The p53 codon 72 (Arg72Pro) polymorphism is associated with the degree of insulin resistance in type 2 diabetic subjects: a cross-sectional study

p53 Arg72Pro polymorphism, adiposity status, and cancer risk: Two case-cohorts within a Japanese prospective study

The tumor suppressor protein, p53, is a critical molecule involved in cancer development. However, the association between p53 Arg72Pro polymorphism and cancer risk remains unclear, possibly due to the pro-tumor potential of p53 under metabolic stress. Here, we hypothesized that the p53 Arg72Pro polymorphism plays different roles during tumorigenesis by adiposity status. We measured baseline body mass index (BMI) and p53 Arg72Pro polymorphism for two case-cohorts, which included 4264 cancers with up to 20 years of follow-up. Multivariable-adjusted hazard ratios (HRs) and confidence intervals (CIs) were estimated using weighted Cox proportional-hazards method. Without consideration of adiposity status, p53 Arg72Pro polymorphism was not associated with cancer risk. However, proline (Pro) homozygous genotype conferred an increased cancer risk for individuals with a BMI <25 kg/m² (HR [95% CI]: 1.12 [1.00-1.26] for total cancer and 1.19 [1.02-1.38] for obesity-related cancer), but not for those with a BMI ≥ 25 kg/m² . The heterogeneous effect of p53 Arg72Pro polymorphism on cancer risk according to adiposity status was indicated (p_{heterogeneity} : 0.07 for total cancer and 0.03 for obesity-related cancer). Furthermore, the association between overweight and cancer risk was only observed in arginine (Arg) carriers, but not in Pro homozygous carriers (p_{heterogeneity} : 0.07 for total cancer and 0.02 for obesity-related cancer). Pro homozygous carriers were more likely to be predisposed to cancer than Arg carriers with normal-weight conditions. In addition, overweight was related to a higher cancer risk in Arg carriers than Pro homozygous carriers. Our findings may suggest the adiposity-dependent dual effects of p53 Arg72Pro polymorphism during tumorigenesis.

Therapeutic Role of Curcumin in Diabetes: An Analysis Based on Bioinformatic Findings

BACKGROUND

Diabetes is an increasingly prevalent global disease caused by the impairment in insulin production or insulin function. Diabetes in the long term causes both microvascular and macrovascular complications that may result in retinopathy, nephropathy, neuropathy, peripheral arterial disease, atherosclerotic cardiovascular disease, and cerebrovascular disease. Considerable effort has been expended looking at the numerous genes and pathways to explain the mechanisms leading to diabetes-related complications. Curcumin is a traditional medicine with several properties such as being antioxidant, anti-inflammatory, anti-cancer, and anti-microbial, which may have utility for treating diabetes complications. This study, based on the system biology approach, aimed to investigate the effect of curcumin on critical genes and pathways related to diabetes.

METHODS

We first searched interactions of curcumin in three different databases, including STITCH, TTD, and DGIdb. Subsequently, we investigated the critical curated protein targets for diabetes on the OMIM and DisGeNET databases. To find important clustering groups (MCODE) and critical hub genes in the network of diseases, we created a PPI network for all proteins obtained for diabetes with the aid of a string database and Cytoscape software. Next, we investigated the possible interactions of curcumin on diabetes-related genes using Venn diagrams. Furthermore, the impact of curcumin on the top scores of modular clusters was analysed. Finally, we conducted biological process and pathway enrichment analysis using Gene Ontology (GO) and KEGG based on the enrichR web server.

RESULTS

We acquired 417 genes associated with diabetes, and their constructed PPI network contained 298 nodes and 1651 edges. Next, the analysis of centralities in the PPI network indicated 15 genes with the highest centralities. Additionally, MCODE analysis identified three modular clusters, which highest score cluster (MCODE 1) comprises 19 nodes and 92 edges with 10.22 scores. Screening curcumin interactions in the databases identified 158 protein targets. A Venn diagram of genes related to diabetes and the protein targets of curcumin showed 35 shared proteins, which observed that curcumin could strongly interact with ten of the hub genes. Moreover, we demonstrated that curcumin has the highest interaction with MCODE1 among all MCODs. Several significant biological pathways in KEGG enrichment associated with 35 shared included the AGE-RAGE signaling pathway in diabetic complications, HIF-1 signaling pathway, PI3K-Akt signaling pathway, TNF signaling, and JAK-STAT signaling pathway. The biological processes of GO analysis were involved with the cellular response to cytokine stimulus, the cytokine-mediated signaling pathway, positive regulation of intracellular signal transduction and cytokine production in the inflammatory response.

