Int J Thyroidol.  2018 Nov;11(2):123-129. 10.11106/ijt.2018.11.2.123.

Relation between RASSF1A Methylation and BRAF Mutation in Thyroid Tumor

• Oh KH
• Jung KY
• Baek SK
• Woo JS
• Cho JG
• Kwon SY

• KMID: 2448982
• DOI: http://doi.org/10.11106/ijt.2018.11.2.123

Abstract

BACKGROUND AND OBJECTIVES
Hypermethylation of the tumor suppressor gene RASSF1A and activating mutation of BRAF gene have been recently reported in thyroid cancers. To investigate the role of these two epigenetic and genetic alterations in thyroid tumor progression, methylation of RASSF1A and BRAF mutation were examined in thyroid tumors.
MATERIALS AND METHODS
During 2007 to 2017, 69 papillary carcinomas, 18 nodular hyperplasia, 3 follicular carcinomas, and 13 follicular adenomas were selected. The methylation-specific polymerase chain reaction (MSP) technique was used in detecting RASSF1A methylation and polymerase chain reaction (PCR)-single-stranded conformation polymorphism and sequencing were used for BRAF gene mutation study.
RESULTS
The hypermethylation of the RASSF1A gene was found in 84.6%, 100% and 57.9% of follicular adenomas, follicular carcinomas, and papillary carcinomas, respectively. Nodular hyperplasia showed a hypermethylation in 33.3%. The BRAF mutation at V600E was found in 60.7% of papillary carcinoma and 27.0% of nodular hyperplasia, but none of follicular neoplasms. The BRAF mutation was correlated with the lymph node metastasis and MACIS clinical stage. There is an inverse correlation between RASSF1A methylation and BRAF mutation in thyroid lesions.
CONCLUSION
Epigenetic inactivation of RASSF1A through aberrant methylation is considered to be an early step in thyroid tumorigenesis, and the BRAF mutation plays an important role in the carcinogenesis of papillary carcinoma, providing a genetic marker.

Keyword

RASSF1A; Methylation; BRAF; Mutation; Thyroid

MeSH Terms

Adenoma
Carcinogenesis
Carcinoma, Papillary
Epigenomics
Genes, Tumor Suppressor
Genetic Markers
Hyperplasia
Lymph Nodes
Methylation*
Neoplasm Metastasis
Polymerase Chain Reaction
Thyroid Gland*
Thyroid Neoplasms
Genetic Markers

Figure

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  Fig. 1 The methylation status of the RASSF1A promoter region was analyzed by MSP; Methylation (m) and unmethylation-specific (u) primers were used. The methylation-specific product (93 bp) and unmethylation-specific product (105 bp) were resolved on 1.8% TBE gel. FA: follicular adenoma, FC: follicular carcinoma, NH: nodular hyperplasia, PC: papillary carcinoma

• 

  Fig. 2 The example of BRAF (exon 15) mutation was analyzed by PCR-SSCP (single-stranded conformation polymorphism) in papillary thyroid carcinoma. The arrow indicates the mutation band. M: mutation, N: normal

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  Fig. 3 Sequencing of the BRAF gene. Heterozygous missense mutation (T1796A/V600E) in exon 15. (A) Papillary carcinoma tissue and (B) nucleotide sequence in the corresponding normal tissue.

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  Fig. 4 The frequency of RASSF1A methylation and BRAF mutation. FA: follicular adenoma, FC: follicular carcinoma, NH: nodular hyperplasia, PC: papillary carcinoma

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