Constitutive heterochromatin DNA fragments are demethylated and decondensed in senescent primary fibroblasts MRC5 and malignant A431 cell line

Abstract

It is commonly accepted that satellite DNA (satDNA) is highly condensed in the interphase. We checked localization, the degree of condensation, and methylation level of centromeric (CEN) and pericentromeric (periCEN) satDNA fragments by immunofluorescent in situ hybridization (immuno-FISH). An antibody against 5-methylcytosine was used for the immunostaining, and satDNA probes were used for FISH. Cells from the normal somatic tissues (placenta cells and lymphocytes), a primary fibroblast cell line (MRC5), and a malignant cell line (A431) were analyzed. CEN satDNA was condensed and highly methylated in all studied cell types. PeriCEN human satellite 3 from chromosome 1 (HS3-1) was condensed in lymphocytes, placenta cells, and in young cells of the primary culture. In senescent fibroblasts and in the malignant cell line A431, the unfolded HS3-1 was observed. An antibody against methylated DNA stained compact patches of the periCEN satDNA and did not stain the unfolded regions. Thus, we observed the unfolding of the HS3-1 in senescent MRC5 and malignant A431. The unfolding was accompanied by partial demethylation of the satDNA that belongs to the constitutive heterochromatin.