CONCLUSION

Curcumin targeted several important genes involved in diabetes, supporting the previous research suggesting that it may have utility as a therapeutic agent in diabetes.

Differential Transcriptional Regulation of Polymorphic p53 Codon 72 in Metabolic Pathways

p53 is a transcription factor that is activated under DNA damage stress and regulates the expression of proapoptotic genes including the expression of growth arrest genes to subsequently determine the fate of cells. To investigate the functional differences of polymorphic p53 codon 72, we constructed isogenic lines encoding each polymorphic p53 codon 72 based on induced pluripotent stem cells, which can endogenously express each polymorphic p53 protein only, encoding either the arginine 72 (R72) variant or proline 72 (P72) variant, respectively. We found that there was no significant functional difference between P72 and R72 cells in growth arrest or apoptosis as a representative function of p53. In the comprehensive analysis, the expression pattern of the common p53 target genes, including cell cycle arrest or apoptosis, was also increased regardless of the polymorphic p53 codon 72 status, whereas the expression pattern involved in metabolism was decreased and more significant in R72 than in P72 cells. This study noted that polymorphic p53 codon 72 differentially regulated the functional categories of metabolism and not the pathways that determine cell fate, such as growth arrest and apoptosis in cells exposed to genotoxic stress.

TP53 codon 72 polymorphism and type 2 diabetes: a case-control study in South Indian population

TP53 functions primarily as a tumor suppressor, controlling a myriad of signalling pathways that prevent a cell from undergoing malignant transformation. This tumor suppressive function requires an activation and stabilization of TP53 in response to cell stressors. However, besides its cancer-preventive functions, TP53 is also known to be involved in diverse cellular processes including metabolism, reproduction, stem cell renewal and development. Indeed, several lines of evidence strongly suggest that TP53 plays crucial role in diabetes. A number of studies have evaluated the association of genetic alterations (single nucleotide variations) in TP53 gene with the development of diabetes. However, the results have not been consistent. The aim of this study was to evaluate whether the C/G polymorphism at codon 72 (Pro72/Arg72), located in exon 4 of TP53, is associated with type 2 diabetes in South Indian population. A total of 74 type 2 diabetic patients and 54 non-diabetic subjects were screened. None of the three genotypes, namely C/C (Pro/Pro), C/G (Pro/Arg), and G/G (Arg/Arg) was found to be significantly associated with type 2 diabetes in our study group. The findings of this study indicate that TP53 codon 72 polymorphism is not associated with increased risk of type 2 diabetes in South Indian population. Further studies with a large cohort size would be necessary to corroborate the observations of this study. Nevertheless, this study represents the first genetic analysis of TP53 variants in South Indian type 2 diabetic patients.

Associations of TP53 codon 72 polymorphism with complications and comorbidities in patients with type 1 diabetes

Abstract

Wild-type TP53 plays an important role in the regulation of immune response and systemic inflammation. In type 1 diabetes (T1D), TP53 pathways are upregulated and an increased susceptibility to apoptosis is observed. We hypothesize that TP53 codon 72 polymorphism could be associated with complications and comorbidities in patients with T1D. We have investigated the associations of the TP53 codon 72 polymorphism with the T1D complications and comorbidities (retinopathy, nephropathy, hypertension, dyslipidemia, autoimmune thyroiditis, and celiac disease) in 350 patients. The key results of our approach are as follows: (1) In diabetic subjects, the Pro/Pro genotype is associated with an increased risk of microvascular complications, dyslipidemia, and celiac disease; (2) the Arg/Arg variant is associated with a decreased risk of autoimmune thyroiditis and celiac disease; (3) the Pro allele is associated with an increased risk of dyslipidemia, autoimmune thyroiditis, and celiac disease. Although further studies are required, our results for the first time indicate that the TP53 codon 72 polymorphism could be considered a genetic marker to predict the increased susceptibility to some T1D complications and comorbidities.

Key messages

We analyzed the TP53 codon 72 polymorphism in patients with T1D.

