Epigenetic regulation of the X‐linked tumour suppressors BEX1 and LDOC1 in oral squamous cell carcinoma

Abstract

The strong associations between oral squamous cell carcinoma (OSCC) and dietary habits such as alcohol consumption (A), betel quid chewing (B) and cigarette smoking (C) and its predominance in men have been well documented; however, systemic analysis of OSCC is limited. Our study applied high-throughput screening methods to identify causative epigenetic targets in a cohort of men with ABC-associated OSCC. We identified BEX1 and LDOC1 as two epigenetically silenced X-linked tumour suppressors and demonstrated a functional link between the transcription of BEX1 and LDOC1 and promoter hypermethylation. Methylation of the BEX1 and LDOC1 promoters was associated significantly (p < 0.0001) with OSCC and were detected in 75% (42/56) and 89% (50/56) of the samples, respectively. We observed concordant increases in the methylation of both genes in 71% (40/56) of the tumours, and potent in vitro and in vivo growth inhibitory effects in OSCC cells ectopically expressing BEX1 and/or LDOC1. Restored expression of BEX1 and LDOC1 suppressed the nuclear factor-κB (NF-κB) signalling pathway, which is the most frequently hyperactivated signalling pathway in OSCC. This suppression might result from decreased p50 and p65 expression. These findings suggest that silencing of BEX1 and LDOC1 by promoter hypermethylation might represent a critical event in the molecular pathogenesis of OSCC and account for the oncogenic effects of ABC exposure and the male predominance of OSCC occurrence. Microarray data are available in the Gene Expression Omnibus (GEO; http://www.ncbi.nlm.nih.gov/geo/)

Leucine Zipper Down-regulated in Cancer-1 (LDOC1) interacts with Guanine nucleotide binding protein-like 3-like (GNL3L) to modulate Nuclear Factor-kappa B (NF-κB) signaling during cell proliferation

“…4 These data suggest the possibility that the increased expression of GNL3L, particularly in gastric cancer, may be due to the absence of inhibitory activity of LDOC1 owing to promoter hyper-methylation. 22,30 Furthermore, analysis of in vivo expression pattern of GNL3L and LDOC1 in various primary cancers from BioXpress database indicates an inverse correlation (Fig. 11), supporting the notion that the interplay between GNL3L and LDOC1 may be critical for cell growth control.…”

Combination of Imatinib Mesylate and AKT Inhibitor Provides Synergistic Effects in Preclinical Study of Gastrointestinal Stromal Tumor

“…Using an FDR of 5%, and FC >2 as cut-offs, five genes were identified that were common to arm 4 versus arm 2S, and arm 4 versus arm 3S comparisons ( Table 1 ). The up-regulation of the BEX1 ( brain expressed X-linked 1 ) gene under combination therapy was of particular interest, as this encoded protein has been implicated as a tumor-suppressor gene (TSG) in various cellular contexts (33-35). Similarly, neuronal pentraxin-1 ( NPTX1 ), which is also strongly up-regulated in response to the combination therapy, has been described as a potential TSG or biomarker in a variety of cancer types (36-38).…”

“…The WTS results for both BEX1 and NPTX1 were confirmed by qRT-PCR in the xenografts from the study, and the induction of BEX1 by the drug combination was also confirmed in IM-sensitive GIST-T1 and IM-resistant GIST430 cell lines, providing cellular models for exploring this finding. Numerous reports in the literature implicate BEX1 and NPTX1 as tumor-suppressor genes or biomarkers in various cancers (33-35,37,38). Both genes have been implicated in connection with pro-apoptotic pathways in different cellular contexts.…”

Brain-Expressed X-linked (BEX) proteins in human cancers

“…Treatment of glioma cells with TSA or 5-AzaC resulted in strong induction of BEX1 and BEX2 expression suggesting an epigenetic suppression of its expression in glioma which was further shown to be mediated through promoter methylation and histone modification [52]. Methylation of the BEX1 promoter was associated significantly (p < 0.0001) with oral squamous cell carcinoma (OSCC) and were detected in 75% (42/56) of the samples [53]. TSA and 5-AzaC treatment substantially elevated BEX2 expression in MLL wild-type AML cells suggesting that BEX2 is epigenetically suppressed in AML as well [23].…”