ABSTRACT
Rearrangements in the vicinity of the centromere of chromosome 1 are over-represented in many types of human cancer and are a characteristic feature of a rare genetic disease called ICF (immunodeficiency, centromeric heterochromatin instability, and facial anomalies). Evidence is presented that implicates DNA hypomethylation in the formation of these pericentromeric chromosomal anomalies. The DNA methylation inhibitors 5-azadeoxycytidine and 5-azacytidine, but not other tested genotoxins, induced the preferential formation of pericentromeric rearrangements of chromosome 1 at a very high frequency in a pro-B-cell line (FLEB14) and at a lower frequency in a mature B-cell line (AHH-1). These abnormal chromosomes appear identical to the diagnostic chromosomal aberrations in the ICF syndrome. A major component of the pericentromeric DNA in chromosome 1, satellite 2, was shown to be hypomethylated in an ICF B-cell line, although DNA from this cell line did not display detectable overall hypomethylation. It is hypothesized that demethylation in certain DNA regions, including in pericentromeric satellite DNA, helps lead to pericentromeric chromosomal rearrangements in lymphocytes from ICF patients and in normal lymphoblastoid cells incubated in vitro with DNA demethylating agents.
Subject(s)
Centromere/genetics , Chromosome Aberrations/genetics , Chromosomes, Human, Pair 1/genetics , DNA Methylation , Adult , Azacitidine/analogs & derivatives , Azacitidine/toxicity , B-Lymphocytes , Burkitt Lymphoma , Cell Line , Cell Line, Transformed , Centromere/drug effects , Chromosome Aberrations/chemically induced , Chromosome Disorders , Chromosomes, Human, Pair 1/drug effects , DNA Methylation/drug effects , DNA, Satellite/metabolism , Decitabine , Face/abnormalities , Fibroblasts , Heterochromatin/genetics , Humans , Immunologic Deficiency Syndromes/genetics , Male , Stem Cells , Tumor Cells, CulturedABSTRACT
5-Azacytidine (azaCR) causes genomic demethylation and decondensation of juxtacentromeric heterochromatin in chromosomes 1, 9, and 16. We determined the karyotypes of a pro-B cell line (FLEB14) treated with azaCR or its deoxynucleoside analog (azaCdR). About 80% of the induced rearrangements were in chromosome 1, and almost 90% of these involved its pericentromeric region. Multibranched figures with up to seven chromosome 1 arms, as well as whole-arm deletions of this chromosome, were the predominant anomalies, often with one normal homolog of chromosome 1 present. Isochromosomes 1 and fusions in the pericentromeric regions of chromosomes 1 and 16 or chromosomes 1 and 9 were also seen. The overlap of the spectrum of chromosomal rearrangements in azaCR- or azaCdR-treated FLEB14 cells and in mitogen-stimulated lymphocytes from patients with a rare genetic disease (ICF) associated with localized DNA hypomethylation supports the hypothesis that the DNA demethylating activity of azaCR is essential for the induction of these pericentromeric rearrangements. These studies may help elucidate the overrepresentation of chromosome 1 pericentromeric rearrangements in many types of cancer cells.
