Epithelial–mesenchymal transition (EMT) is involved in both physiological and pathological processes. EMT plays an essential role in the invasion, migration and metastasis of tumours. Autophagy has been shown to regulate EMT in a variety of cancers but not in head and neck squamous cell carcinoma (HNSCC). Herein, we investigated whether autophagy also regulates EMT in HNSCC. Analyses of clinical data from three public databases revealed that higher expression of fibronectin-1 (FN1) correlated with poorer prognosis and higher tumour pathological grade in HNSCC. Data from SCC-25 cells demonstrated that rapamycin and Earle’s balanced salt solution (EBSS) promoted autophagy, leading to increased FN1 degradation, while 3-methyladenine (3-MA), bafilomycin A1 (Baf A1) and chloroquine (CQ) inhibited autophagy, leading to decreased FN1 degradation. On the other hand, autophagic flux was blocked in BECN1 mutant HNSCC Cal-27 cells, and rapamycin did not promote autophagy in Cal-27 cells; also in addition, FN1 degradation was inhibited. Further, we identified FN1 degradation through the lysosome-dependent degradation pathway using the proteasome inhibitor MG132. Data from immunoprecipitation assays also showed that p62/SQSTM1 participated as an autophagy adapter in the autophagy–lysosome pathway of FN1 degradation. Finally, data from immunoprecipitation assays demonstrated that the interaction between p62 and FN1 was abolished in p62 mutant MCF-7 and A2780 cell lines. These results indicate that autophagy significantly promotes the degradation of FN1. Collectively, our findings clearly suggest that FN1, as a marker of EMT, has adverse effects on HNSCC and elucidate the autophagy–lysosome degradation mechanism of FN1.

上皮间质转化 (EMT) 参与生理和病理过程。EMT在肿瘤的侵袭、迁移和转移中起着至关重要的作用。自噬已被证明可以调节多种癌症中的 EMT，但不能调节头颈部鳞状细胞癌 (HNSCC)。在此，我们研究了自噬是否也调节 HNSCC 中的 EMT。对来自三个公共数据库的临床数据的分析表明，纤连蛋白-1（FN1）的高表达与 HNSCC 较差的预后和较高的肿瘤病理分级相关。来自 SCC-25 细胞的数据表明，雷帕霉素和厄尔平衡盐溶液 (EBSS) 促进自噬，导致 FN1 降解增加，而 3-甲基腺嘌呤 (3-MA)、巴弗洛霉素 A1 (Baf A1) 和氯喹 (CQ) 抑制自噬，导致 FN1 降解减少。另一方面，BECN1突变体HNSCC Cal-27细胞的自噬流被阻断，雷帕霉素不促进Cal-27细胞的自噬；此外，FN1 降解也受到抑制。此外，我们使用蛋白酶体抑制剂 MG132 通过溶酶体依赖性降解途径鉴定了 FN1 降解。来自免疫沉淀分析的数据还表明 p62/SQSTM1 作为自噬接头参与 FN1 降解的自噬 - 溶酶体途径。最后，来自免疫沉淀分析的数据表明 p62 和 FN1 之间的相互作用在 p62 突变 MCF-7 和 A2780 细胞系中被消除。这些结果表明自噬显着促进了 FN1 的降解。总的来说，我们的研究结果清楚地表明 FN1 作为 EMT 的标志物，