MDM2 and colorectal carcinoma: The positive control 5-FU, an antimetabolite used in CRC therapy, triggered a transcriptional p53 response as reflected by strong induction of the ubiquitin ligase MDM2, the cell cycle regulator p21 and the apoptosis factor PUMA, while other apoptosis-related genes, FASR and NOXA, were only slightly induced (Figure 2C).