Investigation of genetic and epigenetic profile of tubulin folding cofactor D (TBCD) gene in malignant and premalignant lesions of the oral cavity

Oral squamous cell carcinoma (OSCC) is the most common type of oral cavity cancers. Since it has high morbidity and mortality rates, molecular studies are needed to unravel epigenetic/genetic mechanisms underlying OSCC development. Precancerous lesions of the oral cavity (OPML) are diseases with different rates of malignant transformation risk. Demokan et al., showed that methylation-dependent-expression loss of TBCD gene in OPML patients via methylation/expression array results from their previous unpublished data (TUBITAK-SBAG-114S497). In our study (IU-BAP-TYL-2019-35409), the methylation and expression status of TBCD gene was investigated in a larger group of OSCC and OPML patients for further validation. The role of the TBCD gene as a differential diagnosis in the conversion of OPML to OSCC has been examined and its usability as an invasive or non-invasive methylation biomarker for early diagnosis of cancer has been tested. In our study, methylation and expression levels of TBCD gene were determined in tumor-matched normal tissue and body fluids (serum, saliva) of 30 OSCC and 30 OPML patients and normal mucosa and body fluid samples of 15 healthy individuals as a control group, and methylation-dependent-expression loss was examined in OSCC and OPML patient groups. The decreased expression levels of TBCD were observed in 60% (20/30) of tumor samples compared with matched-normal tissue, whereas the expression levels were increased in 20% (6/30) of OSCC patients. In OPML subgroups, expression level decreased in 30.8% (4/13) of patients with LP, 42.8% (3/7) of patients with OLD and 50% (5/10) of patients with OLD. We observed that the promoter region of the TBCD gene was methylated in 13,3% (4/30) of tumor tissues in OSCC patients and 10% (3/30) in OPML patients. Methylation was detected in 66.7% (2/3) of patients diagnosed with OLD. It was observed that in 2 of 4 (50%) OSCC patients who had methylation in the promoter region of the TBCD gene, a decrease occurred in the expression level due to methylation. While an increase in expression level occurred in 1 patient, no change was observed in 1 patient. It was observed that in 2 of 3 (%66,6) OPML patients who had methylation in the promoter region of the TBCD gene, a decrease occurred in the expression level due to methylation and an increase in the expression level in 1 patient were observed. There is no methylation was detected in matched-normal tissue, serum and saliva samples of patients with methylation in tumor tissue of both group. Although the changes the expression level and clinical parameters (smoking, stage, anatomic involvement, pathological subgroup) were found to be significant in OSCC and OPML patients, it was observed that methylation observed at low rates had no effect on expression levels. For this reason, it is thought that the decrease in the expression of TBCD gene in tumor samples compared with matched-normal samples may play an important role in OSCC and OPML.