Nasopharyngeal carcinoma (NPC) is an epithelial malignancy with a unique geographical distribution. The genomic abnormalities leading to NPC pathogenesis remain unclear. In total, 135 NPC tumors were examined to characterize the mutational landscape using whole-exome sequencing and targeted resequencing. An APOBEC cytidine deaminase mutagenesis signature was revealed in the somatic mutations. Noticeably, multiple loss-of-function mutations were identified in several NF-κB signaling negative regulators NFKBIA, CYLD, and TNFAIP3. Functional studies confirmed that inhibition of NFKBIA had a significant impact on NF-κB activity and NPC cell growth. The identified loss-of-function mutations in NFKBIA leading to protein truncation contributed to the altered NF-κB activity, which is critical for NPC tumorigenesis. In addition, somatic mutations were found in several cancer-relevant pathways, including cell cycle-phase transition, cell death, EBV infection, and viral carcinogenesis. These data provide an enhanced road map for understanding the molecular basis underlying NPC.nasopharyngeal carcinoma | somatic mutation landscape | NF-κB signaling | whole-exome sequencing | APOBEC-mediated signature
Nasopharyngeal carcinoma (NPC) is a malignant epithelial carcinoma of the nasopharynx. Cylindromatosis lysine 63 deubiquitinase (CYLD), a NF-kB inhibitor, was reported as one of the top mutated candidate genes in NPC. NF-kB is an inducible transcription factor, contributing to cancer via regulating inflammation, angiogenesis, cell proliferation, and metastasis. In this study, the impact of CYLD on regulating the NF-kB signaling pathway and its contribution to NPC development was studied using in vitro and in vivo functional assays, together with single cell RNA sequencing to understand the NPC tumor microenvironment. CYLD was downregulated in NPC clinical specimens and multiple cell lines. Functional assays revealed CYLD inhibits NPC cell proliferation and migration in vitro and suppresses NPC tumorigenicity and metastasis in vivo by negatively regulating the NF-kB signaling pathway. Additionally, CYLD was able to inhibit fibroblast and endothelial stromal cell infiltration into the NPC tumor microenvironment. These findings suggest that CYLD inhibits NPC development and provides strong evidence supporting a role for CYLD inhibiting fibroblast and endothelial stromal cell infiltration into NPC via suppressing the NF-kB pathway.
The long non-coding RNA (lncRNA) NKILA, localized to 20q13.31, is a negative regulator of NF-κB signaling implicated in carcinogenesis. As a CpG island is embedded in the promoter region of NKILA, it is hypothesized as a tumor suppressor lncRNA silenced by promoter DNA methylation in non-Hodgkin’s lymphoma (NHL). By pyrosequencing-verified methylation-specific PCR, NKILA methylation was detected in 1/10 (10%) NHL cell lines, but not in normal peripheral blood buffy coats or tonsils. NKILA methylation correlated with the repression of NKILA in cell lines. Hypomethylation treatment with 5-Aza-2′-deoxycytidine resulted in promoter demethylation and the re-expression of NKILA. In 102 NHL primary samples, NKILA was methylated in 29 (51.79%) diffuse large B-cell lymphoma (DLBCL) and 4 (20%) peripheral T-cell lymphoma cases, but unmethylated in all 26 mantle cell lymphoma cases. Mechanistically, the knockdown of NKILA resulted in promoting IkBα phosphorylation, associated with nucleus translocation of total p65 and phosphorylated p65 in SU-DHL-1 cells, hence constitutive NF-κB activation. Functionally, the knockdown of NKILA in SU-DHL-1 cells led to decreased cell death and increased cellular proliferation. Collectively, NKILA was a tumor suppressor lncRNA frequently hypermethylated in DLBCL. Promoter DNA methylation-mediated NKILA silencing resulted in increased cellular proliferation and decreased cell death via the repression of NF-κB signaling in NHL.
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