HIF-1α or HOTTIP/CTCF Promotes Head and Neck Squamous Cell Carcinoma Progression and Drug Resistance by Targeting HOXA9.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most frequently diagnosed cancer worldwide. However, the clinical outcomes remain unsatisfactory. The aim of this study is to unravel the functional role and regulatory mechanism of HOXA9 in HNSCC. A cohort of 25 HNSCC tumor tissues and normal tissue counterparts was collected. qRT-PCR and western blotting were performed to determine the levels of HOXA9 and epithelial-mesenchymal transition (EMT)-related markers. Cell Counting Kit-8 (CCK-8) and colony formation assays were conducted to monitor cell viability and cytotoxicity. Transwell and wound healing assays were used to determine cell migration and invasion. Annexin V-fluorescein isothiocyanate/propidium iodide (FITC/PI) staining was performed to detect cell apoptosis. Bioinformatic analysis, electrophoretic mobility shift assay and chromatin immunoprecipitation (ChIP) assays were performed to investigate the direct binding between HIF-1α or CCCTC binding factor (CTCF) and HOXA9. Glutathione S-transferase (GST) pull-down and RNA pull-down assays were used to validate the interaction between CTCF and HOTTIP. HOXA9 was upregulated in HNSCC tissues and cells. Knockdown of HOXA9 inhibited cell proliferation, migration, invasion, and chemoresistance but promoted apoptosis in CAL-27 and KB cells. Knockdown of HOXA9 also regulated EMT-related marker via targeting YAP1/β-catenin. Silencing of HOTTIP or CTCF exerted similar tumor-suppressive effects in HNSCC. Mechanistically, HIF-1α or CTCF transcriptionally regulated HOXA9, and HOTTIP/CTCF cooperatively regulated HOXA9 in KB cells. HIF-1α or HOTTIP/CTCF transcriptionally modulates HOXA9 expression to regulate HNSCC progression and drug resistance.