Identification of TRIML2, a Novel p53 Target, that Enhances p53-SUMolylation and Regulates the Transactivation of Pro-apoptotic Genes. Homo sapiens

The tumor suppressor protein p53, encoded by TP53, inhibits tumorigenesis by inducing cell cycle arrest, senescence and apoptosis. Several genetic polymorphisms exist in TP53, including a proline to arginine variant at amino acid 72 (P72 and R72, respectively); this polymorphism alters p53 function. In general, the P72 variant shows increased ability to induce cell cycle arrest, while the R72 variant possesses increased ability to induce apoptosis, relative to P72. At present, the underlying mechanisms for these functional differences are not fully understood. Toward elucidating the molecular basis for these differences a gene expression microarray analysis was conducted on normal human fibroblast cells that are homozygous for P72 and R72 variants, along with subclones of these lines that express a p53 short hairpin (shp53). Approximately three dozen genes were identified whose transactivation is affected by the codon 72 polymorphism. One of these is the tripartite motif family-like 2 (TRIML2) gene, which is preferentially induced by the R72 variant. Importantly, the accumulated data indicate that TRIML2 interacts with p53, and facilitates the modification of p53 with SUMO2. TRIML2 also enhances the ability of p53 to transactivate a subset of pro-apoptotic target genes associated with prolonged oxidative stress, including PIDD, PIG3 (TP53I3) and PIG6 (PRODH). These data indicate that TRIML2 is part of a feed-forward loop that activates p53 in cells expressing the R72 variant, particularly after prolonged stress. Overall design: Normal human fibroblast cells were untreated (0 hour) or following 2 or 4 hours of exposure to 5 Gray of gamma radiation. 3 independent experiments were performed at each time point for each cell line and at each timepoint 2 cell lines were used.