Genomic analysis in oral squamous cell carcinoma detected by restriction landmark genomic scanning

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Although a considerable amount of cytogenetic and molecular data on oral squamous cell carcinoma (OSCC) has accumulated over the last few years, the picture is still incomplete in terms of how genetic alterations are involved in tumor initiations and progression. We, therefore, examined genetic abnormalities in OSCC using restriction landmark genomic scanning (RLGS), a method of two-dimensional gel analysis allowing detection of amplifications and other aberrations in genomic DNA. At first, DNA extracted from each of four oral carcinoma cell lines (Ca9-22, HO-1-u-1, HSC-2, KB) was examined. Isolated cell line and normal oral epithial DNAs were sequentially cleaved with specific restriction enzymes, radiolabelled and separated in two-dimensional gel electrophoresis. Thirteen distinct fragments were commonly amplified in the oral cancer cell lines, six of which were evident in all samples. Secondly, eleven cases of OSCC were also examined in the same manner. Five fragment/spots were found and amplified in at least 64% (7/11) (chromosomenos.4,9-12 or 22) of carcinomas, with one of these sports amplified in 100% (chromosome no.4) of tumor samples. In addition, six other spots were frequently reduced in at least 55% (chromosome nos.15 or 9-12) of tumor tissues. Then, the question of whether the DNA alterations involve not only genetic but also epigenetic change was examined using cell lines-Ca9-22, HO-1-u1, HSC-2 and KB-and treatment with a demethylating agent, 5-aza-2'-deoxycytidine (5-AzaCDR). Intensities of two of the reduced sports were amplified in the cell lines by the 5-AzaCDR treatment, showing that they were due to altered DNA methylation. The current studies provide clear evidence that epigenetic changes, like the methylation are related to oral carcinogenesis.