Detection of global hypermethylation in well-differentiated thyroid neoplasms by immunohistochemical (5-methylcytidine) analysis.
OBJECTIVE
While global hypomethylation of DNA has been found in several malignancies, studies on thyroid tumours have shown controversial results using different techniques. To help resolve this issue, we assessed methylation status using two different techniques in papillary thyroid carcinomas (PTC) and follicular adenomas (FA) and carcinomas (FTC), comparing adjacent non-neoplastic thyroid tissue.


METHODS
A series of 15 FA, 18 FTC and 17 PTC were assessed by: (1) measurement of methylation levels of long interspersed nuclear elements (LINE-1) using a combined bisulfite restriction analysis polymerase chain reaction protocol and (2) immunostaining with an anti-5-methylcytidine antibody that detects methylated DNA regardless of the DNA sequence. Immunostaining was scored by image analysis.


RESULTS
Methylation levels of LINE-1 in FA, FTC and PTC were not significantly different from adjacent normal tissue. There was no significant difference in methylation levels of LINE-1 between FA, FTC and PTC (p = 0.44). By immunohistochemical staining for methylation, the 5-methylcytidine score was significantly higher in tumours than in normal tissue counterparts, for FA (p < 0.001), FTC (p = 0.04) and PTC (p = 0.02). PTC showed the highest 5-methylcytidine expression amongst all tumours which was significantly different from FTC (p = 0.015), but not FA (p = 0.09). There was no correlation in methylation level between LINE-1 and 5-methylcytidine scores for each group and overall.


CONCLUSIONS
Well-differentiated thyroid neoplasms (FA, FTC and PTC) were not found by two independent methods to undergo global hypomethylation as part of an oncogenic sequence from normal tissue to carcinoma. Instead, hypermethylation was detected in all types of tumours, implying that this epigenetic event may contribute to oncogenic development of thyroid neoplasms (both benign and malignant).
Department of Pathology, Faculty of Medicine, Chulalongkorn University, Pathumwan, Bangkok, 10330, Thailand. trcskl@gmail.com.
S
S
Keelawat
Department of Pathology, Faculty of Medicine, Chulalongkorn University, Pathumwan, Bangkok, 10330, Thailand.|Division of Pathology, Hospital for Sick Children, Toronto, Canada.|Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada.
P S
PS
Thorner
Department of Pathology, Faculty of Medicine, Chulalongkorn University, Pathumwan, Bangkok, 10330, Thailand.
S
S
Shuangshoti
Department of Pathology, Faculty of Medicine, Chulalongkorn University, Pathumwan, Bangkok, 10330, Thailand.
A
A
Bychkov
Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.|Center of Excellence in Molecular Genetics of Cancer and Human Diseases, Department of Anatomy, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
N
N
Kitkumthorn
Center of Excellence in Molecular Genetics of Cancer and Human Diseases, Department of Anatomy, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
P
P
Rattanatanyong
Department of Pathology, Chonburi Hospital, 69 Moo 2, Tambon Baan Seaun, Ampur Mueung, Chonburi, Thailand.
W
W
Boonyayothin
Department of Pathology, Faculty of Medicine, Chulalongkorn University, Pathumwan, Bangkok, 10330, Thailand.
U
U
Poumsuk
Department of Pathology, Faculty of Medicine, Chulalongkorn University, Pathumwan, Bangkok, 10330, Thailand.
P
P
Ruangvejvorachai
Center of Excellence in Molecular Genetics of Cancer and Human Diseases, Department of Anatomy, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
A
A
Mutirangura
D018263:Adenocarcinoma, Follicular / Q000378:metabolism*; D000236:Adenoma / Q000378:metabolism*; D002277:Carcinoma / Q000378:metabolism*; D002291:Carcinoma, Papillary; D003562:Cytidine / Q000031:analogs & derivatives*; D019175:DNA Methylation; D006801:Humans; D007150:Immunohistochemistry; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics*; D000077273:Thyroid Cancer, Papillary; D013964:Thyroid Neoplasms / Q000378:metabolism*
D003562:Cytidine; C016568:5-methylcytidine
5-Methylcytidine; Follicular adenoma; Follicular carcinoma; LINE-1; Methylation; Papillary carcinoma