Thesis (Ph.D.)--Chulalongkorn University, 2008

This study aimed to (i) investigate genome-wide LINE-1 methylation level of oral squamous cell carcinomas (OSCCs); (ii) clarify whether LINE-1 hypomethylation can be detected in oral rinses of OSCC patients (1) study the pattern of methylation loss in specific LINE-1s. The combined bisulfite restriction analysis of LINE-1s (COBRALINE-1) and the modified COBRALINE-1 called COBRA unique to LINE-1 (CU-L1) were used to investigate genome-wide LINE-1s and specific LINE-1s, respectively. OSCCs revealed lower methylation levels of LINE-1s than normal oral epithelium and this hypomethylation could be detected in oral rinses of OSCC patients. There was no significant difference in the levels of genome-wide LINE-1 hypomethylation among tumors with different stages, histological grades, locations, history of betel chewing, smoking and/or alcohol consumption. Interestingly, methylation levels of each specific LINE-1 varied among loci. Each individual OSCC had different aberrant methylation levels in each specific LINE-1s. However, each individual OSCC had this aberration at least one of the 14 studied intronic LINE-1s. Moreover, there was still no significant difference in the specific LINE-1 methylation levels among clinico-pathological features of OSCCs. In conclusion, OSCCs possessed genome-wide LINE-1 hypomethylation and this alteration could be detected from oral rinses of OSCC patients by a simple technique, COBRALINE-1. The alteration of methylation levels in each specific LINE-1 was not equally distributed and had no specific character. The aberrant LINE-1 methylation was independent to clinico-pathological features of OSCCs.