Elucidating The Role Of The African-Centric P47s Variant Of Tp53 In Metabolism And Ferroptosis

The tumor suppressor gene TP53 is the most frequently mutated gene in cancer and plays a key role in mediating several processes that are critical for preventing tumor formation and progression. Known as the guardian of the genome, p53 regulates hundreds of genes involved in various pathways such as apoptosis, cell cycle arrest and senescence. In recent years, the role of p53 in metabolism, redox state and ferroptosis has begun to emerge. Our lab has identified an African-specific polymorphic variant of p53 that encodes a serine residue instead of a proline at amino acid 47 (hereafter S47) and predisposes carriers to cancer. The S47 variant is impaired for tumor suppression and ferroptosis, and S47 cells have an altered redox state. We sought to use the tumor prone S47 model as a tool to better understand the role of p53 in tumor suppression. Our results demonstrate that mice carrying the S47 variant have greater metabolic efficiency compared to those with WT p53, along with increased mTOR activity. This difference in mTOR stems from an impaired protein-protein interaction that occurs in S47, ultimately due to a difference in cellular redox state. We next identified PLTP as a p53 target gene that shows decreased transactivation in the S47 variant and mediates ferroptosis resistance by enhancing lipid storage in HepG2 cells. Taken together, this work sheds light on the emerging roles p53 plays in tumor suppression, metabolism and ferroptosis. It also provides a better understanding of an ethnic genetic variant of p53. We expect this work will enable better personalized medicine approaches and therapeutic options for people who carry this variant

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 importe

Prospective functional classification of all possible missense variants in PPARG.

Clinical exome sequencing routinely identifies missense variants in disease-related genes, but functional characterization is rarely undertaken, leading to diagnostic uncertainty. For example, mutations in PPARG cause Mendelian lipodystrophy and increase risk of type 2 diabetes (T2D). Although approximately 1 in 500 people harbor missense variants in PPARG, most are of unknown consequence. To prospectively characterize PPARγ variants, we used highly parallel oligonucleotide synthesis to construct a library encoding all 9,595 possible single-amino acid substitutions. We developed a pooled functional assay in human macrophages, experimentally evaluated all protein variants, and used the experimental data to train a variant classifier by supervised machine learning. When applied to 55 new missense variants identified in population-based and clinical sequencing, the classifier annotated 6 variants as pathogenic; these were subsequently validated by single-variant assays. Saturation mutagenesis and prospective experimental characterization can support immediate diagnostic interpretation of newly discovered missense variants in disease-related genes.This work was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases (1K08DK102877-01, to A.R.M.; 1R01DK097768-01, to D.A.), NIH/Harvard Catalyst (1KL2TR001100-01, to A.R.M.), the Broad Institute (SPARC award, to A.R.M. and T.M.), and the Wellcome Trust (095564, to K.C.; 107064, to D.B.S.).This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/ng.370

Elucidating the Role of the African-Centric P47s Variant of TP53 in Metabolism and Ferroptosis

The tumor suppressor gene TP53 is the most frequently mutated gene in cancer and plays a key role in mediating several processes that are critical for preventing tumor formation and progression. Known as the guardian of the genome, p53 regulates hundreds of genes involved in various pathways such as apoptosis, cell cycle arrest and senescence. In recent years, the role of p53 in metabolism, redox state and ferroptosis has begun to emerge. Our lab has identified an African-specific polymorphic variant of p53 that encodes a serine residue instead of a proline at amino acid 47 (hereafter S47) and predisposes carriers to cancer. The S47 variant is impaired for tumor suppression and ferroptosis, and S47 cells have an altered redox state. We sought to use the tumor prone S47 model as a tool to better understand the role of p53 in tumor suppression. Our results demonstrate that mice carrying the S47 variant have greater metabolic efficiency compared to those with WT p53, along with increased mTOR activity. This difference in mTOR stems from an impaired protein-protein interaction that occurs in S47, ultimately due to a difference in cellular redox state. We next identified PLTP as a p53 target gene that shows decreased transactivation in the S47 variant and mediates ferroptosis resistance by enhancing lipid storage in HepG2 cells. Taken together, this work sheds light on the emerging roles p53 plays in tumor suppression, metabolism and ferroptosis. It also provides a better understanding of an ethnic genetic variant of p53. We expect this work will enable better personalized medicine approaches and therapeutic options for people who carry this variant

The p53 Tumor Suppressor in the Control of Metabolism and Ferroptosis

The p53 tumor suppressor continues to be distinguished as the most frequently mutated gene in human cancer. It is widely believed that the ability of p53 to induce senescence and programmed cell death underlies the tumor suppressor functions of p53. However, p53 has a number of other functions that recent data strongly implicate in tumor suppression, particularly with regard to the control of metabolism and ferroptosis (iron- and lipid-peroxide-mediated cell death) by p53. As reviewed here, the roles of p53 in the control of metabolism and ferroptosis are complex. Wild-type (WT) p53 negatively regulates lipid synthesis and glycolysis in normal and tumor cells, and positively regulates oxidative phosphorylation and lipid catabolism. Mutant p53 in tumor cells does the converse, positively regulating lipid synthesis and glycolysis. The role of p53 in ferroptosis is even more complex: in normal tissues, WT p53 appears to positively regulate ferroptosis, and this pathway appears to play a role in the ability of basal, unstressed p53 to suppress tumor initiation and development. In tumors, other regulators of ferroptosis supersede p53’s role, and WT p53 appears to play a limited role; instead, mutant p53 sensitizes tumor cells to ferroptosis. By clearly elucidating the roles of WT and mutant p53 in metabolism and ferroptosis, and establishing these roles in tumor suppression, emerging research promises to yield new therapeutic avenues for cancer and metabolic diseases

Prospective functional classification of all possible missense variants in PPARG

Abstract Clinical exome sequencing routinely identifies missense variants in disease-related genes, but functional characterization is rarely undertaken, leading to diagnostic uncertainty1,2. For example, mutations in PPARG cause Mendelian lipodystrophy3,4 and increase risk of type 2 diabetes (T2D)5. While approximately one in 500 people harbor missense variants in PPARG, most are of unknown consequence. To prospectively characterize PPARγ variants we used highly parallel oligonucleotide synthesis to construct a library encoding all 9,595 possible single amino acid substitutions. We developed a pooled functional assay in human macrophages, experimentally evaluated all protein variants, and used the experimental data to train a variant classifier by supervised machine learning (http://miter.broadinstitute.org). When applied to 55 novel missense variants identified in population-based and clinical sequencing, the classifier annotated six as pathogenic; these were subsequently validated by single-variant assays. Saturation mutagenesis and prospective experimental characterization can support immediate diagnostic interpretation of newly discovered missense variants in disease-related genes