Pro/Pro genotype is associated with an increased risk of microvascular complications, dyslipidemia, and celiac disease.

The Arg/Arg variant is associated with a decreased risk of autoimmune thyroiditis and celiac disease.

The Pro allele is associated with an increased risk of dyslipidemia, autoimmune thyroiditis, and celiac disease.

Exploring the multiple roles of guardian of the genome: P53

Background

Cells have evolved balanced mechanisms to protect themselves by initiating a specific response to a variety of stress. TheTP53gene, encoding P53 protein, is one of the many widely studied genes in human cells owing to its multifaceted functions and complex dynamics. The tumour-suppressing activity of P53 plays a principal role in the cellular response to stress. The majority of the human cancer cells exhibit the inactivation of the P53 pathway. In this review, we discuss the recent advancements in P53 research with particular focus on the role of P53 in DNA damage responses, apoptosis, autophagy, and cellular metabolism. We also discussed important P53-reactivation strategies that can play a crucial role in cancer therapy and the role of P53 in various diseases.

Main body

We used electronic databases like PubMed and Google Scholar for literature search. In response to a variety of cellular stress such as genotoxic stress, ischemic stress, oncogenic expression, P53 acts as a sensor, and suppresses tumour development by promoting cell death or permanent inhibition of cell proliferation. It controls several genes that play a role in the arrest of the cell cycle, cellular senescence, DNA repair system, and apoptosis. P53 plays a crucial role in supporting DNA repair by arresting the cell cycle to purchase time for the repair system to restore genome stability. Apoptosis is essential for maintaining tissue homeostasis and tumour suppression. P53 can induce apoptosis in a genetically unstable cell by interacting with many pro-apoptotic and anti-apoptotic factors.

Furthermore, P53 can activate autophagy, which also plays a role in tumour suppression. P53 also regulates many metabolic pathways of glucose, lipid, and amino acid metabolism. Thus under mild metabolic stress, P53 contributes to the cell’s ability to adapt to and survive the stress.

Conclusion

These multiple levels of regulation enable P53 to perform diversified roles in many cell responses. Understanding the complete function of P53 is still a work in progress because of the inherent complexity involved in between P53 and its target proteins. Further research is required to unravel the mystery of this Guardian of the genome “TP53”.

Intronic TP53 Polymorphisms Are Associated with Increased Δ133TP53 Transcript, Immune Infiltration and Cancer Risk

We investigated the influence of selected TP53 SNPs in exon 4 and intron 4 on cancer risk, clinicopathological features and expression of TP53 isoforms. The intron 4 SNPs were significantly over-represented in cohorts of mixed cancers compared to three ethnically matched controls, suggesting they confer increased cancer risk. Further analysis showed that heterozygosity at rs1042522(GC) and either of the two intronic SNPs rs9895829(TC) and rs2909430(AG) confer a 2.34-5.35-fold greater risk of developing cancer. These SNP combinations were found to be associated with shorter patient survival for glioblastoma and prostate cancer. Additionally, these SNPs were associated with tumor-promoting inflammation as evidenced by high levels of infiltrating immune cells and expression of the Δ133TP53 and TP53β transcripts. We propose that these SNP combinations allow increased expression of the Δ133p53 isoforms to promote the recruitment of immune cells that create an immunosuppressive environment leading to cancer progression.

Effect of maternal HIV infection, BMI and NOx air pollution exposure on birth outcomes in South African pregnant women genotyped for the p53 Pro72Arg (rs1042522)

