TBC1D14 inhibits ribosome biogenesis to reduce lymph node metastasis in head and neck squamous cell carcinoma by mediating DDX31 ubiquitination

Head and neck squamous cell carcinoma (HNSCC) has great aggressiveness and a high early lymph node metastasis rate. Ribosome biogenesis (RiBi) is frequently hyperactivated in tumors and is strongly associated with oncogenesis. However, its function in HNSCC lymph node metastasis is poorly characterized. Here, we found TBC1D14 expression was downregulated in lymph node-metastatic HNSCC and inversely correlated with Pol I expression. TBC1D14 suppressed RiBi in HNSCC by bioinformatics mining and in vitro experiments. And inhibiting RiBi effectively reduced the proliferation, invasion, and migration capacities of HNSCC cells in vitro. In addition, inhibiting RiBi within TBC1D14-knockdown HNSCC cells suppressed epithelial-mesenchymal transition (EMT). Further in vivo experimentation substantiated that suppression of RiBi in HNSCC effectively attenuated TBC1D14 silencing-induced augmentation of tumor progression and lymph node metastasis. Analysis of our previous proteomic profiling data revealed that DDX31 was significantly downregulated in TBC1D14-overexpressing cells. Further investigations revealed that TBC1D14 inhibited RiBi by promoting the degradation of DDX31 via the ubiquitination pathway. Finally, we found that DDX31 underwent ubiquitination-dependent degradation via the TRIM25-mediated and K63-linked polyubiquitination pathway. Overall, our study demonstrates that TBC1D14 suppresses lymph node metastasis in HNSCC by promoting the ubiquitin-mediated degradation of DDX31 and subsequently inhibiting RiBi, consequently attenuating EMT. These findings revealed novel therapeutic targets for TBC1D14-deficient HNSCC.