Fig. 5. Oxidized protein patterns in SIPS and replicative senescence. SIPS was induced by 10 exposures of AG04431 HDFs to UVB at 250 mJ/cm², five exposures of WI-38 HDFs to t-BHP (Dierick et al., 2002), and a single exposure of IMR-90 HDFs to H₂O₂ (Frippiat et al., 2001). Procedures for detecting oxidized proteins are described in Materials and Methods. (a) Lane 1: control AGO4431 HDFs at early cumulative population doublings (CPDs). Lanes 2, 3: AGO4431 HDFs exposed to a series of 10 UVB stresses and proteins extracted at 24 and 72 hours, respectively, after the last stress. Lane 4: control WI-38 cells at early cumulative population doublings. Lanes 5, 6: WI-38 HDFs exposed to a series of 5 t-BHP stresses and proteins extracted at 24 and 72 hours, respectively, after the last stress. Lane 7: control IMR-90 cells at early at early cumulative population doublings. Lanes 8, 9, 10: H₂O₂ stressed IMR-90 cells, protein were extracted at 6, 24 and 72 hours, respectively, after the stress. Lanes 11, 12: WI-38 cells at early and late CPDs respectively. MW: molecular weights. (b) -tubulin was used as reference protein. The arrows indicate the most evident modifications of the oxidized protein patterns.