Fig. 4.
Down-regulation of p53 levels is required for postmitotic cell cycle reentry. (A) In situ hybridization analysis of Gadd45 mRNA expression in A1 cells and myotubes following the indicated treatments. (B) Percentage of myotubes entering S-phase as measured by BrdU incorporation. Myotubes were induced under normal conditions and incubated for 2.5 d in 10% FCS in the presence of DMSO, 1 µM nutlin3a, or 10 µM α-pifithrin (**P < 0.01). (C) Quantification of p-RBS807/811-positive cells. Myotubes were incubated in 0.25% FCS or 10% FCS with 1 µM nutlin3a or vehicle, then fixed and stained as described. (D) Western blot analysis of myotube extracts—including mononucleates—indicating levels of p-RBS807/811 and β-actin. Values from B and C represent the mean ± SEM, n = 6.