Human chromosome 1 satellite 3 DNA is decondensed, demethylated and transcribed in senescent cells and in A431 epithelial carcinoma cells

Abstract

Constitutive heterochromatin mainly consists of different classes of satellite DNAs and is defined as a transcriptionally inactive chromatin that remains compact throughout the cell cycle. The aim of this work was to investigate the level of condensation, methylation and transcriptional status of centromeric (alphoid DNA) and pericentromeric satellites (human satellite 3, HS3) in tissues (lymphocytes, placenta cells) and in cultured primary (MRC5, VH-10, AT2Sp) and malignant (A431) cells. We found that alphoid DNA remained condensed and heavily methylated in all the cell types. The HS3 of chromosome 1 (HS3-1) but not of chromosome 9 (HS3-9) was strongly decondensed and demethylated in A431 cells. The same observation was made for aged embryonic lung (MRC5) and juvenile foreskin (VH-10) fibroblasts obtained at late passages (32^nd and 23^rd, respectively). Decondensation was also found in ataxia telangiectasia AT2Sp fibroblasts at the 16^th passage. One of the manifestations of the disease is premature aging. The level of HS3-1 decondensation was higher in aged primary fibroblasts as compared to A431. The HS3-1 extended into the territory of neighbouring chromosomes. An RT-PCR product was detected in A431 and senescent MRC5 fibroblasts using primers specific for HS3-1. The RNA was polyadenylated and transcribed from the reverse chain. Our results demonstrate the involvement of satellite DNA in associations between human chromosomes and intermingling of chromosome territories. The invading satellite DNA can undergo decondensation to a certain level. This process is accompanied by demethylation and transcription.

Nuclear Stress Bodies

“…For instance, expression of Sat III sequences is observed in cells treated with 5-Azacytidin, a potent inhibitor of DNA methylation (Eymery et al 2009b). The expression of pericentric transcripts also occurs during replicative senescence at late passages of both primary fibroblasts and cancer cells (Enukashvily et al 2007;Eymery et al 2009b). The fact that an alteration of the heterochromatin structure may favor an accumulation of Sat III transcripts is also suggested by observations made in fibroblasts from patients affected by the Hutchinson -Gilford progeria syndrome (HPGS), in which a complete loss of the heterochromatic marks is accompanied by the expression of chromosome 9 specific Sat III sequences (Shumaker et al 2006).…”

The secret message of heterochromatin: new insights into the mechanisms and function of centromeric and pericentric repeat sequence transcription

“…In most of the cases reported in the literature, accumulation of CT and PCT transcripts occurs at a transcriptional level and is mediated by RNA polymerase II. This is the case in heat-shocked cells Rizzi et al, 2004), in senescent cells (Enukashvily et al, 2007) and during the course of the cell cycle (Lu and Gilbert, 2007). The fact that sense and antisense transcripts are not necessarily present in equal quantity within the cell suggests that, similar to what occurs in S.Pombe (Volpe et al, 2002;Nicolas et al, 2007), transcription is further governed by specific transcriptional regulatory complexes.…”

“…Increased expression of specific transcripts from the 1q12 PCT region is correlated with a demethylation and with a decondensation of the locus (Enukashvily et al, 2007). Given the possible implication of PCT transcripts in heterochromatin structure, it is possible that the accumulation of PCT transcripts in senescent cells serves to (Valgardsdottir et al, 2008).…”

“…This observation is in agreement with reports suggesting that the expression of satellite sequences, observed in senescent and cancer cells, could be facilitated by a demethylation of PCT repeats. Indeed, a constitutive expression of PCT sequences at the 1q12 locus is also observed in A431 epithelial carcinoma cells and in senescent embryonic lung MRC5 cells where the genome is globally highly hypomethylated (Enukashvily et al, 2007). Cells from patients affected with the ICF syndrome (Immunodeficiency, Centromeric instability and Facial anomalies) constitute a powerful model to study the relationship between DNA methylation and expression of pericentric sequences.…”

Genetic Stability of Human Mesenchymal Stem Cells Exposed to X-Rays or Heat Shock in Culture

“…These findings show that chromosomes 1 and 4 were the most fragile in cells exposed both to HS and X-rays (see Figure 1, 2). The increased sensitivity of chromosome 1 was also found in the study of the effect of heat shock on human cell lines [17], [18]. The increased sensitivity of chromosome 4 was typical for human cells after X-rays [19]- [22].…”