Association of TP53 Single Nucleotide Polymorphisms with Prostate Cancer in a Racially Diverse Cohort of Men

Growing evidence indicates the involvement of a genetic component in prostate cancer (CaP) susceptibility and clinical severity. Studies have reported the role of germline mutations and single nucleotide polymorphisms (SNPs) of TP53 as possible risk factors for cancer development. In this single institutional retrospective study, we identified common SNPs in the TP53 gene in AA and CA men and performed association analyses for functional TP53 SNPs with the clinico-pathological features of CaP. The SNP genotyping analysis of the final cohort of 308 men (212 AA; 95 CA) identified 74 SNPs in the TP53 region, with a minor allele frequency (MAF) of at least 1%. Two SNPs were non-synonymous in the exonic region of TP53: rs1800371 (Pro47Ser) and rs1042522 (Arg72Pro). The Pro47Ser variant had an MAF of 0.01 in AA but was not detected in CA. Arg72Pro was the most common SNP, with an MAF of 0.50 (0.41 in AA; 0.68 in CA). Arg72Pro was associated with a shorter time to biochemical recurrence (BCR) (p = 0.046; HR = 1.52). The study demonstrated ancestral differences in the allele frequencies of the TP53 Arg72Pro and Pro47Ser SNPs, providing a valuable framework for evaluating CaP disparities among AA and CA men.

Increased mTOR activity and metabolic efficiency in mouse and human cells containing the African-centric tumor-predisposing p53 variant Pro47Ser

The Pro47Ser variant of p53 (S47) exists in African-descent populations and is associated with increased cancer risk in humans and mice. Due to impaired repression of the cystine importer Slc7a11, S47 cells show increased glutathione (GSH) accumulation compared to cells with wild -type p53. We show that mice containing the S47 variant display increased mTOR activity and oxidative metabolism, as well as larger size, improved metabolic efficiency, and signs of superior fitness. Mechanistically, we show that mTOR and its positive regulator Rheb display increased association in S47 cells; this is due to an altered redox state of GAPDH in S47 cells that inhibits its ability to bind and sequester Rheb. Compounds that decrease glutathione normalize GAPDH-Rheb complexes and mTOR activity in S47 cells. This study reveals a novel layer of regulation of mTOR by p53, and raises the possibility that this variant may have been selected for in early Africa.

Common genetic variants in the TP53 pathway and their impact on cancer

The TP53 gene is well known to be the most frequently mutated gene in human cancer. In addition to mutations, there are > 20 different coding region single-nucleotide polymorphisms (SNPs) in the TP53 gene, as well as SNPs in MDM2, the negative regulator of p53. Several of these SNPs are known to alter p53 pathway function. This makes p53 rather unique among cancer-critical genes, e.g. the coding regions of other cancer-critical genes like Ha-Ras, RB, and PI3KCA do not have non-synonymous coding region SNPs that alter their function in cancer. The next frontier in p53 biology will consist of probing which of these coding region SNPs are moderately or strongly pathogenic and whether they influence cancer risk and the efficacy of cancer therapy. The challenge after that will consist of determining whether we can tailor chemotherapy to correct the defects for each of these variants. Here we review the SNPs in TP53 and MDM2 that show the most significant impact on cancer and other diseases. We also propose avenues for how this information can be used to better inform personalized medicine approaches to cancer and other diseases.

Tumor cells containing the African-Centric S47 variant of TP53 show increased Warburg metabolism

Mutations in the TP53 tumor suppressor gene remain a hallmark of human cancer. In addition to mutation of TP53, single nucleotide polymorphisms (SNPs) in this gene can have a profound impact on p53 function, and can affect cancer risk as well as other p53 functions. Wild type (WT) p53 contains a proline at amino acid 47, but approximately 1% of African-Americans express a p53 allele with a serine at amino acid 47 (Pro47Ser, hereafter S47). In a mouse model for this variant, mice expressing S47 are predisposed to spontaneous cancers. The S47 variant also is associated with increased pre-menopausal breast cancer risk in African American women. We recently reported that S47 tumor cells are resistant to the majority of cytotoxic chemotherapeutic agents, but show increased sensitivity to a subset of anti-cancer agents, compared to tumors with WT p53. In this work, we report on another potentially promising therapeutic vulnerability of S47 tumors. We find that S47 tumors show decreased mitochondrial metabolism, along with increased dependency on glycolysis. S47 tumor cells also show increased sensitivity to the glycolytic poison 2-deoxy-glucose. We propose that the altered metabolism in S47 tumor cells may be yet another potentially-actionable therapeutic vulnerability to exploit in cancer-prone individuals with this genotype.

The transcription-independent mitochondrial cell death pathway is defective in non-transformed cells containing the Pro47Ser variant of p53

Approximately half of all human cancers contain mutations in the TP53 tumor suppressor. In addition to mutations, there are single nucleotide polymorphisms (SNPs) in TP53 that can dampen p53 function, and can increase cancer risk and decrease the efficacy of cancer therapy. Approximately 6% of Africans and 1% of African-Americans express a p53 allele with a serine instead of proline at position 47 (Pro47Ser, or S47). The S47 variant is associated with increased breast cancer risk in pre-menopausal African Americans, and in a mouse model for the S47 variant, mice are predisposed to spontaneous cancers. We recently showed that the S47 variant is impaired for p53-mediated apoptosis in response to radiation and some genotoxic agents, particularly cisplatin. Here we identify the mechanism for impaired apoptosis of S47 in response to cisplatin. We show that following cisplatin treatment, the S47 variant shows normal stabilization and serine 15 phosphorylation, but reduced ability to bind to the peptidyl prolyl isomerase PIN1, which controls the mitochondrial localization of p53. This is accompanied by impaired mitochondrial localization of S47, along with decreased induction of cleaved caspase-3. Interestingly, we show that this defect occurs only for cisplatin and not for camptothecin. These findings show that normal tissues may respond differently to genotoxic stress depending upon this TP53 genotype. These data suggest that toxicity to cisplatin may be decreased in S47 individuals, and that this compound may be a superior treatment option for these individuals.

The African-specific S47 polymorphism of p53 alters chemosensitivity

The TP53 protein is known to affect the sensitivity of tumor cells to cell death by DNA damaging agents. We recently reported that human and mouse cells containing an African-specific coding region variant of p53, Pro47Ser (hereafter S47), are impaired in the transactivation of a small subset of p53 target genes including GLS2 and SCO2, and are markedly resistant to cisplatin. Further, mice containing this variant are markedly predisposed to cancer. Together these findings suggested that cancer-affected humans with the S47 variant might not be effectively treated with cisplatin. To more directly test this premise, we created transformed derivatives of mouse embryo fibroblasts (MEFs) containing wild type p53 (WT) and the S47 variant and analyzed them for chemosensitivity. We find that transformation with E1A and Ras actually reverses the chemosensitivity/transcriptional differences between WT p53 and S47. Specifically, E1A/Ras-transformed S47 cells show increased sensitivity to cisplatin and paclitaxel, and comparable transactivation of GLS2 and SCO2, compared to cells with WT p53. These data suggest that the functional differences between WT p53 and S47 in primary cells may not hold true for transformed cells. They also offer hope that cisplatin and paclitaxel may be effective chemotherapeutic drugs for S47 individuals with cancer.