Potential roles of DNA methylation in the initiation and establishment of replicative senescence revealed by array-based methylome and transcriptome analyses [methylation]

Cellular senescence is classified into two types; replicative and premature senescence. Gene expression and epigenetic changes are different in types of senescence, replicative and premature senescence, and cell types. Normal human diploid fibroblast TIG-3 cells were often used in cellular senescence research, however, their epigenetic profiles were not fully understood. To elucidate how cellular senescence is epigenetically regulated in TIG-3 cells, we analyzed gene expression and DNA methylation profiles among three types of senescent cells, namely, replicative senescent, RAS-induced senescent (RIS) and non-permissive temperature-induced senescent SVts8 cells, using gene expression and methylation microarrays. The expression of genes involved in cell cycle and immune response were commonly either down- or up-regulated among three types of senescent cells, respectively. The sequential alteration of DNA methylation level was observed only in replicative senescent cells in a time-dependent manner, but not in premature senescent cells. The integrated analysis of gene expression and methylation in replicative senescent cells demonstrated that the expression of 759 genes involved in cell cycle and immune response was associated with methylation. Furthermore, hypomethylation occurred at non-CpG island regions (open sea) on the genes with increased expression as well as non-CpG promoter of the genes related to immune response. Several miRNAs regulated by DNA methylation were found to affect the expression of their target genes. Taken together, these results indicate that DNA methylation contributes to introduction and establishment of replicative senescence partly by regulating gene expression. We examined the gene expression and epigenetic difference following senescence among three different types of senescent cells, replicative senescent, RAS-induced senescent (RIS) and senescent SVts8 cells, derived from Normal human diploid fibroblast TIG-3 cells. Gene expression and genome-wide DNA methylation profiles were obtained using SurePrint G3 Human GE microarray 8×60K Ver. 2.0 (Agilent) and Infinium HumanMethylation27/450 BeadChip (Illumina), respectively.