Tumour suppressor protein, p53, plays a role in modulating innate immune responses, DNA repair, cell cycle arrest, senescence and apoptosis. Maternal nitrogen oxide (NOx) air pollution exposure, body mass index (BMI), human immunodeficiency virus (HIV) infection and p53 Pro72Arg (rs1042522) affect foetal growth. We investigated whether the aforementioned factors influence birth outcomes in a South African population. Pregnant women (n = 300; HIV -ve = 194 and HIV +ve = 106) were genotyped for the p53 rs1042522 using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and further stratified based on HIV status, infants' birthweight (BW; NBW: normal BW [>2,500 g] and LBW: low BW [<2,500 g]) and gestational age (GA; NGA: normal GA [>37 weeks] and PTB: preterm birth [≤37 weeks]). A land use regression model was developed to characterize maternal NOx exposure. Pearson's correlation and multivariate regression analysis statistical tests were used to determine the effect of rs1042522 genotyped pregnant women's BMI and NOx exposure on maternal blood pressure and haemoglobin and iron levels, and infants' anthropometric measurements and Appearance Pulse Grimace Activity and Respiration (APGAR) scores. The prevalence of LBW and PTB was 14.7% and 18.7%, respectively. The LBW group had a higher frequency of the variant Arg-allele versus NBW group (47.7% vs. 31.4%, p = .0046, OR = 2.0, 95% CI = 1.26-3.17). No association was observed between NGA and PTB groups. A significant association between BMI and systolic blood pressure (r = .50, p = .00; B = 0.76, p = .002) and birth length (r = -.28, p = .01; B = -0.107, p = .011), and NOx and birth length (r = -.26, p = .08; B = -0.191, p = .046) and birthweight (B = -8.87, p = .048) was observed in HIV-infected mothers with the variant Pro/Arg + Arg/Arg genotypes. Mothers from the LBW group with the variant genotypes displayed an association between NOx and diastolic blood pressure (r = .58, p = .04), blood iron levels (r = -.60, p = .04; B = -0.204, p = .004), APGAR scores at 1 min (r = -.86, p = .00; B = -0.101, p = .003) and 5 min (r = -.75, p = .01) and birth length (r = -.61, p = .04), and BMI and diastolic blood pressure (r = .72, p = .01). In the PTB group, maternal variant genotypes and NOx were associated with blood haemoglobin levels (B = -0.132, p = .045) and APGAR scores at 1 min (B = -0.161, p = .045) and 5 min (B = -0.147, p = .043). Maternal rs1042522 Arg-allele, HIV infection, BMI and NOx exposure collectively play a role in lowering blood iron levels, gestational hypertension and LBW outcomes.

The role of tumor suppressor p53 in metabolism and energy regulation, and its implication in cancer and lifestyle-related diseases

The tumor suppressor gene p53 is mutated in approximately more than 50% of human cancers. p53 is also referred to as the "cellular gatekeeper" or "guardian of the genome" because it protects the body from spreading mutated genome induced by various stress. When the cells receives stimuli such as DNA damage, oncogene activation, oxidative stress or undernutrition, p53 gives rise to a number of cellular responses, including cell cycle arrest, apoptosis, cellular senescence and metabolic adaptation. Related to energy metabolisms, it has been reported that p53 reduces glycolysis and enhances mitochondrial respiration. p53 is also involved in the regulation of other cellular metabolism and energy production systems: amino acid metabolism, fatty acid metabolism, nucleic acid metabolism, anti-oxidation, mitochondrial quality control, and autophagy. Moreover, recent studies have shown that p53 gene polymorphisms affect life expectancy and lifestyle-related disease such as type 2 diabetes, suggesting that there is a certain relationship between p53 function and metabolic disorders. In addition, mutant p53 protein does not only lose the tumor suppressor function, but it also gains novel oncogenic function and contributes to tumor development, involving cellular metabolism modification. Therefore, the importance of multifunctionality of p53, particularly with regard to intracellular metabolisms, arouses therapeutic interest and calls attention as the key molecule among cancer, lifestyle-related diseases and life expectancy.

p53 Functions in Adipose Tissue Metabolism and Homeostasis

As a tumor suppressor and the most frequently mutated gene in cancer, p53 is among the best-described molecules in medical research. As cancer is in most cases an age-related disease, it seems paradoxical that p53 is so strongly conserved from early multicellular organisms to humans. A function not directly related to tumor suppression, such as the regulation of metabolism in nontransformed cells, could explain this selective pressure. While this role of p53 in cellular metabolism is gradually emerging, it is imperative to dissect the tissue- and cell-specific actions of p53 and its downstream signaling pathways. In this review, we focus on studies reporting p53’s impact on adipocyte development, function, and maintenance, as well as the causes and consequences of altered p53 levels in white and brown adipose tissue (AT) with respect to systemic energy homeostasis. While whole body p53 knockout mice gain less weight and fat mass under a high-fat diet owing to increased energy expenditure, modifying p53 expression specifically in adipocytes yields more refined insights: (1) p53 is a negative regulator of in vitro adipogenesis; (2) p53 levels in white AT are increased in diet-induced and genetic obesity mouse models and in obese humans; (3) functionally, elevated p53 in white AT increases senescence and chronic inflammation, aggravating systemic insulin resistance; (4) p53 is not required for normal development of brown AT; and (5) when p53 is activated in brown AT in mice fed a high-fat diet, it increases brown AT temperature and brown AT marker gene expression, thereby contributing to reduced fat mass accumulation. In addition, p53 is increasingly being recognized as crucial player in nutrient sensing pathways. Hence, despite existence of contradictory findings and a varying density of evidence, several functions of p53 in adipocytes and ATs have been emerging, positioning p53 as an essential regulatory hub in ATs. Future studies need to make use of more sophisticated in vivo model systems and should identify an AT-specific set of p53 target genes and downstream pathways upon different (nutrient) challenges to identify novel therapeutic targets to curb metabolic diseases.

