Methylation and Chromosomal Losses in Squamous Cell Carcinoma of the Head and Neck

Hong, Myoung Wha; Hong, Seung Jin; Rhyu, Mun Gan; Sun, Dong Il; Cho, Seung Ho; Kim, Min Sik

Abstract

BACKGROUND AND OBJECTIVES
Methylation of CpG islands is associated with delayed replication, condensed chromatin and inhibition of transcription initiation in many human cancers. Another concern with regards to CpG methlation is unilateral chromosomal losses in head and neck cancer. In this study, we investigated the extent of chromosomal losses and the status of CpG methylation in head and neck cancer in relation with clinicopathologic factors.
SUBJECTS AND METHOD
Both normal mucosa and tumor tissue samples were secured from 17 cases to a total of 34 samples to be examined with a methylation- specific PCR on 15 cancer-linked genes. A total of 29 cases were analyzed for PCR-based loss of heterozygosity (LOH) using a panel of 41 microsatellite markers on 8 chromosomes.
RESULTS
The pattern of methylation changes between the paired normal mucosa and tumor site was variable. Of the total of 206 cases examined for the methylation status of non-CpG island, 34 cases showed hypomethylation changes, 26 cases hypermethylation changes, and 31 cases no methylation changes. Regions containting CpG islands had 8 cases showing hypomethylation changes, 17 cases hypermethylation changes, and 31 cases of no methylation changes. The relationship between methylation and lymph node invasion revealed that, in the event of lymph node invasion, p16 downstream 0.7 kbp, p16 upstream 1.0 kbp, and hMLH1 upstream 1.0 kbp showed hypomethylation, whereas BGLAP upstream 4.5 kbp, Runx3 upstream 1.7 kbp, KIAA downstream 0.4 kbp showed hypermethylation. However, the rest of the genes were not changed. In 29 tumor foci, a LOH was found most frequently on the chromosomes 3p, 8p, 9p, and 13q. Interestingly, although other previous reports have not reported the detection of 8p chromosomal loss in head and neck cancer, this study frequently detected 8p chromosomal loss. Chromosomal loss yielded an overall mean value of 4.79+/-2.2 per tumor focus. A special relationship could not be drawn based on the relationship between the methylation and LOH. But in several genes such as p16 and hMLH1, there were differences between the hypomethylation. Genetic instability was raised when hypomethylation increased.
CONCLUSION
This study showed that the head and neck cancer and its progression generally need the proper level of chromosomal losses to accomplish cancer progression or development. Methylation pattern and LOH might be important rules and target event in head and neck cancer. In the future, experiments to find the point of genetic modification will help the way to prevent the cancer.