Objective·To analyze the expression of mitochondrial related gene SFXN3(sideroflexin 3)in head and neck squamous cell carcinoma(HNSCC)and its effect on cell proliferation.Methods·Mitochondrial related genes and TCGA-HNSCC dataset were obtained from public databases to identify the target gene SFXN3 by using bioinformatic methods.The expression of SFXN3 in HNSCC patient samples was analysed by using the UALCAN database,and survival analyses of patients with different SFXN3 expression levels were performed according to TCGA-HNSCC cohort and GEO cohorts(GSE65858,GSE41613 and GSE27020).By using TCGA-HNSCC cohort and GEO cohorts(GSE40020,GSE210287),the differences in SFXN3 expression levels between therapeutic responders and non-responders were compared.Quantitative real-time PCR(qRT-PCR)was used to verify the expression of SFXN3 in the collected HNSCC tumor and para-tumor tissues,and the expression level of SFXN3 in human normal oral epithelial cells and HNSCC tumor cell lines was detected.With the construction of stable-SFXN3-knockdown HNSCC cell lines,the effect of SFXN3 on the proliferation ability of HNSCC cells was observed by using the Incucyte live-cell imaging analysis system and plate colony formation assay.Transcriptome sequencing was performed on the total RNA of stably-SFXN3-knockdown cells and control cells,and pathway enrichment analysis was performed on the genes with differentially down-regulated expression in knockdown group compared with control group.Results·SFXN3 was highly expressed in tumor tissues of HNSCC patients(P=0.000),and the prognosis of patients in the SFXN3-high-expression group was poor(all P＜0.05).The expression level of SFXN3 in the non-responders was higher than that in the responders(P=0.008),indicating an unfavorable prognosis.High expression of SFXN3 was verified in the collected HNSCC tumor tissues and HNSCC cell lines(all P＜0.05).After the knockdown of SFXN3 expression,the proliferation ability of HNSCC cells decreased,and the number of plate clones decreased(all P＜0.05).RNA sequencing showed that the differentially expressed down-regulated genes in HNSCC cells in the SFXN3-knockdown group were enriched in DNA replication,cell cycle,mitochondrial translation,mitochondrial RNA metabolic process and mitochondrial gene expression pathways.Conclusion·SFXN3 is highly expressed in HNSCC and it has negative correlation with the prognosis of patients.The proliferation ability and plate colony formation ability are inhibited in SFXN3-knockdown HNSCC cells,and these may work by affecting mitochondria function.