Control of metabolism by p53 - Cancer and beyond

p53 is an important tumour suppressor gene, with loss of p53 contributing to the development of most human cancers. However, the activation of p53 in response to stress signals underpins a role for p53 in diverse aspects of health and disease. Activities of p53 that regulate metabolism can play a role in maintaining homeostasis and protecting cells from damage - so preventing disease development. By contrast, either loss or over-activation of p53 can contribute to numerous metabolic pathologies, including aging, obesity and diabetes.

Mutant p53 controls tumor metabolism and metastasis by regulating PGC-1α

Basu et al. show that mutant p53 enhances migration and metastasis of tumors through the ability to bind and regulate PGC-1α and that this regulation is markedly impacted by the codon 72 polymorphism.

Mutant forms of p53 protein often possess protumorigenic functions, conferring increased survival and migration to tumor cells via their “gain-of-function” activity. Whether and how a common polymorphism in TP53 at amino acid 72 (Pro72Arg; referred to here as P72 and R72) impacts this gain of function has not been determined. We show that mutant p53 enhances migration and metastasis of tumors through the ability to bind and regulate PGC-1α and that this regulation is markedly impacted by the codon 72 polymorphism. Tumor cells with the R72 variant of mutant p53 show increased PGC-1α function along with greatly increased mitochondrial function and metastatic capability. Breast cancers containing mutant p53 and the R72 variant show poorer prognosis compared with P72. The combined results reveal PGC-1α as a novel “gain-of-function” partner of mutant p53 and indicate that the codon 72 polymorphism influences the impact of mutant p53 on metabolism and metastasis.

Identification of new candidate genes for retinopathy in type 2 diabetics. Valencia Study on Diabetic Retinopathy (VSDR). Report number 3

OBJECTIVE

To identify genes involved in the pathogenic mechanisms of non-proliferative diabetic retinopathy (NPDR), among which include oxidative stress, extracellular matrix changes, and/or apoptosis, in order to evaluate the risk of developing this retinal disease in a type2 diabetic (DM2) population.

MATERIAL AND METHODS

A case-control study was carried out on 81 participants from the Valencia Study on Diabetic Retinopathy (VSDR) of both genders, with ages 25-85years. They were classified into: (i)DM2 group (n=49), with DR (+DR; n=14) and without DR (-DR; n=35), and (ii)control group (GC; n=32). The protocols included a personal interview, standardised ophthalmological examination, and blood collection (to analyse the DNA for determining the gene expression (TP53, MMP9, and SLC23A2) in the study groups. Statistical analyses were performed using the SPSS v22.0 program.

RESULTS

The TP53 and MMP9 genes showed a higher expression in the DM2 group compared to the GC, although the difference was only significant for the MMP9 gene (TP53: 10.40±1.20 vs. 8.23±1.36, P=.084; MMP9: 1.45±0.16 vs. 0.95±0.16, P=.036), and the SLC23A2 gene showed a significant lower expression in the DM2 vs CG (5.58±0.64 vs. 11.66±1.90, P=.026). When sub-dividing the DM2 group according to the presence of retinopathy, the expression of the TP53, MMP9 and SLC23A2 genes showed significant differences between the DM2-RD, DM2+RD and GC groups (TP53: 9.95±1.47 vs. 11.52±2.05 vs. 8.23±1.36, P=.038; MMP9: 1.47±0.20 vs. 1.41±0.27 vs. 0.95±0.16, P=.021; SLC23A2: 5.61±0.77 vs. 5.51±1.21 vs. 11.66±1.90, P=.018).

