Abstract 781: Sequence variations in TP53 3′UTR affect p53 protein expression and function and patient survival in diffuse large B-cell lymphoma.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma and represents ∼80% of all aggressive lymphomas. DLBCL can be classified into two major subtypes by gene expression profiling. The germinal center B-cell (GCB) subtype possesses gene expression patterns that resemble non-malignant B-cells that have entered the germinal center. The activated B-cell (ABC) subtype expresses many genes that are regulated by NF-κB activation. This agrees with the concept of cell of origin (COO) that subtypes of DLBCL originate from various stages of B-cell differentiation. The TP53 tumor suppressor gene encodes a transcription factor that acts as a sensor of cellular stressors and responds by upregulating various target genes to promote cell cycle arrest, initiate apoptosis, inhibit angiogenesis, and initiate DNA repair. Because approximately 50% of all cancers possess wild-type TP53 coding sequence (CDS), we reasoned that mutations outside the CDS may also promote tumorigenesis and help explain how cancers with wild-type p53 escape p53-regulated pathways. In this study, we determined the nucleotide sequence of the TP53 gene, including the 5′UTR and 3′UTR, in 244 de novo DLBCL tumors with a hypothesis that the TP53 3′UTR is altered in cancer. We sought to evaluate the prognostic importance and functional significance of sequence variation in the TP53 3′UTR in combination with CDS mutation and COO. We found a large number of single nucleotide variants (SNV) in the TP53 3′UTR with the majority of them previously unreported. There was no difference in overall survival and progression-free survival between patients with SNVs and those without. Similarly, no significant difference was found in COO subgroups between patients with and without SNVs. However, when patients are divided into two sets according to their TP53 CDS status, we found that patients carrying a wild-type TP53 CDS and a 3′UTR variant have a better 5-year overall survival than patients carrying a wild-type CDS and a native 3′UTR. In contrast, for patients with mutant TP53 CDS, 3′UTR variation predicts poor survival. Most of the unreported 3′UTR SNVs are located in the sites that are complementary to seed sequences of microRNA that are predicted or experimentally validated to target TP53. We found that three SNVs disrupting the seed match between miR-125b and the TP53 3′UTR affect p53 regulation by this microRNA. Additionally, an annotated SNP (rs78378222) in the TP53 polyadenylation signal (PAS) was uncovered in 3 of 244 patient samples (1.29%). Results from Northern and Western blots indicated that the presence of this SNP significantly affects p53 mRNA production and consequently results in downregulation of p53 protein. Using TUNEL assays, we demonstrate that cells harboring the TP53 PAS mutation exhibit reduced apoptosis upon UV treatment when compared to wild-type control cells. Citation Format: Michael Gordon, Ken H. Young, Yong Li. Sequence variations in TP53 3′UTR affect p53 protein expression and function and patient survival in diffuse large B-cell lymphoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 781. doi:10.1158/1538-7445.AM2013-781 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.