We also found that PDCD4 negatively regulated the cyclin-dependent kinase inhibitor p21Waf1/Cip1 in HUVECs, which agrees with the finding that siRNA knockdown of PDCD4 expression led to increased expression of p21Waf1/Cip1 in HCT116 colon adenocarcinoma cells [34] and human KT1 cells [35]. This evidence concerns the gene PDCD4 and colon adenocarcinoma.