CONCLUSIONS

Genes involved in extracellular matrix integrity (MMP9) and/or apoptosis (TP53), could be considered potential markers of susceptibility to the development/progression of NPDR. Interestingly, the SLC232A2 gene (ascorbic acid transporter) can be considered a protector of the risk of the development/progression of the retinopathy.

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.

Increased Arf/p53 activity in stem cells, aging and cancer

Arf/p53 pathway protects the cells against DNA damage induced by acute stress. This characteristic is the responsible for its tumor suppressor activity. Moreover, it regulates the chronic type of stress associated with aging. This is the basis of its anti‐aging activity. Indeed, increased gene dosage of Arf/p53 displays elongated longevity and delayed aging. At a cellular level, it has been recently shown that increased dosage of Arf/p53 delays age‐associated stem cell exhaustion and the subsequent decline in tissue homeostasis and regeneration. However, p53 can also promote aging if constitutively activated. In this context, p53 reduces tissue regeneration, which correlates with premature exhaustion of stem cells. We discuss here the current evidence linking the Arf/p53 pathway to the processes of aging and cancer through stem cell regulation.

Is p53 Involved in Tissue-Specific Insulin Resistance Formation?

p53 constitutes an extremely versatile molecule, primarily involved in sensing the variety of cellular stresses. Functional p53 utilizes a plethora of mechanisms to protect cell from deleterious repercussions of genotoxic insults, where senescence deserves special attention. While the impressive amount of p53 roles has been perceived solely by the prism of antioncogenic effect, its presence seems to be vastly connected with metabolic abnormalities underlain by cellular aging, obesity, and inflammation. p53 has been found to regulate multiple biochemical processes such as glycolysis, oxidative phosphorylation, lipolysis, lipogenesis, β-oxidation, gluconeogenesis, and glycogen synthesis. Notably, p53-mediated metabolic effects are totally up to results of insulin action. Accumulating amount of data identifies p53 to be a factor activated upon hyperglycemia or excessive calorie intake, thus contributing to low-grade chronic inflammation and systemic insulin resistance. Prominent signs of its actions have been observed in muscles, liver, pancreas, and adipose tissue being associated with attenuation of insulin signalling. p53 is of crucial importance for the regulation of white and brown adipogenesis simultaneously being a repressor for preadipocyte differentiation. This review provides a profound insight into p53-dependent metabolic actions directed towards promotion of insulin resistance as well as presenting experimental data regarding obesity-induced p53-mediated metabolic abnormalities.

The role of the p53 tumor suppressor in metabolism and diabetes

In the context of tumor suppression, p53 is an undisputedly critical protein. Functioning primarily as a transcription factor, p53 helps fend off the initiation and progression of tumors by inducing cell cycle arrest, senescence or programmed cell death (apoptosis) in cells at the earliest stages of precancerous development. Compelling evidence, however, suggests that p53 is involved in other aspects of human physiology, including metabolism. Indeed, recent studies suggest that p53 plays a significant role in the development of metabolic diseases, including diabetes, and further that p53's role in metabolism may also be consequential to tumor suppression. Here, we present a review of the literature on the role of p53 in metabolism, diabetes, pancreatic function, glucose homeostasis and insulin resistance. Additionally, we discuss the emerging role of genetic variation in the p53 pathway (single-nucleotide polymorphisms) on the impact of p53 in metabolic disease and diabetes. A better understanding of the relationship between p53, metabolism and diabetes may one day better inform the existing and prospective therapeutic strategies to combat this rapidly growing epidemic.

A novel type 2 diabetes risk allele increases the promoter activity of the muscle-specific small ankyrin 1 gene

