Changes of the methylation pattern of the c-myc gene during in vitro aging of IMR90 human embryonic fibroblasts

DNA modification by cytosine methylation has received considerable interest in the context of mammalian cell differentiation but is discussed controversially with respect to cellular aging. As the expression of c-myc affects strongly cellular aging and terminal differentiation, we have analysed the sequence-specific methylation pattern of the c-myc gene during proliferative aging in vitro of human embryonic fibroblasts. In this study, both, 5-methylcytidine sensitive restriction enzymes as well as genomic sequencing were used. The overall methylation pattern was found essentially stable during proliferative aging. However, specific hypermethylation of exon II during aging was observed. Futhermore, one specific cytidine located in the consensus sequence of the DNA binding factor PEBP2 was found completely methylated during most of the course of proliferative aging of the cells but became demethylated as the cells reached the end of their proliferative life span. Our results indicate the importance of establishing the sequence-specific changes of the methylation pattern of the genome during in vitro aging.