Figure 4.

T-oligo induces senescence of MCF-7 cells. (a,b) MCF-7 and (c) normal mammary epithelial (NME) cells were treated with T-oligo once for seven days and then were either fixed and stained for senescence-associated (SA) β-galactosidase (β-gal) activity (a), or were supplemented with fresh medium lacking oligonucleotides and 5-bromo-2'-deoxyuridine (BrdU) incorporation (b,c) and retinoblastoma protein phosphorylation (inset) were determined. (a) In MCF-7 cells, T-oligo induced senescence of 61.3 ± 7.7% cells, compared to diluent and control oligo in which 6.3 ± 3.8% and 12 ± 2% of the cells, respectively, were senescent, as determined by SA β-gal activity (p < 0.015). (b) In MCF-7 cells, after T-oligo removal and provision of medium without T-oligo, only 7.4 ± 3.3% of cells displayed BrdU incorporation compared to 30.4 ± 9.8% and 23 ± 6.4% of diluent and control oligo pretreated cells, respectively (p < 0.05). (c) In NME cells, BrdU incorporation did not differ between T-oligo and diluent-treated cultures (7.1 ± 2.2% versus 6.3 ± 1.1% and 7.8 ± 1.2%, respectively; p = 0.5). Inset: MCF-7 cells were treated as above. Despite supplementation of fresh medium lacking T-oligo, no phosphorylation of retinoblastoma protein (pRb) was detected in T-oligo pretreated cultures. C, control-oligo; D, diluent; T, T-oligo.