Figure 8.

Effect of ERK activation on proliferation and senescence. (A) Ras-Raf-MEK-ERK effects in MEFs. Western blots of protein extracts (30 μg) from cells grown in the absence (-) or presence (+) of UO126, a pharmacological blocker of the ERK kinases, MEK1/2. ICR, cells from NT embryo; P+/+ (1) and P+/+ (13), cells from two different p44 homozygous embryos. (B) Recovery of proliferation in p44 homozygous MEFs by pharmacological blockade of ERK. Cells were grown for 48 h in 10 mM UO126 and pulsed for 1 h with BrdU. After fixation, cells were stained with antibody G3G4 against BrdU (green, top panels) to identify nuclei synthesizing DNA and with DAPI (blue, bottom panels) to identify all cell nuclei. Original magnification, 40×. Images were captured digitally and manipulated using Adobe Photoshop, v.7. (C) Reduced cellular senescence in p44 homozygous MEFs by pharmacological blockade of ERK. Cells were subjected to SA-β-gal assay following culture in the absence or presence of UO126, as described above.