Alu Hypomethylation in Smoke-Exposed Epithelia and Oral Squamous Carcinoma

Background: Alu elements are one of the most common repetitive sequences that now constitute more than10% of the human genome and potential targets for epigenetic alterations. Correspondingly, methylation of theseelements can result in a genome-wide event that may have an impact in cancer. However, studies investigatingthe genome-wide status of Alu methylation in cancer remain limited.
Objectives: Oral squamous cell carcinoma(OSCC) presents with high incidence in South-East Asia and thus the aim of this study was to evaluate the Alumethylation status in OSCCs and explore with the possibility of using this information for diagnostic screening.We evaluated Alu methylation status in a) normal oral mucosa compared to OSCC; b) peripheral bloodmononuclear cells (PBMCs) of normal controls comparing to oral cancer patients; c) among oral epithelium ofnormal controls, smokers and oral cancer patients. Materials and
Methods: Alu methylation was detected bycombined bisulfite restriction analysis (COBRA) at 2 CpG sites. The amplified products were classified into threepatterns; hypermethylation (mCmC), partial methylation (uCmC+mCuC), and hypomethylation (uCuC).
Results:The results demonstrate that the %mCmC value is suitable for differentiating normal and cancer in oral tissues(p=0.0002), but is not significantly observe in PBMCs. In addition, a stepwise decrease in this value was observedin the oral epithelium from normal, light smoker, heavy smoker, low stage and high stage OSCC (p=0.0003).Furthermore, receiver operating characteristic (ROC) curve analyses demonstrated the potential of combined%mC or %mCmC values as markers for oral cancer detection with sensitivity and specificity of 86.7% and 56.7%,respectively.
Conclusions: Alu hypomethylation is likely to be associated with multistep oral carcinogenesis, andmight be developed as a screening tool for oral cancer detection.