ABSTRACT
Loss of heterozygosity at 3p21 is common in various cancers including nasopharyngeal carcinoma (NPC). BLU is one of the candidate tumor suppressor genes (TSGs) in this region. Ectopic expression of BLU results in the inhibition of colony formation of cancer cells, suggesting that BLU is a tumor suppressor. We have identified a functional BLU promoter and found that it can be activated by environmental stresses such as heat shock, and is regulated by E2F. The promoter and first exon are located within a CpG island. BLU is highly expressed in testis and normal upper respiratory tract tissues including nasopharynx. However, in all seven NPC cell lines examined, BLU expression was downregulated and inversely correlated with promoter hypermethylation. Biallelic epigenetic inactivation of BLU was also observed in three cell lines. Hypermethylation was further detected in 19/29 (66%) of primary NPC tumors, but not in normal nasopharyngeal tissues. Treatment of NPC cell lines with 5-aza-2'-deoxycytidine activated BLU expression along with promoter demethylation. Although hypermethylation of RASSF1A, another TSG located immediately downstream of BLU, was detected in 20/27 (74%) of NPC tumors, no correlation between the hypermethylation of these two TSGs was observed (P=0.6334). In addition to methylation, homozygous deletion of BLU was found in 7/29 (24%) of tumors. Therefore, BLU is a stress-responsive gene, being disrupted in 83% (24/29) of NPC tumors by either epigenetic or genetic mechanisms. Our data are consistent with the interpretation that BLU is a TSG for NPC.
Subject(s)
Azacitidine/analogs & derivatives , Carcinoma/genetics , Chromosomes, Human, Pair 3 , Epigenesis, Genetic , Nasopharyngeal Neoplasms/genetics , Stress, Physiological/genetics , Tumor Suppressor Proteins/genetics , Alleles , Animals , Azacitidine/pharmacology , Base Sequence , Carcinoma/pathology , Cell Line , Cell Line, Tumor , Cell Transformation, Viral , CpG Islands , DNA Methylation , Decitabine , Enzyme Inhibitors/pharmacology , Gene Deletion , Gene Expression Regulation, Neoplastic , Gene Silencing , Genes, Tumor Suppressor , Humans , Mice , Mice, Nude , Molecular Sequence Data , Nasopharyngeal Neoplasms/pathology , Promoter Regions, Genetic , Protein BindingABSTRACT
Epigenetic silencing of tumour suppressor genes (TSG) inactivates TSG functions. Previously, we identified PCDH10 as a methylated TSG in carcinomas. Here, we detected its frequent silencing and methylation in lymphoma cell lines including 100% Burkitt, 100% diffuse large B cell, 86% Hodgkin, 100% nasal natural killer/T-cell lymphoma and 1/3 of leukaemia cell lines, and in primary tumours but not in normal peripheral blood mononuclear cells or lymph nodes. PCDH10 silencing could be reversed by demethylation with 5-aza-2'-deoxycytidine. Methylation was further detected in 14% of Hodgkin lymphoma sera. Thus, PCDH10 methylation is frequently involved in lymphomagenesis and could serve as a tumour-specific biomarker.
Subject(s)
Biomarkers, Tumor , Cadherins/genetics , Epigenesis, Genetic , Gene Expression Regulation, Neoplastic , Hematologic Neoplasms/genetics , Burkitt Lymphoma/genetics , Cell Line, Tumor , CpG Islands , DNA Methylation , Gene Silencing , Hodgkin Disease/genetics , Humans , Leukemia/genetics , Lymphoma, Large B-Cell, Diffuse/genetics , Lymphoma, T-Cell/genetics , Protocadherins , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
ICF syndrome (immunodeficiency, centromere instability and facial anomalies) is a recessive human genetic disorder resulting from mutations in the DNA methyltransferase 3B (DNMT3B) gene. Patients with this disease exhibit numerous chromosomal abnormalities, including anomalous decondensation, pairing, separation and breakage, primarily involving the pericentromeric regions of chromosomes 1 and 16. Global levels of DNA methylation in ICF cells are only slightly reduced; however, certain repetitive sequences and genes on the inactive X chromosome of female ICF patients are significantly hypomethylated. In the present report, we analyze the molecular defect of de novo methylation in ICF cells in greater detail by making use of a model Epstein-Barr virus (EBV)-based system and three members of the unique cellular cancer-testis (C-T) gene family. Results with the EBV-based system indicate that de novo methylation of newly introduced viral sequences is defective in ICF syndrome. Limited de novo methylation capacity is retained in ICF cells, indicating that the mutations in DNMT3B are not complete loss-of-function mutations or that other DNMTs cooperate with DNMT3B. Analysis of three C-T genes (two on the X chromosome and one autosomal) revealed that loss of methylation from cellular gene sequences is heterogeneous, with both autosomal and X chromosome-based genes demonstrating sensitivity to mutations in DNMT3B. Aberrant hypomethylation at a number of loci examined correlated with altered gene expression levels. Lastly, no consistent changes in the protein levels of the DNA methyltransferases were noted when normal and ICF cell lines were compared.