Downregulation of the DNA Repair Gene DDB2 by Arecoline Is through p53's DNA-Binding Domain and Is Correlated with Poor Outcome of Head and Neck Cancer Patients with Betel Quid Consumption.

Arecoline is the principal alkaloid in the areca nut, a component of betel quids (BQs), which are carcinogenic to humans. Epidemiological studies indicate that BQ-chewing contributes to the occurrence of head and neck cancer (HNC). Previously, we have reported that arecoline (0.3 mM) is able to inhibit DNA repair in a p53-dependent pathway, but the underlying mechanism is unclear. Here we demonstrated that arecoline suppressed the expression of DDB2, which is transcriptionally regulated by p53 and is required for nucleotide excision repair (NER). Ectopic expression of DDB2 restored NER activity in arecoline-treated cells, suggesting that DDB2 downregulation was critical for arecoline-mediated NER inhibition. Mechanistically, arecoline inhibited p53-induced DDB2 promoter activity through the DNA-binding but not the transactivation domain of p53. Both NER and DDB2 promoter activities declined in the chronic arecoline-exposed cells, which were consistent with the downregulated DDB2 mRNA in BQ-associated HNC specimens, but not in those of The Cancer Genome Atlas (TCGA) cohort (no BQ exposure). Lower DDB2 mRNA expression was correlated with a poor outcome in HNC patients. These data uncover one of mechanisms underlying arecoline-mediated carcinogenicity through inhibiting p53-regulated DDB2 expression and DNA repair.

Arecoline arrests cells at prometaphase by deregulating mitotic spindle assembly and spindle assembly checkpoint: implication for carcinogenesis.

One apparent feature of cancerous cells is genomic instability, which may include various types of chromosomal aberrations, such as translocation, aneuploidy, and the presence of micronuclei inside the cells. Mutagenic factors that promote the emergence of genomic instability are recognized as risk factors for the development of human malignancies. In Asia, betel quid (BQ) chewing is one of such risk factors for oral cancer. Areca nut is an essential constitute of BQ and is declared as a group I carcinogen by the International Agency for Research on Cancer. However, the molecular and cellular mechanisms regarding the carcinogenicity of areca nut are not fully explored. Here we reported that arecoline, a major alkaloid of areca nut, could arrest cells at prometaphase with large amounts of misaligned chromosomes. This prometaphase arrest was evidenced by condensed chromosome pattern, increased histone H3 phosphorylation, and accumulation of mitotic proteins, including aurora A and cyclin B(1). To investigate the molecular mechanisms accounting for arecoline-induced prometaphase arrest, we found that arecoline could stabilize mitotic spindle assembly, which led to distorted organization of mitotic spindles, misalignment of chromosomes, and up-regulation of spindle assembly checkpoint (SAC) genes. The SAC proteins BubR1 and Mps1 were differentially modified between the cells treated with arecoline and nocodazole. This together with aurora A overexpression suggested that SAC might be partly suppressed by arecoline. As a result, the arecoline-exposed cells might produce progeny that contained various chromosomal aberrations and exhibited genomic instability.