Western blot analysis of protein products of p53-responsive genes following Tpo and GM-CSF treatment. After an 18-hour factor starvation period, 1 × 10⁶ cells were treated with either Tpo (50 ng/mL), GM-CSF (GM; 100 U/mL), or control serum-free media for 24 hours. Following this, protein levels were analyzed by Western blot analysis as described in Materials and Methods. This figure represents data from one of three experiments which yielded similar results.