LPLUNC1 stabilises PHB1 by counteracting TRIM21-mediated ubiquitination to inhibit NF-κB activity in nasopharyngeal carcinoma

Long-palate, lung and nasal epithelium clone 1 (LPLUNC1) is a tumour suppressor gene in nasopharyngeal carcinoma (NPC), and low expression of LPLUNC1 is associated with poor prognosis. Our previous study showed that LPLUNC1 upregulates Prohibitin 1 (PHB1), a pleiotropic protein that functions as a tumour suppressor gene in various cancers. Low expression of PHB1 was also found to be associated with the poor prognosis of NPC patients. However, the mechanisms by which LPLUNC1 upregulates PHB1 and the potential role of PHB1 in NPC are unclear. Here, we found that LPLUNC1 stabilised PHB1 by inhibiting PHB1 ubiquitination, which is mediated by E3 ligase TRIM21. LPLUNC1 competitively impaired the binding of PHB1 to TRIM21 due to its stronger binding affinity to PHB1, suppressing the ubiquitination of PHB1. Therefore, our study indicates that PHB1 acted as a tumour suppressor gene by inhibiting NF-κB activity. Depletion of PHB1 significantly attenuated the anti-tumour effects of LPLUNC1 in NPC cells, and the inhibitory effect of LPLUNC1 on NF-κB activity was thus reversed. Together, our findings revealed a novel mechanism underlying the anticancer effect of LPLUNC1 and clarified that PHB1 may represent a novel, promising candidate tumour suppressor gene in NPC, with potential therapeutic target value.