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OBJECTIVE: Head and neck squamous cell carcinoma (HNSCC) is the most common type of malignancy in the head and neck region worldwide. The therapeutic strategies for HNSCC remain unsatisfying and limited. Here, we found a population of resistant Bmi1-expressing cells in the presence of cetuximab treatment and reported a novel role of SRY-box transcription factor 18 (SOX18), a member of the SOX family, in promoting HNSCC resistance to cetuximab. This study aimed to investigate the regulatory mechanism of Sox18 in Bmi1-positive cells and to search for better therapeutic targets. METHODS: We successfully obtained Bmi1CreER , RosatdTomato , and RosaDTA mice and identified Bmi1-expressing cells through lineage tracing. SOX18 expression in HNSCC and normal tissues was analyzed by immunohistochemistry, colocalization of Sox18, and Bmi1-expressing cells was analyzed by immunofluorescence, and SOX18 expression in SCC9 cell lines was quantified by western blotting and quantitative real-time PCR. The investigation of the mechanism of SOX18-mediated cetuximab resistance in Bmi1-positive cells was based on the analysis of single-cell RNA-seq data obtained from the Gene Expression Omnibus (GEO) database. Western blotting was performed to verify the results obtained from the single-cell RNA-seq analysis. RESULTS: In our study, we demonstrated that Bmi1-expressing cells were resistant to cetuximab treatment and that depletion of Bmi1-expressing cells improved cetuximab efficacy in HNSCC. We then discovered that Sox18 mediated the stem cell-like properties of Bmi1-expressing cells and promoted cellular cetuximab resistance through an oxidative phosphorylation pathway. There was a significant downregulation of key genes in the oxidative phosphorylation pathway in Sox18 knockout cell lines. CONCLUSIONS: Taken together, the findings of our study suggest that Sox18 mediates the resistance of Bmi1-expressing cells to cetuximab in HNSCC via the oxidative phosphorylation pathway.
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BACKGROUND: Cleft palate is a frequent congenital malformation with a heterogeneous etiology, for which folic acid (FA) supplementation has a protective effect. To gain more insight into the molecular pathways affected by FA, TGF-ß signaling and apoptosis in mouse embryonic palatal mesenchymal (MEPM) cells of all-trans retinoic acid (ATRA)-induced cleft palate in organ culture were tested. METHODS: C57BL/6J mice embryonic palates were explanted on embryonic day 14 and cultured in DMEM/F12 medium with or without ATRA or FA for 72 h. The palatal fusion was examined by light microscopy. Immunohistochemistry was used to detect TGFß3/TGF receptor II and caspase 9 in MEPM cells. TUNEL was used to detect apoptosis. RESULTS: Similar to development in vivo, palatal development and fusion were normal in control medium. ATRA inhibited palatal development and induced cleft palate, which can be rescued by FA. A higher apoptosis rate and caspase-9 in MEPM cells were detected in the ATRA group than in the control or the ATRA+FA group. Compared with the control or the ATRA+FA group, ATRA had little effect on TGF-ß3 in MEPM cells but significantly inhibited TGF-ß receptor II. CONCLUSIONS: Folic acid can rescue the cultured palates to continue developing and fusing that were inhibited and resulted in cleft palate by ATRA. Apoptosis and TGFß signaling in MEPM cells were involved in folic acid rescued ATRA-induced cleft palate.