PDCD4 was shown to repress the transcription of the mitosis-promoting factor cyclin-dependent kinase CDK1/cdc2 via the up-regulation of p21 (Waf1/Cip1), which resulted in the suppression of retinoblastoma protein (Rb) activation and cell growth in Bon-1 carcinoid cells (25). This evidence concerns the gene CDKN1A and carcinoid tumor.