Genome-wide association studies have identified Ankyrin-1 (ANK1) as a common type 2 diabetes (T2D) susceptibility locus. However, the underlying causal variants and functional mechanisms remain unknown. We screened for 8 tag single nucleotide polymorphisms (SNPs) in ANK1 between 2 case-control studies. Genotype analysis revealed significant associations of 3 SNPs, rs508419 (first identified here), rs515071, and rs516946 with T2D (P < 0.001). These SNPs were in linkage disequilibrium (r² > 0.80); subsequent analysis indicated that the CCC haplotype associated with increased T2D susceptibility (OR 1.447, P < 0.001). Further mapping showed that rs508419 resides in the muscle-specific ANK1 gene promoter. Allele-specific mRNA and protein level measurements confirmed association of the C allele with increased small ANK1 (sAnk1) expression in human skeletal muscle (P = 0.018 and P < 0.001, respectively). Luciferase assays showed increased rs508419-C allele transcriptional activity in murine skeletal muscle C2C12 myoblasts, and electrophoretic mobility-shift assays demonstrated altered rs508419 DNA-protein complex formation. Glucose uptake was decreased with excess sAnk1 expression upon insulin stimulation. Thus, the ANK1 rs508419-C T2D-risk allele alters DNA-protein complex binding leading to increased promoter activity and sAnk1 expression; thus, increased sAnk1 expression in skeletal muscle might contribute to T2D susceptibility.

Genetic Modifiers of the p53 Pathway

The tumor suppressor gene TP53 is the most frequently mutated gene in human cancer; this gene is subject to inactivation by mutation or deletion in >50% of sporadic cancers. Genes that encode proteins that regulate p53 function, such as MDM2, MDM4, and CDKN2A (p14(ARF)) are also frequently altered in tumors, and it is generally believed that the p53 pathway is likely to be inactivated by mutation in close to 100% of human tumors. Unlike most other cancer-relevant signaling pathways, some of the genes in the p53 pathway contain functionally significant single nucleotide polymorphisms (SNPs) that alter the amplitude of signaling by this protein. These variants, thus, have the potential to impact cancer risk, progression, and the efficacy of radiation and chemotherapy. In addition, the p53 pathway plays a role in other biological processes, including metabolism and reproductive fitness, so these variants have the potential to modify other diseases as well. Here we have chosen five polymorphisms in three genes in the p53 pathway for review, two in TP53, two in MDM2, and one in MDM4. These five variants were selected based on the quality and reproducibility of functional data associated with them, as well as the convincingness of epidemiological data in support of their association with disease. We also highlight two other polymorphisms that may affect p53 signaling, but for which functional or association data are still forthcoming (KITLG and ANRIL). Finally, we touch on three questions regarding genetic modifiers of the p53 pathway: Why did these variants arise? Were they under selection pressure? And, is there compelling evidence to support genotyping these variants to better predict disease risk and prognosis?

TP53 Arg72Pro polymorphism (rs1042522) and risk of endometriosis among Asian and Caucasian populations

This study was conducted to investigate the association between TP53 Arg72Pro polymorphism (rs1042522) and risk of endometriosis. Studies were retrieved from Pubmed, Embase and HuGENet, and four models [dominant (AA+AG vs. GG), recessive (AA vs. AG+GG), co-dominant (AA vs. AG, AA vs. GG) and allele analysis (A vs. G), combined with odds ratios (OR) and 95% confidence intervals (CI)], were applied to evaluate this association. Fourteen eligible studies from eight countries were included. The pooled analysis identified a significant association between TP53 Arg72Pro polymorphism (rs1042522) and risk of endometriosis [dominant: OR 0.746, 95% CI 0.585-0.952, I(2)=59%; recessive: OR 0.650, 95% CI 0.510-0.829, I(2)=73%; co-dominant (GG vs. GC): OR 0.676, 95% CI 0.637-0.851, I(2)=67%; co-dominant (GG vs. CC): OR 0.564, 95% CI 0.395-0.806, I(2)=74%; allele analysis: OR 0.762, 95% CI 0.654-0.888, I(2)=71%]. In the subgroup analysis, the same positive associations were found among Asians. After removing studies that did not satisfy Hardy-Weinberg equilibrium, significant correlations were confirmed in both the pooled analysis and the Asian subgroup. Three bioinformatic methods (TagSNP calculations, functional prediction and linkage disequilibrium analysis) were used to determine the importance of TP53 Arg72Pro polymorphism (rs1042522), and suggested that this locus may be equally important regardless of ethnicity. In conclusion, TP53 Arg72Pro polymorphism (rs1042522) was positively associated with risk of endometriosis, particularly among Asians. However, its potential role in Caucasians should not be ignored.

