RESUMEN
Epigenetic inactivation by aberrant DNA methylation has been reported for many microRNA genes in various human malignancies. However, relatively little is known about microRNA gene methylation in hepatocellular carcinoma (HCC). Therefore, a systematic screen for identification of aberrantly hypermethylated microRNA genes in HCC was initiated. The methylation status of 39 intergenic CpG island associated microRNA genes was analyzed in HCC cell lines (n = 7), immortalized hepatocytes (n = 2) and normal liver samples (n = 5). Subsequently, 13 differentially methylated microRNA genes were analyzed in primary human HCC samples (n = 40), benign liver tumors (n = 15) and the adjacent liver tissues employing pyrosequencing. Expression of microRNA genes was measured using quantitative real-time polymerase chain reaction (RT-PCR). In addition, DNA methylation and expression of microRNA genes were measured after DNMT1 knockdown or DNMT inhibition. Aberrant hypermethylation and concomitant reduction in expression of intergenic microRNA genes is a frequent event in human HCC: hsa-mir-9-2 (23%), hsa-mir-9-3 (50 %), hsa-mir-124-1 (20%), hsa-mir-124-2 (13%), hsa-mir-124-3 (43%), hsa-mir-129-2 (58%), hsa-mir-596 (28%) and hsa-mir-1247 (38%). Altogether, it affects 90% of the HCC specimens under study. MicroRNA gene methylation is not found in hepatocellular adenoma (n = 10) and focal nodular hyperplasia (n = 5). DNMT1 knockdown or DNMT inhibition reduced microRNA gene methylation and stimulated expression. In primary human HCC specimens hypermethylation and expression of microRNA genes showed an inverse correlation. Concordant hypermethylation of three or more microRNA genes is a highly specific marker for the detection of HCC and for poor prognosis.
Asunto(s)
Carcinoma Hepatocelular/genética , Metilación de ADN , Neoplasias Hepáticas/genética , MicroARNs/genética , Secuencia de Bases , Biomarcadores de Tumor/genética , Carcinoma Hepatocelular/diagnóstico , Línea Celular Tumoral , Islas de CpG/genética , ADN (Citosina-5-)-Metiltransferasa 1 , ADN (Citosina-5-)-Metiltransferasas/genética , Hepatocitos/citología , Humanos , Neoplasias Hepáticas/diagnóstico , Pronóstico , Interferencia de ARN , ARN Interferente Pequeño , Análisis de Secuencia de ADNRESUMEN
MicroRNA (miRNA) genes have been shown to perform a crucial role in breast cancer metastasis. The epigenetic inactivation of such microRNA genes, as a result of aberrant DNA methylation, is frequently found in human tumours including those of the breast, and this is an area of considerable research activity.Pyrosequencing™ is a new quantitative method for the assessment of DNA methylation, with single CpG site resolution. Pyrosequencing™ can easily be performed in a 96-well-plate format with a cost-effective medium-sized throughput.This chapter provides a general outline of DNA methylation analysis, a detailed protocol of the Pyrosequencing™ procedure, and guidelines for the design of new assays. The strengths and limitations of this approach are discussed throughout the chapter.
Asunto(s)
Metilación de ADN/genética , MicroARNs/genética , Análisis de Secuencia de ADN/métodos , Secuencia de Bases , ADN/química , ADN/genética , ADN/aislamiento & purificación , Humanos , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa , Sulfitos/químicaRESUMEN
BACKGROUND: New high-throughput sequencing technologies promise a very sensitive and high-resolution analysis of DNA methylation patterns in quantitative terms. However, a detailed and comprehensive comparison with existing validated DNA methylation analysis methods is not yet available. Therefore, a systematic cross-validation of 454 sequencing and conventional pyrosequencing, both of which offer exact quantification of methylation levels with a single CpG dinucleotide resolution, was performed. RESULTS: To this end the methylation patterns of 12 loci (GSTπ1, p16INK4a, RASSF1A, SOCS1, MAL, hsa-mir-1-1, hsa-mir-9-3, hsa-mir-34a, hsa-mir-596, hsa-mir-663, MINT31, and LINE-1) were analyzed in ten primary hepatocellular carcinoma specimens. After applying stringent quality control criteria, 35749 sequences entered further analysis. The methylation level of individual CpG dinucleotides obtained by 454 sequencing was systematically compared with the corresponding values obtained by conventional pyrosequencing. Statistical analyses revealed an excellent concordance of methylation levels for all individual CpG dinucleotides under study (r2 = 0.927). CONCLUSIONS: Our results confirm that 454 sequencing of bisulfite treated genomic DNA provides reliable high quality quantitative methylation data and identify MAL, hsa-mir-9-3, hsa-mir-596, and hsa-mir-663 as new targets of aberrant DNA methylation in human hepatocellular carcinoma. In addition, the single molecule resolution of 454 sequencing provides unprecedented information about the details of DNA methylation pattern heterogeneity in clinical samples.
