In our study, the combination of bortezomib with 10.0 nM ATRA caused a further upregulation of the p21Waf1/Cip1 levels (Fig. 3A and B, left panel), suggesting that the regulation of p21 also plays an important role in the repression of NB cell differentiation with the combined treatment. The gene discussed is CDKN1A; the disease is neuroblastoma.