The MDM2 inhibitor Nutlin-3 attenuates streptozotocin-induced diabetes mellitus and increases serum level of IL-12p40

Besides its well-established oncosuppressor activity, a key function of p53 in regulating metabolic pathways has been recently identified. Nevertheless, the role of p53 with respect to diabetes mellitus (DM) appears highly controversial. To address this issue, we have used the cis-imidazoline compound Nutlin-3, an inhibitor of MDM2/p53 interaction, which represents a potent and selective non-genotoxic activator of the p53 pathway both in in vivo and in vitro experimental settings. Experimental DM was induced by intraperitoneal injections of low concentrations of streptozotocin (STZ) in C57BL/6N mice (n = 20). A group of control vehicle-injected mice (n = 10) and of STZ-treated mice (n = 10) was co-injected with Nutlin-3. Mice co-injected with STZ + Nutlin-3 exhibited attenuated features of DM with respect to animals treated with STZ alone. Indeed, STZ + Nutlin-3-treated mice were characterized by significantly (p < 0.05) lower levels of hyperglycemia, reduced weight loss, and increased spleen weight. In addition, STZ alone promoted a marked decrease in the levels of several circulating cytokines, including interleukin-12 (IL-12)p40. On the other hand, co-injection of STZ + Nutlin-3 significantly (p < 0.01) counteracted IL-12p40 down-modulation. In vitro experiments performed on the RAW264.7 macrophagic cell line model, used as cellular source of IL-12p40, demonstrated that Nutlin-3 treatment increased IL-12p40 release, strongly suggesting a direct effect of Nutlin-3 on the immune system. Overall, these data demonstrate that systemic administration of Nutlin-3 ameliorates the severity of STZ-induced DM and increases the levels of circulating IL-12p40.

Centenarians as super-controls to assess the biological relevance of genetic risk factors for common age-related diseases: a proof of principle on type 2 diabetes

Genetic association studies of age-related, chronic human diseases often suffer from a lack of power to detect modest effects. Here we propose an alternative approach of including healthy centenarians as a more homogeneous and extreme control group. As a proof of principle we focused on type 2 diabetes (T2D) and assessed allelic/genotypic associations of 31 SNPs associated with T2D, diabetes complications and metabolic diseases and SNPs of genes relevant for telomere stability and age-related diseases. We hypothesized that the frequencies of risk variants are inversely correlated with decreasing health and longevity. We performed association analyses comparing diabetic patients and non-diabetic controls followed by association analyses with extreme phenotypic groups (T2D patients with complications and centenarians). Results drew attention to rs7903146 (TCF7L2 gene) that showed a constant increase in the frequencies of risk genotype (TT) from centenarians to diabetic patients who developed macro-complications and the strongest genotypic association was detected when diabetic patients were compared to centenarians (p_value = 9.066*10⁻⁷). We conclude that robust and biologically relevant associations can be obtained when extreme phenotypes, even with a small sample size, are compared.

The p53 Codon 72 Polymorphism Modifies the Cellular Response to Inflammatory Challenge in the Liver

The p53 protein is a critical stress-response mediator and signal coordinator in cellular metabolism and environmental exposure to deleterious agents. In human populations, the p53 gene contains a common single nucleotide polymorphism (SNP) affecting codon 72 that determines whether a proline (P72) or an arginine (R72) is present at this amino acid position of the polypeptide. Previous studies carried out using human populations, mouse models, and cell culture analyses have provided evidence that this amino acid difference can alter p53 functional activities, and potentially also can affect clinical presentation of disease. The clinical presentation associated with many forms of liver disease is variable, but few of the responsible underlying genetic factors or molecular pathways have been identified. The aim of the present study was to investigate whether the p53 codon 72 polymorphism influences the cellular response to hepatic stresses. A humanized p53 knock-in (Hupki) mouse model was used to address this issue. Mice expressing either the P72 or R72 normal variation of p53 were given an acute-, intermittent- or a chronic challenge, associated with exposure to lipopolysaccharide, D-galactosamine, or a high-fat diet. The results reveal that the livers of the P72 and R72 mice exhibit notable differences in inflammatory and apoptotic response to these distinct forms of stress. Interestingly the influence of this polymorphism on the response to stress is context dependent, with P72 showing increased response to liver toxins (lipopolysaccharide and D-galactosamine), but R72 showing increased response to metabolic stress (high fat diet). When taken together, these data point to the p53 codon 72 polymorphism as an important molecular mediator of events contributing to hepatic inflammation and metabolic homeostasis.