Figure 5. The absence of CRBN activated the p38 MAPK/p53 signaling axis, resulting in p21 upregulation. (A) Endogenous levels proteins as determined by western blot analysis using extracts from mice skin. Proteins were subjected to immunoblotting using the anti-CRBN, anti-p21, anti-p38, anti-p-p38, anti-p53, anti-p-p53(Ser18), and anti–Tubulin antibodies. (B) Relative band intensities determined by densitometric analysis of each protein in blot (A). (C) Western blots analysis using protein lysate from the WT and CRBN KO MEFs. 10mM of SB203580 was treated to each type of cell for 2hr. Proteins were subjected to immunoblotting with the anti-CRBN, anti-p38, anti-p-p38, anti-p53, anti-p-p53(Ser18), anti-p21, and anti–Tubulin antibodies. The tubulin was used as a loading control. (D) The relative band ratio as determined by densitometric analysis of the blots in (C). The results shown are the means ± SEM of five independent experiments *P < 0.05; **P < 0.01; ***P < 0.005; n.s., not significant.