Epigenetic silencing of TTF-1/NKX2-1 through DNA hypermethylation and histone H3 modulation in thyroid carcinomas.

Abstract

Thyroid transcription factor-1 (TTF-1), also known as NKX2-1, is a homeodomain containing transcriptional factor identified in thyroid, lung and central nervous system. In the thyroid, TTF-1 is essential for thyroid organogenesis and governs thyroid functions by regulating various thyroid-specific genes. We previously demonstrated that most differentiated thyroid neoplasms, including follicular adenomas/carcinomas and papillary carcinomas, express TTF-1 at both protein and mRNA levels. However, certain subtypes of thyroid cancers have shown low or negative expression of TTF-1. The aim of our study was to investigate the function of epigenetic modification in dysregulation of TTF-1 in thyroid carcinoma cells. We evaluated the expression of TTF-1 in primary thyroid tissues (normal thyroid, papillary carcinoma and undifferentiated carcinoma) and in thyroid carcinoma cell lines using immunohistochemistry and RT-PCR. Methylation-specific PCR targeting CpG islands of TTF-1 and chromatin immunoprecipitation (ChIP) for histone H3 lysine 9 (H3-lys9) were applied to clarify the correlation of the TTF-1 expression profile and epigenetic status. We also explored whether epigenetic modifiers, including 5-aza-deoxycytidine, could restore TTF-1 expression in thyroid carcinoma cells. In our current study, immunohistochemistry and RT-PCR showed positive expression of TTF-1 in normal thyroids and papillary carcinomas. Meanwhile, most of the undifferentiated carcinomas and the cell lines lost TTF-1 expression. No methylation in the CpG of TTF-1 promoter was detected in normal thyroids or papillary carcinomas. In contrast, DNA methylation was identified in 60% of the undifferentiated carcinomas (6/10) and 50% of the cell lines (4/8). ChIP assay demonstrated that acetylation of H3-lys9 was positively correlated with TTF-1 expression in thyroid carcinoma cells. Finally, DNA demethylating agents could restore TTF-1 gene expression in the thyroid carcinoma cell lines. Our data suggest that epigenetics is involved with inactivation of TTF-1 in thyroid carcinomas, and provide a possible means of using TTF-1 as a target for differentiation-inducing therapy through epigenetic modification.

• Authors: Tetsuo Kondo, Tadao Nakazawa, Defu Ma, Dongfeng Niu, Kunio Mochizuki, Tomonori Kawasaki, Nobuki Nakamura, Tetsu Yamane, Makio Kobayashi, Ryohei Katoh
• Journal: Laboratory investigation; a journal of technical methods and pathology (Lab Invest) Vol. 89 Issue 7 Pg. 791-9 (Jul 2009) ISSN: 1530-0307 [Electronic] United States
• PMID: 19506552 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA Primers
• Histones
• Hydroxamic Acids
• NKX2-1 protein, human
• Nuclear Proteins
• RNA, Messenger
• RNA, Neoplasm
• Thyroid Nuclear Factor 1
• Transcription Factors
• trichostatin A
• Decitabine
• Azacitidine

Topics

• Azacitidine (analogs & derivatives, pharmacology)
• Base Sequence
• Carcinoma, Papillary (etiology, genetics, metabolism)
• Cell Line, Tumor
• Chromatin Immunoprecipitation
• CpG Islands
• DNA Methylation
• DNA Primers (genetics)
• Decitabine
• Epigenesis, Genetic (drug effects)
• Gene Expression Profiling
• Gene Silencing
• Histones (metabolism)
• Humans
• Hydroxamic Acids (pharmacology)
• Nuclear Proteins (genetics)
• RNA, Messenger (genetics, metabolism)
• RNA, Neoplasm (genetics, metabolism)
• Thyroid Gland (metabolism)
• Thyroid Neoplasms (etiology, genetics, metabolism)
• Thyroid Nuclear Factor 1
• Transcription Factors (genetics)