21:T551,Radiotherapy for head and neck cancer can cause serious side effects, including severe damage to the salivary glands, resulting in symptoms such as xerostomia, dental caries, and oral infection. Because of the lack of long-term treatment for the symptoms of xerostomia, current research has focused on finding endogenous stem cells that can differentiate into various cell lineages to replace lost tissues and restore functions. Here, we report that Sox9⁺ cells can differentiate into various salivary epithelial cell lineages under homeostatic conditions. After ablating Sox9⁺ cells, the salivary glands of irradiated mice showed more severe phenotypes and the reduced proliferative capacity. Analysis of online single-cell RNA-sequencing data reveals the enrichment of the Wnt/β-catenin pathway in the Sox9⁺ cell population. Furthermore, treatment with a Wnt/β-catenin inhibitor in irradiated mice inhibits the regenerative capability of Sox9⁺ cells. Finally, we show that Sox9⁺ cells are capable of forming organoids in vitro and that transplanting these organoids into salivary glands after radiation partially restored salivary gland functions. These results suggest that regenerative therapy targeting Sox9⁺ cells is a promising approach to treat radiation-induced salivary gland injury.22:T451,MiR-21-5p is one of the most common oncogenic miRNAs that is upregulated in many solid cancers by inhibiting its target genes at the posttranscriptional level. However, the upstream regulatory mechanisms of miR-21-5p are still not well documented in cancers. Here, we identify a super-enhancer associated with the MIR21 gene (MIR21-SE) by analyzing the MIR21 genomic regulatory landscape in head and neck squamous cell carcinoma (HNSCC). We show that the MIR21-SE regulates miR-21-5p expression in different HNSCC cell lines and disruption of MIR21-SE inhibits miR-21-5p expression. We also identified that a key transcription factor, FOSL1 directly controls miR-21-5p expression by interacting with the MIR21-SE in HNSCC. Moreover, functional studies indicate that restoration of miR-21-5p partially abrogates FOSL1 depletion-mediated inhibition of cell proliferation and invasion. Clinical studies confirmed that miR-21-5p expression is positively correlated with FOSL1 expression. These findings suggest that FOSL1-SE drives miR-21-5p expression to promote malignant progression of HNSCC.

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