Asunto(s)
Metilación de ADN , ADN/química , Análisis de Secuencia de ADN/métodos , Carcinoma Hepatocelular/genética , Carcinoma Hepatocelular/metabolismo , Humanos , Neoplasias Hepáticas/genética , Neoplasias Hepáticas/metabolismo , Análisis de Regresión , Reproducibilidad de los ResultadosRESUMEN
BACKGROUND: Gene silencing due to aberrant DNA methylation is a frequent event in hepatocellular carcinoma (HCC) and also in hepatocellular adenoma (HCA). However, very little is known about epigenetic defects in fibrolamellar carcinoma (FLC), a rare variant of hepatocellular carcinoma that displays distinct clinical and morphological features. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed the methylation status of the APC, CDH1, cyclinD2, GSTπ1, hsa-mir-9-1, hsa-mir-9-2, and RASSF1A gene in a series of 15 FLC and paired normal liver tissue specimens by quantitative high-resolution pyrosequencing. Results were compared with common HCC arising in non-cirrhotic liver (nâ=â10). Frequent aberrant hypermethylation was found for the cyclinD2 (19%) and the RASSF1A (38%) gene as well as for the microRNA genes mir-9-1 (13%) and mir-9-2 (33%). In contrast to common HCC the APC and CDH1 (E-cadherin) genes were found devoid of any DNA methylation in FLC, whereas the GSTπ1 gene showed comparable DNA methylation in tumor and surrounding tissue at a moderate level. Changes in global DNA methylation level were measured by analyzing methylation status of the highly repetitive LINE-1 sequences. No evidence of global hypomethylation could be found in FLCs, whereas HCCs without cirrhosis showed a significant reduction in global methylation level as described previously. CONCLUSIONS: FLCs display frequent and distinct gene-specific hypermethylation in the absence of significant global hypomethylation indicating that these two epigenetic aberrations are induced by different pathways and that full-blown malignancy can develop in the absence of global loss of DNA methylation. Only quantitative DNA methylation detection methodology was able to identify these differences.
Asunto(s)
Metilación de ADN , Neoplasias Hepáticas/genética , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Estudios de Casos y Controles , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
BACKGROUND: The discovery of small non-coding RNAs and the subsequent analysis of microRNA expression patterns in human cancer specimens have provided completely new insights into cancer biology. Genetic and epigenetic data indicate oncogenic or tumor suppressor function of these pleiotropic regulators. Therefore, many studies analyzed the expression and function of microRNA in human breast cancer, the most frequent malignancy in females. However, nothing is known so far about microRNA expression in male breast cancer, accounting for approximately 1% of all breast cancer cases. METHODS: The expression of 319 microRNAs was analyzed in 9 primary human male breast tumors and in epithelial cells from 15 male gynecomastia specimens using fluorescence-labeled bead technology. For identification of differentially expressed microRNAs data were analyzed by cluster analysis and selected statistical methods.Expression levels were validated for the most up- or down-regulated microRNAs in this training cohort using real-time PCR methodology as well as in an independent test cohort comprising 12 cases of human male breast cancer. RESULTS: Unsupervised cluster analysis separated very well male breast cancer samples and control specimens according to their microRNA expression pattern indicating cancer-specific alterations of microRNA expression in human male breast cancer. miR-21, miR519d, miR-183, miR-197, and miR-493-5p were identified as most prominently up-regulated, miR-145 and miR-497 as most prominently down-regulated in male breast cancer. CONCLUSIONS: Male breast cancer displays several differentially expressed microRNAs. Not all of them are shared with breast cancer biopsies from female patients indicating male breast cancer specific alterations of microRNA expression.