Analysis of the TP53 activation response by DREAM component LIN37 knockout and rescue HCT116 cell lines

Most human cancers acquire mutations causing defects in the p53 signal pathway. The tumor suppressor p53 gets activated in response to genotoxic stress and is essential forstopping the cell cycle in order to facilitate DNA repair or to induce apoptosis. The CDKN1A gene encoding for p21WAF1/Cip1 gets activated by p53. p21 then binds to cyclin/CDKcomplexes and prevents phosphorylation of target proteins, among others the pocket proteins RB, p130, and p107. In a hypophosphorylated state, these proteins bind to E2Fproteins to form RB-E2F and DREAM transcriptional repressor complexes. These complexes repress expression of cell cycle genes which stops cell cycle progression at the G1/S andG2/M transitions.Here, we analyze the specific influence of RB-E2F and DREAM on p53-induced cell cycle gene repression and cell cycle arrest. We show that abrogation of DREAM repressor functionby loss of the DREAM component LIN37 results in a reduced potential to repress cell cycle genes. By RNA-seq, we identify genes repressed by the p53-DREAM pathway and alsodescribe a set of genes that gets repressed by p53 independently of LIN37/DREAM. Most strikingly, p53-dependent cell cycle gene repression is completely abrogated inLIN37-/-;RB-/- cells, which also cannot arrest at the G1/S checkpoint.Taken together, we show both LIN37/DREAM and RB are essential components in the p53 pathway to down-regulate G1/S and G2/M genes and to stop cell cycle progression.