Association between cell cycle gene transcription and tumor size in oral squamous cell carcinoma

Abstract

Higher tumor size correlates with poor prognosis and is an independent predictive survival factor in oral squamous cell carcinoma (OSCC) patients. However, the molecular events underlining OSCC tumor evolution are poorly understood. We aimed to investigate if large OSCC tumors show different cell cycle gene transcriptional signature compared to small tumors. Seventeen fresh OSCC tumor samples with different tumor sizes (T) were included in the study. Tumors were from the tongue or from the floor of the mouth, and only three patients were nonsmokers. Samples were categorized according to clinical tumor size in tumors ≤2 cm (T1, n = 5) or tumors >2 cm (T2, n = 9; T3, n = 2; T4, n = 1). The group of tumors ≤2 cm was considered the reference group, while the larger tumors were considered the test group. We assessed the expression of 84 cell cycle genes by qRT-PCR array and normalized it to the expression of two housekeeping genes. Results were analyzed according to the formula 2^{^−DeltaCt}. A five-fold change cutoff was used, and p values <0.05 were considered statistically significant. Ki-67 immunohistochemistry was performed to estimate cell proliferation index. Twenty-nine genes were downregulated in the test group (larger tumors) compared to the reference group (smaller tumors). Among these genes, 13 reached statistical significance: ANAPC4, CUL1, SUMO1, KPNA2, MAD2L2, CCNG2, E2F4, NBN, CUL2, PCNA, TFDP1, KNTC1, and ATR. Ki-67 labeling index was similar in both tumor groups. Our findings suggest that the transcriptional activity of specific cell cycle genes varies according to the size of OSCC tumor, which probably reflects tumor molecular evolution and adaptation to the microenvironment.