Fig. 2

Propagation of human mammary epithelial cells. a Growth kinetics of 12-breast primary epithelial cells (12BPEC) and 14BPEC (population doubling (PD) vs days in culture). b Frequencies of 12BPEC at PD8 and PD41 expressing senescence-associated β-galactosidase marker. c Methylation mean of the p16 ^INK4a gene promoter in 12BPECs at different population doublings, as obtained by pyrosequencing methylation analyses. The red horizontal line represents the frequency of p16 ^INK4a promoter methylation in post-M0 human mammary epithelial cells. d Expression profile of p16 and p53 in 12BPEC at pre-stasis, stasis and post-stasis population doublings. Expression was tested using qRT-PCR, and data were normalized using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) RNA levels