promote MicroRNA-21 expression and chemoresistance in hyaluronan/CD44-activated head and neck squamous cell carcinoma cells.

PMID 21685938


MicroRNAs are often associated with the pathogenesis of many cancers, including head and neck squamous cell carcinoma (HNSCC). In particular, microRNA-21 (miR-21) appears to have a critical role in tumor cell survival, chemoresistance and HNSCC progression. In this study, we investigated matrix hyaluronan (HA)-induced CD44 (a primary HA receptor) interaction with the stem cell markers, Nanog and Stat-3, in HNSCC cells (HSC-3 cells). Our results indicate that HA binding to CD44 promotes Nanog-Stat-3 (also tyrosine phosphorylated Stat-3) complex formation, nuclear translocation and transcriptional activation. Further analyses reveal that miR-21 is controlled by an upstream promoter containing Stat-3 binding site(s), while chromatin immunoprecipitation assays demonstrate that stimulation of miR-21 expression by HA/CD44 signaling is Nanog/Stat-3-dependent in HNSCC cells. This process results in a decrease of a tumor suppressor protein (PDCD4), and an upregulation of i nhibitors of the apoptosis family of proteins (IAPs) as well as chemoresistance in HSC-3 cells. Treatment of HSC-3 cells with Nanog- and/or Stat-3-specific small interfering RNAs effectively blocks HA-mediated Nanog-Stat-3 signaling events, abrogates miR-21 production and increases PDCD4 expression. Subsequently, this Nanog-Stat-3 signaling inhibition causes downregulation of survival protein (IAP) expression and enhancement of chemosensitivity. To further evaluate the role of miR-21 in tumor cell-specific functions, HSC-3 cells were also transfected with a specific anti-miR-21 inhibitor in order to silence miR-21 expression and block its target functions. Our results demonstrate that anti-miR-21 inhibitor not only upregulates PDCD4 expression but also decreases IAP expression and enhances chemosensitivity in HA-treated HNSCC cells. Together, these findings indicate that the HA-induced CD44 interaction with Nanog and Stat-3 has a pivotal role in miR-21 production leading to PDCD4 reduction, IAP upregulation and chemoresistance in HNSCC cells. This novel Nanog/Stat-3 signaling pathway-specific mechanism involved in miR-21 production is significant for the formation of future intervention strategies in the treatment of HA/CD44-activated HNSCC.

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